is the result of extensive fluvial erosion during the Tertiary (2.5 

 - 65 million yr B.P.). Stream flow deepened the valleys extending 

 south from Narragansett Bay and carved north-flowing valleys into 

 the coastal plain escarpment. An intervening lowland was created 

 which directed stream flow to the west. This pre-glacial landscape 

 was greatly modified during the Pleistocene, when New England was 

 glaciated by at least two ice advances (Schafer, 1961; Schafer and 

 Hartsborn, 1965; McMaster and Ashraf , 1973 a, b, and c) . Glacial 

 ice widened and deepened valleys as far as 50 km offshore. 

 Extensive glacial drift, consisting of both stratified and 

 unstratified tills, moraines, and outwash plains, was deposited 

 throughout the region. Two prominent series of glacial end moraine 

 deposits can be traced across the inner shelf and coastal uplands 

 (Schafer, 1961; Schafer and Hartshorn, 1965; Sirkin, 1976 and 1982) 

 (Figure 4-1) . The older, southernmost terminal moraine is the 

 Ronkonkoma-Vineyard-Nantucket Moraine which extends across Long 

 Island, Block Island, Martha's Vineyard, and Nantucket Island. 

 Submerged extensions are indicated in Rhode Island Sound by the 

 irregular submarine topography (Figure 1-1) . This moraine line is 

 believed to mark the terminal position of the Late Pleistocene ice 

 lobes. During glacial retreat (approximately 16,000 yr B.P.), 

 several series of subparallel moraines were formed, the most 

 prominent of which is the Harbor Hill-Charlestown-Buzzards Bay 

 Moraine (Figure 4-1) . This younger moraine overlies the southern 

 shore of Rhode Island and extends to western Cape Cod. Similarly, 

 submerged expressions are revealed by irregular bathymetric 

 configurations from Point Judith to the Elizabeth Islands (Figures 

 1-1 and 4-1) . 



As the ice retreated, topographic highs, created by 

 moraine-capped coastal plain deposits, prohibited drainage of 

 meltwaters to the south. Freshwater lakes developed between the 

 retreating ice and the terminal moraines. Valleys were infilled 

 with glaciolacustrine sediments and outwash deposits. Prior to sea 

 level rise, the lakes are believed to have drained through a breach 

 in the moraine, exposing the post-glacial surface to renewed stream 

 cutting. The glacial terrain controlled the drainage pattern which 

 directed stream flow south out of the Bay and southwest along the 

 landward side of the moraine deposits. During the Holocene, as the 

 rising sea submerged the inner shelf, estuaries and salt marshes 

 infilled valleys and lowlands (approximately 10,000 - 12,000 yr 

 B.P.). Estuarine sedimentation progressed up the trunk valleys of 

 the Bay (9,000 yr B.P.) while waves and currents reworked the 

 glacial drift offshore. Presently in Rhode Island Sound (in non- 

 valley areas) , Holocene deposits form only a thin veneer over the 

 glacial terrain. These deposits consist of the coarser components 

 of the glacial source material: sand, gravel, and boulders. In the 

 Bay, the Holocene sequence is up to 15 m thick. Net nontidal 

 circulation (the result of mixing fresh and salt water) has 

 contributed to the infilling of valleys by silt deposition. 

 Southeast of Prudence Island, surface sediments have been mapped as 

 sand-silt-clay (McMaster, 1960) and are also characterized as gas- 



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