Rock surface beneath the bottom sediments of the bay is highly 

 irregular, attaining minus elevations of about UOO feet in places, 

 with ad,jacent areas forming shallow rock pavements with almost no 

 sediment cover, the rough structiiral configuration having been 

 complicated by extensive pre-glacial erosion to form gorges now 

 under a deep cover of glacial and post-glacial sediments, 



c. The sediments of Narragansett Bay . Borings indicate that 

 the glaciers swept the bay, leaving a cover of their oim, quite 

 thick in places. The usual resulting sequence up-bay, resting on 

 bedrock, is cobbles and boiilder clay or reworked till, a consider- 

 able thickness of outwash silts and sands, capped by a few to 

 fifteen feet of organic silts of recent origin^ while deep gorges 

 in the middle and lower bay areas trapped accumulations of silts 

 and clays, sometimes in excess of 100 feet. 



d. Topography . Topography is governed by geological structure 

 in that heavy outwash deposits from East Greenwich to Quonset pro- 

 vide a low flat plain; fluvio - glacial sands east of Point Nayatt 

 present a slightly and tmdulating terracej and projections of the 

 old sedimentary rock structure stand out as moderately high islands. 

 MaximiOT elevations of about 300 feet occur where the crystalling ' 

 old land nears the bay, notably west of Greenwich Bay. MaxJbmim 

 elevations vjithin the basin attain about 12^ feet. 



12. AREA MAPS 



The area under study appears on standard quadrangle sheets 

 of the U. S, Geological Stirvey at a scale of 1:31,680 and on a 

 Geological S\jrvey topographic map of the states of Massachusetts, 

 Rhode Island and Connecticut at a scale of 1:^00,000. The area 

 is also shovm on the Providence topographic sheet of the Army 

 Map Service at a scale of 1:250,000. Narragansett Bay and the 

 navigable parts of its tributary streams appear on U. S. Coast 

 and Geodetic Survey charts Nos. 236, 278, 352, 353, and 1210, 

 which are now being revised (1956). The Coast and Geodetic 

 Survey is also preparing detail maps, at a contour interval of 

 one foot, of areas in Providence subject to tidal flooding. 



