Chert flakes and other debris recovered from the surfaces of four sites in East Central Illinois revealed the types and frequencies of the different types of chert that were exploited by the people of the Paleo-Indian through Historic cultural periods. Each individual flake was examined and assigned an appropriate type to the best of our abilities. The qualities that aided our identification of each flake were its texture, luster, color, and the types of fossils present or not present in the matrix. The presence of oolites, iron oxide, druse, limestone, iron pyrite, and water-worn surfaces were also helpful in the identification process. Utilizing our online decision tree, chert type descriptions and type key images, with the aid of a magnifying glass, I was able to assign a chert type to each flake. Questionable flakes were discussed and examined further with a microscope before concluding and agreeing upon its type.

Three difficulties in identifying some of the chert flakes include: (1)heat treatment, which alters the color and luster of a flake; (2)small size; and (3) too few identifying characteristcs. Fortuantely I only had these probems with a very limited number of the flakes. Such flakes were assigned to the glacial till category, which is the category for the material that cannot be assigned to one of the other chert types. The Burlington and Elwood-Joliet cherts have a wide range of variation and resemble in many ways glacial till. For this reason, we have decided that Burlington, Elwood-Joliet, and glacial till cannot confidently be distinguished from one another. The results of flake counts are as follows:

 

SITE 1. U. 005
Chert Type	Frequency	Percentage
Glacial Cobble	31	81.58
Not Glacial Cobble	7	18.42
TOTAL	38	100.00

 

SITE (?)
Chert Type	Frequency	Percentage
Glacial Cobble	108	85.71
Not Glacial Cobble	18	14.29
TOTAL	126	100.00

 

SITE 112
Chert Type	Frequency	Percentage
Glacial Cobble	351	97.23
Not Glacial Cobble	10	2.77
TOTAL	361	100.00

 

SITE 115
Chert Type	Frequency	Percentage
Glacial Cobble	45	95.74
Not Glacial Cobble	2	4.26
TOTAL	47	100.00

 

ALL FOUR SITES
Chert Type	Frequency	Percentage
Glacial Cobble	535	93.53
Not Glacial Cobble	37	6.47
TOTAL	572	100.00

 

The results of the chert identification shows that glacial till chert makes up the majority of the flakes left by ancient peoples in East Central Illinois. In an examination of 572 flakes from four sites, only 6.5% were assignable to sources other than glacial till. These flakes were identifed as Dongola, Degonia, Oneota, Harrison County, Mill Creek, Platteville-Galena, and Moline. The non-glacial till flakes were small, almost always thinning flakes, while glacial till flakes included the entire range of flake types. The lack of primary and secondary decortication flakes from non-glacial till sources suggests that prehisotric people reduced the larger flakes at the source before transporting the pieces of chert to this area. Since the vast majority, 93.5%, of the chert flakes we examined were found to be glacial till, we can conclude that the Stone Age people in East Central Illinois most often fashioned their tools from the only available chert source in this area, namely glacial till.