REPORT OF THE CHIEF ASTRONOMER 61 



SESSIONAL PAPER No. 25a 



Microscopically this phase is like the one just described but is yet more 

 strongly charged with water-worn, eminently clastic grains of quartz and feld- 

 spar. The latter stand out conspicuously on the weathered surface; they vary 

 from 0-25 mm. to 1-0 mm. in diameter. 



In this section the feldspars were determined as microperthite, microcline, 

 orthoclase, and very rare plagioclase. One grain of the latter, showing both 

 Carlsbad and albite twinning was found to be probably andesine, near Ab 5 An 3 . 

 A few oolite-like grains of carbonate 0-5 mm. or less in diameter, a number 

 of round grains of chert, and a very few small specks of magnetite complete 

 the list of materials other than the general carbonate base. In grain and 

 structure the base is practically identical with that of the specimens above 

 described. 



Professor Dittrich has analyzed the rock (specimen No. 1326) with result 

 as here noted: — 



Analysis of type specimen, upper Altyn formation. 



Mol. 



SiO, 25-50 -437 



A1„0 3 2-25 -023 



Fe 2 3 .62 -004 



FeO • .38 -005 



MgO 14-77 -369 



CaO 21-65 -387 



Neu,0 -86 -014 



K 2 , 1-27 -013 



H 2 at 110°C -12 



H 2 above 110°C .42 -023 



C0 2 32-03 -729 



99-87 

 Sp.gr 2-768 



Insoluble in hydrochloric acid 29-31% 



Soluble in hydrochloric acid: 



Fe 2 3 -95 



A1 2 3 -19 



CaO 21-92 



MgO 14-29 



The fact that sensibly all the lime is soluble shows that basic plagioclase can 

 be present only in extremely small amount. The ratio of CaO to MgO in the 

 soluble portion is 1-534:1, showing that here too the calcium carbonate is but 

 slightly in excess of the proportion required for true dolomite. 



The approximate mineral composition of the rock has been calculated with 



the following result : — 



Calcium carbonate 39-1 



Magnesium carbonate 30-0 



Quartz and chert 14-7 



Orthoclase molecule 7-2 



Albite molecule 7-3 



Magnetite , .9 



Remainder .8 



100-0 



