ECOLOGY OF ISLE ROYALE. 39 



2. The Topography and its Origin. The most conspicuous and char- 

 acteristic topographic features of the island are its parallel flat-topped 

 rock ridges with the intervening valleys and numerous swamps. These 

 ridges project far out from the main body of the island and form the 

 narrow rock ridges bounding the harbors, and forming a vast number 

 of small islands and low rocky reefs. The tilting, faulting and trunca- 

 tion of these narrow beds clearly shows that the dependence of the 

 topography upon rock structure is one of the most characteristic features 

 of the island. 



The main ridge, the Greenstone Eange, is a divide which extends the 

 entire length of the island, and is fromi about 400 to 500 feet high, 

 with a maximum height of about 550 feet at the northeastern end of 

 the island. At only one place does a drainage line cross the Green: 

 stone. This is a small stream heading in Sec. IT, T. 64 N., E. 37 W. 

 and a tributary to Washington Eiver. This ridge is a truncated lava 

 bed whose outer softer part has been eroded, thus throwing into promi- 

 nence the compact resistant central core. Thus erosion, faulting and 

 the dip of the rocks have combined to produce a northwestward facing 

 escarpment nearly throughout its extent. The fairly flat topped 

 truncated ridges of the island clearly show that their origin must be 

 due to a period of baseleveling and is no doubt related to those exten- 

 sive processes which have produced the Lauren tian peneplain (cf. 

 Euthven, '06, p. 45) of the Superior region. The ridge of second im- 

 portance is the Minong Trap Eange, which lies parallel with the Green- 

 stone, about a mile to the northwest, and reaches a height of about 400 

 feet. Between these ranges lies a valley containing five fairly large 

 lakes, all of which drain across this range to the northward, and the 

 probable faults indicated by Lane ('98, pi. 1) at Todd Harbor and 

 McCargoe Cove are suggestive as to how the ridge has been broken 

 through. Faults seem to have influenced the location of several lakes, 

 such as Angleworm, Lesage, Livermore, Chickenbone, Feldtmann and 

 also the outlet of Lake Eichie into Chippewa Harbor. In addition to 

 these main ranges there are great numbers of lower ones whose heights 

 range from 100 to about 300 feet. East of Lake Feldtmann there is a 

 bold escarpment 130 feet high, which was said by Mclntyre (Foster, 

 '50, p. 506) to afford the "finest view that I have seen on the island." 



The drainage of the island presents some interesting features. Ac 

 each end o^ the island the drainage is mainly along the valleys into 

 the harbors at their ends. Between these two extremes, roughly marked 

 by the area between lakes Desor and Sargent, the drainage, although it 

 may follow the valleys for some distance, is yet to a marked degree 

 acrpss the strata or ridges. Taken as a whole the drainage is very 

 imperfectly developed. Although the island is not extensive, it con- 

 tains numerous small independent streams which drain into the lakes 

 or directly into Lake Superior, but it has no master stream. It seems 

 probable that this is also related to faulting, as also in the case -of 

 the stream, which may be called Malone Creek, that flows into the head 

 of Siskowit Bay. The probable influence of faulting upon the location 

 of lakes has previously been mentioned, and combined with its influence 

 upon streams reinforces the idea of the dominance of structure upon 

 the topography and consequently upon the drainage. But when in the 



