Basins of the Great Lakes. — Spencer. 89 
The deepest part of this valley is-738 feet beneath the surface of 
the lake. From this trough the floor of the lake rises gradually, 
or with occasional low steps, to the northern shore. In short, the 
basin was once an old land-valley traversed by a river. At the 
western end of the lake borings have revealed an old channel. 
having a lateral depth of 292 feet. This is the continuation of 
the canon of the Dundas valley, which is about two and a half 
miles wide, bounded by rocky walls nearly 500 feet high, capped 
with Niagara limestone. Down this valley the waters of the 
ancient Erie basin once flowed". 
If the waters of lake Ontario were withdrawn, its present basin 
would be a broad valley, continuous with that of the St. Lawrence 
valley, having a breadth of thirty or forty miles. Into this plain, 
at a point about twent}* miles east of Toronto, there is a channel, 
approaching the shore, whose bed is 474 feet below the surface 
of the laket. but with boundaries submerged to only 200 feet. 
This depression trends southward and joins that at the foot of 
the submerged escarpment before mentioned:!:. 
.'!. Features of the Eric basin. 
The floor of lake Erie is a broad flat plain, now rarely sub- 
merged to a depth of more than 84 feet, and usually less. Only 
a small area, situated directly south of the western end of lake 
Ontario, is of greater depth, and there the greatest sounding is 
210 feeti But from this region the Erie valley was drained by 
the Grand river and Dundas valleys into the western end of lake 
Ontario, as was shown in 1881 ; for the Niagara river did not 
then exist. Numerous tributaries of the modern shallow lake 
flow over deeply buried channels, the deepest of those discovered 
being 228 feet below the lake-surface, as described by Dr. New- 
berryll, although the tloor of that portion of the lake is nowhere 
over 84 feet below the surface of the water. 
Similar channels, buried to depths below the floor of the east- 
ern end of lake Erie, near Buffalo, have been described b\ Dr. 
Julius Pohlmann'T. The borings into many others in the region 
*See "Discovery of the Preglacial Outlet of lake Erie," etc. 
(See British Admiralty chart of lake Ontario. 
(See IT. S. Lake-Survey charts of lake Ontario. 
gSee U. S. Lake-Survey chart of lake Erie. 
fGeology of Ohio. 
IfPaper reau before the Amer. Assoc. Advanc. Science. L883. 
8 
