22 



For this reason a cycle will be followed here which begins with a con- 

 dition of stress, advances through the process of adjustment to strain, 

 and reaches a condition of relative equilibriuui. The starting point in 

 such a cycle we will consider as the original conditions, and the later 

 activities as the derived ones. The original conditions we will assume 

 to be an uplifted undulating plain, composed of relatively homoge- 

 neous materials, in a humid climate, and covered by a varied vegetation 

 including trees. The elevated condition of the land produces a condi- 

 tion of unstal)le equilibrium or stress for the rain falling upon its sur- 

 face ; and, furthermore, the vegetation will tend to spread over the en- 

 tire surface, and thus exert a certain pressure also These original 

 conditions are, therefore, unstable and destined to change, and mu- 

 lually to influence and regulate one another. 



If we now imagine the rain "turned on" under such conditions, 

 what are the main processes which will operate? The rain falling in a 

 depression will be supplemented by that which drains from the eleva- 

 tions; thus, through the agency of running water, a standing water 

 habitat will have its origin. With this concentration of water will 

 come also a burden of debris from the upland ; and in this way the 

 "constructive" and "destructive" processes will begin at the same time. 

 Plants will invade such a depression and add their remains. Some of 

 the depressions will overflow and the outflowing streams will cut down 

 the outlet to progressively lower levels, and ultimately drain the basin. 

 On the other hand, inwash and organic debris may together accumu- 

 late at such a rate as to raise the level of the basin above ground water 

 and thus transform the conditions to that of land. The progressive 

 stages of the process of degradation thus favor the transformation of 

 the depression and a progressive formation of lakes, which are con- 

 verted into ponds and swamps and ultimately, with drainage, to dry 

 land. For depressions we thus get a genetic series which we may call 

 the lake, pond, and swamp series. This does not classify the depres- 

 sion series according to size, depth, character of water, etc., as in an 

 artificial classification, but in the order of their development or genesis 

 through the agency of running water. Accompanying this sequence 

 there are of course changes in size, depth, etc., but these are subordi- 

 nated in the classification to the developmental sequence centering 

 about the process of the degradation, of the land by the agency of run- 

 ning water. This is therefore a classification of environments, not on 

 the basis of the product, as it might appear from calling it a depression 

 or standing-water series, but upon the basis of the activity or proc- 

 esses of the dominant agent. 



We will assume that all the lakes, ponds, and swamps, due to the 

 original relief of the land, become drained and constructively con- 



