1S81.] "^^^ [Spencer. 



rocks, which, however, gradually sloped both to the northward and east- 

 ward towards the deepest portions of the lakes. From the borings, we see 

 that there were channels, and I think that we are furnished with the data 

 for pointing out where the outlet of Huron formerly flowed, even to a 

 depth sufficiently great to drain the deepest portion of the lake, although 

 filled with some sediment. That portion of the Au Sable flowing northward 

 in an old buried valley, and then turning southward, indicates a portion of 

 the ancient outlet. The channel having been dammed in the Ice Age, has 

 caused the modern river to flow in the capricious manner indicated on the 

 map. This portion of the river reversed, formed an ancient outlet for Lake 

 Huron, and flowed to its south-western angle, then turning eastward, the 

 direction (with gentle curves) was south of eastward across the coun- 

 try to Lake Erie, having Port Stanley on its right, and Vienna on its left 

 bank. It is known that the channel at the former place was 150 feet, and 

 at the latter 200 feet below Lake Erie, and with a suSicient distance be- 

 tween these places to have permitted of a valley four times that depth, 

 even in the Hamilton shales, and underlying Coniferous limestones. At a 

 distance of only a few miles eastward of this line, the Coniferous limestone 

 comes to near the surface of the country, and is exposed by several modern 

 streams. The upper portion of the Thames, the eastern branches of the 

 Au Sable, and other streams belong to Preglacial times with buried chan- 

 nels, were tributaries to this old outlet. 



Throughout the south-western counties generallj^ there is a broad belt 

 underlaid by several hundred feet of Devonian rocks (mostly of shale of the 

 Hamilton group), beneath the drift deposits, which cover them to a depth 

 of from ,50 to 100 feet. 



Two things along this route support the theory that this channel, known 

 to be 200 feet deep (below Lake Erie) and able to drain half of the surface 

 of Lake Huron, was of more gigantic proportions, is the nature of the drift 

 near Port Stanlej^, and the configurations and soundings of Lake Erie. Near 

 Port Stanley, the drift is piled up much deeper than it is usually found in 

 this section of the country, reaching 150 feet above the lake. From which- 

 ever cause (glacier or iceberg), it is just what would be expected along the 

 margin of a valley against which drift-bearing ice would be passing. The 

 other indication is, that if we draw a line from a short distance north of 

 Port Stanley to southward of Vienna (the direction of the valley), it forms a 

 continuation of a nearly direct portion of the present shore, curving slightlj'^ 

 to Long point, just off" which the deepest portion of the lake is found, and 

 around which the channel turns, to the Grand river of Canada. It cannot 

 be justly said that the present configuration of the lake is independent of 

 its Preglacial form. Nor can it be said that the lake is generally silted up 

 to great depths, except in channels, for any such statement is unwarranted 

 by facts, as I have shown from the analogy between the bottoiu of the 

 western end of the lake, and the south-western counties, to be improbable. 



Course of Preglacial Rivers. We are now able to construct an approxi- 

 mately true river map from Lake Huron to the eastern end of Lake Ontario. 



