82 G. M. DAWSON — ROCKY MOUNTAIN REGION IN CANADA 



found formino- a comparatively thin sheet that lies directly on the de- 

 nuded surface of the older rocks without the intervention of any of the 

 earlier members of the Tertiary. As these wide basaltic flows are in most 

 cases known to antedate the great period of river erosion assigned to the 

 Pliocene, they are supposed to be of later Miocene age. It is, of course, 

 possible that local eruptions of more recent date may have occurred, 

 but only one instance of a com})aratively recent or postglacial lava flow 

 has so far been found in the entire Cordilleran region of Canada. This 

 is in the valley of the Nasse river.* 



In the northern interior of British Columbia, lake deposits have been 

 found, in some places, blending above with volcanic materials and capped 

 by horizontal basalts, the whole being very probably referable to the 

 Miocene. In other places, both in British Columbia and in the Yukon 

 district, local flows of basalt are found which may belong either to the 

 Miocene or to the Pliocene. The same is true of isolated basalt patches 

 in the Kettle River countr}^ in the southen part of British Columbia 

 and in East Kootenay. On the Nechacco river and elsewhere, Tertiar}^ 

 shales or clays, with sandstones, of indeterminate horizon are also found. 

 It will be niany 3'ears before all these deposits can be investigated and 

 classified, and it may never be possible to assign an exact position to 

 some of them in the general series. The great y)aucit3% amounting almost 

 to a complete absence, of the remains of the higher vertebrates being 

 particular!}^ unfortunate in this respect. 



In the southern part of the Interior plateau of British Columbia, 

 small areas have been found of sediments that are su})posed to belong 

 to the early Pliocene,t but no fossils have been obtained from them. 

 On the Horsefl}^ river, however, overlying the Oligocene beds already 

 referred to in slight but distinct unconformity, and underlying the 

 boulder-clay, is a deposit of yellowish and in part " cemented " gravels, 

 to which a Pliocene age may be assigned with some confidence. J These 

 gravels are worked for gold, and branches and stems of trees found in 

 the workings have been determined by Professor D. P. Penhallow to 

 represent Sequoia gigantia, S. sempervirens, Juniperus calif ornica, Cupressus 

 macrocarpa^ Thuya gigantia^ and Picea sitcheiisis.% 



The presence of such an assemblage of trees in the inland region 

 north of latitude 52°, indicates the existence of physical and climatic 

 conditions very difl'erent from those now existing there and still more 

 unlike those of the intervening glacial period, while the species them- 

 selves are still living ones. 



♦Summary Report, Geol. Surv. Can., 1893, p. 14 A. 

 fAnnual Report, Geol. Surv. Can., vol. vii (N. S.), p. 74 B. 

 t Ibid., p. 26 A. 

 2 These determinations liave not previously been published. 



