G. M. Dawson — Geology of Bviiish Columbia. 159 



of volcanic rocks. The beds belong evidently to the more recent 

 Tertiary, and though the palaeontological evidence is scanty, it 

 appears probable from this, and by comparison with other parts of 

 the west coast, that they should be called Miocene. 



To the east of the Coast or Cascade Eange, Tertiary rocks are 

 very extensively developed. They have not, however, yielded any 

 marine fossils, and appear to have been formed in an extensive 

 lake, or series of lakes, which may at one time have submerged 

 nearly the entire area of the region described as the interior 

 plateau. The Tertiary lake or lakes may not improbably have been 

 produced by the interruption of the drainage of the region by a 

 renewed elevation of the coast mountains proceeding in advance 

 of the power of the rivers of the period to lower their beds ; the 

 movement culminating in a profound disturbance leading to very 

 extensive volcanic action. The lower beds are sandstones, clays, 

 and shales, generally pale-greyish or yellowish in colour, except 

 where darkened by carbonaceous matter. They frequently hold 

 lignite, coal, and in some even true bituminous coal occurs. These 

 sedimentary beds rest generally on a very irregular surface, and 

 consequently vary much in thickness and character in different 

 parts of the extensive region over which they occur. The lignites 

 appear in some places to rest on true " underclays," representing 

 the soil on which the vegetation producing them has grown, while 

 in others — as at Quesnel — they seem to be composed of drift-wood, 

 and show much clay and sand interlaminated with the coaly matter. 



In the northern portion of the interior the upper volcanic part 

 of the Tertiary covers great areas, and is usually in beds nearly 

 horizontal, or at least not extensively or sharply folded. Basalts, 

 dolerites, and allied rocks of modern aspects occur in sheets, broken 

 only here and there by valleys of denudation ; and acidic rocks are 

 seldom met with except in the immediate vicinity of the ancient 

 volcanic vents. On the Lower Nechacco, and on the Parsnip River, 

 the lower sedimentary rocks appear to be somewhat extensively 

 developed without the overlying volcanic materials. 



The southern part of the interior plateau is more irregular and 

 mountainous. The Tertiary rocks here cover less extensive areas, 

 and are much more disturbed, and sometimes over wide districts — • 

 as on the Nicola — are found dipping at an average angle of about 

 thirty degrees. The volcanic materials are occasionally of great 

 thickness, and the little disturbed basalts of the north are, for the 

 most part, replaced by agglomerates and tufas, with trachytes, 

 porphyrites, and other felspathic rocks. It may indeed be questioned 

 whether the character of these rocks does not indicate that they 

 are of earlier date than those to the north, but, as no direct 

 palasontological evidence of this has been obtained, it is presumed 

 that their different composition and appearance is due to unlike 

 conditions of deposition and greater subsequent disturbance. 



No volcanic rocks or lava flows of Post-glacial age have been met 

 with, though I believe that still farther to the north-west the rocks 

 are of yet more recent origin than any of these here described, and 



