GLACIAL LAKES TAYLOR. 325 



changes in the data wliich he used and have necessitated a modi- 

 fication of liis results. 



Since the discharge returned to Port Huron the St. Clair lliver has 

 cut down its bed about 15 feet and the Detroit liiver half that amount. 

 This has greatly reduced the effect of drowning of tributaries which 

 was produced at first by the return of the full volume after the 

 period of abandonment durmg the time of the Nipissmg Great 

 Lakes. 



In the basins of Lakes Erie and Ontario there are many evidences 

 which indicate recent raising of the water level, such as the drowned 

 stream courses and submerged stumps in Sandusky Bay. These 

 facts seem at first to suggest that tilting of the land w^as very recent 

 or may still be m progress. But the drowning effects in these two 

 basins, at least to depths of 10 or 15 feet, are probably due to the 

 return of the large volume of discharge at Buffalo and Ogdensburg 

 after the relatively long period of small discharge durmg the time of 

 the Nipissing Great Lakes, and not to recent or progressing uplift 

 of the land. 



POST-GLACIAL MARINE "WATEES IN THE OTTAWA AND ST. LAWRENCE 

 VALLEYS AND IN THE LAKE ONTARIO BASIN. 



Wlien the ice sheet withdrew from the basin of Lake Ontario and 

 the northern slope of the Adirondacks the sea entered ui its place 

 and covered a large area. Its approximate limits (fig. 6) are indicated 

 by postglacial clays, gravels and sands, wliich are fossiliferous, and the 

 Hfe remams are largely of marine organisms such as are now living 

 in the Gulf of St. Lawrence. The upper limit of the marine waters 

 was about 350 feet at Plattsburg, N. Y., and 523 feet at Covey Hill, 

 Ontario. It was at least 460 feet at Welsh's Siding near Smith's 

 Falls, Ontario, and may have been much more, for at the last-men- 

 tioned place tlie remains of a whale v/ere found in a gravel bed many 

 years ago, and a minimum upper hmit of maiine submergence is 

 definitely fixed by this occurrence. The height of marme submer- 

 gence at Montreal is reported to be about 625 feet. On the south 

 side of the St. Lawrence River a well-defined beach marks what is 

 taken to be the upper limit of the marine waters, and has been called 

 by Gilbert the Oswego beach. It declines gradually toward the 

 southwest and passes under the present level of Lake Ontario about 

 at Oswego. 



The changes in the level of the waters in the Lake Ontario basin 

 have not been fully worked out, but the marine watere appear to have 

 entered it some time in the later part of the Port Huron stage of 

 Lake Algonquin. The marme connection Vv^as through a strait 25 

 or 30 miles wide and, except for a relatively narrow central depres- 

 sion, not over 40 to 50 feet deep. The uphft appears to have been 

 85360°— SM 1912 22 



