EISE OF PETROLOGY AS A SCIENCE 261 



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. E. Van Hise, 

 with his co-laborers, 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 the 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 analyses which had been made to that date 

 and which he considered were worthy of preservation. 

 Although, naturally, from the status of analytical chem- 

 istry up to that time, most of these would now be con- 

 sidered rather crude, the publication of the work was of 

 great service and marked an epoch in geochemistry. In 

 these tables Roth lists four analyses of American igneous 

 rocks, two from the Lake Superior region by Jackson 

 and J. D. Whitney and two by European chemists, one of 

 whom was Bunsen. The material of the last two was a 



