48 MICHIGAN SURVEY, 1905. 



PART II. ISLE ROYALE. 



1. GENERAL GEOGRAPHY. 



Isle Royale is situated in the northwestern part of Lake Superior on the 

 junction of the 89th degree of west longitude with the 48th degree of north 

 latitude, Fig. 21. It lies northeast and southwest nearly parallel to the 

 north shore of the lake. The topography is striking; several nearly parallel 

 ridges separated by broad valleys run the length of the island, and pro- 

 ject out into the lake at either end (more conspicuously at the north) as the 

 walls of deep fiords. These ridges are all low, the highest not exceeding 

 500 feet. The geology and topography have been discussed by Lane ('98) 

 and Irving ('83), and it is sufficient for this report, to say that the topography, 

 as in the Porcupine Mountains, is closely dependent on the geological struc- 

 ture. The ridges consist of the centers of outcropping sheets of lava, while 

 the valleys between are mostly cut in the inter-bedded elastics as in the 

 Porcupine Mountains. The dip of the rocks, is however, toward the Michi- 

 gan shore, and the escarpments are thus on the north instead of the south 

 side of the ranges. These escarpments are not precipitous in the southern 

 part of the island. There is abundant evidence that the entire island was 

 overridden by the ice sheets of the glacial epoch and that after the final 

 retreat of the glacier it was entirely submerged beneath the Pleistocene 

 Lakes (Lane, '98, pp. 183 and 184). It has not since that time been 

 connected with the mainland, a fact to which many of the peculiarities of 

 its biota are probably due. 



2. LOCATION OF FIELD STATIONS. (FIG. 21). 



Only the southwestern end of the island was examined. Stations were 

 established as follows : 



Station I. Clearing on the Shore of Washington Harbor, Section 29, 

 T. 64 N., R. 38 W. 



Station II. Washington River, Section 29, T. 64 N., R. 38 W. 



Station III. Trail along the Top of Greenstone Range, T. 64 N., R. 

 38 W. 



Station IV. Washington Creek, Sections 28 and 32, T. 64 N., R. 38 W. 



Station V. Tamarack Swamp, Section 20, T. 64 N., R. 38 W. 



Station VI. North Slope of Greenstone Range, Section 32, T. 64 N., 

 R. 38 W. 



Station VII. Lake Desor, T. 64 N., R. 32 W. 



Station VIII. West End of Siskowit Bay, T. 64 N., R. 32 W. 



Station IX. Southwestern End of Minong Trap Range, Section 30, 

 T. 64 N., R. 39 W. 



Station X. Washington Harbor, T. 64 N., R. 38 W. 



3. THE BIOTA CONSIDERED BY STATIONS. 



Station I. Clearing on the Shore of Washington Harbor. This station 

 will not be discussed as it is an artificial clearing into which cultivated species 



