266 EEPORT UNITED STATES GEOLOGICAL SURVEY. 



*"We conceive that the earth's solid crust of anhydrous and prim- 

 itive ingneous rock is everywhere deeply concealed beneath its own 

 ruins, which form a great mass of sedimentary strata, permeated by 

 water. These rocks, at a snflBcient depth, are necessarily iu a state of 

 igneo-aqueous fusion, and in the event of fracture in the overlying 

 strata, may rise among them, taking the form of eruptive rocks." 

 Lyellt says: "The permanent elevation and subsidence of land now 

 observed, and which has been going on throughout past geological ages, 

 may be connected with the expansion and contraction of parts of the 

 solid crust, some of which have been cooling from time to time, while 

 others have been gaining fresh accessions of heat." 



Such and similar views have been advanced to explain the sources 

 from which the volcanic material might be derived. Taking a totally 

 different ground are those explanations of the source of heat which are 

 founded upon purely chemical bases. 



Keferstein, in 1834, | contends that volcanic phenomena have their 

 origin in sedimentary strata, and that they are the result of chemical 

 changes there going on. As Hunt correctly remarks, § Keferstein has 

 placed his hypothesis upon an untenable basis by "ignoring the incan- 

 descent nucleus as a source of heat." Bischoff, who made numerous 

 experiments relative to the fusion of rocks, came to the conclusion that 

 the presence of carbonic-acid gas at great depths would produce decom- 

 position of the silicates. Carbonates would be formed in consequence, 

 and the increase of bulk might readily i)roduce mechanical uplifting of 

 strata and other phenomena. 



My friend, Capt. 0. E. Button, has published a series of highly inter- 

 esting speculations as to the earth's physical evolution. |1 He takes the 

 hydrothermal theory of metamorphism for granted, and assumes that the 

 process is an intensified solvent power over silica, alumina, and other 

 minerals. By this means the original combinations are broken up. He 

 regards the results obtained with reference to the minerals as essentially 

 the same as the soluble hydrates obtained in the laboratory. This pro- 

 duction or change is accompanied by a large diminution of the specific 

 gravity. Although the assumptions cannot be proved, as the entire 

 nature of the process is not understood, we are enabled, judging from 

 analogies, to conceive the possibility and even probability of such con- 

 ditions as Button supposes to take place. 



Making a careful survey of the most prominent hypotheses proposed, 

 and eliminating such features as seem to me irreconcilable with facts 

 observed, I have arrived at a series of results that are set forth in the 

 subjoined pages. It will be necessary to revert to some questions already 

 touched, for the purpose of a complete understanding of the views held. 



Within the interior of the earth's crust we have certain definite zones 

 of heat. To what degree the temperature may rise is immaterial. The 

 distance of these zones from the centre of the earth will vary propor- 

 tionately to the amount of pressure at any given point. In accordance 

 with Herschell, we assume that the deposition of enormous quantities 

 of sediment at any point, or along any line, will eventually produce a 

 flexure or fracture of the underlying masses of rigid rock. This flexure 

 or fracture will be expressed by a movement of the disturbed portions 



* Canad. Jour., May, 1858, vol. iii, j). 207. 

 t Principles of Geology, 1868, vol. ii, p. 242. 

 tNaturgescbichte des Erdkorpers, vol. i,p. 109. 

 § Am. Jour. Sci., July, 1860. 

 11 Penn. Monthly, May, 1876, Philada. 



