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Vanport Siliceous Shale
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Kenneth Burkett


During the Pleistocene epoch, periodic episodes of extensive glaciation intruded deeply into northwestern Pennsylvania covering what are today sections of Erie, Crawford, Warren, Venango, Mercer, and Butler counties. These movements deposited massive drifts of displaced soil and rock that still cover most of the landscape in depths ranging from 3 to more than 50 feet (Crowl and Sevon 1999). This till often contains varieties of Onondaga and Huronian series pebble cherts now deposited far from their derived sources in western New York and Canada. Throughout prehistory, the Native Americans of this region literally lived upon the source of this good quality lithic material from which they manufactured their chipped stone tools and projectile points. Obtaining desirable glacial pebble cherts was an entirely different matter however, for the less fortunate neighbors occupying the unglaciated sections of the Allegheny Plateau.

Glacial Deposits in Northwestern Pennsylvania

Beyond the glacier’s terminus, till occurs only as outwash sediment that is strictly confined within the primary channel of the Allegheny River and its tributaries flowing from the northwest. Without ongoing links of trade, people residing in the uplands to the east of the river would have been required to make extensive journeys to reach the closest available source. As most of the middle Allegheny River Valley is confined within a narrow steep-sided valley without large elevated floodplains, such trips would certainly have been seasonally restricted to periods of very low water level when gravel bars are exposed and accessible. When flowing normally, the river would unquestionably have created a formidable barrier that required crossing in order to reach the upland glacial terraces of the opposite shore. While glacial pebble cherts appear to have always been the preference for tool manufacturing. these people certainly explored their homelands for other lithic outcroppings. When an alternate source of usable material was found it was exploited even when of an inferior quality.


Associated with the Allegheny geologic group, Jefferson County Chert is the single known bedded sedimentary chert that occurs within the geologic strata of northwestern Pennsylvania (Dodge 1998 pers comm.). Jefferson County Chert is actually an opaque siliceous shale with a basically smooth texture. Vanport Siliceous Shale is a more proper name in geologic terms. However, the materials association with Jefferson County and its limited distribution, and previous references to Jefferson County Chert in the archaeological literature, make terminology problematic. This material exists as part of a shaley deposit near the top of the Vanport limestone and is generally intermixed with, or is found just below a zone of siderite. The layer is discontinuous throughout the area and ranges from only a few inches to a little over a foot in thickness. Historically the occurance of the Vanport Siliceous Shale with siderite at the top of the Vanport Limestone was referred to as “buhrstone ore”. Ironstone ore, iron carbonate and ironstone are other names for siderite (Rogers 1858: 568-572). Where the ironstone cap is thinnest, the siliceous shale is generally hard and compact, whereas the ironstone commonly contains a more open or sponge-like structure that in places appears as crusts rather than solid nodules or concretions.

The material frequently contains numerous marine fossil inclusions primarily of the Mesolobus and Lingula genera of brachiopods. Utilizing a Munsell Soil Color Chart (1988) to compare dry raw surface samples, it is found in two principal color ranges which are Black: 5YR2/1 2/0 to a Medium Gray: 10YR 6/1, and a Light Tan: 10YR 6/3 to a Grayish Orange: 10 YR 7/4. A higher quality mottled variant of the lighter colors is also occasionally encountered within the same outcrop, but is much more rare. All of this material exhibits a lighter colored rind after weathering. When subjected to extensive heat it becomes variable shades of a darker red or maroon.

The Vanport Siliceous Shale is similar in color, texture and weathering to some of the darker varieties of the Schoharie/Esopus series cherts that can be found in Carbon County Pennsylvania and Ostego County New York (Holland, pers comm.1989). Early geologists refer to the Esopus cherts as “Bowmanstown Chert”, while Fogelman (Fogelman 1983) referred to it as “Carbon County Chert”, and more recently as Cherry Valley Chert (Fogelman 1999). The resemblance between these two is only visual however, as Esopus originates from the Devonian geologic period, while the Vanport series is Pennsylvanian.

