120 GEORGE MERCER DAWSON. ON THE 



The stoppage of all the gaps to so great a height, however, in the 

 various ranges would imply a coordination scarcely within the 

 bounds of probability ; and on grounds which are stated in the pre- 

 ceding pages, and others which will shortly be referred to, it appears 

 to me more probable that it was by depression of the land as a 

 whole, or elevation of the ocean, that the waters attained the level 

 they are known to have reached in the interior. 



To explain the facts by the action of floating ice, icebergs or 

 pack-ice must be supposed to have entered the central plateau by 

 the low gap through the Eocky Mountains in the Peace-River region, 

 and, reinforced, no doubt, by ice from local glaciers, to have travelled 

 southward under the influence of currents, which found exit by the 

 Eraser river-valley and other southern openings. A depression of 

 3000 feet would open a wide strait from the Arctic Ocean to the 

 Pacific, by the valleys of the Peace-River country, continued south- 

 ward by that of the Fraser ; while sea-water standing at a height 

 equal to the maximum above stated would give depth enough for 

 very heavy ice, and would besides open other avenues in the Rocky 

 Mountains, and many and wide ones through the Coast range and 

 to the south. If such palaeocrystic ice as that met with by the late 

 Arctic Expedition may be supposed to have filled the central basin, 

 it will not be necessary to invoke the action of icebergs to account 

 for the simultaneous, or nearly simultaneous, production of the north- 

 and-south grooving, and deposition of the Boulder-clay. It is 

 worthy of mention that in most places where striation referable to 

 this system occurs, the country to the north is low, suggesting that 

 the localities may have formed islands on the southern margin of a 

 sea in which great ice-pressure may have occurred from time to time. 

 On the supposition of a submergence of three thousand feet or 

 more, very important results might follow with regard to the distri- 

 bution of ocean-currents. The Kamtschatka branch of the warm 

 Japan current would, no doubt, be greatly augmented in size, and 

 flow north-eastward through a widened Behring's Strait, possibly 

 accounting for the apparent absence of glacial traces in Alaska. The 

 outflow of ice-laden polar water would be to the same amount in- 

 creased, causing a wide arctic current to flow southward in the 

 region now forming the Mackenzie river-valley. A part of this 

 would find exit across the great plains and by the Red-River hollow, 

 while a second branch, traversing the Rocky Mountains by the Peace- 

 River gap, would flow down the length of the plateau of British 

 Columbia, accounting for the great transport of material and heavy 

 glaciation found to have occurred in both these regions. 



On any of the above theories the second advance of glaciers from 

 the various mountain-ranges must be supposed to be the last phase 

 of which we have any record. These glaciers appear to have pushed 

 out among the water-rounded materials of some of the lower terraces, 

 after a period of somewhat greater warmth, and before the reeleva- 

 tion was complete, or while a lake, or series of lakes, dammed by 

 glaciers existed. The latter is not an unreasonable supposition when 

 the comparatively small height of water required at this period is 



