718 W. N. Benson — Origin of Serpentine. 



original mineral do not seem to be perfectly convincing, 

 the phenomena described are sufficiently remarkable to 

 deserve careful consideration." 



v. One of the most remarkable features described by 

 Weinschenk was clearly illustrated by the material 

 shown to the writer in Munich. There seems no possi- 

 bility for doubting that, in the case of the slides exam- 

 ined, the rock had been completely changed to serpentine 

 before the formation of numerous cracks, which were 

 filled by very coarse-grained antigorite intergrown with 

 glassy clear olivine, and sometimes with magnesite. The 

 very coarseness of the grain size compared with that of 

 the main mass of the rock suggests a comparison with 

 pegmatite, forming from the residual mother liquor of 

 the magma; and according to Weinschenk, where these 

 veins extend beyond the ultra-basic rock into the sur- 

 rounding calc-schists, they are associated with vesuvi- 

 anite, garnet and other minerals of contact metamorph- 

 ism, which seems to give further indication of their 

 magmatic origin. 5 We may, therefore, concur in the 

 view that the antigorite is here of hydrothermal origin, 

 forming at or before the close of the period of igneous 

 activity, which produced the peridotites. It must surely 

 follow that the prior serpentinization of this peridotite- 

 mass took place at such a depth as almost to exclude the 

 action of meteoric waters, and while large amounts of 

 magmatic water were present. 



These interesting veinlets containing olivine travers- 

 ing serpentine are not without analogy, for similar fea- 

 tures have been noted by Palache (1907), who found a 

 narrow sharply-defined vein of glassy clear olivine two 

 inches in width in the "platey serpentine' ' of Chester, 

 Mass., U. S. A., which had replaced olivine and pyroxene. 

 It is here also clear that the serpentine formed before the 

 intrusion of the olivine vein. 



A possible objection to the hypothesis of the produc- 

 tion of olivine by crystallization from a hydrous mag- 

 matic solution is that as yet it has been formed artificially 

 by methods of dry-fusion only. Nevertheless, the pro- 

 duction of olivine in magnesian limestone at granite 

 contacts is well known, and here the action will be prob- 

 ably a pneumato-hydrothermal one. In any case, the 

 possibilities of experimentation with carbonated solu- 

 tions under conditions of high temperature and pressure 



5 But see Kosenbusch 's alternative suggestion, p. 722. 



