ORIGIN OF PEGMATITES. 723 



water is atmospheric, but is wholly eruptive water. Crosby and Fuller, 

 however, think it is possible that a portion of the water required "for the 

 more perfect hydration and liquefaction of the residuum of the magma may 

 be derived from extraneous sources.'" 1 



It seems to me that to explain adequately all the facts of pegmatization 

 described in various regions of the world, we must conclude that all three 

 processes have been at work — in some cases igneous injection, in some 

 cases aqueo-igneous action, in other cases pure water cementation, and in 

 still other cases combinations of two or all of these processes. It is further 

 believed that there is no sharp separation between these processes, but that, 

 on the contrary, there are all gradations between the three. That is, it is 

 thought highly probable that, under sufficient pressure and at a high tem- 

 perature, there are all gradations betiveen heated waters containing mineral 

 material in solution and magma containing water in solution. In other words, 

 under proper conditions water and liquid rock are miscible in all proportions. 

 This possibility, first published by me in 1896, 6 in precisely the above 

 words, has received almost conclusive experimental verification at the 

 hands of .Barus. As noted on page 80, Barus has shown that at temper- 

 atures below 200° C, and at high pressure, soft glass and water are actually 

 miscible in all proportions. 



From the Avater solutions true cementation takes place ; from the rock 

 solutions, true injection. Pegmatization comprises these and the interme- 

 diate processes. It is not to be expected that under great pressure and at 

 high temperatures there is any sharp line of demarcation between the 

 processes of aqueous cementation and igneous injection. At the surface 

 it is usually easy to sharply separate aqueous from igneous action, but 

 deeper within the earth even the strongest rocks are latently plastic. At 

 great pressure heated waters must have power to absorb a quantity of 

 material far beyond that at the surface of the earth. Truly liquid rock is 

 highly impregnated with water. It therefore is probable that at consid- 

 erable depths we have, on the one hand, material which all would call water 

 solution, and on the other hand material which all would call liquid rock, 

 with no sharp division line between the two. If this be so, there are all 



« Crosby : W. O., and Fuller, M. L., Origin of pegmatite: Tech. Quar., vol. 9, 1896, p. 348. 

 &Van Hise, 0. R., Princrples of North American pre-Cambrian geology: Sixteenth Ann. Rept. 

 U. S. Geol. Survey, 1894-95, pt. 1, 1896, p. 687. 



