14 Smithsonian Exploration in Alaska in 1904 



observed and the ability of the cliffs to maintain their vertical fronts 

 appeared to be due to the fact that their mass is solidly frozen. It 

 was noted that bluffs facing the south appear, under long exposure, 

 to thaw out sufficiently to allow their escarpments to crumble down 

 into gentle slopes. Shallow quicksand bars were encountered along 

 the thirty miles below the mouth of the Old Crow River. 



The Old Crow River flows from the northwest into the Porcupine 

 about sixty miles above New Rampart House. It enters the main 

 river with a bluff along its right bank that exposes hard dark shales 

 rising about twenty feet above the river for half a mile, overlaid 

 by one hundred and fifty feet of the unconsolidated Pleistocene 

 silts already described. Its left bank is bounded by a low wooded 

 flat extending east across the mouth of the valley to a range of 

 high hills about five miles distant. As we ascended this river the 

 following features were noted. After passing for ten miles through 

 a flood plain eroded across the above mentioned silts three distinct 

 terranes have been exposed by the down cutting of this stream. 

 As one ascends the river these are, first, a series of limestones, in- 

 tersected with calcite veins, extending for about eight miles ; then a 

 belt of granitoid rock that confines the river to a gorge estimated 

 to occupy about five miles of its course ; and third, an outcrop of 

 sandstones or quartzites three or four miles wide. This series of 

 hard rocks extend, apparently as an anticlinal uplift, across the 

 lower part of the Old Crow Valley to connect the mass of the Old 

 Crow Mountains, bounding the north side of the Porcupine Valley 

 to the west, with a low range of mountains that trend to the north- 

 east to bound the expanse of the Old Crow Basin on the east. 

 Before the river cut through this ridge of rocks it formed the lowest 

 part of the southeastern rim of a large Pleistocene lake that had 

 an approximate extent of one hundred miles north to south with a 

 width of sixty miles east to west. Today this former lake area lies 

 as a vast elevated undulating plain surrounded by mountain ranges 

 on all sides. Its frozen lacustrine silts have been dissected to the 

 depth of one to two hundred feet by the Old Crow River and its 

 tributaries, which meander through this extensive flat basin in the 

 most intricate manner, presenting many examples of former wan- 

 derings in the occurrence of crescent shaped lagoons or ox-bow lakes 

 at present flood-plain and higher levels. 



The lower banks support dense growths of willows and alders 

 while the higher levels are interspersed with shallow lakes, groves 

 of poplars, considerable patches of spruce, and a scattered growth 

 of birch. The two latter kinds of tree are confined mostly to the 

 higher, better drained areas. 



