488 G. P. Merrill — Augite from Little Deer Isle, Me. 



So far, the case appears to be clearly and conclusively settled 

 as to the origin of the nickel silicates under discussion. Nickel 

 is almost always present in small quantities in olivines, and T. 

 S terry Hunt, in reporting genthite from Michipicoten Island* 

 calls attention to the fact that the metal is rarely absent from 

 the serpentines, steatites, diallages, and actinolites of the Quebec 

 group. Nevertheless, one other possible source of nickel must 

 be noticed. Roth,f in speaking of the genthite from the 

 chrome mines of Pennsylvania, attributes it to the alteration 

 of nickeliferous chromite ; and the almost universal association 

 of the latter mineral with genthite, renders the view deserv- 

 ing of attention. But it must be remembered that chromite 

 alters with great difficulty, while olivine decomposes with ex- 

 treme ease ; and morever the genthite from Oregon contained 

 no chromium, although that metal was diligently sought for. 

 Furthermore, Mr. Diller examined some of the chromite from 

 the Riddle mines, and found that although it was penetrated 

 by crevices filled with secondary minerals containing genthite, 

 the chromite itself showed no evidence of alteration. 



Concerning the other silicates of nickel, described under the 

 names of pimelite, alipite, conarite, rottisite, refdanskite, etc., 

 little need here be said. Some of them are probably similar in 

 origin to the better known genthite, although the conarite and 

 rottisite, which contain small amounts of sulphur and arsenic, 

 probably came from nickeliferous sulphides. For the other 

 minerals above named there is too little evidence upon record 

 to warrant any serious attempt at discussion. 



Laboratory U. S. Geological Survey, March, 1888. 



Art. XLIII. — Note on the Secondary Enlargement of Augites 

 in a Peridotite from Little Deer Isle, Maine / by George 

 P. Merrill. 



While engaged in the study of sections of a peridotite 

 from Little Deer Isle in Penobscot Bay on the Maine coast, 

 the writer observed certain peculiarities of the augitic constit- 

 uent which, if rightly interpreted, seem worthy of notice in 

 the columns of this Journal. 



The rock consists essentially of olivine and augite, with 

 accessory magnetite, chromite, apatite, and rarely a plagio- 

 clase feldspar (?) It therefore belongs to the variety of peri- 

 dotites which Professor Rosenbusch designates as picrite. 



* Report Geol. Survey of Canada, 1863, p. 506. 

 f Allgem. und Chem. Geologie, vol. i, p. 225, 1879. 



