80 G. M. DAWSON ROCKY MOUNTAIN REGION IN CANADA 



The Tertiary sediments of the interior are chiefly those of lake basins, large 

 or small, but the great mass of the Tertiar}^ rocks is composed of volcanic 

 materials, a circumstance accounting for the general paucity of organic 

 remains, which, together with the isolated positions of the known fossil- 

 iferous localities, renders it very difficult to build up a satisfactory^ and 

 connected section of the Tertiary formations/'^ 



Some progress has, however, been made in tliis respect, particularly 

 in the southern part of the Interior plateau of British Columbia, where 

 the following scheme, which may be taken as a term of reference for the 

 whole inland region, has been arrived at.f. The order is descending : 



Feet 



Later Miocene. Upper Volcanic group (maximum thickness). • 3,100 



Tranquille beds (maximum thickness) 1,000 



Earlier Miocene. Lower Volcanic group (maximum thickness apart from 



centers of eruption) 5,300 



Oligocene. Cold water group (at Hat creek) 5,000 



14,400 



Beginning with the oldest member of the above section, it may be ex- 

 plained that more or less isolated series of beds in different parts of the 

 Interior plateau region have lately been classed together provisionally 

 as the Coldwater group. These resemble each other lithologicall}'', and 

 all appear to antedate the beginning of Tertiary volcanic action in this 

 })art of the region. One of their developments, from which the greatest 

 number of fossils has been derived, has frequently been referred to in 

 earlier publications as the " Similkameen beds," but the name Coldwater 

 group is preferred as a general one, including these as a local develop- 

 ment. From the Similkameen beds, plants, insects, and a few fish re- 

 mains have been obtained. These have been described by Sir J. Wm. 

 Dawson, Dr S. H. Scudder, and Professor E. D. Cope, who agree in 

 referring them with probability to the Oligocene. The fish is an Amyzon, 

 like that from the Amyzon beds of Oregon. j; Much farther north, on 

 the Horsefly river, a tributary of the Quesnel, well i)reserved remains 

 of another fish of the same genus have been found, and again in asso- 

 ciation with similar plant remains. Elsewhere plants only, or a few 

 insects, have been discovered. 



The deposits of the Coldwater group consist of conglomerates, shales, 

 and sandstones which not infrequently hold beds of lignite or, as at the 



* For earlier references to the Tertiary deposits of the region, see Geol. Mag., Decade II, vol. 

 viii, foot-notes to pp. 158, 162. 



t Annual Report, Geol. Surv. Can., vol. vii (N. S.), p. 7(3 B. Detailed descriptions of the several 

 groups in the southern part of British Columbia are also given in this report. 



JTertiaryplants of the Similkameen river; Trans. Royal Soc. Can., vol. viii, sec. iv (1890), p. 75. 

 Contributions to Can. Pal., vol. ii, part i. Proc. Acad. Nat. Sei. Phil., vol. xlv (1893), p. 401. 



