topography from Plum Island to Castle Neck, The results were successful, 

 but Duane found that sand bodies migh.t occur in patches because of the 

 unusually rugged bedrock, topography, and a more detailed coring program 

 would be necessary to evaluate furtlier the potential sand deposits in the 

 area. 



Although insufficient transverse profiles were run to prove the matter 

 conclusively, it appears tfiat a bedrock rise occurs beneath major features 

 such as Plum Island and Castle Neck and smaller forms such as Middle Ground. 

 Figure 21 shows the rise under Middle Ground. Figure 25 summarizes two 

 additional traverses tPiat indicate the possibility of bedrock rises. 

 Mclntire and Morgan C1963) found that the northeastern Massachusetts and 

 New Hampshire beaches are anchored on both bedrock and glacial deposits. 



The shallower bedrock depths at Crane Beach allowed determination of 

 the shape of that bedrock surface in greater detail than elsewhere. The 

 surface is cut by preglacial depressions and channels into which glacio- 

 marine clay was deposited apparently before the existence of the barrier 

 island. Figure 26 shows a cross section from data of seismic lines CB-18 

 and CB-19, with the accompanying drill hole CBG. Figure 27 shows the bed- 

 rock configuration beneath the Essex flood-tidal delta. This large sedi- 

 mentary body is apparently sited on bedrock at a shallow depth. Hydro- 

 graphy of the nearby Essex Bay between the rocky headland of Wingaersheek 

 Beach (locally called Coffin Beach) and the southern tip of Castle Neck, 

 indicates that the location of the main channel is restricted by bedrock 

 topography. In addition, the bedrock surface deepens beneath the channel 

 that separates the tidal delta from Castle Neck proper, indicating that 

 this sediment-filled depression once might have contained a deeper Castle 

 Neck River. 



Seismic profiles over the swash bars offshore from the Parker River 

 inlet indicate a deeper bedrock horizon. These profiles are without 

 drill-hole control, but even with the possibility of a "blind-zone" error 

 there is unquestionably a great deal of recent sediment without a bedrock 

 or glacial rise on which to anchor these sediments. Profiles such as 

 these on intertidal sand bars in the nearshore zone suggest that seismic 

 refraction methods could aid in the data collecting for a sand inventory 

 program. In addition, sedimentary horizons detected by seismic methods 

 in deeper water could be correlated with similar horizons beneath inter- 

 tidal and exposed shore formations. 



37 



