sediment (Fig. 17) as evidenced by the composition of cores 18 and 19 

 (Fig. 2). Core 18 contains 15.3 feet (4.7 meters) of type II material; 

 core 19 contains 4,2 feet (1.3 meters), its entire length of type II 

 material. This suggests the type II lithology may continue with depth. 

 Cores seaward of this region contain -medium sand as a primary sediment 

 constituent which tends to become finer with increasing distance from 

 both shore and the Ronkonkoma Moraine. Because the Ronkonkoma Moraine 

 continued east from Montauk Point before Holocene rise in sea level and 

 consequent marine erosion, it is likely that type II sediment also con- 

 tinues east as an erosional lag deposit. This contention is supported 

 by McMaster and Ashraf (1973) who reported patches of coarse bottom 

 sediment on the southein New England shelf at several locations east 

 of Block Island and on line with moraine projections. The only other 

 surface occurrence of type II sediment was found in cores 13 and 14 in 

 Block Island Sound east of Gardiners Island. Core 13 contains type II 

 sediment for the entire length of 6.6 feet (2 meters). Core 14 contains 

 type II sediment for the top 7.5 feet (2.3 meters) overlying 4.5 feet 

 (1.4 meters) of Holocene organic-rich mud. The organic mud imderlying 

 type II sediment in core 14 appears from the seismic records to crop 

 out as type V sediment to the south and west. Based on this evidence 

 it appears that much of the coarse surficial sediment in Block Island 

 Sound may be underlain at variable depths by fine-grained Holocene muds. 



c. Type III Sediment . This sediment is fine to medium sand (0.125 

 to 0.5 millimeter; 3 to 1 phi) (Fig. 20), and is the predominant sediment 

 lithology comprising both the inner shelf floor of south shore Long Island 

 and the adjacent barrier islands (Figs. 12 and 17). Type III sediment is 

 predominantly quartz with minor percentages of opaque heavy materials. 

 The quartz grains generally have a yellowish cast (2.5Y 7/4) except for 

 the grains in several cores at variable depths below the sea floor which 

 exhibit a dusky, reddish-brown color (7. SYR 7/8) as a result of staining 

 by iron oxide. The iron staining appears to be a surface coating occupy- 

 ing cracks and surface depressions on the grains and is apparently abraded 

 off when the sand is exposed to active wave and current forces on the sea 

 floor. Textural trends for type III sediment are subtle, but the mean 

 grain-size diameter for surface shelf sediment from 43 cores decreases 

 from Montauk Point west to Long Beach (Fig. 21). The figure also shows 

 that a greater occurrence of very coarse sand or larger material (>1 

 millimeter, <0 phi) is contained in cores from eastern Long Island than 

 in cores from western Long Island. These observations support work by 

 Taney (1961) and Panuzio (1968) who propose that shoreline erosion of the 

 headland region of eastern Long Island supplies a significant percentage 

 of sediment available for littoral transport westward along the south 

 shore barrier beaches. The predominance of fine to medium sand (type III) 

 on the inner shelf appears to continue across the shelf to the shelf-slope 

 transition where sediments become significantly finer (Schlee, 1973). 

 Occurrence of type III sediment in Gardiners Bay and Block Island Sound 

 is more restricted than on the open shelf to the south of Long Island 

 (Fig. 17). Figure 17 shows that sand mantles sea floor areas adjacent to 

 moraine- covered headlands. Several cores show a transition with depth from 

 clean, well-winnowed type III material down to either Pleistocene outwash 



55 



