GEOLOGY OF THE ATTICA AND DEPEW QUADRANGLES 21 



Spirifer mucronatus mut. hecate Clarke 



" fimbriatus mut. pygmaeus Loomis 



" granulosus mut. pluto Clarke 

 Ambocoelia umbonata mut. pygmaeus Loomis 

 Paracyclas lirata mut. pygmaeus Loomis 

 Tornoceras uniangulare Conrad 

 Orthoceras subulatum mut. pygmaea Loomis 

 Pleurotomaria, 3 species 

 Crinoid stems 



Exposures. A thin lentil occurs in a small ravine half a mile 

 west of Alexander and a similar one in the east bank of Murder 

 creek 40 rods north of the railroad station at Griswold. A I inch 

 lentil appears in the east bank of Ellicott creek one and one-half 

 miles west of Darien Center, and at the iron bridge over Cayuga 

 creek one and one-half miles below Cowlesville, a lentil of more 

 than ordinary thickness and breadth is finely exposed. Another 

 2 inches thick, is in the banks of Little Buffalo creek half a mile 

 below Marilla. There are traces of lentils in the long exposure of 

 this horizon in the banks of Cazenovia creek south of Spring Brook, 

 but they are all very thin. 



GENESEE BLACK SHALE 



The heavy beds of black and dark slaty shale that succeed the 

 light colored Moscow shale in Ontario and Livingston counties 

 were, in Hall's original classification, all included under the term 

 Genesee shale, from their exposure in the Genesee river valley. 

 Subsequent investigations disclosed such differences in the char- 

 acter of these beds as to require, in the interest of clearness and 

 accuracy of description, a division into four distinct members or 

 formations, the lowest of which in the type locality is 90 feet thick 

 and capped by a bed of light gray limestone. The shale composing 

 this member is nearly all densely black and slaty answering to 

 the original description of the Genesee slate, and the use of that 

 term is now restricted to these beds. It thins out from the type 

 locality rapidly toward the west to about 20 feet on the east line of 

 these quadrangles and to less than 2 feet on the western boundary. 



Fossils are not usually abundant in the Genesee, but Chonetes 

 s e t i g e r a occurs in great numbers in the upper part at the ex- 

 posure in Ellicott creek west of Darien Center and at the iron 

 bridge north of Cowlesville. Styliolina fissurella is also 

 common, and Pterochaenia fragilis and small cephalo- 

 pods occur occasionally. 



