EISE OF PETROLOGY AS A SCIENCE 259 



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 

 Rosenbusch with the many modern treatises on petro- 

 graphic methods to be assured of this. 26 It is due on the 

 one hand to the vast amount of careful work which has 

 been done in accurately determining the physical con- 

 stants of rock-minerals* and in arranging these for their 

 determination microscopically, as in the remarkable 

 studies on the feldspars by Michel-Levy, and on the other 

 in researches on the apparatus employed, and in conse- 



* We may mention here, for example, the work in mineralogy of Pen- 

 field, noticed in the accompanying chapter on mineralogy. In addition to 

 the accurate determination of the composition and constants of many 

 minerals, some of which have importance from the petrographic standpoint, 

 we owe to him more than anyone the recognition of fluorine and hyclroxyl 

 in a variety of species, and thereby the perception of their pneumatolytie 

 origin. His papers have been published almost entirely in the Journal. 



