12 Smithsonian Exploration in Alaska in 1904 



presented along which one is able to " track " with only occasional 

 interruptions at precipitous places, where it becomes necessary to 

 carry the tow-line along the top of a cliff or force the canoe against 

 the swift eddies invariably occurring at these places by vigorous 

 use of the oars accompanied by dexterous manipulations of the 

 " pike-pole." 



Above the Lower Ramparts the river swings in wide sweeping- 

 curves as it flows for about twenty-five miles through an alluvial 

 channel across a basin filled with Pleistocene silts, down into which 

 it has cut about one hundred feet. These silts appear to fill the 

 basin of a former fresh-water lake that was barricaded from the 

 extensive Yukon Flat Basin to the west by the low range of the 

 Lower Ramparts and bounded on the east by the higher plateau of 

 the Upper Ramparts. While this basin does not present a great 

 width where the Porcupine flows across it there is every indication 

 that it occupies considerable areas both north and south of the 

 Porcupine and that the considerable stream called the Coleen drains 

 the area occupied by the northward extension of these sediments. 

 For this reason it appears convenient to designate this area of 

 Pleistocene sedimentation between the Lower and L^pper Ramparts 

 as the Coleen Basin. The sediments are imconsolidated silts, sands, 

 and gravels and in one exposure thin seams of lignite were 

 observed. Older rocks similar to those of the Lower Ramparts with 

 some basalt occasionally outcrop along this reach. After making a 

 wide bend to the north through which the channel is divided by 

 alluvial islands with strong currents the valley contracts again to 

 abrupt bounding walls. The rocks here are a massive basalt that 

 forms the western limit of the Upper Ramparts. The walls are 

 higher and more abrupt than those of the Lower Ramparts. They 

 rise from three to five hundred feet above the river and extend to 

 a point about twenty miles above the international boundary or 

 approximately sixtv miles. As is to be expected the river follows a 

 more direct course across this area of hard rocks. It is through 

 this part the river contracts to its narrowest dimensions and reaches 

 its greatest velocities. The basalt extends upstream apparently as a 

 continuous sheet for about thirty miles. or nearly to the boundary 

 line between Alaska and Canada. This basalt sheet edged with 

 vertical cliffs is the conspicuous feature of the river for this distance. 

 The valley gorge is bounded by even, precipitous walls carved out 

 of this rock, which from their dark color lend a sombre appearance 

 to the landscape. The lower surface of the basalt undulates as the 

 older underlying rocks rise or descend along the bottom of the 



