THE PROBLEMS OF GEOLOGY 547 



the same as in the illustrations given, the general doctrine was evolved 

 that the geological results of the past are to be explained by present 

 processes, or the present is the key to the past. While the above 

 conclusions now seem almost axiomatic, we need not go far back to 

 find them astonishing novelties. So far as we are aware, the natural 

 explanation of fossils was first reached by that amazingly versatile 

 genius, Leonardo da Vinci, in the fifteenth century. The conclu- 

 sion that the present is the key to the past required for its formulation 

 the intellect of the great Hutton. 1 It was not announced until 1785, 

 and the doctrine was not generally accepted until after Lyell's 

 Principles appeared in 1830. 



As the science of geology developed, the practice of explaining 

 the phenomena in terms of processes gradually became more com- 

 mon, until, as we have seen, it is dominant in the latest geological 

 text-book. But, as already intimated, the analysis of processes in 

 terms of energy, force, and agent has only begun. It is my belief that 

 at some time in the future a text-book of geology will appear which 

 shall begin with a discussion of the energies, forces, and agents of geo- 

 logy, the understanding of which is necessary in order adequately to 

 comprehend processes. It has been stated that the problem of geo- 

 logy is the reduction of the science to order under the principles of 

 physics and chemistry. This is equivalent to saying that the pro- 

 blem of geology is the discussion of the subject in terms of energies, 

 forces, agents, processes, and results. Such a discussion will constitute 

 the principles of geology. 



It is my deep-seated conviction that by the solution of this problem 

 only can geology be so simplified as to be comprehended with reas- 

 onable fullness by the human mind. When this work is done, the 

 broad principles of the science will be capable of statement with 

 comparative simplicity and brevity. But so broad and complex is 

 the science of geology that a comprehensive statement of the prin- 

 ciples of Jhe entire subject will necessarily be somewhat voluminous. 



Supplementary to the principles of geology, which are applicable 

 to the entire earth, there will be a long series of volumes of the 

 geology of different continents, the various political divisions of 

 these continents, the states under those divisions, or even the minor 



1 How clearly the great Hutton appreciated the doctrine commonly called 

 that of uniformity is shown by the following quotations from his Theory of the 

 Earth: " In what follows, therefore, we are to examine the construction of the 

 present earth, in order to understand the natural operations of time past; to 

 acquire principles, by which we may conclude with regard to the future course of 

 things, or judge of those operations by which a world so wisely ordered goes into 

 decay; and to learn by what means such a decayed world may be renovated, or 

 the waste of habitable land upon the globe repaired." The concluding sentence of 

 his work is: "The result, therefore, of our present inquiry is, that we find no ves- 

 tige of a beginning no prospect of an end." Charles Hutton, Theory of the 

 Earth, Philosophical Transactions of the Royal Society of Edinburgh (1785), p. 218; 

 ibid., p. 304. 



