534 GEOLOGY 



and results. Each of the classes of energy and agent should be taken 

 up, and the different kinds of work done by it discussed. For instance, 

 the work of the force of gravitation through gases, liquids, and solids 

 should be analyzed. To some extent this has been attempted, but 

 very imperfectly indeed. And such discussion has scarcely been 

 seriously undertaken for the other forms of energy. Text-books 

 should consider each of the classes of energy by itself, the nature 

 of the forces it exerts, the processes through which it works, and the 

 results accomplished through the various kinds of agents. 



The general work of each of the agents and the results accom- 

 plished 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, besides 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 streams as entities, 

 or, to use a figure of Chamberlin's, as "organisms." The treatment 

 of the work of gases should involve the subjects of gases of the 

 atmosphere, gases of the hydrosphere, and gases of the lithosphere. 

 The treatment of the agents will be more satisfactory in proportion 

 as the work done by each of the forms of each of the agents is explained 

 under physical and chemical principles in the terms of energy. 



It is plain that the treatment of the energies of geology and the 

 treatment of the agencies of geology will overlap, since one cannot 

 be considered without also considering the other; but this is an 

 advantage rather than a disadvantage, for each of the two points of 

 view is very important in enabling the mind to grasp the composite 

 whole. Just as in the science of physics-chemistry it may some- 

 times be advantageous to consider the subject mainly from the point 

 of view of substance, and at another time mainly from the point of 

 view of energy, and the treatments from both points of view are neces- 

 sary to build up the science of physics-chemistry; so it is necessary 

 to consider the subject of geology from the points of view of energy 

 and of agent, if an approximation to adequate comprehension be 

 gained. 



As already intimated, another point of view from which geology 

 may be considered is the result. This was the chief point of view 

 of the early geological papers and text-books, which were content to 

 tell of phenomena. Phenomena may, and often are, observed and 

 described in advance of their physical-chemical interpretation. But 

 the naming or even the description of the phenomena of the earth, 

 without reference to energy or agent, is very unsatisfactory. And 

 usually the valuable descriptions of before unobserved phenomena 

 are made in connection with theories of their physical and chemical 

 significance. But it is still true that observation and description 



