72 BULLETIN or THE ESSEX INSTITUTE. 



PAGE 



Water-level of wash-plains 105 



Stagnation of ice-sheet 109 



Decomposition in wash-plains Ill 



Economics of wash-plains 116 



Conclusions 117 



Explanation of map, Fig. 7 119 



INTRODUCTION. 



The glacial wash-plains or streaQi deltas and fans of 

 southern New England constitute by far the most impor- 

 tant feature in the pleistocene deposits of the area, for 

 the reason that they cover the larger part of the lowlands ; 

 on these flat spaces the greater number of towns and vil- 

 lages are built ; the sands and gravels determine the 

 nature of most of the problems of local water-supply and 

 drainage ; and because of their scientific bearings in de- 

 termining the history of the glacial retreat across this 

 portion of our country, as well as in the evidence they are 

 thought to afford concerning the attitude of the land and 

 sea at the close of the Glacial Period. The notes which 

 are here brought together present but a crude outline of 

 the results which may yet be gained in this field by a 

 careful mapping and investigation of these old glacial 

 stream deltas. These glacial deposits remain almost as 

 sharply defined as when abandoned by the ice. The growth 

 of forests and the development of sw^amps in the low wet 

 grounds alone offer difficulties to the rapid and satisfactory 

 interpretation of the glacial history of the district. 



The writer has had the opportunity of examining those 

 portions of this area which lie within the geologic field 

 known as the Narragansett Basin of Carboniferous rocks 

 and the islands off the south coast. Some of the leading 

 facts concerning wash-plains occurring about Nan-agansett 

 Bay have already been published as noted in the annexed 

 references to the literature. 



