290 THE EVOLUTION OF PETROLOGICAL IDEAS. 



as to composition, structure, and the like, accumulate faster than 

 they can be interpreted; and our classifications are therefore neces- 

 sarily more or less artificial. But there is that within us which compels 

 us to bring our classifications into accord with our views as to genesis. 

 Phylogen}^ must in the end control classification both in the organic 

 and inorganic worlds. As soon as we realize that any scheme of classi- 

 fication places together objects which ha\ e no genetic relationship, or 

 groups them irrespective of such relationship, we become dissatisfied 

 with it. The old classifications need not be thrown over the moment 

 that their imperfections are glimpsed; but in the end they have to be 

 discarded, and the new ideas find expression in a new classification. 

 Thus 



Thro' the ages one increasing pari;)Ose runs, 

 And the thoughts of men are wideneil with the i>rocess of the suns. 



How far Hutton was in advance of his time on matters relating to 

 petrogenesis is illustrated l)y the fact that more than half a century 

 elapsed before his ideas found expression in systematic treatises. Yet 

 the separation of rocks into igneous, sedimentary, and metamor})liic, 

 and the further sul)division of the igneous rocks into plutonic and vol- 

 canic, follow naturally and logically from his fundamental conceptions. 



The reason for the tardy recognition of what is now generally 

 admitted to l)e the true basis of classification is not far to seek. 

 Hutton was no systematist. Werner, on the other hand, was not onl}^ 

 a keen observer, but he possessed in quite an exceptional degree the 

 power of describing what he observed in precise and definite terms 

 and of grouping his facts according to their supposed relationship. 

 He was, in short, a born systematist, and this, combined with his elo- 

 quence and enthusiasm, gave him a connnanding influence. In looking 

 back at these two striking figures of the heroic age, Werner and 

 Hittton, it is almost impossible to avoid a feeling of regret that the 

 one did not possess what the other lacked. But such regrets are use- 

 less. Let us honor them both. 



The authors of systematic treatises on rocks published during the 

 first half of the century were all under the spell of Werner, and they 

 were still further hampered b}' their ignorance of the composition of 

 those rocks which are of so fine a grain that their constituents can not 

 be determined with the naked eye or with the aid of a simple magni- 

 fying lens. The treatises of Haiiy, Brongniart, and Leonhardt clearly 

 recognized the great natural group of fragmental rocks; but the true 

 limits of the other equally natural groups were, so far as general 

 treatises are concerned, ])rouglit into prominence for the first time in 

 the work by Von Cotta, the Knglish translation of which appeared in 

 1866. 



