30 ROCK-METAMORPHISM. 



this occasion than to briefly show that it is totally invalidated 

 by Dr. Hunt's own dicta. 



Thus, quoting from a lately published exposition of it (in 

 ' Nature/ No.460 ; Aug.22,1878), we proceed : " Plutonists begin 

 to understand that water cannot be excluded from rocky strata,, 

 but is all-pervading, and that at great depths, kept by pressure 

 in a liquid state at an elevated temperature, and having its 

 solvent powers augmented by alkaline salts, it plays a most 

 important part in metamorphism." Nevertheless, from the 

 absence of any references to the matter, the minerals forming 

 the Archaean stratified crystallines cannot, as must be understood 

 from the quotations in the preceding page, have been formed in 

 <f deeply-buried sediments" by " subsequent metamorphism," 

 consequent on their being f situated at great depths " \ 



Dr. Hunt continues, "If, as most Neptunists maintain, the great 

 crystalline series have been derived from the alteration of uncrys- 

 talline ones, which were not only similar to those of palaeozoic and 

 more recent times, but are, in fact, portions of those which in 

 adjacent regions are still known to us in their original unchanged 

 condition, how are we to explain the genesis of the feldspathic 

 and hornblendic rocks which predominate in these crystalline 

 formations? The sandstones and shales from which, on this 

 view, they are supposed to be formed, could never by themselves 

 give rise to the rocks in question, since they are deficient in 

 the alkalies, and to a greater or less extent in the other bases 

 required for the production of the constituent silicates/' He 

 further remarks : " There is no good and sufficient reason 

 for believing in the present existence of any uncrystalline 

 representatives of these crystalline formations, or of any such 

 formation which is not pre-Silurian if not pre-Cambrian in age. 

 There are, however, many examples of local alteration of later 

 sediments by hydrothermal action which have developed in 

 these many crystalline minerals identical with those found in 

 the more ancient rocks." 



to neolite (which is a very exceptional case), if it have been formed as stated, 

 " through the agency of infiltrating waters " holding its constituents in solu- 

 tion, the great probability is that, so far from their having been precipitated 

 in consequence of " chemical reactions," these constituents would have been 

 deposited, like sinters (stalactitic, calcitic, &c.), by the evaporation of the 

 water, 



