B. A. Daly — Mechanics of Igneous Intrusion. 4f 



Table IV. 



843 624 116 



limestones sandstones argillites 



H 2 0— '2Qfo '29 f l'25fo 



H,0+ -73* 1-41 3'71 



CO„ ... 38*03 2-64 2-45 



p j (including carbon- ) 

 ( aceous matter) ) 



? ? -81 



S -11 -03 -25 



CI ■ *0 1 trace trace 



Total... 39-14 4-37 8*47 



exposed in any geosynclinal prism must represent at least six 

 per cent of the whole mass. It is highly probable that this 

 minimum amount of volatile matter has similarly characterized 

 such a series ever since the period in which the series was 

 deposited. 



No petrographer needs to be reminded that none of the com- 

 moner types of igneous rock contains anything like six per 

 cent of original volatile matter. Nevertheless it is instructive 

 to survey the facts actually visible in quantitative analyses of 

 the igneous rocks. Water is the only volatile substance 

 determined in igneous-rock analyses often enough to afford 

 nearly reliable world-averages. From Osann's compilation 

 the writer has deduced the average of H 2 — and H 2 -f- for 

 each of the following groups : 48 granites, 47 diorites, 12 gab- 

 bros, 24 basalts, 5 augite andesites and 11 rhyolites (Table Y). 



Table V. 



H 2 0- H 2 + 



Granite '17 fo -64$ 



Diorite..- -19 .1-2.0 



Gabbro -26 1-35 



Basalt -73 1-03 



Augite-andesite '40 1*48 



Rhyolite '30 1*23 



Clarke's averages for the volatile substances occurring in 

 igneous rocks which have been analyzed according to approved 

 methods are : 



EI„0- -40^ 



H" o 0+ 1-46 



CO, -52 



S -11 



CI -07 



F -02 



Much of the combined water, probably all of the hygroscopic 

 water, and most of the carbon dioxide of these analyzed igne- 

 ous rocks are due to alteration or to absorption at the earth's 

 surface. Allowing for that fact, it seems probable that none 

 of the more widely distributed igneous rocks carries much more 



* Includes organic matter. 



