262 Naumann on Primitive Formations, 



or by the simultaneous action of heat and water, or only by the 

 latter element, are questions whose solution we must still expect 

 from the future. In the meantime the real mode in which the 

 primitive rocks have been formed, is still involved in such obscurity, 

 that they may, with complete justice, be termed cryptogenous rocks* 



Note to the preceding paper ; hy T. Sterry Hunt, M.A., F.R.S. 

 The foregoing sketch of the progress of theoretical views as to 

 the origin of the crystalline rocks, gives an excellent statement 

 of the question up to 1857; since which time more definite notions 

 as to the nature of the metamorphic process, as understood by 

 Hntton and Boue, have begun to be entertained. The problem 

 of rock metamorphism is the conversion of mechanical or chem- 

 ical sediments into definite mineral species, by molecular changes; 

 that is to say, by crystallization, and a re-arrangement of their 

 particles; or by chemical reactions between the elements of the 

 sediments. Pseudomorphism, which is the change of one mineral 

 species into another, by the introduction, or the elimination of 

 some element, presupposes metamorphism ; since only the defi- 

 nite mineral species of metamorphic or plutonic rocks can be the 

 subjects of this process. To confound metamorphism with pseu- 

 domorphism, as Bischoff", and others after him have done, is there- 

 fore an error. It may be further remarked, that, although certain 

 pseudomorphic changes may take place in some mineral species, 

 in veins, and near to the surface ; the alteration of great masses 

 of silicated rocks by such a process, is as yet an unproved hy- 

 pothesis. 



The study of the local metamorphism of sediments in the 

 vicinity of intrusive rocks, goes far to show, in opposition to the 

 opinions of some authors quoted above, that heat has been one of 

 the necessary conditions of metamorphism. In 1857, I showed 

 by experiments, that besides heat and moisture, certain chemical 

 reagents might be requisite, and that water impregnated with 

 alkaline carbonates or silicates, would at a temperature not 

 above that of boiling water, produce chemical reactions among 

 the elements of many sedimentary rocks; dissolving silica and 

 generating various silicates. Some months subsequently, Dau- 

 bree found that in the presence of solution of alkaline silicates, 

 at temperatures above 700° F,, various silicious minerals, such as 

 quartz, feldspar and pyroxene, could be made to assume a crys- 

 talline form ; and that alkaline silicates, under these conditions, 



