many places owing t-o either the greater depth of bedrock or an increase in the 

 coarseness of the material above the bedrock which prevented signal penetration. 



South of mark G to mark N, the lowest reflecting horizon does not have the 

 characteristics of the bedrock reflections in the beginning of the run. The topog- 

 raphy of the horizon is hummocky, and the reflections seem to come from a zone 

 rather than a surface. Bedrock is present between marks G and H and at mark K. 

 Elsewhere, this horizon is probably coarse glacial material of varying thickness 

 resting on bedrock. These deposits may be moraine, till, or stratified drift in places. 

 The depressions between the ridges appear to be partially filled with coarse sediments 

 showing some stratification. The well stratified sediments at fix N strongly suggest 

 glacial outwash . 



The subbottom reflecting horizon over these probable glacial deposits is scat- 

 tered and irregular, and the sediments appear to be draped over the high points of 

 the material below. In some areas, the silts and clays above the subbottom horizon 

 follow the subbottom topography, and in other places they fill in the depressions 

 and tend to reduce the bottom relief. About 500 yards south of fix G, the bottom 

 topography and the subbottom reflections suggest slumping of the sediments from 

 the bedrock high to the south. Slumping may also account for some of the features 

 found between the hummocky peaks below the bottom between marks L and N. 



b. Run II 



In the beginning of run II (Fig. 7), the bedrock appears to be mantled by 

 coarse glacial material, overlaid by the subbottom layer. Continuing south along 

 run II, evidence of bedrock or coarse glacial material is not apparent. It is here 

 that the sediments are thickest, probably on the order of 150 feet, since bedrock is 

 not encountered with over 100 feet of penetration. Beyond mark M the subbottom 

 horizon becomes discontinuous. At mark K,the arcuate subbottom reflections are 

 probably due to lenses of coarse sediments without great lateral extent. The shapes 

 of the reflections are due to the high reflectivity of the material and the spread of 

 the transmitted signal as the ship passed over these reflectors. 



c. Runs VII, VIII, and IX 



Run IX (Fig. 12) begins in the south near the end of run II and extends 

 northward in the western portion of the bay. In run IX, the subbottom is defined 

 better than in run II, but the horizon ends abruptly between marks E and F . Up to 

 this point, the bedrock trace is shown only faintly and intermittently on the record. 

 North of this point it is clearly shown. The subbottom layer apparently consists of 

 coarse material, causing a considerable reduction in signal penetration. The lowest 

 reflecting horizon appears to be bedrock with little evidence of coarse glacial mate- 

 rial above; however, run Vil (Fig. 10), which parallels run IX for a portion of its 



44 



