26 MICHIGAN SURVEY, 1905. 



at the same time it will tend to retreat before the beach and invade the areas 

 at present occupied by the mesophytic forest of the north slope. 



Station II. Substation 2. Above the arbor vitae swamp, the north slope 

 of the first range rises steeply to the top of the ridge and is covered by a 

 dense mesophytic forest. The angle of this slope and the fact that it is 

 formed by dipping strata, makes the drainage so rapid that the soil on the 

 upper part tends to be washed downward and to accumulate at the bottom. 

 The humus formed by the fallen twigs and leaves of the forest prevents in 

 part superficial wash, and most of the water, for this reason, is conducted 

 away under ground. The ravines are thus small and the streams transient. 

 The lower parts of the slope support a dense hemlock forest in which there 

 is deep shade, Fig. 8. The tree cover of this part of the forest consists 

 principally of Hemlock associated with the Balsam Fir, Ironwood, Yellow 

 Birch, isolated White Pines and a few Sugar Maples. The undergrowth 

 of Ground Hemlock and Maple is very scanty, and the humus is thus com- 

 posed chiefly of leaves and twigs of the Hemlock with the exception of 

 localized accumulations of deciduous leaves from the maple underbrush. 

 The soil cover is also scattered and is composed of the Large-leaved Aster, 

 Wild Sarsaparilla, Twinflower, Goldthread, Maidenhair Fern, Wild Spikenard, 

 Rattlesnake Plantain, Dwarf Dogwood, Clintonia borealis, and Lycopodium 

 lucidulum and clavatum. 



The fauna of the hemlock forest is also rich in species. Besides many 

 insects and other invertebrates, there are a number of birds and the toad 

 (Bufo americanus} . The mammals are represented by the Canadian Porcu- 

 pine, Northern Virginia Deer, Northern Plains Skunk, Woodchuck, South- 

 eastern Red and Northern Flying Squirrels, Northeastern Chipmunk, 

 Star-nosed Mole, Large Bobtail Shrew, and the Northern and Woodland 

 Jumping, Canadian White-footed and Red-backed Mice. Owing to the 

 predominance of conifers, it is to be expected that few shells would 

 occur in this forest, but the accumulated leaves of the maple underbrush 

 counteract the unfavorable nature of the coniferous humus and support 

 a somewhat scattered molluscan fauna composed of Zonitoides milium, 

 Vitrea ferrea, Euconulus fulvus, Punctum pygmaeum, Helicodiscus lineatus, 

 Strobilops virgo, Zonitoides exigua, Sphyradium edentulum, Carychium exile, 

 and Agriolimax campestris. 



On the upper parts of the slope, the soil becomes thinner, and there is a 

 noticeable change in the character of the forest. It is still mesophytic, 

 but the Hemlock, Balsam Fir, Ironwood and Yellow Birch give way to a 

 forest composed of the Sugar Maple, Basswood, and Paper Birch, in which 

 the Sugar Maple predominates. This transition is gradual and while near 

 the top of the ridge the Ironwood and Yellow Birch are practically absent, 

 the Hemlock and Balsam Fir may still persist. The undergrowth in this 

 part of the forest is much better developed, Fig. 9, and consists principally 

 of Maple, Basswood and Ground Hemlock. The ground is covered to a 

 depth of several inches with leaves, and the soil cover, although better de- 

 veloped, is practically the same as in the hemlock forest except that the 

 Large-leaved Aster, Indian Pipe and Goldthread seem to become replaced 

 by Cinna latifolia, White-flowering Raspberry, Fly Honeysuckle and I3rake. 



The changes in the environmental conditions with which are associated 

 the changes in the composition of the flora toward the top of the slope do 

 not seem to influence the fauna to a marked extent. As the tree cover is 

 principally affected, the most marked change in the fauna is seen in the case 

 of the birds, which are more closely associated with this type of vegetation. 



