GEOLOGY OF THE W ATKINS AND ELMIRA QUADRANGLES 21 



follows close on the change from the Naples fauna in western New 

 York at a high altitude above the base of the Portage formation 

 In central New York there is no such change but the gradation from 

 the Ithaca fauna out of the Hamilton fauna upward into the asso- 

 ciation which carries species elsewhere concurrent with S p . d i s - 

 j u n c t u s is very easy and it is extremely difficult to draw a divi- 

 sion plane anywhere except on the basis of refined distinctions into 

 successive faunules. Spirifer disjunctus in this eastern 

 region did not appear till this period of " Chemung " deposition was 

 well nigh over. For a precise use of this term Chemung therefore 

 we are thrown back on the original employment of the name and 

 we here cite the explanation of the term as first used by Professor 

 Hall, taken from the third report on the fourth geological district, 

 1839, pages 322-24. 



Chemung group. The tops of the hills and high grounds in the 

 towns of Erin, V eteran, and Catlin, display a group of rocks and 

 fossils very distinct from those last described. The essential differ- 

 ence is the lithological characters of the sandstone of this group in 

 the absence of argillaceous matter in most of the layers, these being 

 nearly a pure silicious rock, harsh to the touch, and generally of a 

 porous texture ; while still a large proportion of the mass consists of 

 compact shales and argillaceous sandstones of a softer texture than 

 those below. The surface of the sandstone layers is rough, while 

 those below are smooth and glossy, and being never rippled, prove 

 that the rocks were deposited in a quiet sea. 



A great variety of beautiful and characteristic fossils occur in the 

 sandstone as well as the shale; many different from those of the 

 group below, while several species exist in both. The principal ones 

 are a species of Delthyris, the shell on each side extending into a 

 wing, (D. alata?) a Leptaena, Orthis, and a species of Avicula 

 or Pterinea, ribbed like the common Pecten ; besides several others 

 of genera and species not before seen in the upper rocks. 



The most northern extension of this group appears on the top 

 of Buck mountain, near Millport, and on the high ground farther 

 west; whence it is traced in the same direction to the valley of Port 

 creek, on the western boundary of the county. The same rocks are 

 found on the hills in Erin, and loose masses from above are scattered 

 through all the low grounds hence to the Chemung river. 



At about the latitude of Horseheads, in the northern part of the 

 towns of Elmira, and Big Flats, this lower portion of the Chemung 