Although the geologic formation containing buhrstone ore is widespread within Armstrong, Clarion and Jefferson counties, it is currently known to outcrop with this fair quality chert only in a relatively small area of less than 60 square miles that is centered approximately four miles south of the borough of Brookville in a locale that is almost entirely within the watershed boundaries of the Redbank Creek.

Jefferson County Chert Outcrop Area

Capping most of the hilltops at the 1540-foot elevation, it is sandwiched between strata containing the Lower Kittanning and Brookville coals. Unfortunately much of the topography at this elevation has been totally modified due to the combined efforts of small scale quarrying of the buhrstone ore for iron production prior to the civil war, and massive coal strip mining activities of the past five decades. This commercial mining also has presumably eradicated a significant number of prehistoric quarrying locations.

Several known prehistoric quarry sites still exist however, the most prominent being the Campbell Quarry Site (36Je47). Recorded by James Herbstritt in 1979. The site is situated directly above Five Mile Run on a narrow hillside bench covering approximately two acres. The layer outcrops on the steep hillside and exists in situ just below the plow zone. Although exposed quarrying pits are no longer obvious, signs of prehistoric mining activity are evident in the form of surface collected artifacts which include a chipped stone pick/digging tool, hammerstones, pitted anvil stones, numerous reject preforms and early stage bifaces, and abundant unworked material and debitage. While excavations have not been conducted at 36Je47, annual plowing often exposes firepits indicating that a locus of temporary campsites was positioned nearby on level ground adjacent the quarry face. Although diagnostic artifacts recovered here are rare, several Archaic period corner-notched projectiles, and part of a greenstone platform pipe of probable Middle Woodland association have been found.

Pitted Anvil Stone, Hammerstones and Chipped Stone Pick

Preforms and Early Stage Bifaces

Nearly directly across the valley, the Boyer site (36Je151) is on another hillside bench at the same elevation. Although partially destroyed by strip mining, debitage and reject preforms are fairly prolific throughout the small remaining undisturbed portions of this now overgrown hillside bench that originally covered at least two acres. The former property owner described how during his childhood, the family had to backfill fairly large barrow pits of presumed prehistoric origin at this site in order to create suitable pasturage. A search of the landscape along the mine highwall bordering 36Je151 verified that a stratum containing the darker variety of this material tops the bedrock just under a once tilled surface. Samples from a non-archaeological context can be easily obtained from this highwall.

Less than 1 mile to the west, the Hall site (36Je15) is an extensively used springhead campsite that borders a winding benchtop outcrop of the chert.. This site appears to have been utilized as a short-term lithic extraction campsite during many millennia, and has produced a significant number of projectile points and stone tools dating from the Early Archaic forward. An interesting number of Middle Woodland Adena points along with cores, microblades and bladelets made of the tan variety of Vanport Siliceous Shale have been found here.

Artifacts Made From Jefferson County Chert

Numerous rockshelters and open-air sites bordering the upper and middle Redbank creek drainage contain enormous quantities of Vanport Siliceous Shale in the form of debitage and lithic rejects. Examples of diagnostic artifacts from these locations represent every major prehistoric occupational period in northwest Pennsylvania except Paleo Indian, with the most common being representative of the Middle Archiac and Late Woodland periods. This poor grade chert was apparently not considered a highly tradable material as it commonly occurs geographically only within a circumscribed radius of less than 50 miles from the source. It is most commonly found in artifact collections throughout Clarion, Jefferson, Elk, Clearfield, Armstrong, Indiana and Forest counties.

