[JOHNSTON-] PLEISTOCENE OSCILLATIONS 15 



of the Fraser valley. It is underlain in places by 50 to 100 feet of 

 stratified silts and clays (part of the Admiralty sediments) which, 

 because of their position near the coast and in the wide open part of 

 the valley, are probably marine, yet so far as is known they contain 

 no marine fossils. The shell beds are overlain in places by an observed 

 thickness of 15 to 20 feet of stratified silt and clay and, stratigraphic- 

 ally, by the post-glacial clays, 100 feet or more in thickness, which 

 are also probably marine, but contain ho marine fossils nor have 

 marine fossils been found in even the lowest of the raised beaches of 

 the district. The apparent absence of marine life in the waters 

 occupying the Fraser valley during the time of deposition of the 

 Admiralty clays and later during the deposition of the post-glacial 

 clays was probably due to the low salinity of the water occasioned 

 by the great inflow of fresh water from the melting ice-sheets. During 

 a part of late Pleistocene time, however, marine life was, as has been 

 show^n, abundant in the waters occupying the valley. 



The Oscillations of Sea-level 



The pre-glacial position of sea-level relatively to the land in the 

 \'ancouver region is not definitely known and is not easily determined 

 because it is difficult to estimate the amounts of glacial over-deepening 

 of the mountain valleys and fiords and to distinguish between valleys 

 formed by normal stream erosion and those of structural origin. 

 It is generally held that, during the Pliocene, the land in this general 

 region stood much higher relatively to sea-level than it does at present, 

 and the absence of marine Pliocene on this part of the coast bears 

 this out. A boring made at Steveston, near the mouth of Fraser 

 river, showed that the Pleistocene and Recent deposits have a thick- 

 ness of about 860 feet below sea-level. This part of the Fraser 

 valley is so wide that ice erosion could scarcely have had much efïect 

 in over-deepening the valley. It is possible, therefore, that, pre- 

 glacially, the land stood about 900 feet higher than it does at present — 

 as was held by G. M. Dawson.^ On the other hand it is possible that 

 the lower part of the Fraser valley is mainly structural in origin and 

 the relationships of the small valleys tributary to the main valley and 

 those tributary to Barrard Inlet suggest that the position of sea-level 

 was not greatly different from what it is at present, but it was prob- 

 ably somewhat lower. 



During the deposition of the Admiralty sediments the land was 

 probably lower relatively to sea-level than it is at present for, as 



1 Trans. Roy. Soc. Canada, 1890, Vol. VIII, Sect. IV, p. 17. 



