Washington — Igneous Rocks from Eastern Siberia. 181 



remarkably close to the paisanite of Magnolia, Mass., but, as 

 the dark mineral here is riebeckite and not acmite, the Siberian 

 rock cannot be called by this name, — an instance of the undue 

 importance attaching to comparatively trivial characters in the 

 present system of classification. 



It also resembles the comendite of Sardinia, differing from 

 this notably only in the absolute and relative amounts of the 

 iron oxides. In all three, it will be noted, the ratios (molec- 

 ular) of the two alkalies are very close to unity. From the 

 most siliceous of Brogger's grorudites (IV) it differs not only 

 in this respect, for in the Norwegian rock the soda greatly 

 preponderates over the potash, but also in the much higher 

 ferric oxide and lower alumina of the latter. 



It is true that comendite is placed by Rosenbusch among the 

 effusive rocks,* as the equivalent of the hypabyssal paisanites, 

 and that we have here no exact knowledge of the geological 

 occurrence of the rock in question. Leaving this point aside, it 

 would seem proper to call our rock a comendite, since the 

 development of aegirite rather that paisanite is characteristic 

 of this, and also because the Siberian specimen resembles a 

 specimen of the Sardinian comendite kindly sent me by Signor 

 Bertolio. 



The mineral compositions of the Siberian and Sardinian 

 comendites are given in la and Ilia below, and are seen to 

 differ only in the relatively greater amount of aegirite as com- 

 pared with augite in the latter. The two are not calculated 

 to 100 per cent, and the difference from the totals of the 

 analyses are accounted for by the H 2 0, etc., of these. 



- la. Ilia. 



Quartz.... _ 31-9 Quartz 3T6 



Orthoclase 30*0 Orthoclase 28*9 



Albite_._ .- 33-0 Albite _ 32-0 



Acmite 0*9 Acmite 4*2 



Augite 2*1 Hyperstene 0*5 



Magnetite 0'9 Magnetite and ) _ 



hematite J 



Recently aegirite-granites from Miask have been described 

 by Pirssonf and Johnsen,^: and, as it was thought that a chem- 

 ical comparison of these with the comendite of Iskagan Bay 

 might be of interest, an analysis was made of the Miask gran- 

 ite. The material for this was very generously given me by 

 Prof. Pirsson, from the specimen already described by him, 

 and I take this opportunity to tender my hearty thanks for his 



* Rosenbusch, Elemente. p. 268, 1901. 



f L. Y. Pirsson, this Journal, vol. ix, p. 199, 1901. 



\ A. Johnsen, Neues Jahrb., '1901, IT, p. 117. 



Am. Jour. Sci.— Fourth Series, Yol. XIII, No. 75.— Makch, 1902. 

 13 



