basin comprising present-day Lake Erie was scoured by Pleistocene age glaciers, 

 and numerous ancestral lakes occupied the basin following the latest glacial 

 retreat about 12,000 years ago. These lakes fluctuated considerably in area 

 and water level elevation depending upon climatic conditions and the degree of 

 crustal isostatic rebound of the outlet to the Erie basin at Niagara Falls, 

 New York. The presence of deeply incised stream valleys, shoreline deposits, 

 and wave-cut shore terraces below present lake levels suggests that several lake 

 stages below present have persisted, and these same features plus old lacus- 

 trine deposits presently subaerially exposed prove that some lake stages have 

 beem significantly higher than at present. The lacustrine deposits and sandy 

 shoreline deposits are particularly evident in the study area. 



Figure 3 shows that the nearshore region in the study area is character- 

 ized by generally shore-parallel contours out to -21 meters with the excep- 

 tion of the Presque Isle platform and spit as defined by the -12-meter con- 

 tour, and a linear topographic feature off Dans Beach that trends northwest. 

 A prominent elongate trough that reaches a maximum depth of about 23 meters 

 parallels the shore about 11 kilometers off Erie. It attains a minimum width 

 of 3.2 kilometers off the base of Presque Isle and widens eastward to a broad 

 and gently sloping plain that reaches depths of 30 meters about 24 kilometers 

 north of Erie. Westward the trough widens gradually to about 6.5 kilometers 

 off the Ohio-Pennsylvania border. 



North of the trough is a north-northwest trending linear ridge that is re- 

 curved as defined by the 20-meter contours in Figures 3 and 4. It has a crest 

 elevation of about -15 meters and is asymmetrical with a steep slope eastward 

 and a more gradual slope westward to -23-meter water depths. The main body 

 of the ridge is 1.5 to 5.5 kilometers wide and extends northward across Lake 

 Erie to the Canadian shore at the base of Long Point (Fig. 4) . This ridge 

 is the major boundary between the deep eastern section of Lake Erie basin and 

 the more shallow central section, and as will be discussed later, has been 

 very important to the origin and evolution of Presque Isle Peninsula. 



3. Data Analysis . 



The seismic profiles collected were visually examined and marked to estab- 

 lish the primary geologic features to depths of about 23 meters below the lake 

 floor, the maximum penetration and resolution of the systems used. Regional 

 geologic reflectors were mapped, identified, and where possible correlated 

 with sedimentary materials recovered in the cores. 



The cores collected were sent to the CERC laboratory where they were split 

 open lengthwise, described, and sampled in detail to include the sediment tex- 

 tural characteristics, sand composition, color, relative strength of cohesive 

 materials, and presence of organic materials that might be radiocarbon dated 

 to give absolute geologic ages of the sediments. Complete logs of the cores 

 (App. A) include water depth at each site, length of recovered sediment, and 

 thickness of each sedimentary unit as measured from the top of the core. The 

 grain-size descriptions are based on the Wentworth classification as shown in 

 Table 1. 



Appendix B contains results from grain-size analysis using the Rapid Sedi- 

 ment Analyzer (RSA) for fine- to coarse-grained sands and sieve analysis for 



