Journal of Archaeological Science 33 (2006) 615e627http://www.elsevier.com/locate/jas

Characterization of bricks and tiles from the 17th-century brick Chapel,St. Mary’s City, Maryland

Ruth Ann Armitage a,*, Leah Minc b, David V. Hill c, Silas D. Hurry d

a Department of Chemistry, Eastern Michigan University, Ypsilanti, MI 48197, USAb OSU Radiation Center, Oregon State University, Corvallis, OR 97331-5903, USA

c P.O. Box 26464, Albuquerque, NM 87125, USAd Archaeology Research Laboratory, Historic St. Mary’s City, P.O. Box 39, St. Mary’s City, MD 20686, USA

Received 8 February 2005; received in revised form 19 September 2005; accepted 26 September 2005

Abstract

The brick Chapel at St. Mary’s City, Maryland, built around 1667, would have been an impressive structure on a colonial frontier where allthe other buildings were built only of wood. While the building is no longer extant, the bricks remaining in the buried foundations hold infor-mation about the technologies and materials used by brickmakers in the 17th-century Chesapeake region. Instrumental neutron activation anal-ysis (INAA) and petrographic analysis of thin sections were used to compare the Chapel bricks and other 17th-century bricks and tiles fromseveral Chesapeake contexts to locally available clay sources. While the composition of the Chapel bricks is generally consistent with thatof clays available in southern Maryland, these historic materials could not be linked to any one deposit, and may reflect the mixing of claysfrom multiple sources. In contrast, building materials from other 17th-century buildings at St. Mary’s City could be more precisely ‘‘matched’’to specific local clay deposits. This paper reports on our initial investigations toward understanding the technology of the Chapel bricks and theirrelationship to other bricks from St. Mary’s City.� 2005 Elsevier Ltd. All rights reserved.

Keywords: Neutron activation analysis; Petrographic analysis; Brick; Maryland; Colonial

1. Introduction

St. Mary’s City (Fig. 1) was founded in 1634 as the capitalof the Maryland Colony. While the ‘‘city’’ began as a sharedNative American site, it progressed into an Italian-Baroquestyle designed town. While almost all of the early buildingswere of frame construction, by the 1670s, a few brick struc-tures existed at the site, including the State House and Prison(1674), and residences like St. Peter’s (1679). None of thesebuildings is extant; when the capital of the colony was movedto Annapolis, Maryland in 1696, St. Mary’s City was aban-doned and the bricks were scavenged for use at other subse-quent sites [20,25e27].

* Corresponding author. Tel.: þ1 734 487 0290; fax: þ1 734 487 1496.

E-mail addresses: rarmitage@emich.edu (R.A. Armitage), mincleah@engr.

orst.edu (L. Minc), dhill1@att.net (D.V. Hill), sdhurry@smcm.edu (S.D. Hurry).

0305-4403/$ - see front matter � 2005 Elsevier Ltd. All rights reserved.

doi:10.1016/j.jas.2005.09.016

The most impressive brick structure at St. Mary’s City wasarguably the Chapel, built around 1667. While no records existof its construction, archaeological investigations in 1938 andagain in the 1980s revealed it to have been a massive cruci-form structure, with foundations nearly 1 m thick and reachingnearly 1.5 m into the ground (Fig. 2a) [28,38]. The Chapel iscurrently being reconstructed on top of the original founda-tions using bricks manufactured from a local clay source(Fig. 2b). Current calculations estimate that approximately100,000 bricks will be required to complete the abovegroundportions of the Chapel.

The volume of bricks required to construct the originalChapel and numerous other brick buildings throughout the Col-onies indicates that brickmaking was an important industry inthe 17th and 18th centuries. The industrial development inthe Chesapeake brought about by the declining profitabilityof Colonial tobacco farming after 1660 has been well docu-mented [24]. The Archives of Maryland [1] record the presence

616 R.A. Armitage et al. / Journal of Archaeological Science 33 (2006) 615e627

Fig. 1. Map of Historic St. Mary’s City, Maryland. Letters indicate clay sampling locations: A, Mill Field; B, Brick Pit; C, Visitor Center Field; D, St. Barbara’s

brickyard; E, St. John’s; F, St. Mary’s Hill. Pleistocene clay-bearing deposits of St. Mary’s City area (after [23]) are also shown, with corresponding Virginia for-

mations: Qk, Kent Island Formation (Poquoson and Lynnhaven members of Tabb Formation); Qm, Maryland Point Formation (Sedgefield member of Tabb For-

mation); Qo, Omar Formation, estuarine facies (Shirley Formation); Qc, Chicamuxen Church Formation (Chuckatuck and Charles City Formations).

and activity of brickmakers even before this date. Seven brickkilns and clamps dating between 1650 and 1695 [24] have beenexcavated in James City County and Williamsburg, Virginia,including Structure 102 [15], which was sampled for this study.Richard O’Connor [35] provides in his dissertation, A Historyof Brickmaking in the Hudson Valley, an excellent review ofthe historical development of colonial brickmaking. He propo-ses that, outside of major towns, many bricks were made on sitein temporary clamps by itinerant brickmakers newly arrivedfrom England. Following the measurement standards of theirhomeland, these brickmakers may have originated the term‘‘English brick,’’ which has long caused confusion about thesource of these materials in Colonial America. The combina-tion of diminishing fuel supplies in England and the cost oftransporting such a bulky material would have made importa-tion of brick from Europe an expensive undertaking; however,there is some evidence of relatively small amounts of brickbeing shipped as cargo or used as ballast during the 17th

century [29]. While O’Connor concludes that locally manufac-tured materials certainly made up the bulk of material excavatedfrom 17th-century East Coast contexts, the fact remains thatrelatively little is known about the organization of brick pro-duction and trade in the American colonies.

Few studies have attempted to determine the source ofbricks and tiles encountered in Colonial archaeologicalexcavations. Gurcke [14] provides a comprehensive overviewof previous work where bricks have been useful in historicalarchaeology. Most analyses of colonial bricks have involvedstatistical comparisons of brick sizes and color to determinewhether they were European imports or of New Worldmanufacture [17,40,42]. A small study used X-ray fluores-cence to examine the chemical composition of bricks fromFort Orange near what is now Albany, New York, but it lackeda sufficient number of samples for a good statistical compari-son [41]. In the Tidewater region, bricks uncovered at theshort-lived 16th-century Roanoke Island settlement were

617R.A. Armitage et al. / Journal of Archaeological Science 33 (2006) 615e627

studied with X-ray and optical methods and found to be ‘‘iden-tical, chemically and physically,’’ to the tested local geologicalmaterials [16:9].

More recently, a compositional study of bricks from NewNetherland/New York used neutron activation analysis (NAA)and inductively coupled plasma mass spectrometry (ICP-MS)[11]. This study found both excellent spatial resolution in distin-guishing brick clays along the Hudson River, and long-termconsistency within the product of a given brickyard, and indi-cates that compositional analyses can play an important rolein identifying where bricks were manufactured [11]. Our workis similar to the petrographic analysis and NAA study that inves-tigated bricks and tiles from York, England to determine theirorigin and examine technological changes over time [4].

