By referring to the files of the Journal, it will be seen that they cover a continually widening range of subjects concerning rocks, and articles of theoretical interest are more and more in evidence, along with those of a purely descriptive character.[130] Thus we find discussions by Becker on the physical constants of rocks, on fractional 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 granodiorite 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 Warren on peridotites from Cumberland, R. I.; on sandstone from Texas by Goldman; and on the petrology of various 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 repository 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.[131] In these works strong divergencies of views and opinions are observed, which is a healthy sign in a developing science.