66 



a series of isolated and somewhat widely separated erosion 

 remnants (see map of Boundary district), the individual 

 units being two small to permit of their delineation on 

 the route map. The rocks composing the formation 

 consists of conglomerates, sandstones and shales with 

 some intercalated tuffs which were laid down in lake 

 and river basins bottomed in most cases by rocks of 

 Palaeozoic age. Some of the shales are carbonaceous 

 and contain plant remains and in a few instances thin 

 seams of lignite. 



OLIGOCENE AND MIOCENE. 



Midway Volcanic group [3] — The Midway Volcanic 

 group consists of a series of lava flows of two distinct 

 volcanic epochs in the Boundary district. The lavas 

 naturally arrange themselves in three groups, the oldest 

 consisting of olivine basalt and augite andesite, the middle 

 group composed of a variety of andesites, and the youngest 

 represented by alkaline trachyte. The oldest and middle 

 groups are referred by Daly to the Oligocene, and the 

 youngest possibly to the Miocene or at any rate after the 

 Kettle River sediments have suffered deformation and ero- 

 sion. 



The lava groups have corresponding intrusive equi- 

 valents ranging from augite gabbro to pulaskite porphyry 

 which cut them as dykes, sills and stocks. These volcanics 

 occur in small isolated areas in the eastern part of the 

 Boundary district west of Christina lake. In the vicinity 

 of Midway however, the lavas are extensively developed 

 both to the north and west. 



Subsequent warping accompanied by faulting has 

 afTected both the Midway Volcanic group and the Kettle 

 River formation. 



QUATERNARY. 



The Cordilleran ice sheet covered the whole of southern 

 British Columbia with the exception of some of the higher 

 peaks. In this area the general trend of ice movement 

 was S. 30° E. The ridges were smoothed into rounded 

 and flowing forms, the main valleys were deepened with 

 consequent truncation of spurs and the development of 

 hanging valleys. With the breaking up of the ice sheet 



