REPORT OF THE CHIEF ASTRONOMER 



75 



SESSIONAL PAPER No. 25a 



volume. The rhombohedral and subrhombohedral crystals average about 0-01 

 mm. in diameter. They are embedded in a base which is partly composed of 

 numerous anhedral granules of the same carbonate but of much smaller size, 

 with diameters varying from 0-001 mm. or less to 0-005 mm. A few minute 

 angular grains of quartz and feldspar and a few dust-like particles of carbon 

 and pyrite are associated with the carbonate. The remainder of the base is a 

 colourless, amorphous to subcrystalline cement whose diagnosis is extremely diffi- 

 cult. Its single refraction is low and its double refraction either nil or extremely 

 faint. These properties are like those noted for the silicious base of the Altyn 

 dolomite. The chemical analysis shows a content of silica and alumina con- 

 siderably in excess of the amounts required for the little clastic quartz and 

 feldspar in the rock. It thus appears that the cement carries both silica and 

 alumina, and it must carry the combined water. True argillaceous matter 

 may be present, as well as amorphous and chalcedonic silica. In none of the 

 thin sections could sericite be detected. 



The specific gravity of six type specimens varies from 2-657 to 2-760, with 

 an average of 2-702. These low values indicate the impurity of the carbonate. 

 The lightening of the rock must, in largest amount, be attributed to the cement 

 of the magnesian part. 



Owing to the extensive and highly irregular rearrangement of the car- 

 bonates in the molar-tooth rock it is not easy to secure a specimen which shall 

 faithfully represent its average composition. A specimen approximating to 

 this ideal was taken from the cliffs of Sawtooth ridge, 1-5 miles east of Lower 

 Kintla lake. Material from this specimen was so selected as to contain 

 magnesian base and calcitic segregation in about their average proportions in 

 nature, and the powdered mixture (specimen No. 1306) was analyzed by Pro- 

 fessor Dittrich. The result is as follows: 



Analysis of Siyeh impure limestone. 



SiO, 



A1 2 3 



Fe 2 O a 



FeO 



MgO 



CaO 



Na„0 



K 2 



H„0 at 110°C. .. 

 H„0 above 110°C. 



C." 



CO. 



Sp. gr 



Portion insoluble in hydrochloric acid. 

 Portion soluble in hydrochloric acid : 



Fe„0, 



Alo'O, 



OaO. 



MgO 



35-58 



340 



1-56 



•87 



10-09 



19-72 



•51 



1-21 



•17 



2-93 



•03 



23-80 



99-87 

 2-741 



Mol. 

 593 

 033 

 010 

 012 

 252 

 352 

 008 

 013 



163 



54 i 



40-69 c 



2-17 



1-87 



19-76 



8-95 



