132 DEPAMM&NT OF TEE INTERIOR 



2 GEORGE V., A. 1912 



"brought about merely as a consequence of deep burial and without the help 

 of tangential pressure or ordinary dynamic metamorphism. All transitions 

 exist in the ledge or even in a single hand-specimen between the metargillite 

 and the feldspathic quartzite. For this reason alone it would be difficult to 

 form an accurate conception of the average composition of this western phase 

 of the Kitchener. It is certainly less silicious and more micaceous than the Cres- 

 ton. Possibly one-third of the thickness is made up of silicious metargillite ; the 

 remainder, of the quartzite with its own subordinate admixture of once- 

 argillaceous and feldspathic material with the essential quartz. 



The average specific gravity of three type specimens of the quartzite is 

 2-705; that of three type specimens of the silicious metargillite is 2-738. The 

 average for the whole western phase, estimated on the above-mentioned quan- 

 titative ratio of the two types in the formation, is about 2-716. 



Variations on this relatively simple scheme of composition are extremely 

 rare throughout the thousands of feet of beds composing the western phase. 

 In a very few thin strata the quartzite is spangled with large plates of biotite, 

 each about 1 cm. in diameter. As in similar beds of the Creston these foils 

 run at all angles through the rock; they appear to be simply greatly enlarged 

 equivalents of the staple biotite individuals of the normal rock. 



At a few other horizons, especially toward the top of the formation, the quart- 

 zite contains conspicuous round, blackish concretions somewhat flattened in 

 the planes of bedding. They measure from two to three inches or more in 

 greatest diameter. With the microscope the concretions are seen to be com- 

 posed of quartz and feldspar grains cemented by abundant biotite and limonite 

 with a small amount of sericitic mica. The feldspars are usually glassy and 

 belong to the usual species, orthoclase, microperthite, and a well-twinned 

 plagioclase, probably andesine. These minerals and the quartz occur in grains 

 from 0-04 mm. to 0-,3 mm. in diameter and thus of the average size character- 

 istic of the interlocked essential minerals of the enclosing quartzite. The most 

 noteworthy feature is the plainly clastic form of all these grains of quartz and 

 feldspar. Most of them are angular but the largest quartzes are often dis- 

 tinctly rounded. There is no sign of secondary enlargement. We appear to 

 have, then, in the heart of these concretions the only surviving relics of the 

 original clastic form. The destruction of the clastic outlines through static 

 metamorphism has been arrested through the secretion of the mica and iron 

 ore in which the quartz and feldspars now lie. These clastic grains are 

 separated from the metamorphosed substance of the enclosing sandstone, and, 

 a* 1 , a rule, are separated from each other. 



Eastern Phase. — In the heart of the Yahk range, for a distance of twelve 

 miles, measured along the Boundary line, the Kitchener formation appears to 

 have been completely eroded away, the mountains there being composed of the 

 underlying Creston and of heavy masses of intrusive gabbro. To the westward 

 of this area the Kitchener steadily preserves the lithological habit which has 

 just been described. The first outcrops of the Kitchener on the eastern side of 



