CHAPTER III. 



GLACIAL HISTORY OF THE NARRAGANSETT BASIN. 



The interpretable history of this basin, so far as it has depended on the 

 action of ordinary streams and of the sea, has already been set forth. This 

 account of the effects of the solar energy which has been applied through 

 the atmosphere needs to be supplemented by some consideration of the 

 work which was done during the Glacial periods. The account which will 

 here be given of the work will in the main be restricted to the phenomena 

 that are in some measure peculiar to the field, for the reason that the surface 

 geology of New England is to be the subject of a separate publication by 

 the Geological Survey. Any full discussion of these matters in this memoir 

 would therefore involve an undesirable repetition. 



We may first note that the deposits formed during the times repre- 

 sented by the conglomerates of the Carboniferous series have a character 

 which warrants the hypothesis that they are to a considerable extent the 

 products of glacial action. The view that this age was a period of recurrent 

 ice work has already been ably presented by the late Dr. James Croll. 

 Here, as elsewhex*e along the Appalachian district, the supposition is sup- 

 ported by an array of facts which deserve more attention than they have 

 received. These facts, as they are exhibited in the country from Alabama 

 to the St. Lawrence, will be briefly set forth. 



CARBONIFEROUS CONGLOMERATES. 



Iii the Southern States the conglomerates of the Carboniferous periods 

 are, with rare and unimportant exceptions, made up of pebbles of quartz, 

 which, as has been noted by several observers, are evidently the remains 

 of the undecayed veinstones that survived the decay which, in the pre- 

 Carboniferous, as in the modern time, greatly affected the rocks that were 

 exposed to the atmospheric agents. The great thickness of these quartz 



