BY HENRY C. RICHARDS. M.SC. S 



4. Metamorphic Rocks. ..... defy syetematic treat- 

 ment at the present time. 



The above may. be taken to fairly represent the jiosi- 

 tion at that period. 



On all four points very gi-eat advances have been made 

 since that time : the systematic classification of rocks 

 is on a much sounder basis and the sedimentary and meta- 

 morphic rocks have been more closely studied, also 

 we find that as the result of the labours of many, but 

 particularly Van Hise and Grubenmann. metamorphic 

 rocks are now capable of fairly systematic treatment. 



The year 1901 was not marked by any great develop- 

 ment. Dr. Teall in his Presidential Address to the Geo- 

 logical Society of London, dealt with the consolidation 

 of rocks from molten-magmas and their differentiation 

 into species. After discussing these matters thoroughly 

 in the light of the most recent investigations, he concludes 

 thus : ■■ The origin of petrographical species, so far as the 

 igneous rocks are concerned, is a problem the final solution 

 of which has been handed on by the nineteenth century to its 

 successor." 



The year 1902, however, saw the launching of the 

 "Quantitative C'lassification of Igneous Rocks."" by Cross, 

 Iddings, Pirsson, and Washington. 



This classification was an entirely new system for the 

 classification and nomenclature of igneous rocks. ''It is 

 a chemico-mineralogical system based on its own principles 

 and is in nowise an attempt to reduce any one of the exist- 

 ing systems to a chemical basis, or to formulate any of them 

 in a chemical way." A new nomenclature was demanded 

 in this classification and all igneous rocks are classified 

 on a basis of their chemical composition. 



It is essential for the use of this system of classifica- 

 tion to know the chemical composition of the rock, either 

 actually by chemical analysis, approximately so by phy.sical 

 means, or by microscopic optical methods indicated by the 

 authors. 



This scheme of classification has been most ingeniously 

 worked out, and no doubt was the result of very great labour 

 on the part of the authors. While its adoption has not, 

 however, been universal, it is used to some extent bv almost 