This study investigates whether the bricks used in the con-struction of the Chapel at St. Mary’s City can be correlatedwith areas where archaeological evidence indicates past brickmanufacturing. While the volume of bricks used in buildingsat St. Mary’s City strongly suggests local manufacture, manyof the bricks from the Chapel have a unique appearance incomparison with bricks from other historic structures at thesite. Differences include wide variations in color, sometimes

Fig. 2. Photographs of the Chapel showing: (a) Latin cross plan observed dur-

ing excavation before reconstruction began; (b) artist’s rendering of the new

brick Chapel superimposed onto the reconstruction as of autumn 2004.

even within a single brick, as is shown in Fig. 3. Only theChapel bricks contain dark inclusions, which often have vitri-fied margins (Fig. 3, inset). Variations in firing environmentmay have influenced the appearance of the vitrified inclusions.Because the vitrified inclusions are not common to other brickswithin the city, the question has arisen as to whether the Chapelbricks in particular were made using non-local materials or us-ing a distinct technology. To determine this, we have used geo-logical and chemical methods to compare bricks from theChapel foundation with other bricks, tiles, and local clays.

2. Materials

2.1. Raw materials: local clays

The terrain of Southern Maryland consists of uplands (eleva-tions typically>100 feet) and lowlands (elevations typically 0e50 feet), with a distinct, intervening slope marking the transition[J. Reger, personal communication 2003]. Historic St. Mary’sCity sits at about the 40-foot elevation on part of the lowlandalong the east bank of the St. Mary’s River; the nearest uplandis barely a mile away from the river’s edge. Surface depositsat St. Mary’s City belong to four Quaternary formations(Fig. 1, inset) along with several undivided and undifferentiateddeposits derived from weathering of these formations [23]. TheKent Island (Qk), Maryland Point (Qm), Omar (Qo), and Chica-muxen Church (Qc) Formations (Fig. 1, inset) consist of sedi-ments reworked from adjacent highlands and deposited inshallow estuarine environments during the middle to late Pleis-tocene [23]. All of the formations contain silty and sandy claysranging in color from dark gray-green to orange. McCartan [23]correlates the St. Mary’s County formations with those observed

Fig. 3. Contrast-enhanced image of the broken end of Chapel brick sample

‘‘Chapel 13’’, showing variations in color within a single brick and (inset)

characteristic dark inclusions with vitrified margins.

618 R.A. Armitage et al. / Journal of Archaeological Science 33 (2006) 615e627

in the Coastal Plain of Virginia, indicating significant continuitybetween the geologic deposits of the two areas of study.

Clays were sampled from six locations at St. Mary’s City rep-resenting the predominant surface deposits (Fig. 1, inset). Ar-chaeological finds suggest that two of these locationsdtheMill Field site and St. Barbara’sdmay have functioned as brick-yards during the late 17th century; both are within the Qo forma-tion. Forman [10] reports having observed mullion brick wastersdeposited in a pit from excavations at the Mill Field, and inter-preted this as evidence of brickmaking activity. Subsequent sys-tematic investigation of the site area in 1985 discovereda surface scatter of overfired and underfired bricks in thissame area [37]. Similarly, evidence from St. Barbara’s is basedon surface observations; neither area has been investigated withsubsurface techniques by staff of the Historic St. Mary’s Citymuseum [H. Miller, personal communication 2002]. Locationswith no demonstrated indications of historical brickmaking ac-tivity were sampled to determine the range of variation in localraw material sources. The locations include the field adjacent tothe Visitors’ Center (Qo formation), a location referred to as theBrick Pit (Qo formation) which was in an unoccupied zone ad-jacent to the Chapel site, and at the base of a deeply excavatedcultural feature near the St. John’s house (Qm formation).Finally, the Qc deposit was sampled near the St. Barbara’s‘‘brickyard’’ area; samples from two distinct layers wereremoved from a trench dug near the transition slope for a waterline, located along Mattapany Road on the St. Mary’s Hill(Fig. 1, F).

To prepare clay source samples for analysis, approximately150 mL raw clay was levigated in deionized water. No strati-fication occurred in any of the samples, which were allowed todry until workable, formed into tiles, and fired in a muffle fur-nace under oxidizing conditions as described in Table 1. Theclay obtained from the cellar bulkhead within the St. John’ssite was treated as if it were a brick sample as it was collectedas hardened material. A sample of the raw cellar bulkheadclay, as well as a piece of the hardened material fired to1000 �C were abraded, rinsed, and crushed for INAA.

2.2. Historic brick and tile

Brick and tile samples were selected from the Chapel andfrom five contemporary structures within St. Mary’s City. Othersamples were acquired from other nearby 17th-century

Tidewater sites (including Jamestown and Flowerdew Hundred,VA) and from London, England (Table 2). To remove surfacecontamination, all samples were abraded using a tungsten-carbide rotary tool, rinsed with deionized water and left to dryovernight at room temperature. Portions of the abraded andrinsed materials were selected for petrographic analysis orcrushed for instrumental neutron activation analysis (INAA).

3. Methods

3.1. Petrographic analysis

Standard (27 � 47 mm) petrographic thin sections weremade from 27 samples of brick, tile, and fired clay. The sec-tions were examined using a Nikon Optiphot-2 petrographicmicroscope. Aplastic inclusions were examined to determinemineral (or rock fragment) identity, grain size (using the Went-worth grain size scale), grain shape, and volume percentagecomposition using standard petrographic techniques and com-parative charts [34].

3.2. Instrumental neutron activation analysis (INAA)

A total of 67 samples was prepared for neutron activationanalysis. Approximately 200 mg of crushed brick was encapsu-lated and submitted for irradiation; analyses were initiated atthe University of Michigan’s Ford Nuclear Reactor and com-pleted at Oregon State University’s Radiation Center. In eachcase, the samples were exposed to two separate irradiationsand a total of four separate counts of resulting gamma activity,following protocols established for the multi-element analysisof archaeological materials [2,5,6,13,30,33]. Details of the ex-perimental conditions are provided in the Appendix. Elementconcentrations were determined for 31 elements (Table 3) usingas comparison standards three replicates of SRM NIST1633A(coal fly ash [12,18]). Determination of Ca used SRMNIST688 (basalt [12]). Interlaboratory calibrations, based onthe New Ohio Red Clay check standard, indicated that differen-ces in analytic results between labs were not significant.

