1 88 1. "i^ Trans. N. V. Ac. Scz\ 



Dec. 5. 1 88 1. 



Regular Business Meeting. 



The President, Dr. J. S. Newberry, in the Chair. 



Twenty six persons present. 



Dr. Newberry exhibited an ancient perforated stone axe from 

 Europe, consisting of dioryte, and remarked that the aboriginal 

 tribes of America never attained to the degree of skill required in 

 the perforation of stone implements for the insertion of wooden 

 handles. 



The following paper was read by Dr. Alexis A. Julien. 



The Volcanic Tuffs of Challis. Idaho, and other West- 

 ern localities. 



(Abstract). 



In a paper recently read before the Academy it was shown that a 

 certain compact white almost structureless rock, otten porcellanous in 

 texture, occuring abundantly in the Western Territories, and variously 

 styled "trachyte," "rhyolyte," "porphyry," etc., {e.g., at Leadville, 

 Colorado, in the Black Hills of Dakota, etc.), is a sedimentary form of 

 a highly silicious volcanic tuff, probably derived from the finest detritus 

 of trachytes, rhyolytes, and quartz-porphyries. A series of specimens 

 collected by Prof. Newberry, during the last and previous summers, 

 and kindly put in the author's hands for lithological examination, has 

 furnished the material for the following additional notes on this inter- 

 esting but neglected group of widespread American rocks. 



I. Coarse pumice-tuff of Challis, Idaho. 



The rock is quite compact, schistose, of a gray color with dull white 

 spots. The latter consist of pumice in finely fibrous grains, from i 

 to 5 mm. in length. Quartz and feldspar are seen in small angular 

 flakes, sometimes reaching 0.5 mm. in length : hornblende commonly 

 in fibrous black fragments, about i mm. in diameter: and much 

 biotite, brownish-green, sometimes brownish-black, with greasy lustre, 

 in hexagonal scales, often up to 2 to 3 mm. in size. 



The thin sections present under the microscope numerous grains, 

 generally angular, of several minerals, varying in size up to 3 or 4 mm.: 

 pumice in rounded to sub-angular fawn-colored fragments lying at all 

 angles, commonly made up of straight or curved fibres, and often in- 

 cluding glassy lenses filled with crystallites : a triclinic feldspar, in clear 

 grains, sometimes including minute globules of glass, and possessing 

 fine lamellation, beautifully striated in polarized light, the remaining 

 traces ol crystalline outhnes indicating that these grains are all of frag- 

 mentary, never of indigenous formation : quartz, in water-clear angular 



