Basins of the Great Lakes. — Spencer. 01 
the eastern side, has a hight of 500 feet. Whilst the deepest 
sounding at the modern outlet of the lake is only 252 feet, there 
are adjacent channels buried to unknown depths. But these have 
been imperfectly explored. Into this shallower portion of the 
lake, however, the fjord of Grand Traverse bay has a northern ly 
trend ; it is 612 feet deep. This and the lesser fjords indicate 
the existence somewhere of a deep channel connecting with the 
Huron basin, as much as the river-valleys buried beneath the 
Drift materials of the modern floor of lake Erie prove deep 
channels throughout that basin, although not shown by the sound- 
ings ; 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 ; 
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 
pre-Pleistocene valley, as its margins have been filled with Drift, 
arid now form broad plains bounding the lake. Beneath these 
deposits 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 original lv drained, and 
thus established the relationship of the Erie with the Ontario 
basin. But the most important series of borings were those be- 
tween Georgian bay and lake Ontario, for here we have the con- 
necting-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 
05 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 
