REPORT OP THE STATE PALEONTOLOGIST 1902 1155 



Cumberland basin 1 as well as in central New York laid down in 

 the Mississippian sea. 2 The overlapping of these deposits was 

 caused by the gradual subsidence of a mountain barrier which 

 separated the two basins, and which as subsidence took place 

 caused the overlapping edges of the successive deposits in these 

 two basins gradually to approach each other, the thinned edge 

 of each resting on the Lower Siluric shales. At the close of the 

 Clinton there was a reelevation of the barrier, and the Niagara 

 deposits do not overlap the Clinton formation and rest on the 

 Lower Siluric shales, but in central New York the eastern ex- 

 tension of the Niagara is found resting on the Clinton. The 

 effect of this uplift on the limits of the Niagara deposits in the 

 Cumberland basin is not so apparent, but none seem to have been 

 deposited in New York. 



From late Niagara time subsidence again took place, and the 

 Salina deposits of the Mississippian sea in New York spread east 

 over the Niagara and Clinton formations, and the thinned edge 

 rests on the Lower Siluric shales. A similar condition of over- 

 lap is found in the deposits of the Salina age in the Cumberland 

 basin. In the region of the Helderberg the Salina deposits of 

 the Mississippian sea are separated from those of the Cumberland 

 basin by quite an interval, but in southeastern New York, where 

 the barrier was lower, they must have been very close together, 

 and the last deposits may have mingled and a few Eurypterus 

 passed from the Salina sea into the Cumberland basin. 



With the clearing of the water brought about by the subsidence 

 of the barrier, the Salina stage was brought to a close, and we 

 have the Atlantic waters spreading over the late Salina sea. 

 The spreading of the Atlantic waters over this area brought with 

 them an Atlantic fauna. This invasion is known as the Helder- 

 bergian, or it may be properly designated the Cobleskill invasion, 

 since it was during Cobleskill time that we have the first invasion 

 of an Atlantic fauna into the interior following the Salina age. 

 This invasion of the Atlantic waters explains in part the deriva- 

 tion of the fauna of the Cobleskill limestone as found in Schoharie 

 county. 



1 N. Y. State Paleontologist. An. Rep 't. 1901. p. 638. 

 a Am. Ass'n. Adv. Sci. Proc. 1894. 42 : 129-69. 