3.3. Scanning electron microscopyeenergy dispersiveX-ray spectroscopy (SEMeEDS)

To determine the relationships between the observed inclu-sions and the bulk clay, we selected for SEMeEDS two

Table 1

Comparative local clays sampled

Clay source Location on Fig. 1, inset Firing temperatures ( �C) Formation

Mill Field A 100, 427, 800, 1000 Omar (Estuarine fades)

Brick Pit B 100, 427, 800, 1000 Omar (Estuarine fades)

Visitor Center Field C 100, 427, 800, 1000 Omar (Estuarine fades)

St. Barbara’s D 100, 427, 800, 1000 Omar (Estuarine fades)

St. John’s upper level E (approx. 15e50 cm below surface) 100, 427, 800, 1000 Maryland Point

St. John’s lower level E (120e150 cm below surface) 100, 427, 800, 1000 Maryland Point

St. John’s cellar E, cellar bulkhead (>150 cm below surface) Raw, 1000 Maryland Point

St. Mary’s Hill upper level F (15e60 cm below surface) 100, 427, 800, 1000 Chicamuxen Church

St. Mary’s Hill lower level F (>60 cm below surface) 100, 427, 800, 1000 Chicamuxen Church

619R.A. Armitage et al. / Journal of Archaeological Science 33 (2006) 615e627

Chapel bricks that typified the extremes of appearance (andthus, likely the firing conditions) described in Section 1.This would allow us to compare the inclusion compositionto that of the clay, and to determine the microscopic character-istics of the vitrified margins. Two thin sections from petro-graphic analysis were diamond-polished, coated with carbon,and examined using the Hitachi S3200 SEMeEDS at the Elec-tron Microprobe Analysis Laboratory at the University ofMichigan.

4. Results

4.1. Petrographic analysis

A summary of the optical mineralogy results is provided inTable 4. Across all samples, the predominant aplastic inclu-sions were sand-size grains of quartz and alkali feldspar. Other

Table 2

Historic materials selected for analysis

Sample Site and description

Bricks from St. Mary’s City Chapel (n ¼ 16), ca. 1667

Chapel 1 ST1-103-2425P

Chapel 2 ST1-103-2425P

Chapel 3 ST1-103-2425P

Chapel 4 ST1-103-2425P

Chapel 5 ST1-103-2425P

Chapel 6 ST1-103-2425P

Chapel 7 ST1-103-2425P

Chapel 8 ST1-103-2425P

Chapel 9 ST1-103-2425P

Chapel 10 ST1-103-2425P

Chapel 11 ST1-103-2425P

Chapel 12 ST 1-103-2826, stratum E

Chapel 13 ST1-103 DCZ

Chapel 14 ST1-103 D/BV

Chapel 15 ST1-103-2425P

Chapel 16 ST1-103-2425P

Bricks from other buildings at St. Mary’s City (n ¼ 7)

Priest’s House 1 ST1-103-1715E, adjacent to Chapel site, 1670s

Priest’s House 2 ST1-103-1715E/AP, adjacent to Chapel site

St. John’s, Phase I ST1-23, Phase I, 1638

St. John’s, Phase II ST1-23, Phase II, 1676

Van Sweringen ST1-19, possibly of Dutch manufacture, 1670s

St. Peter’s ST1-31, after 1670

State House ST1-172B, 1674

Tiles (n ¼ 6)

Chapel roof tile ST1-103 flat roof tile

Structure 100 Jamestown, VA flat tile

Structure 19 Jamestown, VA pantile

Structure 115 Jamestown, VA pantile

Structure 102 Jamestown, VA flat tile

Flowerdew Flowerdew Hundred flat tile, near Hopewell, VA

Kiln wasters (n ¼ 2)

Rogers kiln Pottery waster from Wm. Rogers’ kiln, Yorktown,

VA

Jones kiln Pottery waster from Morgan Jones’ kiln,

Westmoreland County, VA

‘‘Spanished’’ bricks from London, 18th c. (n ¼ 2)London 1 KEW98, Compter Prison, London, 1787

London 2 GHT00, Blossom’s Inn, London, 18th c.

common inclusions were biotite and quartzite, usually onlypresent at trace levels. Within the sand fraction, however,marked differences were observed. Among the local clays, tilesmade from the Brick Pit, Mill Field, and Visitor Center Field(Qo) locations displayed a strong bimodal distribution of siltto very fine sand (VFS) and medium to coarse sand. In contrast,clays sampled from the Qm and Qc formations displayed a uni-modal distribution of aplastic quartz inclusions, although theseclays differ in both the quantity and size of sand inclusionsnoted (Table 4). Of the historic bricks, only one of the struc-tures at St. Mary’s, the Priest’s House, had bricks displayingthe distinctive bimodal distribution within the sand fractionthat matched the predominant local (Qo) clays. All the Chapelbricks, as well as the one brick from St. Peter’s, display a strongunimodal distribution in the silt to VFS fraction, most similar intexture to the upper stratum from St. Mary’s Hill (Qc). Interest-ingly, the brick from the St. John’s house differed in the distri-bution of aplastic quartz inclusions from the clays immediatelysurrounding that site (Qm).

The Chapel bricks differ in other significant ways, as well.Chapel brick samples generally contain fine-grained roundedred pellets with sharp to merging boundaries that can be de-scribed as soil pisoliths or soil papules (redeposited induratednodules of an older soil material, [7]), or argillaceous clayfragments [43]. Further, many of the Chapel brick samplesshow clear variations in both matrix color (from reddish to yel-low, Fig. 3) and texture (up to 50% VFS compared to approx-imately 25% elsewhere), indicating either intentional mixingof clays or zonation within the utilized source. The St. Peter’sbrick sample contained clay fragments/soil papules andshowed evidence of clay mixing, similar to many of the Chapelbricks. Of the clay sources examined, only the samples fromthe St. Mary’s Hill area contained both significant soil pap-ules/clay fragments and evidence of zonation.

Many of the Chapel bricks contained voids with dark vitri-fied margins. In some cases, the void boundaries were distinct,while in others they graded into the matrix. The mineralogy ofthe boundaries differed little from that of the surrounding ma-trix, though silt-sized opaque minerals were observed on theinner surfaces of some of the rims. While the Chapel bricksdiffer from local clays, they also differ markedly from Europe-an samples. The purported ‘‘Dutch’’ brick recovered from theVan Sweringen site at St. Mary’s City is dominated by silt-sized aplastic components and exhibits no clay mixing. TheLondon bricks are similarly fine textured, but contain a distinc-tive suite of chert and shale rock fragments.