Artifact counts from surface and excavation collections make it quite obvious that the use of this material rapidly diminishes as one moves outward from the Jefferson County source, and the glacial cherts become more readily available. An excellent comparison is two Archiac period sites both within the Redbank drainage. The Hillview site (36Je60) is located within 1 mile of the three major quarry sites described herein. Nearly 100% of the 22,024 lithic debitage flakes and debitage and 46 Brewerton projectiles (84% of the total) from this site are made of Vanport Siliceous Shale. Further downstream along the Redbanks main channel, the Fishbasket Forks site (36Ar135) is nearly equal distances (15 miles) between the Allegheny River and the Jefferson County sources. This site has produced 146 Brewerton projectile points and 1422 debitage flakes of which only 14 points (33% of the total) and 144 flakes (10% of the total) are made of Vanport Siliceous Shale.

Vanport Siliceous Shale has been sporadically recognized and reported in archaeological contexts outside of this geographic region. James Herbstritt reported Late Woodland projectile points of this material at the Bonnie Brook Site (36Bt43) in Butler County (Herbstritt 1981), and also notes its presence within the upper Clarion and Driftwood/Sinnemahoning watersheds (Herbstritt pers. comm. 1999). Jack Holland reports finding Vanport Siliceous Shale at a site near Sinnemahoning, in Cameron County, and at two sites on Kettle Creek which are located on the West Branch of the Susquehanna River in Clinton County (Holland, pers. comm. 1992).

Jefferson County Chert Distribution Area


While Vanport Siliceous Shale was not a widespread, highly prized or heavily utilized lithic resource, it is important that archaeologists recognize this material, it’s distribution and cultural relationships. As its use appears confined to a limited geographical area, a detailed inventory of this material may help to identify resource utilization and regional movements patterns and by prehistoric humans within northwestern Pennsylvania.

This paper provides previously unreported information on prehistoric quarry/workshop sites in Jefferson County associated with the Vanport Geologic member. These unusual hillside/upland bench locations where slopes greater than 10 – 15% grade are dominate the sites landscape is noteworthy. Future archaeological surveys in the Middle Allegheny Drainage where the potential for such site types is great should take into account the “Steep Terrain Model” to assist in identifying these unique archaeological sites.


This paper resulted from the ongoing encouragement and personal support of John D. (Jack) Holland, Director of the Holland Lithic Laboratory at the Buffalo Museum of Science. I would also like to thank Clifford Dodge, Geologist with the Pennsylvania Geologic Survey for assistance with geological information, and James Herbstritt of the Pennsylvania Historical & Museum Commission for his continued advice and insight.


Crowl, George H and Sevon, W. D.
1999 Chapter 15 - Quaternary. The Geology of Pennsylvania, Special Publication 1. Pennsylvania Geological Survey, Harrisburg, PA

Fogelman, Gary L.
1983 Lithics Book. The Pennsylvania Artifact Series, Booklet No. 34. Fogelman Publishing Company, Rd 1, Box 240 Turbotville, PA

Fogelman, Gary L.
1999 Pennsylvania Chert. Fogelman Publishing Company, Rd 1, Box 240 Turbotville, PA

Herbstritt, James T.
1981 Bonnie Brook: A multicomponent Aboriginal Locus in West-Central Pennsylvania. Pennsylvania Archaeologist 51 (3):1-51

Holland, John D.
1999 The Cherts of Northwestern Pennsylvania: Indigenous and Otherwise, Unpublished manuscript presented to the Annual meeting of the Society for Pennsylvania Archaeology, April 24th at Brookville, PA

Inners, John D
1999 Chapter 40 – A, Metallic Mineral Deposits-Sedimentary and Metasedimentary Iron Deposits. The Geology of Pennsylvania, Special Publication 1. Pennsylvania Geological Survey, Harrisburg, PA

Matlack, Harry A
1990 Indians of Clearfield County Self published Rogers, H. D
1858 The geology of Pennsylvania – a government survey: Pennsylvania Geological Survey, 1st series, Volume 2

Munsell Soil chart
1988 Munsell Color, Macbeth Division of Kollmorgen Instruments Corporation, Baltimore, MD.

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