Pre- Cambrian Bocks, etc. 279 



Doubtless since the masses of rock known as serpentine occur in 

 such various ways, and are so heterogeneous in composition, they 

 may well be allowed to have had more than one origin. Dr. Hunt 

 long ago pointed out the differences between the ophiolites of the 

 quondam Laurentians ^ associated with Eozoon, and the more massive 

 rocks consisting mainly of serpentine, which are so often associated 

 with small quantities of nickel. Professor Bonney, too, has always 

 been desii'ous of showing that his views as to the alteration of 

 olivine rock being the chief source of serpentine, do not necessarily 

 extend to what he calls " serpentinous " rocks, which he admits may 

 be the result of the alteration and hydration of mixed silicates. Ou 

 the other hand, Dr. Hunt (p. 168), as a concession to those who 

 maintain the occurrence of eruptive serpentine, allows that the final 

 result of heat aided by water on silicated rocks would be their 

 softening and in certain cases their extravasation as plutonic rocks, 

 which are to be regarded as, in all cases, altered and displaced 

 sediments. Sterry Hunt has, in fact, a rooted objection to internal 

 magmas, although he allows that some basalts may possibly be 

 portions of an original igneous mass, which antedated the appearance 

 of liquid water at the surface of the globe. 



The fundamental difference between Dr. Hunt and Professor 

 Bonney is more especially shown where the former considers the 

 subject of olivine rocks in their relations to serpentine. He sees no 

 reason why the olivine and enstatite found in greater or less quanti- 

 ties in serpentine rocks should not represent the crystallization of 

 anhydrous silicates in the midst of amorphous hydrous silicates ; 

 and in this way he endeavours to outflank those who insist upon 

 the presence of these minerals, and especially of olivine, as proof 

 that serpentine has been derived from their hydration. It is, in 

 fact, a battle between the chemist who can point to the paragenesis 

 of hydrous and anhydrous minerals — as for instance, grains of 

 corundum in bauxite — and the microscopist who can show how 

 readily olivine is pervaded by cracks filled with serpentine as a 

 proof of the instability of that mineral. 



It is certain that recent discoveries have made ns acquainted with 

 conditions where it would be difficult to assign any other than an 

 aqueous origin to large masses of olivine, unless we are prepared to 

 assert that such rocks as the schists of Mount Ida in the Troad for 

 instance are igneous. Indeed, it would seem that the more we 

 accept the " Archeean " as opposed to the metamorphic origin of the 

 crystallines, the more doubtful shall we become as to the eruptive 

 character of many of these magnesian rocks, or of the massive ser- 

 pentines having been derived from the hydration of olivine. At any 

 rate, if such hydration has taken place on a large scale, it must 

 have been made under conditions very difi"erent from those which 

 now obtain on the surface of the earth. 



The difficulty with regard to the oxygen ratios, to which the 



^ If we understand the present Director of the Canadian Survey, he no lonj^er 

 regards the Grenville series as Laurentian, that designation being restricted to the 

 gneiss without limestone, which alone represents the fundamental series. 



