18 THE ROYAL SOCIETY OF CANADA 



could only have been in part due to this cause. No evidence as to 

 what extent the apparent rise of sea-level was due to this cause was 

 found in the Vancouver region. Bretz^ has pointed out that the 

 existence in the Puget Sound region of outwash gravels near sea-level 

 and the occurrence of post-glacial marine shells at higher altitudes 

 shows that crustal movement was downward after the retreat of the 

 ice, and that this does not bear out the conception of isostatic adjust- 

 ment, consequent on déglaciation. It is possible, however, that the 

 marine shells are not post-glacial in age but belong to an earlier period 

 of marine submergence, indicated by the occurrences in the Fraser 

 valley, and that th£ third advance of the ice in the Vancouver region 

 did not reach the Puget Sound region. 



No evidence was found in the Vancouver or Fraser delta region to 

 support R. A. Daly's'* view that a general lowering of sea-level of about 

 20 feet occurred during post-glacial time, for there is no marked 

 raised beach or any large extent of delta deposits at about 20 feet 

 above sea-level. The lower beaches are somewhat stronger than the 

 higher beaches, indicating a slowing down in the rate of uplift, but 

 even the lowest raised beaches are not exceptionally strong and are 

 difficult to trace. They suggest almost continuous uplift but at 

 varying rates. The upper limit of marine submergence is not well 

 marked although the sea must have stood at a high level for a con- 

 siderable length of time, for the stratified clays occur in places in the 

 Fraser valley at various altitudes up to over 400 feet above the sea 

 and must have been in large part formed when the sea stood at a high 

 level. The absence of well-marked beaches at high levels is probably 

 due to the occupancy of parts of the region by the ice-sheet and to 

 the comparatively rapid uplift of the land, and the thickness of the 

 clays at high levels is probably due to the source of supply of the 

 materials — the melting ice-sheet — ^being near at hand and the supply 

 being most abundant at that time. 



Summary 



The evidence regarding Pleistocene and post-Pleistocene oscilla- 

 tions of sea-jevel in the Vancouver region, although incomplete and 

 unsatisfactory ii) some respects, strongly suggests that the oscillations 

 of sea-level were chiefly due to uplift and depression of the land and 

 that two main periods of depression and uplift occurred, corresponding 

 in time to two main advances and retreats of the ice-sheet. The 



3 Ibid., p. 236. 



4 Geo!. Mag., Vol. 57, p. 246, 1920. 



