OF ARTS AND SCIENCES. 223 



the strata of the Champlain series at the village of Chazy, and at 

 Potstlarn itself, is explained in two ways. First, there is sufficient 

 distance between Saratoga and Chaz}- for a local deposit of limestone 

 to be made in one place and not in the other. But it is still more 

 important to observe that at Chazy and at Potsdam the Potsdam rock 

 lias formed a beach during the whole time of the Champlain deposits. 

 The character of this beach has been preserved iu so striking a man- 

 ner, that one would think it had been abandoned by the sea but a few 

 years, even iu our own day ; it was greatly eroded and all its upper 

 beds were destroyed shortly after the dislocation, and before the first 

 deposits of the '' Calciferous " and of " Chazy limestone." 



It is almost certain that this important discovery by Mr. Walcott 

 will not be the only one, and that this upper part of the Potsdam will 

 be found along the line of the Tuconic, from Lake Champlain to Ala- 

 bama. It has been pointed out and described long since in Wisconsin 

 and Minnesota. 



If we complete the theoi'etic vertical section already given in 1881 

 for the Lake Champlain region, and taking account of the discovery 

 of the zone of Paradoxides on the borders of the Atlantic, we have 

 the following section. 



