GROWTH OF GEOLOGY. 2Y3 



outstrip his master.* Undertaking, for the first 

 time, ^' a systematic study of rock-sections as an end 

 in itself," as Williams says, Zirkel began rapidly to 

 lay the foundations of modern petrography. But 

 with his name that of Rosenbusch must be immedi- 

 ately coupled; both as investigators and as teachers, 

 they stand as the leaders of petrographical enquiry. 



Among the earlier petrologists one of the most 

 original and suggestive was Hermann Vogelsang, 

 whose Philosophy of Geology (1867) is still looked 

 upon with great admiration, who is also memorable 

 for his persistent and successful attempts to get 

 nearer the secret of petrogenesis by reproducing ex- 

 perimentally results similar to those which have oc- 

 curred in nature. We cannot, however, pursue the 

 history, and to mention even the names of those who 

 have done great service in petrography since Zirkel 

 and Rosenbusch became recognised leaders, would 

 serve no useful purpose in a sket<5h like this. One 

 classification has succeeded another, and no petrolo- 

 gist seems satisfied either with his own or his neigh- 

 bour's ; the question of " species '' seems as puzzling 

 as in biology; and there can be no solution until the 

 static results of description are illumined by a theory 

 of rock-genesis. To this, through keen struggle for 

 existence among conflicting opinions, every year 

 brings us nearer. 



Mineralogy. — Turning to the department of petrog- 

 raphy, which restricts itself to minerals, we may note 

 that in the early days of mineralogy the physical as- 

 pect, the study of crystalline form, specific gravity, 

 hardness, etc., received most attention. Of especial 

 importance was the work of Haiiy who, without de- 



* See F. Zirkel. Die Einfuhrung des mikroskops in das 

 mineralogischgeologische Studiuvi, Leipzig, 1881. 



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