Although the possibility of the Chapel bricks being Europe-an imports is unlikely, considering the volume of materialsnecessary, some speculation has been made that the brickswere manufactured locally, but using a European brickmakingtechnology, called ‘‘Spanishing,’’ whereby debris and coal ashwere added to the clay mixture before firing [21,22: 11]. Thiswas common practice in London in the 17th century, particu-larly after the Great Fire of 1666 [39]. Despite the fact thatcoal ash specifically would not have been present in the colo-nies, a similar local process using wood ash or other debrismight leave characteristic inclusions. To investigate this

Table 3

Elemental concentrations for 31 elements determined by INAA

Al,

%

Fe,

%

Ca,

ppm

Ti,

ppm

V,

ppm

Dy,

ppm

Mm,

ppm

K,

ppm

As,

ppm

La,

ppm

Lu,

ppm

Sm,

ppm

Na,

ppm

U,

ppm

Yb,

ppm

Local clays

Omar Formation (Qo)Average Mill Field clay 4.11 1.78 1300 4600 56.8 3.9 210.7 9500 4.8 24.0 0.369 4.5 2550 2.7 2.7

SD 0.34 0.18 300 600 7.8 0.5 32.1 900 0.3 2.1 0.033 0.3 160 0.4 0.3

Average Brick Pit clay 4.77 2.37 700 4400 69.3 3.6 177.2 9600 6.6 21.6 0.337 3.5 2300 2.7 2.3

SD 0.26 0.07 600 200 4.5 0.4 9.6 1000 0.5 1.6 0.039 0.3 120 0.3 0.3Average Visitor’s Center Field clay 5.17 2.45 1100 5100 77.4 4.2 233.1 10700 6.3 27.5 0.421 4.7 2670 3.1 2.9

SD 0.74 0.44 700 900 13.6 0.3 33.8 1600 0.7 3.0 0.027 0.3 280 0.5 0.2

Average St. Barbara’s brickyard clay 5.57 2.44 700 5500 78.6 5.0 375.6 12300 7.5 30.0 0.493 5.5 3130 3.7 3.3

SD 0.69 0.30 1400 600 7.4 0.7 63.4 700 0.5 3.0 0.067 0.6 360 0.8 0.3

Maryland Point Formation (Qm)

Average St. John’s cellar bulkhead clay 3.17 1.30 1900 4000 40.1 3.1 159.1 9800 3.4 17.8 0.274 3.3 1820 1.8 1.9

SD 0.44 0.14 200 500 2.4 0.1 21.3 1200 0.5 2.3 0.031 0.4 260 0.3 0.2Average St. John’s upper clay 3.21 1.83 1000 3300 53.1 2.7 151.4 5200 5.2 16.4 0.262 3.3 1170 2.1 1.7

SD 0.52 0.22 1200 400 11.3 0.7 18.3 1100 0.7 2.2 0.035 0.9 150 0.3 0.2

Average St. John’s lower clay 1.82 1.42 n.d. 2700 31.8 3.2 142.0 3200 3.3 14.6 0.245 3.9 610 1.4 1.7

SD 0.22 0.30 500 4.9 1.0 24.7 600 0.4 3.8 0.059 1.2 80 0.2 0.3

Chicamuxen Church Formation (Qc)

Average St. Mary’s Hill upper clay 3.90 1.91 n.d. 7500 65.2 5.4 150.9 5000 6.5 33.5 0.628 6.4 1460 4.0 4.5

SD 0.19 0.04 500 5.9 0.4 39. 8 1300 0.3 0.5 0.013 0.3 40 0.3 0.1Average St. Mary’s Hill lower clay 10.33 6.73 n.d. 6100 173.4 3.8 80.0 9800 22.1 33.6 0.428 4.7 750 4.2 3.2

SD 0.38 0.39 200 8.5 0.3 8.4 600 1.1 1.5 0.026 0.2 40 0.2 0.1

Brick ChapelChapel roof tile 5.98 1.94 1300 7500 80.2 6.7 158.0 13800 0.7 36.3 0.512 5.9 2890 4.2 3.5

Chapel 1 6.09 2.88 1400 7400 100.6 5.7 108.6 14100 6.9 37.9 0.552 6.1 2010 4.7 3.7

Chapel 2 7.94 4.57 n.d. 6600 146.8 5.2 121.7 15400 7.5 38.9 0.452 6.0 1550 5.0 3.5

Chapel 3 6.89 4.92 1300 7100 124.5 4.7 152.8 12900 3.8 38.0 0.510 6.0 1660 4.3 3.0

Chapel 4 6.58 4.68 1100 6500 138.4 5.1 103.8 15900 0.5 37.2 0.510 5.9 1360 5.3 3.8

Chapel 5 5.68 2.68 1600 7200 84.1 5.3 108.8 13700 4.1 36.7 0.539 5.9 2100 4.5 3.7

Chapel 6 6.21 4.27 800 7300 91.0 5.5 123.4 12400 8.0 39.9 0.528 6.5 1620 4.1 3.6

Chapel 7 6.81 4.91 3700 5800 119.3 4.9 128.3 13100 8.6 36.8 0.499 5.9 1950 5.2 3.0

Chapel 8 7.83 5.42 800 7400 155.3 5.2 122.1 14700 2.1 40.1 0.495 6.0 1680 4.5 3.2

Chapel 9 7.05 4.72 1000 7200 124.1 5.1 110.9 13200 0.6 37.3 0.479 5.7 1520 4.6 3.5

Chapel 10 5.68 3.08 1000 6000 96.8 5.1 115.2 12600 1.8 36.4 0.513 5.7 2070 4.3 3.5

Chapel 11 5.29 2.61 1400 7100 90.9 5.5 118.9 12200 0.6 36.3 0.478 6.1 2030 4.0 3.7

Chapel 12 6.26 3.28 1700 7300 116.0 5.6 105.5 12600 0.9 38.3 0.529 6.6 1700 4.0 3.7

Chapel 13 5.75 2.91 1300 7300 107.4 5.5 105.3 14000 0.9 37.9 0.530 6.3 2160 4.6 4.2

Chapel 14 4.83 2.49 n.d. 6600 70.9 5.9 107.2 11100 5.9 34.6 0.540 6.2 2340 6.0 3.5

Chapel 15 5.64 3.28 n.d. 7600 80.2 5.8 153.4 10700 10.2 37.3 0.523 6.1 1870 3.4 4.0

Chapel 16 4.99 2.25 2200 7600 92.7 5.7 127.8 10900 0.8 37.6 0.550 6.5 2400 4.1 4.2

AVERAGE CHAPEL BRICK 6.47 3.92 1400 7000 115.0 5.3 117.3 13600 3.6 37.8 0.509 6.1 1800 4.5 3.5

SD 0.82 1.02 800 1000 22.5 0.3 13.3 1200 3.1 1.2 0.028 0.3 260 0.4 0.3

Historic buildings, St. Mary’s City, MD

Priest’s House #1 4.65 1.97 900 4800 65.7 5.4 478.3 12100 0.6 32.1 0.425 6.2 2410 2.5 3.9

Priest’s House #2 5.29 2.29 1500 6200 76.4 5.8 571.5 10100 3.1 350 0.496 6.7 3050 3.1 3.9

St. John’s, Phase I 5.08 2.87 3400 6000 84.4 4.8 92.0 9100 10.5 26.4 0.412 4.9 1660 2.4 3.2

St. John’s, Phase II 4.71 2.52 2300 3800 83.6 4.6 69.3 10800 2.4 28.9 0.412 5.6 910 2.4 2.6

Van Sweringen, presumed Dutch 6.79 3.42 31500 3800 71.5 5.6 1226.6 20600 15.9 39.6 0.455 7.7 6470 3.0 3.8

State House 5.59 3.82 2400 5400 77.4 4.8 125.7 12200 11.2 30.1 0.395 5.1 1340 3.1 2.7

St. Peter’s 6.86 4.93 1200 6000 117.6 4.5 110.1 13700 4.1 35.2 0.438 5.3 1400 6.4 2.8

