ECOLOGY OF ISLE ROYALB. 31 



found in both the seasoned and the decayed wood. A few beetles were 

 taken along the trail; Quedkis fulf/ides, Tachinus vicinnoniius and 

 Geotrupes hlaclchunin. Shells were abundant: Strohiloj)s virgo, Vitrea 

 Mnneyana, Eucon-wlvs chersinus polygyratus, Zonitoides arhorca, Z. c.ri- 

 gua. PalUfera dorsalifi, Pyraiiddula alteniata and P. cronkheitvl 

 anthonyi. 



Station IV, '0-',. Washington Brook. Of. Ruthven, .'06, p. 50. This 

 station was examined on the slope back of the Club-house. It is a 

 swamp forest along the border of a xevy small stream, Fig. 50. Part of 

 the forest is being cleared. 



Station Y, '04. Tamarack Swamp. This swamp was not visited in 

 1905. Cf. Ruthven, '06, p. 50. 



Station VI, 'OJf. ^orth Slope of Greenstone Range. Cf. Ruthven, '06, 

 p. 49. 



Station VII, '04. Lake Desoi: Cf. Ruthven, '06, p. 51. A few addi- 

 tional records are: The dragonfly, Enallagtna e<€sulans, the water strider, 

 Gerris remigis, the fish, Goregonus artedi. At the end of the trail (III, 

 '04) at Desor, the beetle, Melanotus paradoxus, and the spider Dolomedcs 

 idoneus, were taken. 



Station VIII, '04. Western End of Siskowit Bay. The large clearing 

 and burned ai'ea at the head of Siskowit Bay marks the site of a former 

 town, the county seat. A well-defined graded road leads from near the 

 north shore of the Bay wes.tward amd north to an old mining camj), 

 This road is being invaded in places by Birches and Aspens. This exten- 

 _ sive clearing was overgrown with many introduced plants and was 

 given only a cursory examination. The following vertebrates were ob- 

 served: Sharp-tailed Grouse, (of which several were seen), the Hare, 

 Toad and Garter Snake. The snails, Polygyra alholahris and Pyramidula 

 alternata, and the grasshopper Stenoiothrus cwrtipennis were found 

 here. The limits of this station were changed somewhat from those 

 given in 1904. 



Station IX, '04- Southwestern End of Minong Trap Range. Cf. Ruth- 

 ven, '06, p. 51-52. No additional collections were made here in 1905. 



Station X, '04. Washington Harior. Cf. Ruthven, '06, p. 52. No 

 additional collections were made at this station in 1905. 



III. THE EVOLUTION OF THE GROSS BNVIBOX JIENT. 



1. Geological Succession. In his report on the Porcupine Mountains, 

 Ruthven ('06) has summarily outlined the general geological history 

 of the Lake Superior regipn. It is only necessary, therefore, for our 

 purpose, to repeat some of this history and to enlarge upon those 

 phases peculiar to Isle Royale. The structural geology of Isle Royale 

 has been studied in detail by Lane ('98) and is relatively simple. The 

 different rock formations are in narrow strips nearly parallel with the 

 long axis of the island, while the dip of the rocks is toward the basin 

 of Lake Superior., The rocks north of Siskowit Bay consist of the trun- 

 cated beds of ancient lava flows, interrupted by a small amount of inter- 

 bedded sedimentary rocks. Although these tilted and truncated beds are 



