REPORT OF THE CHIEF ASTRONOMER 421 - 



SESSIONAL PAPER No. 25a 



The most heavily crumpled and metamorphosed sediments are those of the - 

 Attwood and Anarchist series, which appear to correspond directly with the- 

 Pend D'Oreille and Sutherland schist series of the Eossland mountains. Here 

 again the Paleozoics are so thoroughly mashed, kneaded, and welded that veryy 

 little can be said as to the detailed structure of these rocks all the way from" 

 Christina lake to Osoyoos lake. 



Most of the volcanic rocks occurring in the ' Boundary Creek district ' are 

 much less deformed than the Paleozoics, though generally showing high dips, 

 The relations are so like those of the Eossland volcanics that the writer is pro- 

 visionally assigning the Phoenix volcanic group also to the Mesozoic. The • 

 mashing of the Paleozoics is assigned to the late- Jurassic orogenic revolution;, 

 the sharp upturning of the Phoenix volcanics to the post-Laramie revolutions 



As already pointed out, the Midway volcanic formation and the associated-' 

 Kettle Eiver (Oligocene) sediments form a mass of rock which either fills a 

 broad syncline prepared on an earlier Tertiary surface, or else represents &> 

 down-faulted block of the Oligocene rocks which have thus subsided relatively 

 to the Paleozoic terranes of Attwood mountain and Anarchist-mountain plateau. 

 The former relation seems the more probable. Post-Oligocene, probably late 

 Miocene faulting and moderate uptilting have affected the Kettle Eiver and 

 Midway formations which, in contrast to the other two divisions of the rocks in 

 the western part of the Columbia mountain system, show low dips. 



At least two unconformities are registered in the relations shown in the 

 Boundary belt. The Kettle Eiver beds are in striking unconformity to the 

 underlying Paleozoics and the (probably Jurassic) plutonic bodies. The 

 relatively little sheared and altered basic volcanics of the ' Boundary Creek dis- 

 trict ' mapped as the Phoenix group, are believed to be unconformable upon the 

 crumpled Attwood series. A third unconformity may exist between the tilted 

 Oligocene Midway volcanics and the alkaline flows and breccias composed of 

 rhomb-porphyry, trachyte, and shackanite. 



The region where traversed by the Boundary belt, does not seem to show &> 

 single unbroken fold of any importance. The various strata are either mashed' 

 into an undecipherable complex or are faulted, with displacements which are 

 registered best in the bedded rocks of the Tertiary formations. The many west- 

 ward-facing and northwestward-facing scarps on the lava beds forming th®~ 

 ridges north of the Kettle river between Ingram creek and Eock creek, are im 

 part to be explained by a number of faults. These separate long narrow blocks 

 which appear to be successively downthrown on the northwest. (See Plate 73,.. 

 Figure B). The gravel and sand of the river bottom between the Kettle 

 river bridge and Eock creek covers the trace of a strong east-west fault separating: 

 the uptilted sandstones on the north from the more flat-lying basaltic lavas oe 

 the south of the river. Much of the dislocation so manifest to north and south 

 of Eock creek itself has been accomplished by sharp faulting which is thoughfe 

 to be contemporaneous with the intrusion of the Eock Creek chonolith. 



Though far less important here, batholithic intrusion has affected the 

 Paleozoic rocks in a way quite similar to that in which the oldest terrane of the 

 Eossland mountains has been affected. In the Boundary Creek district the- 