Virginia tiles and kiln wastersJamestown, Structure 102, flat tile 7.39 1.99 2300 8800 89.9 9.9 194.2 15900 0.5 45.4 0.661 7.7 3230 4.9 4.7

Jamestown, Structure 100, flat tile 7.70 1.93 1800 6500 108.9 5.9 144.3 17200 1.4 41.2 0.491 6.8 2930 4.4 3.2

Jamestown, Structure 19, pantile 9.24 5.85 n.d. 4600 106.1 8.2 670.1 34300 8.1 53.3 0.579 10.2 6360 4.1 4.2

Jamestown, Structure 115, pantile 7.24 3.34 2900 4200 102.9 5.6 236.7 23000 16.0 41.9 0.488 7.9 6300 4.7 3.4

Flowerdew Hundred flat roof tile 7.95 4.57 2300 7700 117.8 4.8 179.5 16800 0.5 40.0 0.406 5.7 1760 4.1 2.8

Wm. Rogers pottery kiln waster 9.14 2.55 5900 6500 133.4 6.4 129.5 21700 13.0 47.3 0.572 9.0 3470 4.1 3.7

Morgan Jones pottery kiln waster 7.37 1.61 n.d. 6300 104.4 7.0 72.8 14200 3.5 46.0 0.638 8.1 2760 4.4 4.2

Comparative Old World samples

London, Compter Prison, 1787 6.40 4.42 14700 4300 145.7 7.0 564.0 19900 36.3 46.4 0.469 9.3 2860 2.8 3.8

London, Blossom’s Inn, 18th c. 5.42 4.32 4849 4600 106.3 6.0 588.7 17100 7.2 35.8 0.500 8.2 3090 2.7 3.4

In ppm, except %Al and %Fe. n.d., not detected.

Sb,

ppm

Ba,

ppm

Ce,

ppm

Cs,

ppm

Cr,

ppm

Co,

ppm

Eu,

ppm

Hf,

ppm

Nd,

ppm

Rb,

ppm

Sc,

ppm

Ta,

ppm

Tb,

ppm

Th,

ppm

Zn,

ppm

Zr,

ppm

0.44 293 55.1 2.5 40.1 6.5 0.87 10.75 23.1 57 6.4 1.09 0.65 7.6 50 337

0.11 32 5.2 0.2 3.0 1.0 0.09 0.79 3.8 2 0.5 0.10 0.11 0.6 10 80

0.37 264 46.5 2.8 46.5 6.1 0.67 9.81 17.9 58 7.7 0.99 0.54 8.2 50 300

0.09 26 3.6 0.2 2.0 0.3 0.03 0.53 3.0 6 0.2 0.07 0.06 0.4 10 610.40 303 60.1 3.0 51.5 7.6 0.91 11.31 23.2 66 8.0 1.24 0.74 8.9 60 329

0.25 66 6.3 0.3 8.9 0.9 0.12 1.04 4.0 6 1.3 0.14 0.14 1.3 10 86

0.59 342 63.4 3.2 51.4 8.0 0.96 11.67 24.1 72 8.3 1.21 0.77 9.6 50 348

0.06 76 7.2 0.4 7.0 0.4 0.10 1.38 4.0 14 0.9 0.20 0.17 1.1 0 94

0.84 192 38.9 1.6 28.1 4.9 0.68 9.00 16.8 47 4.5 0.74 0.56 5.3 50 157

0.14 51 6.0 0.2 3.5 0.2 0.10 2.07 5.9 12 0.5 0.01 0.07 0.5 0 560.38 148 37.3 1.9 32.9 4.4 0.56 7.36 11.9 34 5.1 0.74 0.47 5.4 30 177

0.07 41 3.3 0.3 5.4 0.2 0.15 0.81 4.0 7 0.5 0.07 0.14 0.6 0 38

0.50 95 29.5 1.0 20.7 4.0 0.70 6.19 14.8 16 2.8 0.55 0.57 3.5 10 180

0.62 24 6.6 0.1 4.1 0.7 0.18 1.75 4.9 4 0.3 0.05 0.18 0.8 10 23

0.69 185 70.1 3.5 48.2 4.5 1.09 18.76 29.9 56 7.0 1.79 0.99 9.3 30 536

0.04 40 3.4 0.1 3.3 0.1 0.14 0.22 3.6 5 0.2 0.10 0.09 0.1 0 81.04 207 58.8 7.9 97.4 7.0 0.82 10.17 26.4 101 15.1 1.40 0.60 15.8 40 316

