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land is much greater than that in water, either fresh or salt. In other 

 words the land habitats are the most complex on earth. For simplicity 

 in handling this involved problem, an ideal series will also be followed, 

 and instead of attempting to discuss all the principles involved, only 

 such will be mentioned as may be illustrated by a single example. This 

 will serve to show the application of the method. We shall consider 

 the process of degradation of the land, such as might be developed 

 during a topographic cycle of erosion, and as applied to a snow-capped 

 conical mountain in a temperate humid region. 



Let us consider the series of processes which operate upon such a 

 mountain. The snow and rain which fall upon it are in unstable equi- 

 librium, the snow creeps or plunges down the slopes, and the water 

 flows down. In the zone of ice and snow physical and mechanical 

 changes preponderate ; but at lower altitudes, with the melting of the 

 snow and ice, on account of the higher temperature, chemical changes 

 become more prominent and supplement the mechanical work of run- 

 ning water. Here, also, plants and animals become an important factor 

 in modifying the processes of change by hastening or retarding the 

 processes of degradation. We thus see that on different parts of a 

 mountain there are important modifications in the processes of degra- 

 dation. The same general processes which operate to form lakes, ponds, 

 swamps, brooks, creeks, and rivers, are also at the same time producing 

 changes in the land habitats. The entire surface of such a mountain is 

 undergoing change, but because of the concentration of degradative 

 progress near its base, particularly on account of the concentration of 

 the drainage there, ravines and valleys develop here more rapidly and 

 converge toward the main divide, the mountain top. As these ravines 

 and valleys enlarge, the mountain is lowered ; and ultimately all is re- 

 duced to a plain, and to baselevel. The condition of stress which existed 

 upon the slopes of such a mountain as degradation progressed, became 

 relatively adjusted at that place, but where the degraded materials 

 were deposited a stress was becoming cumulative, and it is this ever 

 changing adjustment of stresses which makes natural processes unend- 

 ing. 



With the degradation of the mountain, progressively higher zones 

 are lowered ; the snow cap disappears ; the region above the tree limit, 

 and later the lower parts, are spread over a large area, and the moun- 

 tainous character is largely gone. In this manner and at the same time 

 as the land is degraded to a lowland by running water, in the water 

 itself a series of habitats is developing, and thus all the environment 

 is being transformed, along relatively distinct but mutually interde- 

 pendent lines, toward the same general direction or condition — a rela- 



