BY HENRY C. RICHARDS, M.SC. 5 



displacement permitting intrusion ; that marginal 

 assimilation in the preparation of subterranean magma 

 chambers is quite subordinate to magmatic overhead stop- 

 ing, and that abyssal assimilation, in contrast to marginal 

 (hybabyssal) is responsible for the preparation or notable 

 modifications of magmas whence come, through differentia- 

 tion, the igneous rocks of the globe. 



We thus have the putting forward of Daly's " Over- 

 head Stoping Theory,'' which has met with fairly general 

 acceptance. 



One other publication during the year which deserves 

 special notice is the " Chemical Analyses of Igneous Rocks," 

 by H. S. Washington and pubhshed as Prof. Paper 14 

 U.S. Geol. Survey. This work is a collection of analyses 

 published from 1884-1900 with a critical discussion of the 

 character and use of analyses. The value of this publica- 

 tion to petrographers and chemists has been very great 

 indeed, and although published ten years ago, it continues 

 to be used to a considerable extent. 



After the specially rich year in 1903 we find rather 

 leaner times in 1904, 1905, 1906, in the productions of 

 works dealing in a general way with Petrology. " Die 

 Kristallinen Schiefer," by U. Grubenmann, in 1907, was an 

 all important work. The author presented therein a highly 

 systematic treatment of the crystalline schists — some- 

 thing which had been sought after for a considerable time. 

 Grubenmann explained the characteristics of the 

 crystalline schists and their occurrence in the crust of the 

 earth, according to physico-chemical laws. He made a 

 threefold division of the crust of the earth and these three 

 zones in a general way correspond to Van Hise's two zones. 

 He gave an exhaustive treatment of the effects in each 

 zone with their determining factors and divided up the rock£^ 

 into twelve groups. The work was a valuable contribu- 

 tion to oiu' knowledge of metamorphic rocks, in that it 

 summarised the existing knowledge, added new material, 

 put forth a new theory, and set out a classification which 

 although recognised by the author as not a perfect system, 

 has proved of very great value. 



In 1908 Dr. H. C. Sorby shortly before his death 

 presented to the Geol. Society of London, a highly important 



