Notices respecting New Boohs. 221 



pentine rock, the mineral is a secondary product. This confusion 

 is continued in the authors' speculations as to the origin of such 

 serpentines as that of the Lizard. It has been shown during 

 the last few years by several independent observers that, che- 

 mically and microscopically, there are the strongest reasons for 

 believing that these serpentines are in all cases altered peridotites. 

 The process of transition from the wholly unaltered olivine rock to 

 that in which every characteristic structure of the olivine has been 

 obliterated has been laboriously traced and described : yet Messrs. 

 King and Sowney simply reiterate their opinion, that it has been 

 derived by methylosis from a " dolerite (wacke or melaphyre) like 

 that of Bufaure in the Tyrol" *. No suggestions are made as to the 

 means by which the large percentage of silicate of alumina (neces- 

 sarily present in the felspar of a dolerite, and usually a very obsti- 

 nate constituent, declining to yield to this kind of methylotic action) 

 has been removed ; and but little confirmatory evidence is adduced 

 beyond the vague statements of authors who lived before the micro- 

 scope was applied to petrology. In the same hasty way, the bron- 

 zite crystals in the Lizard serpentine are held to be pseudomorphs 

 after black augite ; and a chemical and microscopical demonstration 

 that they cannot be distinguished (allowing for partial hydration) 

 from varieties of enstatite is cited as confirmatory of their idea 

 that the " crystals are pseudomorphs of chlorite after augite." 



"We do not deny the possibility of the alteration of augite into a 

 mineral which might be mistaken for enstatite or bastite ; but after 

 a considerable experience in the microscopic study of augite and its 

 changes, we could not accept the statement without a clear demon- 

 stration. 



The above case, however, is simply illustrative of a tendency 

 which runs through and vitiates the whole work, viz. to postulate 

 the very points which are of vital importance to the argument, and 

 which are denied by not a few authorities at least as experienced as 

 the authors themselves. The following are a few instances of 

 begging the question : — Augite and hypersthene are placed among 

 mineral species "common to ordinary metamorphics." The authors 

 are surely aware that at any rate normal augite cannot be called 

 common in metamorphic rocks, and that the metamorphic origin 

 of any important mass of hypersthene rock is a matter of dispute. 

 The "green marble of Connemara" is assumed to be post-Archsean, 

 and the Upper G-neiss series of Scotland Lower Silurian ; but the 



* The authors' remark about the opinion that " ophite, or its essential 

 component serpentine," has originated from peridotic rock, is in itself a 

 proof of their hasty way of looking at an adverse opinion. "It cannot be 

 denied that the common occurrence at Snarum of pseudomorphs of ser- 

 pentine after peridote, and the frequent association of the two minerals in 

 other places, may be taken as good, evidence in favour of this view; but 

 it would be just as reasonable to assume that basalt, because it usually 

 contains a large proportion of peridote, was generated out of masses of this 

 mineral." Just as reasonable \ Is there any evidence of the replacement 

 of olivine by a lime-felspar, accompanied, too, as it would here be, by an 

 entire change of the intimate structure of the rock ? 



