86 



CAPE COD GEOLOGY 



indicated by profound dislocation of the beds already laid down, the sea covered 

 the area, spreading blue clay from Long Island to Marthas Vineyard and prob- 

 ably also northward along the east coast to Scituate or farther north. This was 

 the best marked and possibly the last recorded submergence of the south coast 

 of New England, though other lower stands of the land are suggested by the 

 partly effaced terraces of the succeeding Manhasset and Vineyard deposits. 



During the Wisconsin stage of glaciation, the last stage, two lines of frontal 

 moraines were left in the district, one on the outer islands, including Nantucket, 

 and the other on the Elizabeth Islands and Cape Cod. The interval between 

 these two ice advances was relatively short, the remnants of the ice of the first 

 not having entirely melted before the second advance. The interval between the 

 Wisconsin glaciation and the next preceding one was much longer than the time 

 which has elapsed since the Wisconsin ice disappeared from New England. The 

 duration of the intervals between the other advances is not so clearly shown. 

 The interval following the first ice advance appears to have been long enough 

 to allow waves or streams to work over very thoroughly the glacial drift, much 

 as it is being worked over now. 



During Pleistocene time elevation and subsidence in this region appear to 

 have alternated, the epochs of elevation corresponding to periods of glacial 

 advance and epochs of depression to periods of deglaciation, but this generaliza- 

 tion is not firmly established. At the time of the last ice advance the land south 

 of Boston appears to have stood somewhat higher than it is now. The coast 

 at Portland, Maine, has risen as much as 300 feet above sea level, and there has 

 been no change near Lynn, Mass. A depression of 40 fathoms in the latitude of 

 Nantucket since the Wisconsin stage would explain all the observed phenomena 

 of submergence along the coast and account for several features on the floor of 



the sea. 



Postglacial and recent events consist of the establishment of the existing 

 fauna and flora on the land occupied by the Wisconsin glacier. The outer islands 

 were occupied by animals and plants that established themselves there before 

 the Sounds came into existence. The flora of the southern pine barrens was 

 carried northward to the maritime provinces of Canada, which appear to have 

 stood higher during the Wisconsin stage than they stand now. 



The box tortoise, the black snake, and the mole on Marthas Vineyard, the 

 brown snake and the mole on Nantucket, and field mice on all the outer, least 

 accessible islands can be explained only by assuming a former connection be- 

 tween the islands and the mainland. Some evidence of the length of time that 



