454 Dr. W. A. Tilden, On the Gases enclosed 



Since this observation, I find that the presence of hydrogen in 

 crystalline rocks has been recognised by other observers, notably by 

 A. W. Wright (' Amer. J. Sci.,' Ser. 3, vol. 12, p. 171). In the course 

 of a study of the gases from meteorites, Wright obtained from a 

 certain " trap " rock, the origin and character of which is not stated, 

 at a low red-heat, " about three-fourths of its volume of mixed 

 gases, which were found to contain about 13 per cent, of carbon 

 dioxide, the residue being chiefly hydrogen. Another specimen of 

 trap containing small nodules of anorthite was examined at the 

 request of Mr. G. W. Hawes, who had observed gas cavities in a 

 thin section of the mineral prepared for microscopic examination. 

 This gave off somewhat more than its own volume of gas, which was 

 found to contain some 24 per cent, of carbon dioxide." 



Professor Dewar and Mr. Ansdell have also examined one or two 

 rocks in the course of their researches on meteorites (' Roy. Inst. Proc./ 

 1886). They found that both gneiss and felspar, containing graphite, 

 yield gas, which, upon analysis, was found to have the composition 

 stated below. 



Occluded gas 

 in volumes 

 of the rock. , CO 2 . CO. H 2 . CH 4 . N 2 . 



Gneiss 532 , 82'38 2'38 13*61 0'47 1-20 



Felspar T27 94'72 0'81 2'21 0'61 1-40 



Dewar and Ansdell remark that " the small quantity of marsh gas^ 

 no doubt, comes from the disseminated graphite, but the presence of 

 the hydrogen is more difficult to explain, and requires further inves- 

 tigation." 



I have lately been following up this question, and have obtained 

 results which present some points of considerable interest. For 

 materials I have been indebted chiefly to my colleague, Professor 

 Judd, who has also supplied information as to the probable geological 

 age of the specimens of rocks and minerals tested. All that I have 

 examined yield permanent gas when heated in a vacuum. This gas 

 varies in amount from a volume about equal to that of the rock or 

 mineral to about eighteen times that volume. It usually consists of 

 hydrogen in much larger proportion than that found by the observers 

 just quoted, together with carbon dioxide and smaller quantities of 

 carbon monoxide and hydrocarbons. Every specimen has been 

 examined by the spectroscope for helium, but in no case could D 3 be 

 recognised, or any other line which would lead to a suspicion of the 

 presence of this substance. The gas is very frequently, but not 

 always, accompanied by water in notable quantities. 



The gas is apparently wholly enclosed in cavities which are visible 

 in thin sections of the rock when viewed under the microscope, but 

 as they are extremely minute, very little gas is lost when the rock is 



