366 P. E. Raymond — Fauna of the Chazy Limestone. 



to the top of the beds at Valcour Island. Taking the base of 

 the Orwell section at 424 feet, the upper 407 feet are lacking. 

 The thinning in the 17 miles from Crown Point to Orwell is 

 122 feet, or 7*1 feet per mile, while the gradient to the top of 

 the Chazy at Valcour Island is 7'01 feet per mile. The close 

 correspondence of these gradients and the small gradient of 7 

 feet per mile for 58 miles are significant, and seemingly indi- 

 cate a base-leveled surface of this land during the Chazy- 

 Lowville interval. 



Representation of Chazy Time in other Regions. 



The Chazy was formerly identified by various geologists as 

 covering a large area, but more recently it has been held that 

 while certain formations may have been laid down during 

 Chazy time, the typical rocks and fossils of this period are 

 restricted to the region of the Champlain and Ottawa valleys 

 and the islands in the Gulf of St. LaAvrence. 



The St. Peter's Sandstone. 



One of the formations which has long been correlated in 

 time with the Chazy is the St. Peter's sandstone, which in 

 Iowa, Minnesota, and parts of Illinois underlies the lowest 

 member of the Mohawkian series. The fauna'* of this forma- 

 tion is meagre and is contained in a few layers near the top. 

 It is made up chiefly of Mollusca, all closely allied to Trenton 

 forms. J^sone of the species are found in the Chazy ; hence 

 no new light is thrown on the correlation by the later studies 

 of the Chazy fauna. On lithological grounds, James has cor- 

 related it with the Chazy of the Ottawa Valley, but there are 

 no species common to the two formations. From the close 

 relationship of its fauna to that of the Mohawkian (Trenton) 

 it seems probable that the St. Peter's was deposited during 

 Stones River time. 



Stones River Group. 



In the Columbia, Tennessee, folio of the U. S. Geologic 

 Atlas, Ulrich has stated that the lower part of the Stones 

 River group, including the Lebanon, Ridley, Pierce, and Mur- 

 freesboro limestones, is to be correlated in time with the Chazy 

 of New York State. 



This statement is evidently based mainly on stratigraphic 

 grounds, as Ulrich and Schuchertf have held that the Low- 



* F. W. Sardeson, Bull. Minnesota Acad. Sci., vol. iv, No. 1, pt. 1, p. 64, 

 1896. 



f Paleozoic Seas and Barriers, Eept. N. Y. State Pal. ; Bull. 52, N". Y. 

 State Mus., 1902, p. 633. 



