35< 



E. M. KINDLE 



has been given by Dr. John M. Clarke 1 and requires no restatement 

 here. A lower temperature of the water doubtless accompanied 

 the deepening of the sea during early Genesee time and was prob- 

 ably the chief immediate cause of the complete disappearance of 

 the shallow water fauna of the Hamilton from a large part of the 

 Devonian sea with the appearance of the pelagic Genesee fauna. 

 The sea became shallow again during Chemung time. This is shown 

 by the ripple-marked sandstones which may be seen in Chemung 

 sediments from New York to southern Virginia. That the rem- 

 nant of the Hamilton fauna which had survived till Chemung 

 time in the shallow coastwise waters in the eastern margin of the 

 Devonian sea found in the Chemung sea a temperature similar 

 to that of the old Hamilton sea is attested by such colonies as the 

 one which has been described from Virginia. 



The distribution of Tropidoleptus carinatus in the Chemung 

 sediments as detached, often widely separated, colonies is in some 

 degree comparable with that of Ostrea virginica along the present 

 Atlantic coast. This warm-water species is unknown along wide 

 stretches of the northern New England coast but in the Gulf of 

 St. Lawrence nourishes in waters, which in their deeper parts 

 afford a habitat for such Arctic forms as Mya truncata. That a 

 low temperature is as essential to the life of the latter as is a high 

 temperature to the former is illustrated by the fact that while 

 in the Gulf of St. Lawrence M. truncata is found in the deeper waters 

 only, in Greenland waters it is said to be sufficiently common at 

 low water to furnish food for the Arctic fox and other land animals. 2 

 The character of the geographical conditions which permit repre- 

 sentatives of the south Atlantic and north Atlantic coast faunas 

 to live on adjacent parts of the sea bottom is indicated in the 

 following quotation from Doctor MacBride. 



The whole north coast of Prince Edward Island is fringed by a series of 

 parallel sand-bars, and it is owing to this circumstance that the oyster is able 

 to nourish there. All who know the coast of the Gulf of St. Lawrence are 

 aware that the water even in summer is very cold; so cold indeed that though 



1 Op. cit. 



2 J. F. Whiteaves, Catalogue of the Marine Invertebra of Eastern Canada (Geol. 

 Surv. of Canada, iooi), 148. 



