294 E. BRAINERD — THE CHAZY FORMATION. 



and variety of the strata of the Calciferous and Chazy zones were greatly 

 underestimated, and their wealth of fossils was unsuspected. Had it been 

 otherwise, Billings would have had to describe fewer new species from the 

 Lower Silurian of Canada, and some of the difRcult problems of the " Quebec 

 group" would have been more easily solved. 



We purpose, in the present paper, to present a comparative view of several 

 representative sections of the Chazy formation in the Champlain basin. We 

 shall omit all details of stratigraphy, and present only the results of our 

 study as regards the thickness and sequence of the strata and their charac- 

 teristic fossils. These local details have been thoroughly worked out, and 

 will be presented elsewhere with maps and sections giving actual profiles 

 and dips. In the diagram herewith presented (plate 11) the strata are re- 

 stored to the horizontal attitude so as to indicate more clearly the correlation 

 of the beds in the several sections. 



A further preliminary statement should be made concerning the bounda- 

 ries of the Chazy. The upper boundary is the Black River, a black, massive 

 pure limestone, 30 to 50 feet in thickness, easily recognized and remarkably 

 uniform throughout the Champlain valley. The lower boundary, or the top 

 of the Calciferous, is less distinctly recognized by geologists. We have consid- 

 ered it to be a tough iron-gray, fine-grained, magnesian rock, usually weath- 

 ering yellowish or drab, 300 to 400 feet in thickness. Wherever this horizon 

 is exposed in the lake region, these magnesian rocks appear, though they are 

 wanting in the region east of the lake. The few fossils that occur in occa- 

 sional beds of limestone, and the general lithological character of the mass, 

 would seem to ally it to the strata below. Furthermore, whenever any of 

 these outcrops are mentioned by the older geologists, the rock is always 

 referred to the Calciferous. 



The Detailed Sections. 



Section at Valcour Islcmd. — The first section of the Chazy to be described 

 is that of Valcour island, about six miles south of Plattsburgh, New York. 

 This island, two miles in length and one mile in breadth, with deep bays 

 and high promontories, consists almost wholly of the Chazy rock, which here 

 attains a maximum thickness of nearly 900 feet. The island seems to have 

 been hitherto unexplored by the geologist. On Professor Emmons's map of 

 Clinton county it is colored as Calciferous ; but no Calciferous rock occurs 

 except at the southern extremity just beneath the usual level of the lake. 

 Above it appear the strata of the Chazy, dipping 20° or 30° eastward, and 

 rising in cliffs 30 to 50 feet in height along the southeastern shore. It is the 

 most impressive display of limestone to be seen along the lake. From a 

 boat we can here behold, in one view, measures of the Chazy over 600 feet 



