Geology and Natural History. 



411 



and volcanic groups, and again subdivided according to the plan 

 whose outline is shown in the succeeding notice. The remainder 

 of the work is composed of a description of the distribution of 

 igneous rocks in the British Isles. While the volume is intended 

 especially for British students, who may desire to attain a knowl- 

 edge of the elements of petrography, there are doubtless many 

 teachers of the subject in this country who will desire to acquaint 

 themselves with the author's methods and ideas of this subject. 



l. v. P. 

 7. Classification of the Plutonic Rocks; by F. H. Hatch; 

 Science Progress No. 10, 1908, pp. 1-21, reprint. — The writer 

 believes that the physical differences between the abyssal granu- 

 lar rocks and the glassy or porphyritic ones is so great that any 

 scheme of classification which presumes to be of a natural, as 

 opposed to an artificial, character must recognize this. Assum- 

 ing then that the plutonic group is a natural one, he proposes a 

 subdivision of it on chemical grounds, according to the silica con- 

 tent, these groups being again subdivided according to the alkali 

 and calc-alkali contents. In this the " ultra basic " rocks (peri- 

 dotites, etc.), are not included. This gives rise to the following 

 grouping, which sufficiently illustrates the scheme proposed : 



Acid 



Group 



SiO s >66#- 



Alkali Series 



Fels- 



pathoid 



Series 



Soda 

 Series 



Soda- 

 Granite 



Sub- 

 Family 



Potash 

 Series 



Potash 

 Granite 



Sub- 

 Family 



Monzonite 



Series 



Adamellite 

 Sub- 

 Family 



Calc- 

 alkali 

 Series 



Granodiorite 

 Sub- 

 Family 



Granite Family 



Intermedi- 

 ate Group 



Si0 2 52-66^ 



Nephelite 

 Svenite 



Sub- 

 Family 



c -. Potash- 



Soda- c 

 c; ., Syenite 

 Svenite /-oi -± \ 



Sub- (Pl g" i e b mte) 

 Fami 'y Family 



Syenite Family 



Monzonite 

 Family 



Diorite 

 Family 



Basic 

 Group 



Si0 2 <52; 



Ne P^ lite -:Essexite 



^ b £ro Sub- 



Sub- T-, ., 



-j-, ., .bamily 



Farm y J 



Shonkinite 

 Sub- 

 Family 



Kentallenite 

 Sub- 

 Family 



Alkali-Gabbro Family 



Gabbro 

 Family 



l. v. P. 



