398 THE CANADIAN NATURALIST. [Vol. viii. 



To recapitulate, a wide hollow deeply scored by rivers, probably 

 extended from the south of Vancouver Island to the Columbia, 

 in later Tertiary times. The northern part of this, now occupied 

 by Puget Sound, may or may not have been planed down by an 

 ice-sheet, but was deeply filled and levelled up with drift during 

 the glacial submergence and retreat of the great glaciers. Being 

 afterwards elevated to a height possibly 600 feet or more greater 

 than the present, streams again began to excavate their channels, 

 guided no doubt in the first instance by such ill-defined longitu- 

 dinal hollows as the sea currents, flowing north and south, had 

 before formed. This action continued long enough for the pro- 

 duction of deep and wide river valleys in the drift deposits, and 

 in Borne cases in the more prominent parts of the underlying 

 Tertiary rocks. Lastly, a resubsidence to the present stage hav- 

 ing occurred, the sea water filled the river valleys, of which the 

 gently-sloping sides soon became eroded at the water-line into 

 eea-cliffs, and tide flats were formed at the mouths of the streams 

 and wherever ditritus was abundant along the shores. 



