Bl 
channels which is shown in Fig, 4 (100, 101). Spencer suggested that Lake 
Michigan had a preglacial outlet to the south or southwest (95). 
Upham (125, 128) took exception to Spencer’s interpretation of the 
direction of the Laurentian preglacial drainage, and offered the theory that 
“A great trunk stream flowing south along the bed of Lake Michigan drew 
its chief tributaries on one side from the basins of Lakes Huron, Erie and 
Ontario, and the other side from the basin of Lake Superior.” He held 
that during the latter half of the Cretaceous period nearly all the drainage 
area which now forms Minnesota and the drainage basin of the Missouri 
river was depressed and covered by the sea, while the contiguous area 
forming the Great Lakes region was dry land and continued so up to the 
coming of the Ice Age. 'Phe divide separating this area from the basins 
draining to the Atlantic, extended “along the Allegheny mountain belt and 
directly onward northeasterly to the Adirondacks, turning thence north- 
westerly across the Ontario highlands . . . to the present height of 
land north of Lake Superior.” Spencer’s preglacial stream system was, 
therefore, probably limited to the headwater streams now represented 
by the Lake Champlain basin and the Saguenay and Ottawa rivers. 
Lately Grabau (43) has interpreted the preglacial drainage of the 
Great Lakes region in a manner different from Spencer and Upham. His 
theory briefly stated is this: The old surface of the pre-Cambrian rocks 
was worn away by long continued erosion and there were laid down upon 
them horizontally, but unconformably, the newer beds of Ordovician and 
Silurian rock. Then followed an uplift greater in the north, tilting the 
pew beds southward with a dip of about 25 feet per mile. Following the 
uplift was a period of erosion, wherein the region “suffered an enormous 
amount of denudation, having been brought to the condition of a low nearly 
level tract or peneplain a little above sea level.” Then the surface was sub- 
merged and beds of Devonian limestone, shales, and sandstones were laid 
down over it. The sea bottom became dry land and another cycle of erosion 
began. “Che uplifted beds formed a “broad essentially monotonous” coastal 
piain sloping gently southward. Consequent streams flowed southward down 
the slope. The great master streams developed were the Saginaw, Dundas 
and Genesee rivers, and probably some of the Finger lake valleys. As ero- 
sion proceeded, the sloping harder beds endured and cuestas were formed, 
living their steeper slopes to the north. Along the foot of the escarp- 
quents the subsequent streams flowed to the master streams, The Buffalo, 
