232 L. V. Pirsson — Rise of Petrology as a Science. 



crystallization, and on differentiation; by Cross on 

 classification; by Adams on the physical properties of 

 rocks ; by Daly on the methods of igneous intrusion ; by 

 Wright on schistosity; by Fenner on the crystallization 

 of basaltic magma; by Bowen on differentiation by 

 crystallization; by the writer on complementary rocks 

 and on the origin of phenocrysts ; by Smyth on the origin 

 of alkalic rocks ; by Murgoci on the genesis of riebeckite 

 rocks ; and by Barrell on contact-metamorphism. These 

 may serve as examples, selected almost at random, from 

 the files of the Journal, and we find with them articles 

 descriptive of the petrology of many particular regions, 

 which often contain also matter of general interest and 

 importance, such as papers by Lindgren on the grano- 

 diorite and related rocks of the Sierra Nevada; by 

 Ransome on latite ; by Cross on the Leucite Hills ; by 

 Hague on the lavas of the Yellowstone Park; by Pogue 

 on ancient volcanic rocks from North Carolina ; by "War- 

 ren on peridotites from Cumberland, R. I. ; on sandstone 

 from Texas by Goldman; and on the petrology of vari- 

 ous localities in central New Hampshire by Washington 

 and the writer. Such a list could of course be much 

 extended and other papers of importance be cited, but 

 enough has been said to indicate how important a reposi- 

 tory of the results of petrologic research the Journal has 

 been and continues to be. 



In thus looking backward over the list of active 

 workers we are involuntarily led to pause and reflect 

 how great a loss American petrology has sustained in 

 the premature death of some of its most brilliant and 

 promising exponents ; it is only necessary to recall the 

 names of R. D. Irving, G. H. Williams, G. W. Hawes, 

 J. F. Williams and Carville Lewis, to appreciate this. 



The store of material gathered during these years has 

 led to the publication of extensive memoirs, in which the 

 science is treated not from the older descriptive side, but 

 from the theoretical standpoint and of classification. 25 

 In these works strong divergencies of views and opinions 

 are observed, which is a healthy sign in a developing 

 science. 



It should be also noted that along with this evolution 

 on the theoretical side there has been a constant improve- 

 ment in the technique of investigating rocks. It is only 

 necessary to compare the older handbooks of Zirkel and 



