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



strength of certain rocks, with the depth of some earthquakes and other 

 pressure data of interest. By the side of the temperature column I 

 have placed Bell's diagram of blast-furnace reactions,* with various other 

 thermal data of interest. 



From these we may, to make our conceptions definite, guess some- 

 what at the zone whence the different rocks are derived. I have avoided 

 any calculations in this paper, first, because I thought the evidence could 

 be just as well presented and be more interesting without them ; second, 

 the data are really too uncertain to give any closer results than can be 

 got from qualitative methods ; and, third, if I once got started in calcu- 

 lations I should need a whole bulletin. 



Probable Reactions of gas-making Elements. — The behavior of a few ele- 

 ments first claims our attention. Oxygen at high temperatures largely 

 or wholly dissociated steadily combines, at first with carbon to carbonic 

 oxide at about 1200° centigrade, then perhaps with iron and silicon to 

 ferrous iron, in such compounds as olivine, and then also magnetite, 

 forming some carbon dioxide (CO,). It would probably not attack the 

 free hydrogen at all until the iron was all oxidized. About 400° centi- 

 grade is a peculiar point where the affinities of carbon monoxide (CO) 

 for another atom of oxygen and those of iron or the same element are 

 about balanced, and there is a tendency for carbon monoxide (CO) to 

 divide into carbon and carbon dioxide (COJ. Not far below this is the 

 critical temperature of water, and about here any spare oxygen would 

 combine with any free hydrogen. Very soon we shall be altogether in 

 an oxidized rock and below the critical temperature of water, when the 

 pressure would immediately convert steam into water. 



At first the carbide of iron or graphite or diamond would gradually 

 oxidize. Under certain circumstances hydrocarbons form. Nitrogen, 

 would be inert generally, but might form ammonia compounds. Proba- 

 bly sulphur early combines with iron in the troilite of the meteorites and 

 pyrrhotite of the gabbros, and may turn to pyrite, but more likely becomes 

 H^S or oxidized and furnish its SOg for hauynite, the solfataras, and escap- 

 ing alkaline sulphates, so often found in volcanoes. It would thus set 

 free much heat. Fluorine is probably most abundant in the acid zone as 

 silico-fiuorides, and chlorine more abundant in the basic zone. 



The top of the acid zone will probably be about where the pressure is 

 enough to crush any rock. There will occur at this level a sudden in- 

 crease of pressure on the enclosed water, which very likely may produce 

 decided changes in physical condition. About here also may be the 

 level of no strain, where lateral compression ends — the starting place of 

 many earthquakes. As granites often contain enclosures of carbon 



* Iron and Steel, plate G et passim. 



