THE GASES IN ROCKS. 



It has been known for a long time from microscopical studies that 

 some minerals inclose minute cavities which contain both liquid and gas- 

 eous matter. For a much shorter period it has been known that various 

 igneous rocks, when exposed to red heat in a vacuum, evolve several times 

 their volume of gas of quite variable composition. Since these gases occur 

 in proportions entirely different from those of the constituents of the air, 

 it has not seemed probable that they were derived directly from our 

 present atmosphere, unless the rocks manifest some power of selective 

 absorption not now understood. The apparent difficulties involved in this 

 conception have suggested that some earlier atmosphere was rich in those 

 gases. This involves a hypothesis relative to the changes through which 

 the atmosphere has passed, and leads on to a theory of its origin and that 

 of the earth itself. An alternative hypothesis regards these gases, not as 

 the products absorbed by a molten earth from its surrounding gaseous 

 envelope, but as entrapped in the body of the earth during its supposed 

 accretion, and hence that they are a source from which accessions to our 

 present atmosphere might be derived. 



A study of these gases in the rocks has seemed, therefore, to give 

 promise of results of some value to atmospheric problems and, perhaps, to 

 those of cosmogony. Because of this, it appeared advisable to determine 

 more widely the range and the distribution of these gases, their relations 

 to other geologic phenomena, and the states in which the gases, or gas- 

 producing substances, exist in the rocks. The desirability of supplementary 

 work will become more evident when it is noted that, while a considerable 

 number of investigators have analyzed the gases in rocks, as will appear in 

 the following historical statement, nearly all have contented themselves 

 with a few determinations, and that even a full compilation of all such 

 results leaves much to be desired from a geological point of view. 



HISTORICAL SKETCH. 



As early as 1818 the attention of Sir David Brewster was called to the 

 subject of inclosed water by the explosion of a crystal of topaz when 

 heated to redness ; but his studies were not published until 1826. In the 

 mean time, Sir Humphry Davy opened the cavities in a few crystals and 

 examined chemically the imprisoned liquid and gas. 1 Piercing a cavity in 

 several cases suddenly caused the inclosed gas-bubble to contract to from 

 one-sixth to one-tenth of its original volume. The gas was thought to be 

 pure nitrogen. The basaltic rock from the neighborhood of Vicence con- 



1 Sir Humphry Davy, Phil. Trans. 1822, Pt. n, pp. 367-376 ; Ann. de Chim. et Phys., 

 t. 21 (1822), pp. 132-143. 



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