6 DEVELOPMENT OF PETROLOGY. 



memoir on the '' Application of Quantitative Methods 

 to the Study of Rocks." He applied experimental physics 

 to the study of various sedimentary and metamorphic 

 rocks and gave the results of many years experiment and 

 reflection. Like all scientific writings of this distinguished 

 author, it was marked by a great wealth of experimental 

 detail and showed the great bearing of accurate quantitative 

 methods on the study of these rocks. During this year, 

 R. A. Daly in the ''Origin of Augite Andesite and of 

 related Ultra-basic Rocks," strongly supported the early 

 riews of Scrope, Darwin and others as to the efficiency of 

 fractional crystallization in the formation of igneous rocks, 

 and stated his belief that the syntectic (assimilation) theory 

 and the fractional crystallization theory were essential and 

 principal elements in the final solution of the genetic prob- 

 lem of the igneous rocks. 



The publication of the " Natural History of Igneous 

 Rocks," by Alfred Harker, of the University of Cambridge, 

 in 1909, was of great importance as the work was of an 

 epoch-making nature. Within the few years previous to its 

 publication, a great number of papers, making important 

 contributions to the science of petrology, had been written 

 and a work giving a systematic presentation of the exist- 

 ing knowledge on the subject was needed. Harker "s work 

 supplied this want and his lucid treatment of the subject 

 has made this publication a most popular one amongst 

 students of petrology. 



Harker believed that a correlation exists between 

 the general geological history and igneous activity of a 

 given region, that igneous action is the result of crustal 

 movements, and that these movements produce magmatic 

 differentiation over continental areas, so that we have 

 magmas of different composition in regions affected by 

 <lifferent kinds of crustal movements. 



Harker accepts the idea of differentiation and explains 

 petrological provinces as due to differentiation over large 

 areas, and the origin of different types within a given pro- 

 vince is also explained as due to differentiation. 



Harker, in his final chapter speaks of the American 

 quantitative classification as marking " a retrograde 

 movement, for here the artificial element is applied to the 

 complete exclusion of the natural." 



