104 



these considerations, gravel may be more widespread than is 

 indicated on the surface sediment charts, but below the depth 

 of penetration of a snapper sampler. 



The gravel could either have been derived from outcrops 

 on the outer edge of the shelf or from the land adjacent to 

 the bay. The fragments are too large to be carried by present 

 day currents or waves in overlying shelf water, so they must have 

 been trsmsported by streams or surf action in some previous 

 geologic time of lower sea level. This conclusion was also 

 reached by Shepard and MacDonald (1938, p. 213). The 

 restriction of large patches of gravel to the outer shelf 

 suggests that this may be the source area. However, the 

 great diversity of lithology of the gravel probably indicates 

 that streams carried at least part of the material from some 

 inland source having a complex geologic structure. Whether 

 the gravel was derived from erosion of the rock area on the 

 shelf or by erosion of the uplands and transported to the 

 area by streams during a lower stand of sea level is problem- 

 atical. There is evidence, however, that the gravel is a 

 relic sediment that was deposited in the early part of Recent 

 time or in the Pleistocene period (Shepard and MacDonald, 

 1938? Revelle and Shepard, 1939). The large size of some of 

 the cobbles and rock fragments, abundant pholad borings, high 

 concentration of CaC03, and the attachment of coral and bryo- 

 zoans are taken to mean a long period of stability in the 

 marine environment since the material was deposited. 



