24 MICHIGAN SURVEY, 1905. 



There are numerous pools on this beach, Fig. 6, in the angular spaces 

 formed by the removal, presumably by ice, of portions of rock between 

 the joint planes. These pools are, as a rule, above the reach of the highest 

 waves, so that during the summer they are not flooded by the cold water 

 of the lake. Their temperature is thus higher than the lake water. In 

 several readings taken August 6, 7 and 8, the temperature of the water in 

 these pools varied from 60 F. to 68 which was 10 higher than the lake 

 water as it broke on the lower beach. The vegetation in these pools is very 

 scanty, consisting chiefly of Algae which line the sides. The small number 

 of species is probably due to their isolation and shallowness (6 to 18 inches), 

 and to their smooth sides which make it difficult for the plants to gain a 

 foothold. The fauna is much better represented than the flora. Besides 

 a number of minute forms such as Crustaceans, Hydra, etc., there are a 

 number of the higher aquatic forms characteristic of quiet water habitats. 

 The insects are represented by water-boatmen, water-striders, and caddis-fly 

 larvae, and the snails by Physa ancillaria, Limnaea desidiosa, Planorbis 

 pawns and occasionally, near the Lower Beach by Limnaea decollata. 

 These forms are found in all of the larger pools with the exception of Limnaea 

 decollata which only occurred in the lower pools that are occasionally flooded 

 by the waves. When these pools are flooded by an exceptionally high wave, 

 they are often temporarily united with the lake and with each other which 

 suggests a way by which certain forms may migrate along a shore of this 

 kind. With the destruction of this beach these pool habitats will be de- 

 stroyed, as pools of this kind cannot exist on a sandy beach. 



The Upper Beach is above the reach of both summer and winter waves, 

 and the environmental conditions are consequently more favorable than 

 those of the Lower and Middle Beaches. The principal factor that still 

 makes the habitat an unfavorable one for plants is the poor foothold afforded 

 by the substratum. The soil, however, increases in amount at the edges 

 of the joint planes thus affording a foothold for small trees and shrubs, Fig. 

 6, and to this soil is added a small amount of humus formed by decaying 

 logs and annuals. Owing to these conditions, the flora presents a curious 

 assemblage of forms. It is composed of the forms of the Middle Beach, 

 Goldenrod, Beach Pea, Vetchling, Lobelia, Hare-bells, etc. ; the fern, Poly- 

 podium vulgare; the heaths represented by the Bearberry, Great Bilberry 

 and Dwarf Huckleberry that constitute the next society, and a number of 

 trees and shrubs such as the Arbor Vitae, Mountain Maple, Mountain Ash, 

 Large-leaved and Quaking Aspens, Juneberry, Eastern Ninebark, Dwarf 

 Cherry, Wild Raspberry and Canadian Buffalo-berry, that in this region 

 form a transitional zone between exposed habitats and the mesophytic 

 forest. The fauna of this beach is in many respects similar to the fauna 

 of the Middle Beach from which it cannot be distinctly separated. The 

 forms found here which are not, as a rule, found also on the Middle Beach 

 are the grasshoppers Camnula pellucida, Circotettix verruculatus, Melanoplus 

 atlanis and Melanoplus femoratus, and the Lake Superior Chipmunk. The 

 grasshoppers, as a rule, remain closely within the limits of this beach, with 

 the exception of the forms of Melanoplus which are occasionally found 

 also on the Middle Beach. The chipmunks are also seldom observed far 

 from the drift logs that characterize this habitat. 



The beach as a whole is thus, in a general way, divided into three habitats 

 by the dominance of different processes which bring about different en- 

 viromental conditions, but these divisions, as may be seen from the photo- 

 graphs, are not sharply denned. The Lower Beach in general possesses 



