lOG The Position of the Cincinnati Group. 



while we find its lower beds, from Wayne county westward to the 

 Niagara river, characterized by peculiar fossils, we find the' upper beds 

 containing many species which pass upward into the Niagara Group. 

 Indeed, there is no line which can be designated between these two 

 groups which shall mark the limits of the organic products. It is 

 true, nevertheless, that by far the greater part of the fossils of the two 

 groups are distinct ; and the small number in the lower Group, of 

 those which we regard as proper to the Niagara Group, are for the 

 most part inconspicuous, and not so well developed as they are in the 

 Niagara." 



Again, he says : 



" In tracing the Clinton Group westerly, we find its aflSnities more 

 with the rocks below, or that the material and fossils recognized on 

 the one side as the Clinton formation are not strongly separated ffom 

 the upper beds of the Hudson River Group ; and studied in these lo- 

 calities alone, they might be regarded as constituting part of the same. 

 On the other hand, the Niagara becomes defined as a calcareous group, 

 and the line between it and the strata below is strongly drawn. The 

 base of this limestone would everywhere be recognized as the base of the 

 Upper Silurian rocks, while the strata below are marked by fossils 

 which belong to the Lower Silurian fauna." 



The Niagara Group consists of the Niagara shales and limestones, and 

 the Guelph and Leclaire Groups. At Lockport and Niagara Falls it 

 consists of 80 feet of shales and 164 feet of limestones. The Guelph 

 Group takes its name from the town of Guelph in Canada, where it is 

 about 160 feet in thickness. It is like the Niagara limestones on 

 which it rests, a dolomite, and on Manitoulin Island, where the lime- 

 stones are 405 feet thick, it is 100 feet in thickness. The greatest 

 thickness in Ohio, Indiana, or Illinois, will not, probably, exceed 400 

 feet, but in Tennessee it is found 1,700 feet thick, and is subdivided as 

 follows : 1st, Clinch Mountain sandstone, consisting of shales and sand- 

 stones, 700 feet ; 2d, the White Oak Mountain sandstone, 500 feet ; 

 3d, the Dyestone Group of shales and sandstones, which takes its 

 name from an iron ore which is sometimes used as a dyestone, 300 

 feet; and 4th, the Meniscus limestone, which takes its name from a 

 lens or menicus-shaped fossil sponge, named by Roemer Astreaspongia 

 meniscus, 200 feet. 



Prof. Hall says : 



" The rocks of this group, where best developed in Western New 

 York, consist of a mass of shale, succeeded by one of limestone, the 

 passage from the former to the latter taking place by the gradual in- 