0.17 54 2.8 0.4 3.8 0.5 0.13 0.10 2.0 13 0.8 0.13 0.13 0.9 10 59

0.98 241 75.0 4.1 63.2 5.7 1.19 13.24 38.8 75 9.9 1.53 0.88 11.7 80 259

0.62 340 73.8 4.6 71.9 4.4 1.05 14.01 30.1 85 11.0 1.63 1.12 12.3 30 364

0.72 357 73.9 6.6 92.0 6.0 1.07 10.17 29.5 112 14.1 1.39 0.79 12.6 50 244

0.77 320 76.0 5.5 85.4 6.0 1.10 11.46 27.0 98 12.7 1.48 0.86 13.0 70 281

0.37 309 71.9 5.5 83.9 4.9 1.09 12.26 30.4 103 11.8 1.47 0.85 12.6 50 306

0.64 322 73.2 4.4 68.3 4.4 1.05 14.75 28.4 87 10.6 1.49 0.95 11.9 50 340

0.70 279 77.0 4.9 81.7 5.3 1.16 13.06 29.0 94 11.5 1.56 0.84 12.5 50 340

0.57 320 70.2 5.6 82.6 6.8 1.09 10.75 29.1 89 12.7 1.32 0.76 12.2 80 318

0.71 366 79.1 6.7 100.9 6.6 1.14 11.08 28.8 123 14.8 1.55 0.85 14.2 60 272

0.63 340 73.7 6.0 88.6 5.2 1.06 11.20 28.5 107 13.1 1.44 0.94 12.9 50 356

0.54 271 71.1 4.8 71.4 5.1 1.07 12.20 29.4 78 10.4 1.44 0.87 11.9 40 326

0.62 361 71.8 4.2 64.9 4.1 1.12 14.37 26.6 79 9.8 1.48 0.83 11.2 40 354

0.73 297 74.6 4.5 74.4 4.6 1.17 13.05 32.0 80 10.9 1.41 0.79 11.8 40 333

0.48 337 73.3 4.4 70.6 4.7 1.08 14.81 30.6 83 10.4 1.49 0.86 12.0 30 373

1.72 319 76.1 3.8 61.4 4.4 1.19 15.62 36.5 64 9.4 1.54 1.01 12.0 40 273

0.78 330 72.5 3.7 69.3 4.3 1.12 14.48 26.7 69 10.2 1.47 0.83 12.1 30 404

0.50 324 77.4 3.9 65.3 4.6 1.20 16.17 25.8 84 9.4 1.57 0.95 11.6 50 388

0.62 325 73.8 5.2 79.8 5.2 1.10 12.55 29.2 94 11.8 1.47 0.87 12.4 50 324

0.11 30 2.4 0.8 10.6 0.9 0.04 1.59 1.4 14 1.5 0.08 0.09 0.7 20 39

0.40 319 72.1 2.6 45.2 7.8 1.13 12.08 22.2 62 7.1 1.22 0.85 8.5 60 297

0.58 467 84.3 3.0 53.3 8.7 1.25 13.68 28.7 70 8.3 1.44 0.98 10.0 70 283

0.53 227 53.0 3.7 53.2 5.2 0.85 13.16 22.8 68 8.6 1.09 0.71 8.8 50 327

0.60 192 61.8 3.9 56.5 5.5 1.06 11.33 25.4 70 8.3 0.88 0.72 7.3 40 275

0.99 692 80.1 9.9 101.3 17.6 1.50 8.05 31.7 121 12.6 1.14 1.05 13.0 80 151

1.19 264 67.4 4.7 63.5 7.5 0.96 13.86 27.0 75 10.1 1.19 0.82 10.7 50 262

1.25 412 70.3 6.8 89.8 5.1 1.00 9.95 43.1 86 14.3 1.28 0.80 13.2 50 179

1.62 514 91.3 5.1 65.4 7.9 1.52 15.60 48.4 99 12.3 1.64 1.46 11.1 80 308

0.74 443 80.8 5.1 66.3 7.0 1.30 14.02 37.1 75 13.8 1.39 1.08 12.2 80 268

0.74 546 113.8 6.6 76.7 19.9 1.96 5.73 55.4 172 17.6 1.30 1.44 14.8 130 70

1.21 325 75.0 12.4 105.0 11.5 1.39 6.94 40.8 151 13.0 1.07 0.86 12.0 100 122

1.41 477 78.9 6.4 79.5 10.4 1.11 10.31 36.0 143 14.6 1.58 0.90 12.7 70 194

2.33 659 101.8 7.1 96.9 5.9 1.72 11.22 55.5 118 18.1 1.51 0.93 14.2 90 235

1.22 454 97.8 6.1 81.8 10.0 1.74 14.13 52.9 99 15.5 1.46 1.25 12.5 60 258

12.73 394 80.5 6.3 107.3 63.8 1.45 6.34 65.7 60 13.3 0.89 0.76 8.6 170 162

3.46 456 167.7 5.0 106.6 52.7 1.57 10.90 39.1 92 11.5 0.89 1.01 9.9 40 279

622 R.A. Armitage et al. / Journal of Archaeological Science 33 (2006) 615e627

Table 4

Summary of petrographic analysis results

Quartz aplastic grains Other aplastic grains Clay fabric

Sample Location

on Fig. 1

Silt to VFS

0.0625 to

0.125 mm

Fine sand

0.125 to

0.25 mm

Medium to

coarse sand

0.25 to 2 mm

Silt-sized

brown

biotite

Other Clay

pellets

Vitrified

material

Evidence

of clay

mixing?

Omar, QoMill Field A 25% 10% e Trace Plagioclase (1) e e e

Brick Pit B 25% e 15% Trace Quartzite 1% e e e

VC Field C 25% e 15% Trace Quartzite (trace) e e e

St. Barbara’s D 60% e 1% e e <5% e e

Maryland Point, Qm

St. John’s Upper E e 85% Trace Trace e e e e

St. John’s Lower E e 85% Trace Trace e e e e

Chicamuxen Church, Qc

St. Mary’s Hill Upper F 40% e Trace Trace e 1% e No

St. Mary’s Hill Lower F 10% e e e e e e Yes

Brick Chapel building materials

Chapel 4 50% e Trace Trace e e 50% No

Chapel 5 25e50% e 1% e Chalcedony (1) Trace e Yes

Chapel 7 25e50% 1% e e e 10% e Yes

Chapel 9 35% e 5% e e Trace 15% Yes

Chapel 12 25% e 5% e e 5% 50% Yes

Chapel 13 40% e 5% e e 3% 3% Yes

Chapel 15 60% e 1% Trace Polycrystalline quartzite (1) 10% e Yes

St Mary’s Chapel tileb 50% Trace e e e ea e e

Other 17th-c. bricks, St. Mary’s CityPriest House 1 40% Trace 10% e e e fragment (1) No

Priest House 2 25% e 15% Trace e e e No

St John’s, Phase I 35% e e 1% e e e No

Van Sweringen 40% e e Trace e 1% e No

St Peter’s 10% e Trace Trace e 1% e Yes

State House 40% e e e e e e No

Comparative 17th-c. materials, VAFlower Dew Hundred tileb Trace 10% e e e Trace e e

Jamestown Str. 102 tileb Trace 10% e Trace Epidote (1) Trace e e

Morgan Jones kiln waster 50% e e e e e e e

‘‘Spanished’’ bricks, London

Compter Prison 25% 25% e e Shale, chert, zircon (1 ea.) e e Yes

Compter Prison, replicate 25% 25% Trace e Rock fragment, chert (1 ea.) e e Yes

Blossom’s Inn 45% 5% e e Shale (2) e e e

a Observed visually in tile fragment, but not in thin section.b Thin section samples under 70 mm in size; may not be representative of the larger object.

possibility, additional sample tiles were made using the localclays in combination with charcoal, wood ash, beach sand,and crushed oyster shell (all of which would have been abun-dantly available in 17th-century Maryland). No vitrified re-gions were observed in any of these experimental tiles,regardless of firing temperature, which ranged from 540 to1100 �C. None of these experimental materials were includedin the INAA or petrographic studies. Two 18th-century bricksfrom London which were manufactured using the ‘‘Span-ishing’’ technology were provided by I. Betts at the Museumof London Specialist Services to compare the resulting inclu-sions to the vitrified areas in the Chapel bricks. While fugitivepores (without vitrified margins, resulting from the combus-tion of organic material) occur in both the Chapel bricks andthe ‘‘Spanished’’ bricks from London, there were fewer

vitrified areas overall in the London bricks. These observationsand the differences in mineralogy strongly indicate that theChapel bricks were not manufactured using a ‘‘Spanishing’’technique like that used later in London.

4.2. INAA

INAA results are given in Table 3. Petrographic analysisdetermined that the local clays contained large and variableamounts of sand, which is predominantly quartz (SiO2). Nei-ther Si nor O can be easily measured using INAA. The addi-tion, or natural presence, of large amounts of quartz sandeffectively dilutes the contribution of the clay component inthe bulk sample and hence reduces the concentrations of ele-ments associated with that component. To determine the extent

623R.A. Armitage et al. / Journal of Archaeological Science 33 (2006) 615e627

of this dilution effect, each element concentration (Table 3)was plotted against aluminum concentration. Aluminum wasselected for comparison because it is a major elemental com-ponent of clay minerals and thus can be used as a measure ofthe clay content of a sample.

