78 



great numbers. The black carbonaceous muds hardened to 

 form the black, bituminous, Marcellus shales, which imme- 

 diateh^ overlie the Corniferous limestone.* These shales, in 

 many places, are full of fossils, chiefly brachiopods and 

 pelecypods, indicating that these ancient mud-flats had their 

 tenants similar to the mud-flats on the modern sea-coast. 

 Streaks of coaly matter show how abundant was the vege- 

 tation, which, by its incomplete decay, gave rise to the 

 bituminous matter in these shales. 



During the Marcellus (Minuta) epoch, there were several 

 minor oscillations, which, however, as their record is not 

 revealed in any of the sections discussed in the preceding 

 chapters, will be passed over. It may simpl}^ be remarked 

 that after the accumulation of a number of feet of the black 

 shale, more calcareous shales were formed, indicating the 

 deepening of the water. Deeper water conditions were 

 finally estabhshed tow^ards the close of the Marcellus 

 (Minuta) epoch, as recorded in the first sections on the lake 

 shore. The pure water of the Corniferous (Acuminatus) 

 epoch, however, was not re-established until very much 

 later, and then only over limited areas. 



In our own region, as the waters became deeper and 

 purer, new forms of life appeared, i)rol)ably through immi- 

 gration from other regions where they originated. In the 

 gradual appearance of these species in the Transition shales, 

 w^e have recorded the long struggle to w^hich the new-comers 

 were subjected before they finally became established. By 

 the time that the thirty feet of Transition shales had accu- 

 mulated above the Marcellus beds, the water had become 

 pure enough for the sudden development or immigration ol 

 the fauna of the Strophalosia bed. Silt and gritty material 

 were still carried in, and constitute a large proportion of the 

 material in the bed, but there was no longer any paucit}' ol 

 living forms. Strophalosia, Bellerophon, Loxonema and 

 Orthoceras flourished in great numbers, and their shells 



*These can be well seen in the beds of Cayuga and other creeks. 



