ECOLOGY OF ISLE ROYALE. 23 



of the log cabin used by our party. The logs were thoroughly infested 

 by beetle larvae, and attracted vast numbers of parasitic Hymenoptera. 

 For this reason, insect collecting about the cabin was of an exceptional 

 character, and included a considerable variety of species. From the 

 adjacent forest a number of trees had been cut, but this did not material- 

 ly influence this locality, except near the shore. 



Station V, Substation 2. Heath Zone and Beach. This locality in- 

 cludes a strip of rocky coast on the south shore of the island, a short 

 distance east of the entrance of Siskowit Bay, Fig. 29, and extends from 

 the edge of the water back to the forest. This is an exposed section of 

 the coast and is unprotected by offshore islands, so that easterly storms 

 from the open lake have full sweep on this shore. The slope is a fairly 

 uniform rock surface, with an upward slant of about 10 degrees, and 

 is composed of amygdaloidal lava. Crevices of various dimensions, from 

 a mere crack to a deep rock ravine, extend obliquely up the slope. One 

 of these ravines, the only large one, divides this station into two sections 

 east and west. The eastern section of the slope is covered by a Gladonia- 

 Jtmiperus procumhens society, while the western section is occupied by 

 a Cladonia-Juniperus w«Mc-Huckleberry society. Thus there are three 

 fairly well defined natural divisions of this part of the coast, the beach, 

 the procumhens, and the nana societies. 



1. The Beach. The low angle of the slope, and the exposed situation 

 and deep offshore water all combine to make the beach zones quite wide 

 (four or five paces) upon this slope. No collections were made upon the 

 submerged beach and only a few specimens were taken upon the lower. 

 The characteristic species, however, were a small hemipterous shore in- 

 sect. Said a ligata, a caddis fly, and ants. Above the lower beach is a 

 wide upper one, characterized by a dark green moss (Grimmia) and 

 crustaceous lichens. 



A number of rock pools occupy the oblique crevices which extend 

 up the beach. The largest of these is shown in Fig. 30. This is a pool 

 about 4x8 feet in diameter and contains about 15 to 18 inches of 

 water. On the surface of the water were fragments of insects, water 

 striders, Gerris remigis, and on the bottom, dragonfly nymphs (No. 14), 

 while caddis fly larvae crawled upon the sides and bottom. No algal 

 growth was visible. The character of this insect life suggests a pool 

 of some duration, but the absence of shells suggests a lack of permanent 

 water. Numerous basin-like depressions, a few inches in depth, occur 

 on the lower beach and on the foliaceous lichen-covered portions of the 

 middle beach. The sharp angles of some of the pools show tliat these 

 are occasionally produced by the removal of small blocks of rock. Most 

 of the pools, however, occur in crevices. From one of the large pools 

 a frog, Rana clamitans (No. 120), was taken, clearly showing how tad- 

 poles may reach such pools. 



In the crevices and behind angular rock projections occur Hare-bells, 

 Yarrow, Ninebark, and an interesting succulent Saxifrage, Saxifraga 

 aizoon, Fig. 31, and some grasses. In the crustaceous lichen zone is 

 a greenish moss, Grimmia, and in the crevices are Bearberry, Juniperus 

 procumbens, and Arbor Vitae. 



2. The Cladonia-Juniperus procumbens Society of the Eastern Section. 

 About ten paces farther up the slope, Fig. 32, this crevice society spreads 



