10 MICHIGAN SURVEY, 1908. 



tation consists of algae, which grows in moderate abundance, though 

 not luxuriantly, as found about the Gull Eookery (V, 10), or at the 

 fishermen's camp at Rock Harbor, a fact which suggests that the aibun- 

 dance of suitable nitrogenous material is much greater in such places 

 than in the open lake water. With the development of the fall storms, 

 Mr. J. A. Malone states that these rocks (V. 10) are washed free of 

 the algae, thus evidentlr necessitating a repopulation of these surfaces 

 each season. 



The characteristic fauna secured in the shallow water shore margins 

 were the snails, Limnaea stagnalis. L. emarginata, and Physa sayii. A 

 small fish, the Miller's Thumb, Z' ran idea franklini, is also fairly abun- 

 dant and characteristic of this shore. 



Upon low rocky shores beach pools, Fig. 5, are occasionally found 

 which, when favorably located, are supplied with water by the ordinary 

 summjer waves, otherwise by storm waves and rains. The precarious 

 existence of life in such places is indicated by the general type 

 of the fauna, which shows exceptional power of locomotion, usually 

 coupled with a short life cycle. The immature stages of insects 

 are rather characteristic, as shown by nymphs of the water boat- 

 men, Corixa, dragonflies and Caddis fly larvae. Water beetles were 

 represented by Rhantus Mnotatus, and the snails by Limnaea emarginata 

 and Planorbis parvus. The Gulls and Spotted Sandpipers should be 

 mentioned as birds which frequent these conditions. 



The Middle Beach. This beach occupies the strip of shore over which 

 the winter waves retreat as they fall to the upper summer storm limit. It 

 is thus seen that the Middle Beach is only a temporary or summer aban- 

 donment of part of the upper shore, which is repeatedly claimed by the 

 winter waves. In summer this strip is exposed to denudation; in the 

 fall amd early winter, to the fury of the waves, and, later, it is covered 

 with ice. Driftwood and debris tend to lodge here and to accumulate. 

 It is an important region of biotic invasion for land forms. Beach 

 pools are also developed in this area, upon the abandoned wave cut ter- 

 races of earlier lake levels. Upon the cliff faces, sloping rock shores and 

 shingle beaches, little is found that is favorable to life, but upon the 

 protected sand of the Middle Beach, relatively favorable conditions for 

 many organisms are found during its period of exposure. The character 

 of the substratum of the Middle Beach varies from rock to shingle, 

 gravel and sand. 



The characteristic features of the vegetation, where the wave action 

 is not too severe, are the fruits which are washed ashore by the waves, 

 together with certain annuals and lichens. The fauna varies with the 

 character of the conditions. The open character of this beach and the 

 relative abundance of animal food makes such situations favorable for 

 spiders of the genus- Pardosa. The same open character makes the 

 shores a favorable patrol for certain butterflies, particularly Basilar- 

 cMa arthemis. Insects and snails washed ashore by the waves also 

 characterize this habitat. 



The Upper Beach. This part of the beach is beyond the reach of the 

 waves, and forms the transition between the open beach area and the 

 inland forests. The width of this belt varies greatly with the gradient of 

 the shore. Where the beach is continuous with a more or less bare rock 



