This Week in Pennsylvania Archaeology comes to you from archaeologist Robert Bodnar with help from geologist Robert C. Smith II and archaeologist Hettie L. Ballweber. Mr. Bodnar and colleagues have been investigating metarhyolite quarries in the South Mountain area of Adams and Franklin Counties of south-central Pennsylvania for many years. The following is a preliminary report on their recent work at one quarry location.
By way of background, metarhyolite (commonly listed as rhyolite in the older literature) is a metamorphosed volcanic rock found in different colors, most commonly dark blue or banded but this quarry is located in the less common, purple variety. The material flakes well and is good for stone tool manufacture. Native Americans began using it at least 10,000 years ago and beginning 4000 years ago, it was intensively used and traded in the Susquehanna, Delaware and Chesapeake Bay drainages. The research presented below is the initial step in understanding how groups of Native Americans used these quarries and how this material was distributed throughout the Middle Atlantic region.
Mr. Bodnar can be contacted at firstname.lastname@example.org with any questions you might have. We hope you enjoy this presentation.
Seeing Purple: Archaeological Investigations of a Prehistoric Metarhyolite Quarry on South Mountain in Adams County, Pennsylvania.
On June 16, 1994 an article was published in the Gettysburg Times titled: County’s First Industry: Rhyolite Richness. It was written by the late Dr. Louis S. Morgan of Wichita, Kansas. Morgan grew up on a farm in Adams County, Pennsylvania and attended high school in Gettysburg. It was during his childhood that he was expected to follow behind his family’s horse-drawn plow. During this arduous task, he had fun collecting the prehistoric artifacts (he notes sometimes made from purple rhyolite - aka metarhyolite) that the plow would turn up.
The metarhyolite stone artifacts (spear points, etc.) that Dr. Morgan happily collected were the finished products of an industrial process that began at one of the prehistoric metarhyolite quarries that dot the landscape on South Mountain in Adams and Franklin Counties in Pennsylvania.
Based on the analysis thus far, it is postulated that a Middle Woodland, Selby Bay phase (dating 1800 to 1100 years ago), single component quarry site was discovered. Thomas Mayr (1972) first defined the Selby Bay phase characterized by Selby Bay points. Henry Wright (1973) recorded some variants of the Selby Bay point (stemmed, lanceolate, and side-notched) among other things. With respect to the quarry under investigation, Curry and Kavanagh (1991) as well as Mayr (1972) note that one of the most common Selby Bay traits is their almost exclusive use of metarhyolite for their flaking material. The Selby Bay quarrymen traveled from the coastal plain areas to the distant Catoctin and South Mountains for their desired metarhyolite, although some trading cannot be ruled out. A radiocarbon date of A.D. 410 +/- 30 was obtained from Trench 1 in 2019. The dated charcoal sample was removed from a burning event located near the bedrock at 93 centimetres in depth. This date fits well within the Selby Bay Cultural Complex A.D. 300 – 700 (Wright 1973) and A.D. 200 – 900 (Inashima 2008). In addition to the radiocarbon date, five Selby Bay related artifacts have been recovered from the two trenches.
Based on the evidence gathered thus far, the Selby Bay quarrymen were likely following an industrial quarry site procedure consisting of: material extraction, reduction and removal of low grade material, and rough-out/preform production (Sullivan and Rozen 1985). Some limited final tool production also took place. The target “ore” here seems to be an aphanitic phase of the circa 564 million year old Catoctin Metarhyolite (Aleinikoff et al., 1995). This formation began as a near surface volcanic flow that was later metamorphosed forming metarhyolite. The matrix appears to be a dusky purple and the interstitial igneous flow breccia with various, more reddish hues (personal communication Smith II, 2020). In Trench 1 the target ore was dusky purple in the form of buried float slabs near the bedrock interface. In Trench 2 the target ore seems to be a dusky purple with more reddish hues occurring as float.
Heavily worked float boulder protruding from the northern wall of Trench 2. The photo scale is one meter.
When interpreting the extraction process that took place, research from Hatch (1993) lends some guidance. His quarry development model proposes three stages of extraction which seem to fit, with modification, the evidence that is being uncovered at the current quarry site.
Stage one involves the quarrymen detaching a suitable piece of material from an exposed bedrock source or simply selecting useable surface material. Cresson (2015 personal communication) states that the quarrying of exposed surface material is common during the Middle Woodland period (2100 to 1100 years ago). To aid in the detachment process, large hand held hammerstones were most likely employed. Hammerstones are the principle quarry tool being found at the site. Ritchie (1929) states that “the hammer is the tool of tools. No single implement was more indispensable to primitive man”. The quarry site hammerstones were made predominantly from diabase, but metarhyolite, quartz, metabasalt, and quartzite were also observed in decreasing amounts. Most of the hammerstones are broken and many are very fragmented. Two types of diabase hammerstones were used. The most common type was medium-grained York Haven Diabase, and the second type was a fine-grained Rossville Diabase (personal communication Smith II, 2020). Interestingly, the nearest diabase source is many miles distant and some of the fragments weigh up to 19 pounds. Tremendous effort was put forth by the quarrymen just to get the diabase hammerstones to the site.
|Diabase hammerstones: 19 pound medium-grained quarry boulder left, smaller Rossville Diabase pictured|
Stage two of Hatch’s quarry development model would involve the quarrymen digging around a near surface exposure in order to get at the targeted ore. Two hoe-like metarhyolite digging tools were recovered from the quarry excavation which would help with this task. Hatch states that stage two can be a progression into stage three. That would depend on the surface exposure’s size, and whether targeted ore was encountered as bedrock.
Finally, stage three, as Hatch describes, would be a progression to larger, deeper, and more labor-intensive quarry pits.
Initial data from Trench 2 indicates that the quarrymen began digging at an exposure (stage two) and then followed the targeted ore vertically and horizontally. As the quarry workers exposed, extracted, and reduced the targeted ore, they discarded their waste behind them leaving a larger deeper pit (stage three) filled with the debris of their labor.
Two different reduction technologies (tool making strategies) were likely being employed at the site: discoidal core reduction (Terradas 2003) and staged bifacial reduction (Callahan 1979). During the Selby Bay Middle Woodland Period both technologies were used (Stewart 1992 and Cresson n.d.). Evidence of discoidal core reduction at the site included numerous discoidal cores, trihedral platform flakes, and flake preforms.
Basically, this reduction method is straight forward: hit then flip, hit then flip in a circular fashion. When the core is flipped, the flake scar on the reverse side becomes the next striking platform (Clarchaeology 2013).
Example of flake preform (personal communication Nissly, 2020).
Exhausted discoidal cores were numerous at the site. Sizes varied from large 11+” in diameter to smaller 2.5” in diameter.
Evidence of the staged bifacial reduction technology from the site.
Dr. Morgan ended his article in the Gettysburg Times with a hope that his donation of thousands of artifacts (some purple) might someday be beneficial to a person wanting to learn more about the great rhyolite industry that drew a distant people, like the Selby Bay, to a place now called Adams County, Pennsylvania.
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