REPORT OF TEE CEIEF ASTRONOMER 



53 



SESSIONAL PAPER No. 25a 



show a tendency to assume the rhombohedral form, the habit characteristic of 

 the grains in true dolomite?. 



In many of the laminae of the rock (0-2 mm. to 1 mm. in thickness) the 

 minute rhombohedra are embedded in a compound, colourless to pale-brownish 

 base. It is composed in part of very minute, anheclral grains of glass-clear 

 substance. These range in diameter from 0-01 mm. to 0-05 mm. A few of 

 them are undoubtedly quartz; the great majority have the single and double 

 refraction of orthoclase. In addition to the rhombohedra of carbonate, the base 

 is charged with abundant black, opaque dust. The particles of the dust average 

 under 0«0l mm. in diameter. Since the rock decolourizes before the blow-pipe 

 it seems clear that the dust is largely carbon, though hematite and probably 

 magnetite are also represented in some amount. 



Some laminae of the rock are seen to be specially charged with roundish 

 clumps and lenses of minute orthoclase crystals. (Figure 7.) These are inter- 

 locked and in all of three thin sections made from two different hand-speci- 

 mens, show no trace of a clastic origin. They give the writer the impression 

 of having been introduced and crystallized from solution, or at least segregated 

 in their present positions from the general mass of the rock." The few quartz 

 grains interlock with the orthoclase and are just as clearly not of clastic origin. 



Professor M. Dittrich analyzed a typical specimen of the rock, (No. 1338) 

 with the result shown in Col. 1 of the following table. The extraordinary 

 abundance of potash prompted a second determination of the alkalies in the 

 same rock-fragment; this time the potash showed 6-12 per cent and the soda, 

 0-25 per cent. A different fragment of the same large hand-specimen gave 

 ILr. M. F. Connor 5-54 (also 5-71) per cent of potash and 0-24 (also 0-l'3) per 

 cent of soda. The average of all four determinations is entered in Col. 2, the 

 other oxides being given in the amounts shown in Professor Dittrich's total 

 analysis. Col. 3 shows the molecular proportions corresponding to Col. 2. 



Analysis of the Waterton dolomite. 



Si0 2 



Al 2 6 3 



Fe 2 3 



FeO 



MgO 



CaO 



Na,0 



K 2 



H,0, at 110°C. .. 

 HjO, above 110 C C. 

 C0 2 



Sp.gr 



Insol. in hydTOcMoric acid.. . 

 Soluble in hydrochloric acid : 



Fe 2 3 



Al 2 O s 



CaO 



MgO 



1. 



2. 



3. 





Mol. 



30-46 



30-46 



508 



6-86 



6-86 



oe.s 



4-53 



4-53 



028 



1-89 



1-89 



026 



10-07 



10-07 



252 



16-02 



16-02 



286 



•87 



•38 



006 



5-71 



5-77 



062 



•11 



•11 





1-31 



1-31 





22-55 



22-55 



513 



100-38 



99-95 





2-749 







42-S0% 



4-91 



2-03 



16-23 



9-69 



