[JOHNSTON] PLEISTOCENE OSCILLATIONS 17 



have a maximum tliickness of at least 300 feet below sea-le\xl. The 

 valley appears to have been formed by stream erosion rather than by 

 ice because of its narrowness. It is, therefore, probable that the land 

 stood considerably higher than now, during this period of retreat of 

 the ice-sheet. 



The second advance of the ice-sheet was followed by a period of 

 partial retreat of the ice, during which period, for a time at least, 

 the sea stood 50 to 100 feet higher than it does at present, as is shown 

 by the occurrences of marine fossils already described. A third 

 advance of the ice-sheet took place but probably did not extend much 

 beyond the Fraser valley. Depression of the lan<;J relatively to sea- 

 level followed the third advance of the ice, but was at first of small 

 amount, as is shown by the occurrence near New Westminster of the 

 glacial outwash fan 50 to 100 feet above sea-level. At the time of 

 final retreat of the ice-sheet the depression of the land was much 

 greater. 



The post-glacial marine submergence in the Vancouver region is 

 well established. It is held by Burwash' that the sea stood at least 

 760 feet and perhaps 800 feet higher than now. There is no doubt 

 that it stood at least 650 feet higher, for well-terraced delta deposits 

 occur at the mouths of the valleys tributary to Burrard Inlet on the 

 north sidC' at \'arious elevations up to this height and it is possible, 

 as stated by Burwash, that it was much higher. The beaches and 

 terraces formed during the period of post-glacial uplift are in places 

 numerous and fairly well-developed but individual terraces or beaches 

 cannot be traced for any great distance and the upper limit of marine 

 submergence is not definitely marked. Hence it is difficult to deter- 

 mine in this region the character of the uplift, whether differential or 

 not. The fact, however, that in the vicinity of Victoria, on Vancouver 

 Island, the upper limit of marine submergence is only about 250 feet- 

 and near Nanaimo only about 400 feet shows that the amount of 

 uplift increases in the direction of retreat of the ice-sheet or towards 

 the centre of ice accumulation. The great number and comparatively 

 weak character of the raised beaches show that uplift was somewhat 

 rapid and nearly continuous. It was probably, therefore, associated 

 with déglaciation and is isostatic in character. The post-glacial 

 oscillation of sea-level must have been in part the result of the general 

 rise of sea-level due to the return to the sea of the water bound up in 

 the ice-sheets, but the magnitude of the oscillation shows that it 



1 Ibid., p. 93. 



- Charles H. Clapp., Geo). Surv. Canada, Guide Book No. 8. Part 3, p. 2S6, 1913. 