For the local clays from the Qo and Qm deposits, most el-ements covaried positively with Al as expected. The Chapelbricks, which lacked the medium and coarse sand fractions(Table 4), had higher overall concentrations of most elements(Table 3). Significantly, however, a few key elements includ-ing Hf, Zr, and Ti did not covary with Al in the Chapel bricksor in the St. Mary’s Hill (Qc) clays (Fig. 4). These elementsare characteristic of heavy mineral sands, where Hf substitutesfor Zr in zircons and Ti represents rutile. The negative corre-lation in Fig. 4 indicates that the Chapel bricks contain Zr min-erals that do not naturally occur in the Qo and Qm deposits.The Qc deposit, represented by the upper stratum at St. Mary’sHill, may be the source of these heavy mineral sands.

Because it is impossible to directly visualize all of the rela-tionships between sample groups based on all of the elementsmeasured by INAA, principal component analysis (PCA) istypically employed to reduce the dimensionality of the data.PCA is a mathematical procedure that transforms the originalvariables, based on their degree of inter-correlation or covari-ance, into a fewer number of principal components, which aresimply linear combinations of the original variables that max-imize the amount of covariance accounted for and which arethemselves uncorrelated [9]. The resulting principal compo-nents represent the major dimensions of variability withinthe data set, and can be interpreted from the total structure co-efficients, or the degree of correlation between the originalvariables and the new composite one. A plot comparing theprimary principal components will thus illustrate the overalldifferences in elemental compositions among groups ofsamples.

Fig. 4. Bivariate plot of Zr and Al showing negative correlation between the

Chapel bricks and the local clays. Ellipses indicate 95% confidence limits.

In the trace-element data, the first principal component ac-counts for over 50% of the variance (Table 3). Aluminum andmost other elements correlate positively with the first principalcomponent, a pattern consistent with simple dilution[31,32]din this case, by quartz sand temper. In contrast, thesecond principal component (accounting for an additional15% of the variance) represents the heavy mineral sand com-ponent (Ti, Hf, Zr), which negatively covaries with cobalt,manganese, antimony, and arsenic.

Based on their scores on the first two principal components,local clays from the Qo and Qm formations are broadly similarto each other in composition (Fig. 5a); their distribution alongPC1 suggests that textural differences and dilution effect theelement dilution to a variable degree. In contrast, clays fromthe Qc formation, particularly those of the upper deposit, arequite distinct; here, the low scores on PC2 reflect the unusuallyhigh concentrations of elements associated with heavy mineralsands.

Among the historic bricks and tiles, bricks from the Priest’sHouse and St. John’s show strong similarities to the predomi-nant local (Qo) clay grouping (Fig. 5b). In contrast, the Chapelbricks show minimal overlap with the Qo clays and initiallyappear most similar to clay of the lower Qc stratum. The St.Peter’s brick (which is similar in appearance and mineralogyto the Chapel bricks) groups with the Chapel based on chem-ical composition as well.

Multivariate probabilities of group membership confirmthese general conclusions. Based on scores on the first fourprincipal components (jointly accounting for 86% of the vari-ance), the Mahalanobis distance statistic indicates that none ofthe Chapel bricks had greater than a 1% probability of belong-ing to the local Qo, Qm, or combined QoeQm clay groups,although bricks from the Priest’s House and from St. John’s,along with the Chapel flat tile, could be assigned to these localclay sources (P > 0.05). Small sample sizes precluded testingthe affiliation of the Chapel bricks with the upper or lower Qcclays. Conversely, none of the Qo, Qm, or Qc clay sampleshad greater than a 1% probability of membership in the groupdefined by the Chapel bricks, although the brick from St. Pe-ter’s had a high probability of group membership (P ¼ 0.53).

Relative to other historic materials, the Chapel bricks dooverlap with the Virginia group on the first two PCs, indicatinga general similarity in composition. However, based on themultivariate probabilities of group membership, none of theVirginia samples showed a significant probability of belongingto the Chapel brick composition group. Two of the Virginiasamples (the Morgan Jones kiln waster and the flat tile fromJamestown structure 100) showed a low probability of belong-ing to the QoeQm clay group, a similarity probably reflectingthe spatial continuity of these deposits in VA as well. In con-trast, the 18th-century ‘‘Spanished’’ bricks from London, aswell as the ‘‘Dutch’’ brick from the Van Sweringen site atSt. Mary’s City, are clearly distinct and separate from the threegroupings in Fig. 5b. This suggests that if any of the presumedNew World materials were imported from Europe, they wouldlikely exhibit this significant difference. While the pantilesfrom Virginia appear to be similar to the European materials

624 R.A. Armitage et al. / Journal of Archaeological Science 33 (2006) 615e627

Fig. 5. Principal component analysis showing sample groups: (a) local St. Mary’s City clays, grouped by geologic formation; (b) building materials in relation to

the three clay-bearing formations sampled. Ellipses indicate 95% confidence limits.

based on PC1 and PC2 (Fig. 5b), cluster analysis on all fourPCs indicate that the pantiles are more similar to the other Vir-ginia materials than to the European bricks.

4.3. SEMeEDS

NAA can only describe differences in bulk chemistry be-tween materials. Our results from the INAA show only thatthe Chapel bricks form a group distinct from those of the localclays. To compare the localized chemistry of the inclusionswith the bulk clay composition, we utilized SEMeEDS as de-scribed in Section 3. Samples ‘‘Chapel 5’’ and ‘‘Chapel 13’’were selected for further analysis because they visually repre-sented the extremes of the macroscopically-observed inclusiontypes. While some of the other samples contained more of thecharacteristic inclusions, these two contained some of the larg-est inclusions. The major difference in composition from brickmatrix to the clay fragment or soil papule in Chapel 5 was inFe, which increased markedly in the inclusion (ranging from2e6% in the clay to w60% in the inclusion). The inclusionsin Chapel 13 were mostly black vitrified areas surroundingvoids (Fig. 3, inset). The black vitrified margin was chemicallysimilar to the bulk, but with a slightly higher concentration ofK (1.7% in the clay to 2.3% in the vitrified region). A back-scattered electron image of this vitrified rim (Fig. 6) showssmall crystals of relatively high-atomic number elements (pre-dominately Fe) clustering at the void edge. These crystalsprobably formed through the action of a localized flux, suchas K, Mg, or Na, during firing of the bricks [8]. As Fe-bearingclay minerals break down during firing, recrystallization ofiron oxides can occur [36]. The vitrified inclusions, therefore,

appear to occur naturally from the Fe-rich clay fragments un-der as yet undetermined firing conditions.

5. Discussion

The Chapel bricks form a distinct chemical population fromthe sampled local clays (Fig. 5b; Table 3). Based on the sim-ilarities in chemical composition, the Chapel bricks mostclosely resemble comparative materials from Virginia, al-though the multivariate probabilities do not indicate a directmatch. Though importation from the nearby Virginia

Fig. 6. Backscattered electron micrographs of a void within Chapel brick sam-

ple 13. Note the vitrified rim and iron-rich crystallites (bright white) at the void

edge.

