A WORKABILITY COMPARISON OF THREE ONTARIO CHERTS

(A Flint Knapper’s Perspective)

By: Dan Long

Published in Kewa, the newsletter of the Ontario Archaeological Society, London Chapter

Introduction

The intent of this paper is to present a comparison of the workability of three lithic materials used for the manufacture of chipped stone tools by prehistoric peoples in southern Ontario, from a flint knapper’s perspective.

There are several factors which can affect the workability of such materials for the production of chipped stone tools. The dominant factor is, naturally, the ability of the knapper. All other factors are a result of variability within the stone itself. These factors of lithic variability include: the initial size and shape of a given piece of raw material, toughness and grain size of that material, inclusions (both mineral and fossil), the presence of vugs or cavities due to mineral dissolution, hydration and the existence of pre-existing seams or fractures.

Onondaga

Onondaga chert is of Middle Devonian age and occurs in the Onondaga Formation. (Ely and von Bitter, 1989:17; Parkins 1977) In Ontario three members of this formation contain chert; the Edgecliff, Clarence and Moorehouse (in ascending order). And in New York state two additional chert bearing members of the Onondaga Formation have been identified: the Nedrow and Seneca members (Jack Holland....personal communication). The material used in these experiments was obtained near the Lake Erie shoreline west of Port Colborne, Ontario and is of the Clarence member.

Of the three materials, I find that Onondaga, while being the toughest, is also the most consistent in the way it fractures. It provides the most predictable fracture and is available in the largest pieces. Because of these factors it can generally be worked from the form of a spall rather than an angular block. Inclusions are rare, especially in the form of macro fossils, but coarse areas of lower silica content are generally present in most pieces of any size. They appear as somewhat granular pockets that tend to exhibit a sugary appearance in fresh material. When patinated, these pockets will appear brown in colour in contrast to the gray of the surrounding chert, and in extreme cases, where buried in very acidic soils, dissolution or pitting may be evident. These areas often prove to be tougher and less workable than the surrounding, higher grade rock, but I have found that these grainy areas are much easier to flake through when the piece is fresh from the ground and hydrated. Given the opportunity to dry out, these areas become extremely tough and will often cause the premature termination (step or hinge fracture) of a flake driven into this part of the stone.

Onondaga is a fairly forgiving material in that the knapper can often “get away” with a poorly executed or inaccurate percussive blow that would have spelled disaster when knapping other, more workable lithic materials. Striking platforms on Onondaga preforms are required to be

stout and well abraded. The material responds well to aggressive percussion. Being a petrolithic chert, Onondaga exhibits a highly unusual characteristic when knapped; it gives off the scent of crude oil when freshly flaked. And strangely enough, the higher the silica content of a given piece........the stronger the smell!

Heat treating of Onondaga produces no change in workability. Experiments have shown no change in the ease of flaking with gradually increased temperatures up to the point that thermal damage occurs (crazing and pot-lidding).

Fossil Hill

Occurring as part of the Fossil Hill Formation (Ely and von Bitter, 1989:22) of the Niagara Escarpment, this chert is middle Silurian in age and is best known for its extensive use by Paleoindian peoples (e.g. Storck and von Bitter 1989). The material used for these experiments was obtained from bedrock sources near the town of Red Wing, Ontario.

I find Fossil Hill chert to be a most unusual material. Of all of the cherts I have worked over the last 14 years, this is one of the most variable. Fossil Hill demonstrates the most variability in any one given piece of rock.

Having only worked Fossil Hill from one source, I can only comment on what I have seen from this outcrop. A major consideration affecting anything to be manufactured from this stone is the amount of fracturing evident in the material when it comes out of the ground, as there are numerous fractures running vertically throughout the blocks. Generally this translates into a block, rather than a spall as the starting point for any reduction. This immediately results in a limitation of the size of the final product as material is wasted in producing an edge suitable for the removal of long thinning flakes. In my experience most bedded material, when quarried, will provide the longest blanks from the horizontal plane of the outcrop, but due to this vertical fracturing the longest pieces of Fossil Hill chert are vertically oriented. This may be a possible explanation as to why the banding in most Ontario fluted points made out of Fossil Hill chert is perpendicular to the long axis of the point and not parallel to it as one would expect to find in most bedded materials (see Roosa and Ellis, 2000:84-85).

Inclusions are sometimes a problem in Fossil Hill, and generally they are mineral as opposed to fossil. Pockets of iron pyrite and quartz crystal of up to 1 cm. in diameter are fairly evident in some pieces and often of a size large enough to render a piece unknappable (especially if a Paleo point is the desired outcome) as these inclusions create weak areas in the blank.

As previously mentioned, I found this material to be extremely variable and therefore somewhat unpredictable. Most of the blocks I worked showed banding in two or three varieties; glossy gray, white and a mixture of gray and white that I refer to as “lace” due to its appearance.

