241 



Like the Coldwater group, the rocks of the Spence's 

 Bridge Volcanic group have been much broken and 

 metamorphosed prior to the outpouring of the Mid-Ter- 

 tiary lavas. 



In the vicinity of Ashcroft, carbonaceous shales, sand- 

 stones, and conglomerates occupy a local synclinorium 

 striking nearly north and south. The western portion of 

 the inlier is more steeply inclined and folded than the 

 eastern, where the rocks appear to overlap flatly the Jura- 

 Trias formation. This formation has been referred on 

 lithological grounds to the Lower Cretaceous, and correlated 

 with the Queen Charlotte Islands formation on the Pacific 

 Coast. 



Another inlier of Lower Cretaceous rocks occurs near the 

 mouth of Botanie creek about two miles (3-2 km.) above 

 Lytton. There, however, the dark shales, grey sandstones 

 and conglomerates are much disturbed and slickensided. 



The (probably Eocene) Coldwater group consists of con- 

 tinental sediments which include coarse fluviatile conglomer- 

 ates, sandstones, and shale, with occasional coal. The 

 deposits occupy erosion troughs cut into an older Cre- 

 taceous erosion surface. They have been locally upturned 

 and eroded before the eruption of the younger Tertiary 

 volcanics. 



The Kamloops Volcanic group consists of basalts (both 

 amygdaloidal and vesicular types), agglomerates and 

 breccias, with smaller quantities of younger mica trachytes 

 and various porphyrites. In the railway section the forma- 

 tion has an average thickness of about 2,500 feet (760 m.). 



These lavas have a wide distribution through the Belt 

 of Interior Plateaus, and as a rule lie almost horizontal. 

 In places, however, they have been broadly folded into 

 synclinal basins and anticlinal domes. The latter have 

 been eroded away leaving the synclines at present exposed 

 chiefly on the hill tops. Quite locally, but not within 

 the limits of this section, these lavas have been tilted to 

 vertical or nearly vertical positions. 



Near the base of the Kamloops volcanics, a considerable 

 thickness of evenly bedded tuffs occur — the Tranquille beds 

 of G. M. Dawson. They are, as a rule, pale in colour and 

 contain plant remains, thin coal seams, and occasionally 

 fossil fish of lower Miocene or Oligocene age. 



Deposits of Pleistocene age are very plentiful, and consist 

 of Glacial till, gravels, sands, clays and silts. 



