492 MICHIGAN SURVEY, 1908. 



ern . border — east of the Kocky Mountains — and as this sheet retreated 

 northward it spread with the forests into the area now occupied. It 

 also seems likely that their main headquarters were in the region south 

 of the Great Lakes and eastward, because the probable aridity of the 

 Great Plains in Glacial times would be unfavorable to extensive forest 

 growth. The Glacial and post-Glacial migrations of the Red Squirrels, 

 as far as they can be inferred, may explain some of the peculiarities of 

 their present range. The Red Squirrel is a representative member of 

 what I have elsewhere called the Northeastern Biota: (Adams, '05), 

 some of whose members have, in Glacial and post-Glacial times, invaded 

 the glaciated region from the south and have spread northwest to the 

 Pacific coast in Alaska as well as eastward, in Labrador, to the Atlantic 

 coast. 



It also seems probable that the geographic isolation and the peculiar- 

 ities of the Black Hills Red Squirrel {S. hudsonicus dalwtensis Allen) 

 may be explained, in part, if it be considered a glacial relict which has 

 become isolated by the change of climate attending the decline of the 

 Ice Age. The incomplete development of the lateral black line, which 

 usually occurs in the summer pelage of this group, is of special interest 

 in this connection. 



In addition to the typical form there are 9 or 10 varieties of this 

 species which have a range from southern Alaska to Washington, Oregon, 

 Idaho, northern Utah, Montana, Wyoming, South Dakota, southern 

 Minnesota, Wisconsin, northern Illinois, Indiana, southward to North 

 Carolina and northward to Labrador. The Red Squirrels are doubtless 

 one of the best groups of North American mammals for a study of the 

 laws of geographic variation, and is a group of undoubted Mexican or 

 Central American origin (cf. Coues & Allen, '77, p. 670) ; the Isle Royale 

 form being the one which has departed the fartherest from its region of 

 origin. This species, judging from its geographic range, has apparently 

 crossed the Rocky Mountains from the east, perhaps near the Canadian 

 boundary. 



3. Castor canadensis canadensis Kuhl. Northeastern Beaver. In all 

 probability the Beaver is extinct upon Isle Royale, although it formerly 

 occurred there. We saw no one who had any recent information of its 

 occurrence. Mr. J. H. Malone, reported that a Mr. Butterfleld had seen 

 a beaver dam on a creek at the head of Hay Bay in 1878. About that 

 time Mr. Malone found beaver cut stumps and remains of a dam on the 

 short stream which forms the outlet of Siskowit Lake. The U. S. Land 

 Office map indicates the site of "old" beaver dams as follows : SW. 14 

 Sec. 13, T. 64 N., R. 38W. NE. 1/4 Sec. 15, T. 64N. R. 37W. and NE. % Sec. 

 9, T. 63 N., R. 38 W. The Survey fui"nishing the data for this map was 

 made by Wm. Ives in 1848. 



Ecological Notes. — The Beavers of Michigan have been given more 

 study than any other native mammal found in the State, and at the 

 same time they have perhaps contributed more toward our knowledge 

 of the natural history of the American species than those from any other 

 locality. The extensive and important investigations referred to were 

 made in Marquette County about 50 years ago by Lewis H. Morgan, 

 and were published in 1868 in his volume entitled "The American Beaver 

 and His Works." This publication, to which reference should be made 