These areas all responded differently to knapping pressures. The gray areas were the most unusual. In addition to being the tougher of the three bands, it also repeatedly demonstrated a highly irregular trait that I haven’t witnessed in any other material. Percussion flakes would, on occasion, “dive” into the piece creating something of a concavity near the middle of a blank.

This type of diving flake can be generated intentionally and was used to produce certain artifact types (ie: Texas Montells and some Turkeytails) that are actually thinner in the middle than near the edges, but I have not personally seen any evidence of this technique demonstrated on any points from Ontario. This knapping strategy was used to create wide, thin points and would

have been a technique counter-productive to the making of Paleo points, which generally exhibit a median ridge.

The areas of white banding, although not as glossy as the gray, worked a little more easily and much more predictably. The “lace” areas were the least desirable as these areas proved to have less tensile strength and often proved crumbly when flaked; special care has to be taken in order to ensure that flakes do not terminate in step fractures. When preparing a preform for fluting, if this material was at the base I would intentionally shorten the piece to eliminate the lacy area knowing that it would never withstand the stress to which a fluting nipple is subjected.

There appeared to be no difference in Fossil Hill worked wet (hydrated) or dry and although heat treating did produce increased glossiness and some colour change to pale pink, no appreciable difference in workability was noted.

Given this variability, I am of the opinion that the early Paleo peoples of Ontario chose this material primarily for its aesthetic value.

Lockport

Lockport chert, like Fossil Hill chert, is middle Silurian in age and occurs in the Goat Island member of the Lockport Formation. (Ely and von Bitter, 1989:20). This material was obtained from a dry creek bed on the top of the Niagara Escarpment at Mount Albion Rd., Hamilton.

Of the three materials discussed here I found the Lockport chert to be the easiest to flake from the standpoint of toughness. The greatest limiting factor in this material is size.....or lack thereof. Most of the pieces worked came in the form of small cubes, as opposed to the Fossil Hill which generally started out as elongated rectangular pieces.

Lockport is a fairly chalky material when fresh but seems to exhibit more glossiness when patinated. It has less tensile strength than either Onondaga or Fossil Hill, making it easier to flake, but as the knappers’ adage goes, “Easy to make......easy to break!” I was pleased and surprised to find that this material was strong enough to withstand fluting attempts. As with most materials of a chalky nature, step fracturing can be a factor. As a result of this tendency to step fracture, it’s in the knapper’s best interest to adjust his reduction strategy accordingly. As a rule, the trade-off is to take shorter flakes as opposed to the longer flakes that are possible in a material with a higher silica content. Materials of this type also require considerably more abrasion during pressure flaking to prevent platform collapse.

There are a variety of inclusions in Lockport, including a good number of visible fossils. I did find that most of the inclusions are well silicified and didn’t hinder flaking in any way. However, there are areas of tough, sandstone-like material with a markedly grainier texture that appear frequently and are completely unflakeable. Heat treating of this material produced a slight colour change to pale pink, but no increase in glossiness or workability was noted.

Conclusions

As is the case with most lithic materials, there is a range of workability in any given type of chert and a variability between cherts of different types. This variability and the constraints of the natural size and shape of the lithic material affects the ease with which artifacts may be produced, both in prehistory and the present. The physical composition of a material will, to a certain extent, determine what range of tools may be produced from it due to the principles of fracture mechanics and the ability of the rock to do what is asked of it by the knapper. The size and thinness of an artifact, although more dependent on the flint knapper’s skill, is greatly determined by the character of the raw material used to produce that artifact.

References

Eley, Betty E. and von Bitter, Peter H.

1989 “Cherts of Southern Ontario”

Royal Ontario Museum, Publications in Archaeology, Toronto, Ontario.

Holland, John D. (Jack)

Holland Lithic Laboratory

Buffalo Museum of Science

http://www.hollandlithiclaboratory.com/

Parkins, William

1977 Onondaga Chert: Geological and Palynological Studies as Applied to Archaeology.

Unpublished MSc Thesis, Department of Geological Sciences, Brock University,

St. Catharines, Ontario

Roosa, William B. and Christopher Ellis

2000 Fluted Points and Other Bifacial tools. In An Early Paleo-Indian Site Near Parkhill, Ontario

by Christopher Ellis and D. Brian Deller, pages 67-96. Canadian Museum of Civilization,

Archaeological Survey of Canada, Mercury Series Paper, Number 159.

Storck, P.L. and P. von Bitter

1989 The Geological Age and Occurrence of Fossil Hill Formation Chert: Implications for Early

Paleo-Indian Settlement Patterns. In Eastern Paleoindian Lithic Resource Use, edited by

Christopher Ellis and Jonathan Lothrop, pages 165-189. Westview Press, Boulder, Colorado.