CHEMUNG GROUP. 
179 
27. CHEMUNG GROUP. 
48. 
No. 1. Tricostate avicula (A. tricostata). No. 3. Prolate delthyris (D. prolata). 
2. Chemung cypricardite (C. chemungensis). 4, Membranaceous strophomena (S. membranacea), 
No. 5. S. membranacea, upper valve? 
Between the Ithaca and the Chemung group, no precise line of division was observed. A 
high ridge was seen rising above the inclined plane at Ithaca ; the rocks to the south contained 
none of the brownish sandstone of the Ithaca group, and there were different fossils noticed 
in the two : upon these differences the Chemung group was founded. The best section of the 
district for examining the two groups, is from the head of Cayuga lake to Factoryville. At 
Chemung narrows, the evidence of difference appeared to be conclusive ; so also in the counties 
of Tioga and Broome, where, probably with one exception in the latter county, no lower rocks 
than those of the Chemung group exist. 
The Chemung group consists of sandstone and shales, more or less slaty, and mixtures in 
endless proportions of the two; the former furnishes good building stone and flagstones; the 
latter being often soft, decomposable masses, but in a less degree than the shale of the Ha¬ 
milton group. The sandstone in no part of the group shows well defined layers, in which 
respect it resembles the lower ones. The layers are also indistinct, and incapable of being 
traced from place to place by any mineral character noticed. Nor has there been time to 
ascertain, as before mentioned, if their fossils followed a definite order, so usual with these 
bodies ; a subject which requires time, and much patient investigation to determine in a mass 
of its thickness. 
