60 
JOURNAL OF MAMMALOGY 
September 19, spending the greater part of their time on Outer and 
Madeline Islands. On this last visit, however, little attention was 
devoted to mammals. 
HISTORICAL SKETCH OF THE GEOLOGY OF THE APOSTLE ISLANDS 
If one should look at a detailed map of the western end of Lake 
Superior there will be seen extending northeasterly from the Wisconsin 
shore a prominent peninsula, the terminal portion of which appears to 
have been submerged and separated into a number of islands. This is 
exactly what has taken place. In earlier geological times these islands 
were connected en masse with the mainland. During the Glacial 
Period a tilting began which has even increased since then and is prob- 
ably still in progress (Martin, Wisconsin Geol. and Nat. Hist. Surv., 
Bull. 36, p. 424, May, 1916). The separation of the Apostle Islands 
from the mainland is due largely to submergence of old stream valleys 
during this tilting. The exact time of permanent separation is believed 
by some to have occurred since the last glaciation of the region, but the 
fact that the greatest amount of tilt in evidence since the Nipissing 
Stage of Lake Superior (which was late in the Glacial Period) is con- 
siderably less than one-half the depth of the water in the channel 
between the mainland and Oak, Basswood, and Madeline Islands, 
would tend to throw some doubt on such a theory. Be that as it may, 
during the Glacial Period the terrestrial fauna of the islands was com- 
pletely destroyed by submergence of the islands in Glacial Lake Duluth 
which maintained a level about 500 feet above that of Lake Superior 
today. Lake Duluth slowly changed to the Lake Algonquin stage 
which stood some 350 feet above the present lake and was of sufficient 
depth to submerge all of the islands except Oak Island (altitude 480 
feet above Lake Superior). So complete was this glacial destruction of 
the topography of the islands that there is no trace whatever of an old 
drainage system on any of them. It would seem therefore that the 
terrestrial fauna must be of comparatively recent ingression. 
PHYSIOGRAPHICAL FEATURES OF THE APOSTLE ISLANDS 
Turning now to the present, we find the islands 23 in number and 
varying in size from Madeline Island which is over 12 miles long and 
nearly 3 wide, to Little Manitou Island (or Gull Rock) which is only 
300 feet long and 30 feet broad basally, narrowing to about 5 feet in 
