BASINS OF THE GREAT LAKES OE AMEKICA. 531 



feet per mile, in mean direction of N. 20° E. This will account for 

 a portion of the barrier closing the Georgian outlet of Lake Huron. 

 The more elevated beaches in the region of Lake Huron, record a 

 still greater change of level. 



At the outlet of Lake Erie, Mr. Gilbert and mjself find a differ- 

 ential uplift of about two feet per mile, and this is sufficient to ac- 

 count for the recently formed basin of Lake Erie. 



The warping affecting the Michigan Basin has been that towards 

 the north and east; and even in the buried channels south of 

 Lake Michigan there is no evidence of an ancient drainage to the 

 south, as their beds were too high compared with those of the 

 northern, although the latter have been elevated recently by warping. 



10. ConclusioThS from the Observations. 



The valleys of the great lakes here studied are the result of the 

 erosion of the land-surfaces by the ancient St. Lawrence (named 

 Lcmrentian) Eiver and its tributaries, during a long period of con- 

 tinental elevation, until the streams had reached their base-lines 

 of erosion, and the meteoric agents had broadened the valleys. This 

 condition was at the maximum just before the Pleistocene period. 



The closing of portions of the old Laurentian Yalley into water- 

 basins occurred during and particularly at the close of the Pleis- 

 tocene period, owing, in part, to Drift filling some portions of the 

 original valley, but more especially to terrestrial warpings of the 

 Earth's crust, which, to a sufficient degree, is measurable. 



Discussion. 



The Chairman noted that there were one or two Eellows who had 

 a local knowledge of the area, but the question of the origin of lake- 

 basins in general was raised in the paper. 



Dr. HiisDE did not think that Dr. Spencer's explanation of the 

 origin of the American lake-basins was the true one. The sub- 

 merged deep channels of the alleged ancient rivers, to which the 

 lake-erosion was said to be due, were traced towards the east end of 

 Lake Ontario, where they ceased ; and their discontinuity through 

 the barrier formed by the hard gneissoid region of the Thousand 

 Isles was attributed to differential elevation, or so-called earth - 

 warping. This assumed warping where barriers existed could 

 always be brought in to account for them. He (the speaker) asked 

 where the beaches existed near Kingston, at the east end of Lake 

 Ontario, on the difference of level of which, the supposed warping was 

 based. Erom his own observations on the region, he doubted the 

 existence of the alleged buried channel between Lakes Huron and 

 Ontario, and he did not think that the acknowledged great thickness 

 of Drift now covering the elevated area between these lakes should 

 be regarded as proof of the presence of a former channel directly 

 connecting them. With reference to the supposed old channel 

 between Lake Erie and Lake Ontario, by way of the Grand Eiver 

 and the Dundas valley, the water of Lake Erie was supposed to 



