BASIN'S OF THE GEE AT LAKES OP AMERICA. 527 



basin, although not shown by the soundings ; for the Lake-Michigan 

 valley is carved out of undisturbed and almost horizontal Palaeozoic 

 rocks, the newest of which are Coal-Measures. 



The southern basin of Lake Michigan is separated from the 

 northern by a plateau submerged to a depth of from 300 to 342 feet ; 

 whilst the southern basin itself is now 576 feet deep. The area 

 of this portion of the basin is now much smaller than that of the 

 Prepleistocene valley, as its margins have been filled with Drift, 

 and now form broad plains bounding the lake. Beneath these de- 

 posits is a deeply buried channel, leading to the valley of Lake 

 Huron, and to be noted further on. 



6. Buried Valleys revealed by Borings. 



The deep wells revealed the existence of the buried channel down 

 which the waters of the Erie Valley originally drained, and thus 

 established the relationship of the Erie with the Ontario Basin. 

 But the most important series of borings were those between Geor- 

 gian Bay and Lake Ontario, for here we have the connecting-link 

 between the valleys of the upper lakes and that of Lake Ontario, 

 and indeed the key to the origin of the valleys of the lakes. 



Between Georgian Bay and Lake Ontario, a distance of about 

 95 miles, a portion of the country is comparatively flat or com- 

 posed of a series of rising plains ; but there are also high trans- 

 verse ridges of Drift, having a general trend of east and west. It 

 is upon the northern side of the Drift ridges that Lake Simcoe, with 

 a diameter of about twenty miles, is situated. But upon the 

 northern side of Lake Simcoe there is another series of Drift ridges 

 trending towards the north-east. Both of these series of ridges rise 

 to between 200 and 550 feet above Lake Huron, these measurements 

 being the extreme variation in their height. 



Erom Georgian Bay to near Lake Simcoe, for a distance of thirty 

 miles, the country is low and flat, with a known absence of rock to 

 far below the level of the bay. Lake Simcoe is 140 feet above 

 Georgian Bay, but upon its northern side, at Barrie, a well has been 

 sunk in the Drift, without penetrating it, to a depth of 280 feet 

 below its surface. Thirty miles further inland, south of Lake 

 Simcoe, at jS'ewmarket, a well was in the process of being bored. 

 It had reached a level below Georgian Bay and was yet in Drift 

 deposits when visited. In another well, several miles to the west- 

 ward, near the side of the ancient buried valley at Beeton, rock was 

 reached at 50 feet below the surface of Georgian Bay. 



Between Newmarket and Richmond Hill there are several deep 

 wells on the heavy Drift ridges which cross the country. But at 

 Eichmond Hill, at a height of 217 feet above Georgian Bay, there 

 is a well 400 feet deep without penetrating the Drift. This proves 

 the thickness of the Drift of the higher ridges crossing the old 

 Valley north of the well to be not less than 700 feet in the old 

 channel. Southward of Eichmond Hill the country falls away in a 

 series of more or less rolling steppes to Lake Ontario, but these 



