a. Shale Bedrock . Figure 6 shows the extent and general relief of the 

 bedrock surface based on the seismic data and logs from three deep borings. 

 Because of the limited penetration on some profiles, bedrock was not mapped 

 in detail throughout the study area; however, contour trends were drawn 

 from the data points in Figure 6. Shale crops out along the shoreline in the' 

 study area but is covered in some areas by glacial and lacustrine deposits and 

 unconsolidated masses of material from cliff slumping. Figures 7, 8 (profile 

 A) , and 9 show that the shale surface slopes lakeward and crops out at the lake 

 floor to water depths of 9 to 12 meters. The relief is sometimes irregular; 

 Figure 6 shows that bedrock reaches a maximum depth of -87 meters about 17.6 

 kilometers northwest of Presque Isle. Clearly, its depth in all areas, except 

 within several hundred meters of the shore, is great enough to not interfere 

 with dredging operations. 



BO-SO 

 42°20'4- 



80°O5 

 + 42°20' 



flpproi 

 Assumed 

 //////// Outcrop Areo 



I 2 3 15 6 7 

 STATUTE MILES 



CONTOURS IN METERS 

 Figure 6. Map of the shale bedrock surface. 



b. Glacial Deposits . These unconsolidated sediments, which com- 

 prise the largest volume of any sedimentary unit in the region, overlie 

 the shale bedrock and are most important as sources of sand and gravel. 

 Several of the seismic profiles show that the offshore ridge originated 

 as a glacial moraine that crossed the Lake Erie basin and was at one time 

 continuous from shore to shore before development of modern Lake Erie. 

 Its unofficial name is the Long Point-Erie Moraine. Parts of the moraine 

 appear to be unstratified and may contain very coarse materials such as 

 boulders; however, most of the ridge appears to be stratified and composed 

 of poorly sorted, fine to very coarse sands and gravel. The main body 



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