REPORT OF THE CHIEF ASTRONOMER 391 



SESSIONAL PAPER No. 25a 



it is a white marble. From its instant and violent effervescence with acid the 

 rock must be considered as low in magnesia. At a couple of localities it is 

 tinted a dark gray, as if by included carbonaceous matter. In one thin section 

 the polygonal structure of a coral-fragment was found, but, in spite of long 

 search, no useful fossil was detected at any point. The lack of organic remains 

 is amply accounted for by the wholesale recrystallization of the limestone, which 

 has generally lost all trace of bedding. 



West of the Kettle river none of the limestone pods is known to be over 

 200 feet in thickness. On Deer Hill, three miles west of Midway, a more con- 

 siderable marble-like mass occurs, but it is cut off on all sides by igneous 

 rocks. Still larger bodies of what is probably the same limestone have been 

 mapped by Mr. Brock in the belt between Grand Forks and Midway. 



The greenstone occurs in broken, massive to schistose bands throughout 

 the whole length of the Boundary belt from the Kettle river to the Osoyoos 

 batholith. Their structural relations are even more elusive than those of the 

 limestones. It is probable that both injected and effusive basic rocks are 

 represented but the latter are believed to be the more important in volume. 

 They form beds in phyllites and quartzites. Like the limestones the lavas can 

 seldom be traced far along the strike; they have evidently undergone the pro- 

 found faulting, stretching, and mashing which has affected the other members 

 of the series. The accompanying alteration has been so great that original 

 tuffaceous or vesicular phases have been almost entirely obliterated. 

 So far it has proved impossible to locate the top or bottom of any of the lava 

 flows, to correlate the different bands or to find the aggregate thickness of the 

 lavas. It appears certain only that the aggregate thickness represents many 

 hundreds of feet and possibly several thousand feet. 



The greenstones ■ are notably uniform in their present composition and 

 were probably as nearly uniform originally. The lavas must have been basic, 

 either basalt or basic andesite. Fourteen thin sections have been examined 

 under the microscope. In no case was original material present in any large 

 Quantity. Both massive and schistose phases are composed in ever-varying 

 proportions of secondary, actinolitic amphibole; quartz; plagioclase of medium 

 basicity; epidote; calcite; chlorite; and magnetite. The rock- types thus include 

 massive greenstone, chloritic schist, epidotic schist, hornblende schist, and true 

 amphibolite. The constant recurrence of these banal characters and varieties 

 seems to show pretty clearly the common origin of the greenstone members 

 throughout the Midway mountains and Interior Plateaus as sampled along the 

 Boundary line — a. derivation from the same basic magmatic types whence have 

 come so largely the greenstones of the world. 



Nature of the Metamorphism. — A prominent feature oi all the members of 

 the Anarchist series is their notable metamorphism. The cause of such recrys- 

 tallization is by most geologists found in ' dynamic metamorphism.' Of late 

 years Termier and others have raised the question whether this principle has 

 had an essential part in the production of the crystalline schists. In fact, 



