234 Revieivs — King and Rowney on Eozoon Canadense. 



opposite swing of the chemico-geological pendulum, and belong to 

 that school which Delesse in his latter days designated as meta- 

 morphitime a. Voutrance. Perhaps the truth may ultimately be found 

 to lie somewhere between the two schools. Without prejudice one 

 may truly say that it seems only reasonable to pi'edicate an intimate 

 relation between the original composition of a mass of rock and its 

 present composition. If the contrary should turn out to be the 

 case on the very extensive scale claimed by the authors, we must 

 conclude that manj'^ a chapter in the earth's history has been blurred 

 beyond the hope of deciphering. 



Ophites. — There are so many different views as to the origin of 

 serpentines and serpentinous rocks that the whole question abounds 

 with pitfalls and snares, which are made worse owing to the 

 different values attached to names by the various anthors. Perhaps 

 we may regard the subject as a sort of triangular duel between 

 (1) the advocates of original precipitation, (2) the advocates of the 

 alteration of magnesian silicates, and (3) the advocates of indis- 

 criminate substitution. As the authors are disposed to believe that 

 almost any sort of replacement maj"^ occur, they see no difficulty in 

 the original constitution of any kind of rock, and may cite Dr. 

 Heddle as suggesting that the structure of the " serpentine of the 

 hill of Towansieff would lead to the conclusion that gneiss was the 

 original." This last is certainly an extreme case of the theory of 

 indiscriminate substitution. Doubtless, however, the authors would 

 be prepared to account for it, somewhat as follows : First the 

 muscovite of the gneiss would be magnesiated into phlogopite ; this 

 again would be methylosed into talc, and thus we should have 

 a sort of protogine. Now protogine, accoi'ding to the definition at 

 page 2, is already a " sub-silacid Ophite." In this way, since 

 "serpentynite " belongs to the silacid section, a relationship between 

 the two is at once set up. Any quartz or felspar that might be in 

 the way would of course be got rid of by a further wave of the 

 methylotic wand, and, presto ! your gneiss is converted into serpen- 

 tine. 



Again, because a pseudomorph of serpentine after tremolite can be 

 adduced from the St. Gothard, it is assumed that there can be no 

 difficulty in understanding that a diorite should be methylosed into 

 Ophite. That depends very much upon the precise meaning at- 

 tached to the word " Ophite." If chlorargyllites, chlorite-schists, 

 and protogines are to be included, the wideness of the definition 

 makes any statement of the kind a pretty safe one. To the notion 

 that hydration of magnesian minerals and sediments is one great 

 cause of " serpentinization" most people would say, Agreed. But the 

 nature of the resultant should bear some relation to the composition 

 of the original, especially in the case of large rock masses. A rock, 

 for instance, originally poor in alumina, would yield a resultant 

 containing a large proportion of serpentinite (hydro-ferro-magnesian 

 silicate). Some would restrict the term serpentine to such rocks, 

 and would regard them as having been derived from masses where 

 peridote (olivine) predominated. This is perhaps too stringent a 



