medium- to coarse-grained sand mixed with gravel (Fig. 12). The area with 

 greatest potential is the ridge-platform moraine complex; the moraine ridge seg- 

 ment off Dans Beach is considerably lower in potential. Figure 7 shows the loca- 

 tions of representative profiles B to F and I to for the first area and profile 

 H for the second area. Interpretations are shown in Figures 8, 9, and 13 to 18. 



A total of 13 cores (2, 5 to 10, 15 to 18, 22, and 25) are fairly evenly 

 distributed over the Long Point-Erie ridge to the Canadian border and all con- 

 tain clean, generally medium to coarse sand with varying percentages of pebbles 

 and gravel. The minimum thickness of sand is 0.76 meter (core 22, Fig. 17), 

 while the maximum recovery is 3.9 meters (core 17, Fig. 16). The average sand 

 thickness for the 13 cores is 2.3 meters; however, the seismic profiles show 

 that sand and gravel are about 5 to 6 meters thick in the main body of the 

 ridge and thin to zero at the flanks where contact is made with the firm la- 

 custrine clay. 



The area of the ridge shown in Figure 12 has been computed to be 20.3 mil- 

 lion square meters; using a conservative figure of 1.7 meters for thickness, 

 the estimated volume of sand is 37.2 million cubic meters. 



The platform to the west and slightly lakeward of Presque Isle has a 

 glacial origin in common with the Long Point-Erie ridge, and the seismic 

 profiles and cores 28, AO, and 41 show the platform is composed of generally 

 medium to coarse sand and pebbles overlying silty fine sands or firm lacus- 

 trine clay. Detailed bathymetric charts and the profiles (see Fig. 8, pro- 

 file B) show that the platform surface is made up of several irregular shoals 

 which semiparalled the Presque Isle shore and have maximum relief of about 

 4.5 meters. The. origin of these shoals is likely to be related to glacial 

 processes with subsequent reforming and winnowing of the topmost sediment 

 by modern lake processes. However, the shoals could also be relict, drowned 

 beach ridges from an earlier and more lakeward position of Presque Isle. 



Although there has been some speculation, based on historic migration rates, 

 that Presque Isle has migrated considerable distances since its formation, this 

 study has shown that it is the product of erosion of glacial sediments on the 

 adjacent platform and ridge. This suggests that Presque Isle has migrated no 

 more than 8 kilometers in the past several thousand years. 



The area on the platform encompassing cores 28, 40, and 41 (Fig. 12) is 

 about 1.7 million square meters, using a sand thickness of 0.9 meter, the esti- 

 imated volume of material is 1.6 million cubic meters. However, there are sev- 

 eral important factors that should be considered before the shoals on the plat- 

 form are viewed as borrow sources. The other CERC cores on the platform and 

 the grab samples show that the sediments from the platform are more variable 

 in grain size and composition than the sediments from the offshore ridge. 

 Therefore, the chances are greater that this material may have high propor- 

 tions of silt, clay, and very fine sand, which would lessen its potential for 

 being stable as fill. A second and possibly even more important consideration is 

 that these shoals may be directly related to the nearshore sand transport regime, 

 which would affect alongshore wave energy distributions along Presque Isle. 

 Sand from Presque Isle beaches may move offshore and incorporate with the shoals 

 under storm conditions, and then return to the shoref ace-beach under fair-weather 

 conditions. If a borrow pit were dredged in water that is too shallow lit- 

 toral processes may remove sand from the shore zone in an attempt to refill the 



22 



