ANIMALS AND THEIR ENVIRONMENTS ADAMS. 531 



esses involved in their origin. There are thus many degrees or 

 stages in the development of a genetic classification, the first step of 

 which is to determine the orderly sequence of changes. In a certain 

 sense, in its broadest application, the process method is universal and 

 includes the genetic, but until their mutual relations become clearly 

 recognized and are generally understood both should be emphasized. 



Particular attention should be called to the fact that the activity 

 of an agent results in a process, and processes give us the laws of 

 change. Many processes are reversible; that is, a process may go 

 forward in one direction and then become reversed and proceed in 

 the opposite direction. Other processes are nonreversible, and oper- 

 ate in only one direction, being in a sense orthogenetic, as in the later 

 stages of the ontogenetic process. 



Let us summarize the main characteristics and principles involved 

 in the dynamic and genetic method. They have been well expressed 

 by Keyes (1898), and for my purpose are arranged as follows: 



A truly genetic scheme for the classification of natural phenomena thus 

 always has prominently presented its underlying principle of cause and 

 effect. * * * To begin with, an adequate scheme should be based directly 

 upon * * * agencies. * * * All products must find accurate expres- 

 sion in terms of the agencies. * * * The primary groupings of the * * * 

 processes must be based, therefore, upon the manner in which these agencies 

 affect the * * * materials. * * * Constructive and destructive agencies 

 can be recognized only when the phenomena are made the basis for the scheme. 

 Processes are merely operative. If coupled with products at all, in classifica- 

 tion, all must be regarded as formative or constructive. The product's de- 

 struction, its loss of identity, is wholly immaterial. The action of agencies is 

 merely to produce constant change. 



Van Hise (1904) has formulated other principles of the process 

 method as follows: 



The agent is the substance containing energy which it expends in doing work 

 upon other substances. The substance upon which work is done may thereby 

 receive energy and thus become an agent which does work upon other sub- 

 stances; and so on indefinitely. Indeed, the rule is that one process follows 

 another in the sequence of events, until the energy concerned becomes so dis- 

 persed as to be no longer traceable. Theoretically this goes on indefinitely. 



* * * We have seen that the action of one or more agents through the 

 exertion of force and the expenditure of energy upon one or more substances 

 is a geological process. It is rare indeed, if it ever happens, that a single 

 agent works through a single force upon a single substance. * * * If 

 geology is to be simplified the processes must be analyzed and classified in 

 terms of energies, agents, and results. Each of the classes of energy and agent 

 should be taken up, and the different kinds of work done by it discussed. 



* * * The general work of each of the agents and the results accomplished 

 should be similarly considered. Not only so, but the work of the different 

 forms that each of the agents takes should be separately treated. Thus, be- 

 sides considering the work of water generally, the work which it does both 

 running and standing must be treated. The first involves the work of streams ; 

 the second the work of lakes and oceans. This Involves the treatment of 



