1882.] 147 [Julien. 



exactly the same way as that fully studied and described by Zir- 

 kel and others in the chrysolitic lavas, etc., of numerous foreign 

 localities. All the transition-varieties occur in abundance, from 

 that in which the serpentine is diffused among the olivine-gran- 

 ules, merely as a minute fibrous network, or as films enveloping 

 olivinec-ores — to that in which only minute particles of olivine 

 survive as the nuclei of the granules — and to the final result of 

 a true and complete serpentine, always, however, granular in 

 structure, and often retaining the original lamination. The ser- 

 pentine is also generally found in such localities as a vein-deposit, 

 i. e., white or greenish marmolite, filling or lining the fissures of 

 the rock, or occupying branching contraction-cracks throughout 

 the mass. The talcose alteration has generally progressed more 

 or less in association with the ophiolitic, and then a talcose ser- 

 pentine has resulted, rich in disseminated scales of talc and 

 hematite (gothite?). It is in such serpentines that bronzite is 

 found, in brilliant bronze-colored scales, two to three mm. in 

 diameter. 



5. Dioeitic. The last and perhaps most interesting alteration 

 of all, confined to a single locality, consists of an internal conver- 

 sion of the olivine into amphibole (a bright, grass-green variety 

 which Dr. Genth has identified as smaragdite or kokscharoffite) 

 and albite, sometimes with abundantly disseminated particles of 

 ruby red corundum, producing a peculiar variety of dioryte or 

 gabbro. 



Again, this very rock has been subsequently attacked by a sec- 

 ondary process of alteration, the albite-grains being enveloped by 

 an alteration-crust of margarite, and the condition of the hornblende 

 modified. The result of this action is a coarse margaritic gabbro, 

 whose weathered surface is peculiarly rough and warty. 



On the whole, it appears that the view which has been sug- 

 gested, 1 founded on certain phenomena observed in the corundum- 

 veins, that these secondary rocks and many schists have been 

 mainly derived from the alteration of corundum, finds not the 

 least confirmation from my studies, and is, indeed, strongly con- 

 tradicted by facts observed in the field. The corundum it sell is 

 in all cases, both in the veins and the particles found in the gabbro 

 a secondary or alteration product. All the phenomena of altera 



IF. A. Genth, loc. cit., 31, 45. 



