300 E. BRAINERD— THE CHAZY FORMATION. 



Crown Point Section. — Westward from Cornwall, toward Lake Champlain, 

 the beds of the Chazy rapidly decrease in thickness. The same fact is notice- 

 able southward from Valcour along the lake shore. The top and the bottom 

 of the formation are the first to disappear. Neither the "Bhynchonella beds " 

 nor the ''slaty limestone " are to be seen south of Valcour. The Lower Chazy 

 and Upper Chazy contract to small proportions, and finally disappear. Then 

 the Middle Chazy begins to contract, and also disappears. 



We present a carefully measured section at Crown Point fort to illustrate 

 this fact. We find there in ascending order : 



J 1 1. Sandstone and slate interstratified . . . .23 feet. 



I 2. Impure limestone containing Orthis platys, BiU. . * 25 feet. 



B. Beds containing Madurea magna, Leseuer . . . 200 feet. 



1. Dark-gray, massive limestone, weathering in darker stripes, 

 an inch wide, containing the large Bucania seen elsewhere 

 at this horizon . . . . . .40 feet. 



2. Tough silicious and magnesian rock passing into a two-foot 

 bed of pure sandstone . . . ^ . .17 feet. 



C 



Aggregate thickness ..... 305 feet. 



Orwell Section. — An exposure in Orwell, Vermont, one mile northeast 

 of the village, presents only 50 feet of Madurea strata lying between the 

 Calciferous and the Black River. 



Distribution of the Chazy. 



West and south of this point, through central New York and the tract 

 west of the Adirondack region as far north as the Thousand Islands, 

 the Chazy is altogether lacking. When it reappears to the northward, along 

 the Ottawa river and in the vicinity of Montreal, it apparently consists of 

 the measures that first disappear to the south in the Champlain valley. They 

 are described by Logan as whitish sandstones interstratified wdth bands of 

 green shale, followed by beds " composed almost entirely of Bhynchondla 

 plena," and are supposed not to exceed 150 feet in thickness. This answers 

 well to the top and bottom of the Valcour section. No beds containing 3Ia- 

 clurea magna are reported from Canada to the west of the outlet of Lake 

 Champlain. These facts could be easily accounted for by supposing at the 

 north an elevation of the sea-bed during the middle of the Chazy period, and 

 at the south a simultaneous depression and submergence. If in the interven- 

 ing region the submergence was continuous, w^e should have the whole forma- 

 tion and the maximum thickness at the northern end of Lake Champlain. 



