720 W. N. Benson — Origin of Serpentine. 



(1903), but there is a divergence of opinion on this point. 

 See alternatives suggested by Mojsisivics, Tietze, Bitt- 

 ner and Kispatic, summarized by the last named (1900).] 

 Otis Smith (1904) has also drawn attention to this fea- 

 ture pointing out its bearing on the hydrothermal origin 

 of serpentine. He noted that the basal Eocene conglom- 

 erates, lying on the serpentines of the Mount Stuart 

 Complex in Washington, U. S. A., contain pebbles of ser- 

 pentine exactly similar to that of the serpentines of the 

 complex itself. Though the age of these serpentines is 

 indefinite, it is probable that they belong to the general 

 series of ultrabasic rocks that were formed during the 

 late Mesozoic orogenic movements in western U. S. A. 



All of these observations confirm Weinschenk's state- 

 ment (1894) that the serpentinization has been completed 

 by the end of the orogenic epoch in which the peridotite 

 was formed. 



vii. But although cumulative evidence thus points to 

 the serpentinization by magmatic waters during the same 

 orogenic epoch of vulcanicity as produced the peridotite, 

 it does not appear that this followed directly after the 

 ultrabasic intrusion, and without further magmatic-dif- 

 ferentiation. Indeed, in many cases it seems that the 

 peridotite remained anhydrous while several later intru- 

 sions of magma occurred, before expulsion of the residual 

 magmatic water. In the case of the serpentine of the 

 Lizard, Flett and Hill have concluded (1912) that the 

 hydration of the peridotites occurred at a "compara- 

 tively late period in their history," at least after the 

 intrusion of the veins of gabbro; Bonney (1914) concurs 

 in this. The serpentines in the Ivrea Zone, northern 

 Italy, are by Novaresse (cited by Rosenbusch 1907) 

 referred to the after-action of the diorites upon perido- 

 tites, while in numerous cases serpentinization is consid- 

 ered to be the effect of magmatic waters accompanying 

 the intrusion of granite as the latest differentiate from 

 the same magma as gave rise to the peridotites. Thus 

 Low (1906), Barlow (1910), Diller (1910), and Dresser 

 (1913), conclude that the hydration of the peridotite in 

 the regions studied by them (eastern Canada and Ari- 

 zona), was brought about in a large measure by mag- 

 matic solutions derived from intrusions of granite in or 

 near the serpentine masses, stating that hydration is 

 most complete in the vicinity of the granite. This view 



