28 MICHIGAN SURVEY, 1905. 



case the migration of the societies would also have taken place down the slope, 

 following the receding lake beach. 



Station II. Substations 8 and 4- These substations are located in an 

 artificial clearing and will not be discussed. The species that occur here 

 will be found in the annotated lists. 



Station II. Substation 5; and Station III. The north slope of the first 

 range rises directly to the top of the ridge at an elevation of about 900 feet. 

 Over the crest there is a sharp descent of several rods to the brink of the 

 precipitous escarpment that overlooks the valley of Carp river, Fig. 10. 



The effect of the dynamics of the mountain top are very conspicuous. 

 The exposed rock is unprotected from the forces which cause disintegration, 

 for as fast as it is broken up the particles are washed away, and thus the 

 first soil to accumulate is in the exposed edges of joint planes. The soil 

 washed down the north slope on Section 21, Fig. 11, is checked and held in 

 front of the forest, \vhich advances as the soil becomes sufficient to support 

 it. On Sections 13 and 14, Fig. 10, the forest has advanced to the crest so 

 that no soil from the bald areas is washed down the north slope. The soil 

 formed on the south side of these areas, meeting with no obstruction, is 

 washed over the precipice and accumulates in a narrow strip along the top 

 of the talus slope, while that which is washed laterally from the top into 

 depressions in the crest is also checked to a certain extent by the encroach- 

 ing forest. The concentration of water in these inequalities causes them 

 to be deepened into ravines, situated at right angles to the crest, and much 

 of the material derived in this way is carried over the cliff and deposited 

 as alluvial cones on the talus slopes below; these alluvial cones join the 

 ravines above forming broad saddles across the ridge, Fig. 10. The face 

 of the cliff is also exposed to weathering agencies that tend to pry loose 

 portions of the rock between the joint planes. The larger fragments fall 

 to the bottom of the cliff and go bounding down the talus slope, often start- 

 ing minature landslides of the talus material. The slope thus lies at the 

 angle of repose of the material and is very unstable, Fig. 17. As a rule, the 

 larger the fragment the farther down the slope it will go before coming to 

 rest, and the strip of fine material at the top of the slope, which was formed 

 partly from the soil washed over the cliff from the bald areas above, receives 

 constant additions from the fine material that is loosened from the cliff 

 face. Toward the bottom of the slope, the conditions become more stable, 

 and the talus blocks are being disintegrated and decomposed into a residual 

 soil. The mountain top, cliff, and talus slope habitats thus offer virgin 

 conditions for plant and animal societies, and it is in localities such as these 

 that the pioneer societies are found. 



If the results of the processes at work on this ridge be summarized, it is 

 evident that they are tending to lower the ridge toward a base leveled plain, 

 thus changing the present conditions toward those found on the lower parts 

 of the north slope. 



Station II. Substation 5; and Station III. Substations 1 and 4. The biota 

 of the north slope of the first range, pushes through the saddles and down 

 the alluvial cones on the south side and mingles with the biota of the forest 

 in the valley of Carp River, Fig. 10. From the north side and the saddles 

 it extends upward and surrounds on three sides the bare areas of the higher 

 parts of the ridge, but, owing to the changed environmental conditions, 

 it becomes modified in its composition near the crest. The Hemlock and 

 Balsam Fir and finally the Sugar Maple become replaced by a zone of aspen 

 and oak, consisting principally of the Quaking Aspen, Paper Birch, Red and 



