length, shows features believed to be characteristic of coarse glacial sediments. 

 The lack of similar reflections Is probably due to the scales of the recordings. Run 

 VII has a vertical exaggeration of about 15 times, while run IX has an exaggeration 

 of 60. Run VII Is probably the most representative of the actual subbottom 



conditions . 



North of mark B on run VII, the bottom Is bedrock thinly covered by sediments. 

 Run VIII also shows a bedrock bottom only thinly covered by sediment. Slumping 

 Is suggested by the subbottom reflections at mark F on run VII . 



d. Runs III, IV, V, and VI 



Runs III, IV, and V (Fig. 8) begin near mark R on run II and cover the 

 area southward, the deepest part of the bay. The maximum depth Is about 540 feet 

 shown on run IV. The deepest portions of the basin seem to be bedrock thinly cover- 

 ed by sediments. The sediments thicken to the north and west. Run VI (Fig. 9), 

 continuing south from the end of these three runs, again shows bedrock covered by 

 sediments which become thinner and spotty to the south. 



e . Run XI 



Run XI (Figs. 13 and 14), in the northwest approaches to the bay, shows 

 mostly bedrock with sediments filling many of the depressions. From beyond fix E 

 to fix H the sediment cover Is thicker, and the subbottom horizon Is present In places. 



VI. CONCLUSIONS 



The sediments and subbottom evidence Indicate that glaclatlon and marine 

 submergence were the cause of most of the topographic and sedimentary features 

 found in the bay and Its approaches. Although Penobscot Bay undoubtedly owes 

 its majormorphological features to preglacial stream erosion, subbottom evidence 

 indicates that glacial erosion was largely responsible for forming the basin in the 

 entrance to the bay. As Interpreted from the Sonoprobe records, the floor of the 

 basin is bedrock mantled by a relatively thin layer of sediments. The southern 

 flank of the basin has a thicker cover of sediments, but all indications are that bed- 

 rock and not coarse glacial debris lies beneath these deposits. Personal observations 

 of glacial strlatlons on Mt . Battle, 7 miles north of Rockland, Indicate glaclatlon 

 parallel to the length of the bay. This direction of Ice movement would tend to en- 

 courage glacial scour of the valley floor. Although the topography of the land areas 

 does not support this view, the bedrock geology does add a degree of credence. The 

 granite contact, shown on Figure 18, probably strikes northeast through the southern 

 flank of the depression. The granite lies to the south whereas more easily eroded 

 rocks lie to the north . 



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