Spencer.] ^-^^ [March 18, 



When was the advent of such a drainage system for this continent? 

 Some of our American friends, who have advocated the sub-aerial and 

 fluviatile origin of the lakes, have placed it back to the Devonian Age. 

 About the commencement, we know nothing. It would be safer to place 

 it after the Palaeozoic time, for probably some portions of the Province of 

 Ontario were covered with carboniferous deposits, as well as Michigan and 

 Ohio, which have subsequently been removed by denudation. 

 . Outlet of Lake Huron. The south-western countries of Ontario are dotted 

 with borings for oil. From these well- records, one can draw only a single, 

 conclusion, that they are underlaid by drift (mostly stratified and perhaps 

 wholly) to a depth of not more than 100 feet below the surface of Lake 

 Erie, and that generally to not more than 50 feet. There are deeper bor- 

 ings in drift, it is true, but these may be fairly considered as in buried 

 channels. For instance, at Detroit the drift is 130 feet deep. Again, at 

 Port Stanley, it is 150 feet below the surface of the lake ; at Vienna it is 

 200 feet below Lake Erie. If we draw a line from near the northern angle 

 of the Au Sable river (of the south) to east of Vienna, we have a boundary to 

 the deeply drift filled basin of south-western Ontario ; for at Tilsonburg, 

 St. Mary's and elsewhere (just east of this line) the hard limestones come 

 to near th3 surface of the country much above the level of Lake Erie. 

 Excepting a few shales, at Kettle Point, all the south-eastern shores of this 

 lake are composed of sand dunes and other Post-Tertiary deposits. The 

 upper portion of the Thames and Au Sable rivers are in conspicuously 

 Preglacial beds filled with drift. The Au Sable after turning northward 

 continues in a partly re-excavated valley to a point within a mile of Lake 

 Huron, and then turns at an acute angle and runs for a dozen miles south- 

 ward parallel, and very close, to the lake before emptying into it. 



Now, if we look at the large geological map of Canada, it will be seen 

 that the region underlaid by Upper Devonian shales extends south-eastward 

 from Lake Huron, forming a narrow belt across the country to Lake Erie. 

 Dr. Hunt has shown, that in places these shales are four or five hundred 

 feet thick, beneath the drift. On a careful study, it will be seen that these 

 south-western countries of Ontario simply formed a continuation of the 

 valley of Lake Erie to Lake Huron, or vice versa. The depth of this val- 

 ley, or plane, as we have seen, does not exceed 100 feet below the lake 

 level (Erie), except in channels, and generally less than that depth ; while 

 the waters in adjacent portions of Lake Erie vary in depth from 30 feet, at 

 the western end, to a maxium depth of 84 feet further eastward, where re- 

 moved from the mass of modern sediments now being brought down by 

 the western rivers. From these facts, but one conclusion can be drawn, 

 and that is, the deepest western portion of Lake Erie is not silted up to a 

 greater depth than the difference between its soundings and 100 feet ; ex- 

 cept in channels, such as the Cuyahoga. 



From these figures it will be seen that the country including the greater 

 portion of Lake Erie, the south-western counties of Ontario, and the 

 southern portion of Lake Huron formed one nearly uniform plane, in shale- 



