CHEMUNG GROUP. 



179 



27. CHEMUNG GROUP. 



48. 



No. 1. Tricostate avicula (A. tricostata). No. 3. Prolate delthyris (D. prolata). 



2. Chemung cyphcaidite (C. cbemungensis). 4. Membranaceous strophomena (S. membranacea). 



No. S. S. membranacea, upper ralre ? 



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. 



