32 The America7i Geologist. July. is99 
If the moraines be supposed to mark successive halting places 
of that barrier it at once becomes apparent that their disposi- 
tion in the basins is precisely such as is required to explain 
the beaches and outlet channels. It is hard to see how marine 
submergence can have any definable relation to features which 
have a demonstrable dependence upon a receding dam or bar- 
rier. 
TJic Significance of the Ubly Channel. 
One of the most significant and characteristic features found 
in the area of these lakes is the Ubly outlet channel. It is in 
some respects a truly remarkable thing. Its situation so far 
cut towards the end of the thumb and the fact that it hugs the 
foot of the Port Huron-Saginaw moraine in its re-entrant angle 
presents a combination of facts favoring great ice-dams and 
glacial lakes perhaps as clearly and forcibly as anything that 
has ever been found. 
The thumb of Michigan projects out into the open waters 
of lake Huron about 60 miles. Its crest, not counting the mo- 
rainic hills which lie upon it, is a trifle over 200 feet above the 
lake and this altitude runs out to within 20 miles of its end. 
The head of the outlet channel is about 30 miles back from the 
point and 210 feet above the lake. The channel has a long 
summit swamp connected with its head and a gravel delta at its 
foot, and bowlders and gravel and sand bars show the direction 
of flow to have been from east to west. Thus, the thumb is 
almost a promontory and the channel crosses its back from 
east to west half way out towards its end. How can the exist- 
ence of a great river channel in such a situation be explained? 
How is it related to the different explanations which have been 
suggested for the waters that made the old shore lines of this 
region? 
Besides ice-dams, the only alternative explanations of the 
expanded waters of the Great Lake region are, (i) Marine sub- 
mergence due to subsidence of the land, and (2) Lakes re- 
tained by land barriers due to tilting or unequal uplifts or sub- 
sidences of the land. If we adopt the marine hypothesis we 
must either ignore entirely all the old outlet channels or re- 
gard them merely as cols near sea level and more or less 
modified by tidal action. As has been pointed out by Mr. Lev- 
