40 



NEW YORK STATE MUSEUM 



the outcrop at the Seneca mill, previously mentioned, and it forms 

 the crest of the fall at Bellona. Fossils are usually found abund- 

 antly in one or more layers at nearly all outcrops but the fossilifer- 

 ous layers are not the same at all localities, and a large portion 

 of the rock is almost barren. 



At Bellona the two upper layers are to a large extent made up 

 of corals, many of them of great size. 



The characteristic fossils of the horizon are : Hypothyris 

 c u b o i d e s Sowerby and Schizophoria tulliensis 

 Hall, with many species from the lower beds [see Mus. bul. 63]. 



Genesee black shale 



Lying next above the Tully limestone is a mass of densely 

 black bituminous shale that on exposure becomes very fissile and 

 splits into thin flat plates. 



Owing to their rigidity these shales are traversed by parallel 

 series of joints from an inch to 3 feet apart intersecting each other 

 at different angles and producing in cliff exposures striking effects 

 like buttresses and bastions, and on surf ace exposures tessellations, 

 triangles, rhomboids, diamonds and kindred forms. 



Rows of spheric concretions and thin calcareous layers occur, 

 specially in the lower beds, and nodular masses of iron pyrites are 

 common throughout the formation. Thin flags of sandstone 

 appear in the upper part at some localities but they are not con- 

 tinuous. 



The Genesee shale is abundantly exposed in the cliffs along the 

 Keuka outlet between Keuka Mills and Seneca Mills and along 

 the south branch of Kershong creek in the northeast corner of the 

 Penn Yan quadrangle. 



On these quadrangles this formation is about 100 feet thick. 

 It diminishes gradually toward the east and disappears near Smyrna, 

 Chenango co., and also toward the west, running out entirely in 

 the town of East Hamburg, Erie co. It however reappears and is 

 12 inches thick on the shore of Lake Erie, 13 miles farther southwest 

 at the mouth of Pike creek. 



The entire formation is exposed in numerous ravines and cliffs 

 along the shores of Canandaigua, Seneca and Cayuga lakes and 

 in the Genesee valley in Fall Creek ravine and in the ravine of 

 Little Beard's creek at Moscow, but not directly upon the banks 

 of the Genesee river. 



Fossils are rare and poorly preserved in this shale. Lignites 

 and conodont teeth occur very sparingly in the densely black beds 



