Igneous Hocks and Volcanos. 199 



In the presence of a solution of alkaline carbonate. I there also 

 suggested that the silicates of alumina in sedimentary rocks may- 

 combine with alkaline silicates to form feldspars and mica, and 

 that it would be possible to crystallize these minerals from hot 

 alkaline solutions in sealed tubes. In this way I explained the 

 occurrence of these silicates in altered fossiliferous strata. My con- 

 jectures are now confirmed by the experiments of Daubree, which 

 serve to complete the demonstration of my theory of the normal 

 metamorphism of sedimentary rocks by the interposition of heated 

 alkaline solutions. 



But to return to the question of intrusive rocks : Calculations 

 based on the increasing temperature of the earth's crust as we 

 descend, lead to the belief that at depth of about* twenty-five miles 

 the heat must be sufficient for the igneous fusion of basalt. The 

 recent observations of Hopkins, however, show that the melting 

 points of various bodies, such as wax, sulphur and resin are greatly 

 and progressively raised by pressure, so that from analogy we 

 may conclude that the interior portions of the earth are, although 

 ignited, solid from great pressure. This conclusion accords with 

 the mathematical deductions of Mr. Hopkins, who, from the pre- 

 cession of the equinoxes, calculates the solid crust of the earth to 

 have a thickness of 800 or 1,000 miles. Similar investigations 

 by Mr. Hennessey however assign 600 miles as the maximum 

 thickness of the crust. The region of liquid fire being thus re- 

 moved so far from the earth's surface, Mr. Hopkins, suggests the 

 existence of lakes or limited basins of molten matter which serve 

 to feed the volcanos. 



Now the mode of formation of the primitive molten crust of the 

 earth would naturally exclude all combined or intermingled water, 

 while all the sedimentary rocks are necessarily permeated by this 

 liquid, and consequently in a condition to be rendered semi-fluid 

 by the application of heat as supposed in the theory of Scrope 

 and Scheerer. If now we admit that all igneous rocks, ancient 

 plutonic masses, as well as modern lavas, have their origin in the 

 liquefaction of sedimentary strata, we at once explain the diversi- 

 ties in their composition. We can also understaud why the pro- 

 ducts of volcanos in different regions are so unlike, and why the 

 lavas at the same volcano vary at different periods. We find an 

 explanation of the water and carbonic acid which are such con- 

 stant accompaniments of volcanic action, as well as the hydro- 

 chloric acid, sulphuretted hydrogen and sulphuric acid, which are 



