REPORT OF THE CHIEF ASTRONOMER 153 



SESSIONAL PAPER No. 25a 



veloped during the recrystallization of the rock. As in so many other phases of 

 the geosynclinal sediments, the abundance of this feldspar, which is so rare in 

 normal sandstone, is an interesting problem. 



That much of the microperthite is of metamorphic origin is suggested, 

 not only by the microscopic relations, but also by the fact that this feldspar 

 has been formed in special abundance and in clearly non-clastic forms within 

 the metamorphic collars developed in the Wolf and Monk sediments where 

 they are cut by intrusive granite. Nevertheless some of the microperthite has 

 the outlines and relations of clastic grains similar to those found so abundantly 

 in the sandy dolomites of the Lewis series, where there is little chance that 

 the feldspar is of metamorphic origin. 



The specific gravity of the conglomerate-grit phases varies from 2.- 630 

 to 2-683; that of the more micaceous, sandy, and argillaceous phases, from 

 2-729 to 2-895. The average of twenty specimens selected to represent the 

 whole formation, is 2-720. 



Dewdney Formation. 



By insensible gradations the Wolf formation passes into the conformably 

 overlying Dewdney formation. The plane separating them is thus an arbitrary 

 one. In its typical development, however, the younger formation, while chemi- 

 cally very similar to the older, is finer-grained and thinner-bedded — a banded 

 quartzite. Excellent exposures through its whole thickness appear on both 

 sides of the Dewdney trail, from which the formation has been named. Other 

 complete sections were measured on traverses southeast and south of Mt. 

 Ripple. The thickness seems to be tolerably constant throughout the Boundary 

 belt. At the trail the following section was roughly measured: — 



Columnar section of Dewdney formation. 



Top, conformable base of Eipple formation. 



375 feet.— Medium to thick-bedded banded quartzite. 

 30 " Coarse conglomerate. 

 120 " Banded quartzite. 

 225 " Coarse conglomerate. 

 1,250 " Thick-bedded, banded quartzite. 



2,000 " Base, conformable top of Wolf formation. 



The formation consists, in the main, of light gray and greenish-gray 

 quartzite, well and rather uniformly banded. Interbedded with the quartzite 

 are subordinate dark greenish-gray strata which were originally argillaceous, 

 but are now felted aggregates of quartz, feldspar, biotite, sericite, and iron 

 oxide. These rocks generally weather gray and only rarely brown. Thick 

 bedding is the rule, each of the massive plates averaging three feet more or 

 less in thickness. They are composed either of single strata of quartzite, or 

 of well-knit composite masses of highly indurated sandstone and silicious 

 metargillite in alternating layers. 



