REPORT OF THE CHIEF ASTRONOMER 325 



SESSIONAL PAPER No. 25a 



tain (southeast slope) and Record mountain ridge, the divide between Malde- 

 and Little Sheep creeks, and the bluffs on the west, side of the Columbia river 

 about four miles north of the line. The following brief description of a typical,, 

 relatively unaltered phase relates to one of the younger flows occurring on the 

 unnamed conical peak west of the Murphy creek-Gladstone trail and about two 

 miles north of Stony creek. The volcanic rocks are there exceptionally well 

 exposed above tree-line, where thick sheets of highly porphyritic latite alternate 

 with more basaltic sheets and with coarse agglomerates composed of these lavas-.. 

 The latite when fresh is a deep greenish-gray to almost black rock bearing 

 abundant phenocrysts of tabular plagioclase up to 3 mm. in greatest diameters 

 and of smaller, stout prisms of greenish-black pyroxene. 



Microscopic examination shows that the rock is uncrushed, the phenocrysts- 

 being unstrained and almost perfectly unaltered. The plagioclase is the more- 

 abundant. On (010) and in the zone of symmetrical extinctions for simul- 

 taneous Carlsbad-albite twins, individual crystals give extinction angles appro- 

 priate to the series from labradorite, Ab 3 An 4 , to bytownite, Abj An 3 . Occasionally 

 one of these basic individuals is surrounded with a narrow rim of orthoclase. 

 The average plagioclase phenocryst has about the composition of labradorite, 

 Ab„ An.,. The pyroxene is a common, non-pleochroic, pale greenish augite of 

 diopsidic habit. 



The ground-mass has been somewhat altered, with the generation of uralite' 

 in small needles, zoisite in rather rare granules, chlorite, abundant biotite, and 

 more sericitic mica in minute foils and shreds. Orthoclase was not certainly 

 detected in the ground-mass, which was originally hyalopilitic, with plagioclase 

 microlites embedded in glass. Magnetite and apatite occur in the usual well- 

 formed crystals. 



A specimen collected at this locality (No. 543) and answering to the fore- 

 going description has been analyzed by Mr. Connor, with result as follows. 

 (Table XIX., Col. 1.) :— 



Table XIX. — Analyses of augite latites, Rossland district and Sierra Nevada. 



1. la. 2. 



Mol. 



Si0 2 



Ti0 2 



A1 2 3 



FeA 



FeO 



MnO 



MgO 



CaO 



SrO 



BaO 



Na 2 



K 2 



H 2 at 11Q°C 



H 2 above 110°C 



P 2 O s 



54-54 



•909 



56-19 



•96 



•012 



•69 



18-10 



•177 



16-76 



1-14 



•007 



3-05 



4-63 



•064 



4-18 



•10 



•001 



•10 



4-56 



•114 



3-79 



5-85 



•104 



6-53 



•15 



•001 



tr. 



•21 



•001 



•19 



3-38 



•055 



2-53 



5-44 



•058 



4-46 



•10 





•34 



•50 





-66 



•46 



•004 



•55 



100-12 



100-02 



Sp.gr 2-745 



