56 THE ROYAL SOCIETY OF CANADA 



It is improbable that this material could have been carried 

 eastward across the lately uplifted Rocky mountains, and there are 

 no notable deposits of Eocene age remaining today towards the north, 

 that could represent such material. There is, however, a considerable 

 area of Eocene lying to the west and south of the Fraser canon the 

 constituents of which might have been derived from the Interior 

 Plateau and Coast ranges. The Eocene formation of Fraser delta 

 and Puget sound covers an area of over 20,000 square miles and 

 contains deposits the thickness of which is stated to range from 3,000 

 feet at the Fraser river to 10,000 feet about Puget sound and 20,000 

 feet farther south. ^ The rocks in it consist of sandstone, shales and 

 conglomerates, the materials of which could readily have been derived 

 from the igneous and sedimentary rocks lying to the north and east. 

 In Fraser delta, Leroy states that the formation indicates estuarine 

 conditions of deposition, or in other words deposition in an arm of the 

 sea running some distance inland to the east. The present shape of 

 the formation as mapped is roughly deltoid, with its apex near the 

 lower end of Fraser canon, giving a suggestion that it was down that 

 course that the material was carried which was deposited in the Eocene 

 estuary. Slight though it is, the presence of this Eocene area, its 

 shape and composition is the first evidence we have of a stream acting 

 along the present course of the Fraser canon. 



The Eocene beds of the delta have been only slightly disturbed 

 and are still almost horizontal. Their relation to the underlying 

 and adjacent rocks of the Coast range on their northern border suggests 

 that the country bordering the estuary in which these Eocene beds 

 were laid down was at that time one of considerable relief. On the 

 other hand, however, it is believed the Interior Plateau region was, 

 in the same period, reduced to a region of comparatively mature 

 relief. In the Eocene period, therefore, the same contrast in topo- 

 graphic conditions existed as exists at the present time. In other 

 words if, as we have suggested, the Fraser river was in operation in 

 Eocene times its course from the interior to its mouth would have been 

 from a region of low relief through a bordering hilly country of relat- 

 ively greater relief down to the sea. While this line of drainage might 

 have been developed as a result of the Laramide revolution, during 

 Eocene times it would have passed through all the stages of youth and 

 at the close of that period reached a condition of maturity. 



The geological record of the southwestern part of British Colum- 

 bia shows that there were no great disturbing influences by which 



^ Leroy, O. E., Report on a Portion of the Main Coast of British Columbia 

 and Adjacent Islands, Geol. Surv. Can., No. 996. 



