L. V. Pirsson — Rise of Petrology as a Science. 229 



themselves to this field of research and the store of 

 accumulated knowledge concerning rocks from all parts 

 of the world, and their relations grew apace. The work 

 of Teall has been noticed and among others might be 

 mentioned the name of Brogger, whose first contribu- 

 tion 16 in this field gave evidence that his publications 

 would become classics in the science. 



In America there appeared in this period a number of 

 eager workers, trained in part in the laboratories of 

 Rosenbusch and Zirkel, whose researches were destined 

 to place the science on the secure footing in this country 

 which it occupies to-day. Among the earlier of these may 

 be mentioned Whitman Cross, R. D. Irving, J. P. Iddings, 

 G. H. Williams, J. F. Kemp, J. S. Diller, B. K. Emerson, 

 M. E. Wadsworth, G. P. Merrill, N. H. Winchell, and 

 F. D. Adams in Canada. Others were added yearly to 

 this group. As a result of their work a constantly grow- 

 ing volume of information about the rocks of America 

 became available, and one has only to examine the files 

 of this and other journals and the listed publications of 

 the National and State Surveys to appreciate this. 



In this Journal, for example, we may refer to papers 17 

 by Emerson on the Deerfield dike and its minerals, and 

 on the occurrence of nephelite syenite at Beemersville, 

 N. J. ; to various interesting articles by Cross on lavas 

 from Colorado and the pneumatolytic and other min- 

 erals associated with them; to important papers by 

 Iddings on the rocks of the volcanoes of the Northwest, 

 and those of the Great Basin, to primary quartz in 

 basalt, and the origin of lithophysae; to the results of 

 researches by G. H. Williams on the rocks of the Cort- 

 landt series, and on peridotite near Syracuse, N. Y. ; to 

 papers by Diller on the peridotites of Kentucky, and 

 recent volcanic eruptions in California; to articles by 

 R. D. Irving on the copper-bearing and other rocks of the 

 Lake Superior region, and to Kemp on dikes and other 

 eruptives. in southern New York and northern New 

 Jersey. Other publications would greatly extend this 

 list. 



The Petrologic Era. 



As the chief facts regarding rocks, especially igneous 

 rocks, as to their mineral and chemical composition, their 

 structure and texture and the limits within which these 



