52 MICHIGAN SURVEY, 1905. 



that grows nearly prostrate on the rock, associated with Juniperus nana, 

 Mountain Ash, White Pine, and Quaking Aspen. Near the shore the White 

 Spruce, Balsam Fir and Paper Birch come in, forming the forest of the region. 

 The succession on these points is evidently represented by four stages, the 

 Uchen-moss, grass-sedge, heath, and coniferous societies. The history of 

 the pools is somewhat different. There is evidence that these are being 

 filled in places by Sphagnum and other mosses, and on this moss such 

 bog forms as Ledum groenlandicum, Cassandra, Black Spruce and Tamarack 

 are occasionally found. These forms must, however, in time be succeeded 

 by the forms of the upland forest. 



In listing the fauna of the outer end of the ridge, the Herring Gull should 

 be mentioned as one of the most characteristic forms, for hundreds of in- 

 dividuals were often observed on this ridge during the summer. As in the 

 Porcupine Mountains, a number of molluscs push out in advance of the 

 forest on the heath mat. In the dry soil among the roots of these plants 

 was found, Pyramidula striatella, Zonitoides exigua, Vitrea binneyana and 

 Acanthinula harpa. 



Station X. Washington Harbor. As may be seen from the map, Wash- 

 ington Harbor is a long narrow bay lying between the Minong Trap and 

 Greenstone Ranges, on the southwest end of. the island. It attains a depth 

 of 6 to 9 fathoms and has a rocky bottom, that rises nearly to the surface 

 in places as reefs. 



The fauna of the deeper waters, as represented by the collections, consists 

 of the Lake and Brook Trout, Herring, Sucker, Muskallunge, Yellow Perch 

 and Couesius pliimheus. Among the rocks near shore the Millers Thumb 

 (Cottus ictalops) is found, and the molluscs, Limnaea stagnalis var.. 

 Limnaea summassi, Physa sayii, Physa sp. and Planorbis exacuous. Of 

 these forms the two Limnaeas were the most characteristic and were par- 

 ticularly abundant on the northeast end of the harbor. 



4. SUMMARY AND CONCLUSIONS. 



On account of the preliminary nature of the work done on Isle Royale, 

 but few conclusions will be drawn. It will be seen at once, however, that 

 while the biota of the Porcupine Mountains possess many southern forms, the 

 Isle Royale societies are characteristically boreal, the bog forms are less re- 

 stricted, the sedge, cassandra, shrub and coniferous societies are better rep- 

 resented on the river flood-plains, and many of the forms of the coniferous 

 society occur in the climax forest. This makes the climax forest society of 

 Isle Royale, of the northeastern North American type. The bog forms are 

 thus boreal types having the same affinities, and their spreading out in this 

 region from the restricted habitats which they occupy to the south may be ac- 

 counted for by the fact that the environmental conditions with which they are 

 associated, toward the north tend to become of general or of geographic ex- 

 tent, so that these forms ultimately come to form the climax society. Thus 

 several forms that about Ann Arbor have been recorded only from tamarack 

 swamps, such as the snails, Philomycus dorsalis, and Pallifera hempMlli (col- 

 lected by Miss Jean Dawson) , and the Varying Hare, Star-nosed Mole, and Red 

 Backed Mouse, are all boreal spedes (Bailey, '96), that toward the 

 north tend to become of general distribution. 



It will be noticed in the annotated lists, however, that while most of the 

 species have northeastern affinities, a number of forms collected on Isle 



