30 NEW YORK STATE MUSEUM 



reaches of tlie ravines farther north ; in Bristol hollow near the 



lower part of the Randall gully and also in the Reed and Wilder 



ravines. 



Middlesex black shale 



It has been customary to regard the Genesee group of strata as 

 closing with the foregoing and to place the Middlesex shale at the 

 base of the Portage series. This Middlesex shale is a very black, 

 somewhat slaty shale with thin arenaceous gray flags in the upper 

 and lower portions. When Professor Hall introduced the desig- 

 nation Genesee shale for the black shales in the Genesee river sec- 

 tion, he expressed the opinion that eventually it might be found 

 advisable to include them within the limits of the Portage forma- 

 tion. We have shown that on paleontologic grounds this is neces- 

 sary, and it is clearly apparent that the geologic character of the 

 deposit shows that the Genesee black shales are but an intro- 

 ductory phase of Portage sedimentation repeated in the Middle- 

 sex and Rhinestreet bands. The Middlesex shale attains a thick- 

 ness of 35 feet where fully exposed in the Middlesex valley and 

 decreases westward to 25 feet in the valley of Honeoye lake, just 

 beyond the west line of these maps. 



Fossils are of great rarity. Plant remains occur in the shales, 

 and these have also afforded a single specimen of the goniatite 

 Sandbergeroceras syngonum. Occasionally a char- 

 acteristic lamellibranch of the Cashaqua shales above appears in 

 the gray flags of the lower beds. This mass of black shale is con- 

 tinuous westward to Lake Erie but it decreases gradually in thick- 

 ness till on the Lake Erie shore at the mouth of Pike creek there 

 are but about 6 feet of it remaining. The rock is well exposed 

 in the Middlesex valley in most of the ravines between the Lee 

 schoolhouse and the village of Middlesex. It is seen on the road- 

 side on the east side of the swamp at the head of the lake and in 

 the Canandaigua lake valley by the road 1^ miles ®outh of 

 Woodville, also on the road leading west at the head of the lake 

 and in the Standish, Coye, Granger, Lapham, Cook, Hicks point 

 and Seneca point ravines, by the side of the Academy road 1 mile 

 south of Cheshire. In the Bristol valley it may be observed in 



