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



attack of careful, accurate and persistent work in the 

 field, under the microscope and in the chemical labora- 

 tory, with the aid of the garnered knowledge in petrol- 

 ogy, stratigraphy, physiography, and other fields of 

 geologic science, their mystery has in large part given 

 way. The inaugural work of Lehmann, Lossen, Barrois, 

 Bonney, Teall, and other European geologists, was par- 

 alleled in America by that of R. D. Irving, owing to whose 

 efforts the Lake Superior region became the chief place 

 of study of the metamorphic rocks in this country. 

 Irving soon obtained the assistance of Gr. H. Williams, 

 who had been engaged in the study of such rocks, and the 

 latter published a memoir on the greenstone schist areas 

 of Menominee and Marquette in Michigan 30 which will 

 always remain one of the classics in the literature of 

 metamorphic rocks. Irving 's own contributions to 

 petrology, though valuable, were cut short by his 

 untimely death, but the study of this region under the 

 direction of his associate and successor, C. R. Van Hise, 

 with his co-laborors, has yielded a mass of information 

 of fundamental importance in our understanding of met- 

 amorphism and the crystalline schists. Its fruitage 

 appears in the memoir by Van Hise 31 which is the author- 

 itative work of reference on metamorphism, and in 

 various publications by him and his assistants, Bayley, 

 Clements, Leith, and others. The work of the Canadian 

 geologists, and of Kemp, Cushing, Smyth and Miller in 

 the Adirondack region, should also be mentioned in con- 

 nection with this field of petrology. 



Chemical Analyses of Rocks. 



It has been previously pointed out that, as the science 

 of petrology grew, chemical investigations of rocks in 

 bulk were undertaken. The object of such analyses was 

 to obtain on the one hand a better control over the 

 mineral composition and on the other to gain an idea of 

 the nature of the magmas from which igneous rocks had 

 formed. The earliest analysis of an American rock of 

 which I can find record is of a "wacke" by J. W. Webster 

 given in the first volume of this Journal, page 296, 1818. 



During the next 40 years a few occasional analyses 

 were undertaken by American chemists, by C. T. Jackson, 

 T. Sterry Hunt, and others. In 1861, Justus Roth pub- 

 lished the first edition of his Tabellen, in which he 

 included all analvses which had been made to that date 



