262 A. C. LANE GEOLOGIC ACTIVITY OF THE EARTH's GASES. 



The gradual silicification of the older rocks and the metamorphism of 

 the crystalline schists may be in part due to this cause, being like a 

 contact-zone for the earth's interior. 



i. Their activity would accentuate the crumpling of the earth's surface 

 by abstracting material below and adding part of it to the crust. 



j. They would affect the cooling and thermal gradient of the earth, 

 and hence also other estimates of its age based thereon. 



Relative Importance of Points discussed. — As to the points presented in 

 the preceding section it should be noticed that they are not all of the 

 same order. 



The first three are primary, while the others follow from them. Yet 

 they describe effects which, though they would naturally follow from 

 the state of things outlined in the first three propositions, might be 

 insignificant in quantity or overruled by other factors not taken into 

 consideration. Indications of such effects would tend to sustain the 

 whole body of theory, but negative results would not be at once fatal 

 to it. 



In enlarging on the evidence for these conceptions I shall not gener- 

 ally go into minute details which are found in the books referred to, but 

 rather point to Unes of facts familiar to the members of this Society most 

 interested, because they have worked upon them themselves. 



Absorbed Gases. 



Given off rather than combined. — That the earth absorbed gases needs no 

 elaborate argument in view of the well known occlusion of various gases 

 by various metals,* of the general tendency df liquids to absorb gases 

 and in view of the fact that standard writers like Geikie,t who do not 

 attribute volcanic activity exclusively or mainly to this source, acknowl- 

 edge the fact. 



That these gases would tend to be given off in cooling and solidifica- 

 tion X would also be beyond doubt, unless it were true that they entered 

 into combination more rapidly yet. Here is one of the two main doors 

 for question. That the tendency to combine does not increase more 

 rapidly than the tendency in solidifying to give off gases is indicated by 

 the occurrence of uncombined water in volcanic glasses, by the giving 

 off of steam and other vapors, by the occurrence of liquid enclosures in 

 plutonic rocks, and, in general, by the fact that rocks must solidify at 

 temperatures at which chemical affinities begin to weaken. 



*See Table 1. Also Dammer's Handbuch der Anorg. Chemie, vol. i, 1892. article " Okklusion." 

 t Text-book of Geology, 1893, pp. 10, 193, 265. 



% But as a fluid tends to absorb gas in cooling, relief of pressure is needed to permit the escape 

 of gas from a fluid. This is Reyer's position, I think. 



