GEOLOGY OF THE PENN YAN— HAMMONDS PORT QUADRANGLES 39 



total thickness of 150 to 165 feet and the Menteth limestone, a 

 stratum somewhat similar in character to the Tichenor and which 

 has been sometimes mistaken for it, is interstratified 75 feet above 

 the base. There are numerous exposures of the Moscow shale in 

 central and western New York, among the most favorable of which 

 eastward from this quadrangle are: along the east shore of Cayuga 

 lake for 10 miles north of Ludlowville; in ravines and cliffs at the 

 south end of Skaneateles lake and Otisco lake ; in the Fellows Falls 

 ravine 2 miles west of Tully, and at Tinker's falls near Fabius ; and 

 toward the west, in several ravines along both sides of Canandaigua 

 lake between Tichenor point and Black point ; along Little Beard's 

 creek at Moscow ; along Murder creek and Ellicot creek near Darien ; 

 along Smoke creek at Windom, Erie co., and on Eighteen Mile 

 creek and the Idlewild and South Shore cliffs on Lake Erie at 

 North Evans. 



The characteristic fossils of the Moscow shale are listed in New 

 York State Museum bulletin 63 to which the reader is referred. 



NEODEVONIC 



Tully limestone 



The Tully limestone is a bed of hard, dark bluish limestone 

 that on exposure is inclined to separate into small angular blocks. 

 It overlies the Moscow shale from Gorham, Ontario co. on the 

 west to Smyrna, Chenango co. on the east and is exposed on the 

 Penn Yan quadrangle at Seneca Mills on the Keuka lake outlet at 

 6oo A. T., where it produces a cascade 14 feet high. 



Here it occurs in several heavy layers that aggregate 12 feet in 

 thickness. Some are compact and durable, but a large portion 

 of the limestone, throughout the entire line of outcrop, has a sharp, 

 brittle texture and, after exposure, breaks easily into small angular 

 fragments. The extreme western outcrop of the formation is on 

 Gage's creek, 5 miles southwest of Gorham, Ontario co., and about 

 1 mile from Canandaigua lake. It is here 31 inches thick. It 

 increases toward the east slowly to 28 feet at Tully, Onondaga co., 

 and is not known east of Smyrna, Chenango co., where it consists 

 of several thin layers separated by shales. It is abundantly 

 exposed along both sides of Cayuga lake in the vicinity of Ludlow- 

 ville and' northward to King's Ferry and also on the east side of 

 Seneca lake from Lodi Landing to Ovid. 



It appears in two small undulations on the west side of Seneca 

 lake and finally emerges from the water on the north side of 

 Plum point. It is well exposed on the Keuka outlet, a mile below 



