312 GEOLOGY. 



The life of the bay, as shown by the fossils, was somewhat unlike that which 

 had inhabited the same region during the preceding epoch. Both in the Chazy 

 basin, and in a long narrow channel to the east (the Levis channel, extending 

 from Newfoundland to near Albany) the fauna of this epoch had more likeness 

 to that of Europe than to that which lived at the same time in the Mississippi 

 basin. 1 After the Chazy limestone had attained a thickness of several hundred 

 feet, the Chazy basin appears to have been drained, and at about the same time 

 the sea again invaded New York, entering from the south and west, and the 

 deposition of limestone (the Middle Ordovician) was resumed on the surface 

 which had for a time been land. The fossils of the new formation are unlike 

 those of the formation on which it rests. Later, the deposition of limestone 

 gave place to the deposition of mud (Utica shale). During this epoch, connection 













-^gfe • ^fttiul 



^% ; 



L • 















w 



§ tin 



















Fig. 131. — Trenton Falls, Trenton, N. Y. The locality whence the Trenton 

 formation derived its name. (Darton, U. S. Geol. Surv.) 



was again made between the Atlantic and the eastern interior sea by way of 

 the St. Lawrence valley, 1 as shown by the migration of animals from the former 

 body of water to the latter. After the Utica formation had reached a thick- 

 ness varying from a few feet in some places to a few hundred feet in others, it was 

 buried beneath other sediments (the Hudson River or Lorraine formation) con- 

 taining the relics of a somewhat different fauna. The successive changes in 

 faunas probably indicate changes in the geographic conditions of the region 

 though their character and extent are not definitely known. With the excep- 

 tion of the changes noted above, the Ordovician seems to have been, for this 

 region, a period of general quiet, though oscillations of relative level between 

 land and sea doubtless took place more than once during its progress. 



1 Ulrich and Schuchert, N. Y. State Museum, Bull. 52, pp. 633-663- 



