THE TYPE EXPOSURE OF THE CHAZY. 297 



In the exposures at Chazy the base of the formation is not reached. The 

 interstratified slate and sandstone always seen along the lake wherever this 

 horizon is exposed, is not disclosed at Chazy. The lowest rock seen is about 

 100 feet of iron-gray, fine-grained limestone, in beds one or two feet in thick- 

 ness. It differs in appearance from the slaty limestone, number 2 of the 

 Valcour section, and resembles the beds at the base of number 3, though it is 

 of much greater thickness. 



The remaining 200 feet of Group A, at Chazy, are quite the same as the 

 corresponding strata at Valcour. We again meet with beds filled with 

 Orthis costalis, strata consisting of crinoidal fragments, and the layer of 

 red-spotted marble. About 90 feet from the top is the horizon of Sealites 

 angulatus, found only at Chazy. Twenty-five feet from the top is a layer 

 containing numerous gasteropods, Bellerophon rotundatus, Bucania sulcatina, 

 Baphistoma striata, R. staminea and Metoptoma dubia, all described by 

 Professor Hall. 



Group B Sit Chazy is also essentially the same as at Valcour, only of less 

 thickness by 80 feet. The twenty-foot gray layer is found 50 feet from the 

 base, and is often oolitic. 



The lower division of Group C here exhibits peculiar features. It is only 

 23 feet thick, and consists of alternating beds of two very distinct kinds of 

 rock. One is a dove-colored, fine-grained, brittle and very pure limestone, 

 containing small nodules of calcite; the other is a tough, silicious, iron-gray 

 dolomite, weathering yellow. One of the upper beds of limestone contains 

 undetermined species of Murchisonia and Orthoceras and the same large 

 Bucania seen in the equivalent strata of Valcour island. Above these are 

 the BhyncJionella beds, 100 feet thick. The middle portion of the mass is a 

 pure, light-gray, coarsely granular limestone, sometimes with red spots, com- 

 posed largely of crinoidal fragments. The uppermost 24 feet of Group C is 

 concealed. If this be added to the measures already described, the total 

 thickness at Chazy will become 732 feet, although there may be another 

 hundred feet concealed at the base. 



Isle La Motte Section. — Six miles east of Chazy village this formation is 

 again exposed to view over the southern half of Isle La Motte. The strata, 

 with a somewhat sinuous strike, dip northward at an angle of 3° to 5°. 

 After 60 feet of the Calciferous, we have all the members of Group A well 

 displayed along the shores and in numerous quarries : 



1. Layers of sandstone and slate containing Lingula and Orthis . 23 feet. 



2. Silicious limestone with seams of tough slate containing : Cam- 



erella breviplicata, Bill. ; Orthis porcia, Bill. ; Strophomena 

 aurora, Bill. ; Strophomena camerata. Con. ; Zygospira acu- 

 tirostra, Hall ; Asaphus eanalis, Con. ; Cheirurus vulcanus, 

 Bill. ; Illcenus crassiGauda,Wah\. (?) ; Bemipleurides schlothei- 

 mi, Bill. . . . . . . .55 feet. 



