MICHIGAN ACADEMY OF SCIENCE. 
209 
A FEW NOTES ON THE 
MOLLUSC A OF THE DOUGLAS LAKE 
REGION. 
II. BURRINGTON BAKER. 
Last summer, with the assistance of two students (Misses Robertson 
and Loomis), I made quite an extensive collection of molluscs in the 
region of the Biological Summer School at Douglas Lake. An attempt 
was made to study the ecology of the shells of that region, and among 
the general relationships', to be dealt with in a future paper, there were 
a few points which appeared to be of especial interest. 
During the different oscillations of the level of the Great Lakes after 
the retreat of the glacial ice, the distribution of the land and water, 
and the connections between the different smaller lakes and the main 
lakes in this region, was often very different from at present. From 
the adjoining map (Plate - — ) of the northern portion of the southern 
peninsula of Michigan, it will be seen that, at the time of the highest 
Lake Algonquin Beach, the northern limit of the mainland was south 
of Burt Lake ; and that the remainder of the peninsula was flooded, 
with the exception of a large island north of the present site of Pe- 
toskey and nine small islands to the east of this largest one. At this 
time, then, Douglas and Burt Lakes were simply deeper portions of 
the channels between these islands, and were directly connected with the 
Great Lakes. Later, the ice melted back so that the Ottawa outlet 
drained the water down to below the level of the present Lake Huron ; 
but, with the upward tilting of the land in the northern portion, the 
water returned to the highest Nipissing level so that a channel thru 
the beds of the present Mullet, Burt, and Crooked Lakes separated 
a large island enclosing Douglas Lake . 1 
At present, as was probably also true at the time of the Nipissing 
Great Lakes, Douglas Lake is connected with Burt Lake by Maple 
river, a small creek flowing thru many tamarack swamps. This creek 
has too soft and mucky a bottom to allow the free migration of 
Goniobasis livcsccns (Menke), a shell very abundant in Burt Lake and 
the Straits of Mackinac, and it is not found in Douglas Lake altho 
there are many places in that lake that appear to be equally favorable to 
it. This, it appears to me, is pretty good proof that this shell was not 
present in the glacial Lake Algonquin but is a later immigrant from 
the south. 
The other prominent shells of these lakes are shown in the following 
diagram : 
STRAITS OF MACKINAC. 
L. emarginata Say, and approaching var. canadensis (Sowerby). 
Physa ancillaria magnalacustris Walker. 
’“Outline of The History of the Great Lakes,” Frank Leverett. 12th Rept. Mich. Academy of 
Science, 1910; pp. 35-39. 
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