625R.A. Armitage et al. / Journal of Archaeological Science 33 (2006) 615e627

settlements could account for these similarities, historicalunderstandings of the political relationship between the build-ers of the Chapel and the colonists in Virginia make such anexplanation highly unlikely. The Chapel was built for RomanCatholics and under the supervision of Jesuit priests. Virgin-ians, like their fellow Protestants in both New and old Eng-land, had a quite intolerant view of Roman Catholics in the17th century. For example, during the original voyage to foundthe colony, Lord Baltimore directed the expedition to avoidstopping in Virginiadspecifically mentioning Jamestowndinfear that the colonists would be molested [19:133].

Alternatively, the compositional similarity to Virginia arti-facts may reflect the underlying continuity in geologic forma-tions between these areas. As noted above, the geology of St.Mary’s County, Maryland is not dominated by any one geologicformation. All four of the formations in St. Mary’s City corre-late with those found at the sites of Flowerdew Hundred,Jamestown, Yorktown (the location of the William Rogerskiln), and the Morgan Jones kiln in coastal WestmorelandCounty [3,23].

There are at least two possible scenarios for the source of theChapel bricks. First, the bricks used in the Chapel and the ma-terials from Virginia may have all been made utilizing the clayfrom one of the more distant, untested formations such as theKent Island (Qk) or Park Hall (a clay-bearing Tertiary forma-tion nearly 1 km from the St. Barbara’s brickyard) in southernMaryland or the equivalent formations in Virginia. These for-mations, however, lie at a greater distance from the Chapelsite than the Qo, Qm, and Qc clays already sampleddclayswhich were demonstrated to have been suitable and utilizedfor brick manufacture in historic St. Mary’s City. The econom-ics of brick production make it very unlikely that either thesource materials or the finished bricks were transported overa long distance.

It is also possible that the Chapel bricks and those from someof the St. Mary’s City buildings were made from a mixture oftwo deposits, such as the Omar and the older ChicamuxenChurch Formation, which lies topographically above the Omarin the transition slope between lowland and upland (Fig. 1, in-set). That would explain the relative compositions. The claysfrom these two formations could have been combined either in-tentionally or inadvertently during excavation. This is consistentwith the visual appearance of some bricks showing two distinctcolors of clay, and is supported by both the petrographic analysisand the chemical composition determined by INAA. While sim-ulated, mathematical mixtures of local clays did not exactlymatch the composition of the Chapel bricks, mixtures involvingthe upper stratum of the Qc deposit as a source for heavy mineralsands show strong similarities to them.

According to McCartan [23], the non-clay fractions fromall four Pleistocene formations contain small amounts ofheavy minerals including zircon, rutile, and ilmenite. Thesource areas for these heavy minerals would lie in the crystal-line metamorphic rocks of the Piedmont and in the ‘‘multi-generational’’ sediments from the Appalachians further tothe west [J. Reger, personal communication 2003]. The ParkHall Formation of southern Maryland is located at the highest

point of the upland terrace and contains sediment derived di-rectly from the Piedmont and Appalachian Mountains [23].The position of the Qc deposits immediately downslope sug-gests that they have been most heavily influenced, through ero-sion and redeposition of the heavy mineral sands.

The nature of the inclusions characteristic of Chapel brickshas not been conclusively determined. They appear to be relatedto firing conditions and chemical environment, probably form-ing from indurated clay pellets that are naturally occurring inthe source material. The black vitrified regions do not resem-ble the inclusions formed using the ‘‘Spanishing’’ process.

6. Conclusions

Some of the bricks used at St. Mary’s City, such as thoseused in the Priest’s House, were clearly made using the sandyclay of the Quaternary deposits of Southern Maryland. Whilethe Chapel bricks do not exactly match the tested locally avail-able clays at St. Mary’s City either chemically or mineralogi-cally, they do bear strong similarities to modeled mixtures ofthese materials. Compared to 18th-century English bricksthat were manufactured using the ‘‘Spanishing’’ process, theChapel bricks do not appear to have been prepared in thesame manner. The inclusions instead appear to be naturally oc-curring and similar in bulk composition to the brick matrix.The chemical compositions of the London and ‘‘Dutch’’ bricksare distinct from that of the Chapel bricks, indicating that thelatter are highly unlikely to be bricks manufactured in Englandusing the ‘‘Spanishing’’ process. The Chapel bricks may havebeen manufactured predominantly from clay obtained fromfurther afield, such as from the Kent Island Formation (Qk,Fig. 1, inset) or corresponding surface deposits from the Vir-ginia Coastal Plain. Alternatively, the Chapel bricks representa complex mixture of local clay sources (likely involving theQc clays) that defies recognition through simple mathematicalmodels.

Although the exact source of the St. Mary’s Chapel bricksremains a fascinating mystery, we conclude with a positivenote. Bricks used in the reconstruction of the Chapel are beingmanufactured from local (Qo) clays from the Visitor’s Centersite (C). Future generations of archaeologists will be able toseparate these reproduction bricks from the original Chapelbricks quite easily, based on their distinctive geochemistryand petrography. This study of building materials from colo-nial Tidewater sites will, we hope, lay the groundwork for fur-ther studies that will aid in understanding the history ofbrickmaking technology in the 17th century.

Acknowledgements

Research funding was provided by DOE University ReactorSharing Program and the Seller’s Research Fund. Thanks to:Nan Richards and Carre Zalma, former EMU students; T.P.Smith and I. Betts, Museum of London Specialist Services;Frannie Skomurski, Eric Essene, and Carl Henderson, Geo-sciences, and James Halloran, Materials Science and

626 R.A. Armitage et al. / Journal of Archaeological Science 33 (2006) 615e627

Engineering, all University of Michigan; geologist Ian Armit-age, Andrews Environmental Engineering, Inc.; and PaulHuey, New York State Office of Parks, Recreation, andHistoric Preservation, for their input, advice, and samples.Special thanks to James Reger, Maryland Geological Survey,and the anonymous reviewers for their helpful comments,revisions, and suggestions in preparing the manuscript.

Appendix. INAA experimental conditions

Data for elements with short half-life isotopes were based ona 1-min pneumatic-tube irradiation, followed by two separatecounts (500 s) of gamma activity after a 13-min and 2-h decay.Data for elements with intermediate and long half-life isotopeswere determined through an extended (7e10 h) core-face irradi-ation, followed by two counts of gamma activity after a 5-dayand 4-week decay (for 5000 s and 10,000 s, respectively), usinga 30e40% high-purity germanium (HPGe) detector. At the FordNuclear Reactor, the pneumatic facility experienced a thermalneutron flux of 2 � 1012 n cm�2 s�1, while the in-core irradia-tion facility utilized experienced an average thermal neutronflux of 4 � 1012 n cm�2 s�1. At the Oregon State University-Radiation Center, the pneumatic facility experiences a thermalneutron flux of 1�1013 n cm�2 s�1 at 1 MW power, while thecore-face rotating rack experiences an average thermal neutronflux of 1 � 1012 n cm�2 s�1.

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