1 6 Bulletin 6 i6 



PART II. 



The Ithaca Sections. 



Stratigraphy . — The rocks of the Portage and the Ithaca groups 

 outcrop along the sides of Cayuga lake valley about Ithaca, 

 New York. The Portage rocks rest upon the black Genesee 

 shale, and are terminated above by the Ithaca shale. Tough 

 sandstone flags, often wave-marked, together with beds of more 

 arenaceous charadler, constitute the Portage rocks, which are 

 here about 250 feet in thickness. The base of the Portage is 

 sharply defined by a fine-grained, hard, blue sandstone about 3 

 feet in thickness. From Esty's glen to the point where the 

 base of the Portage passes below the surface of the lake, the 

 dip is more than 100 feet to the mile. Near Ithaca the dip be- 

 comes less, and to the south it is very slight for several miles. 



The soft argillaceous beds which lie above the Portage have 

 been called the Ithaca shale by Prof. Williams. These shales 

 are often stained a reddish brown by iron. Lenticular layers of 

 sandstone sometimes occur in these shales. Above the base of 

 the Ithaca shale 25 or 30 feet, it loses its arenaceous chara(5ter 

 and is replaced by the sandstone flags and intercalated shales 

 which contain the typical Ithaca fauna. These beds are fossili- 

 ferous for a thickness of nearly 400 feet. The rocks containing 

 the Ithaca fauna are followed by nearly 600 feet of barren 

 sandstone flags which extend to the tops of the hills about Ith- 

 aca. The fossiliferous beds of the Chemung do not appear in 

 the immediate vicinity of Ithaca, but several miles to the south 

 they form the tops of the hills along the southern extension of 

 Cayuga valley above the barren strata. 



The numerous deep gorges of the streams entering the Cayuga 

 valley afford excellent exposures of the rocks about Ithaca, from 

 the base of the Portage to the top of the Ithaca group. Ten 

 secflions through these rocks have been carefully studied and 

 the results are given in the following pages.* 



*NoTE. — The sedlions are numbered in the order in which they were 

 studied. All of the specimens on which the lists of species are based are 

 in the Paleontological Museum. Two numbers are attached to each speci- 

 men, the first indicating the secflion, and the second the stratigraphic posi- 

 tion or station in the section from which it came, e.g., 1-2 refers to the 

 second station in the Fall Creek sedtion. 



