94 RECONNAISSANCE IN NORTHERN ALASKA IN 1901. 



RECENT Mil). MICK. GROUND ICE, DINK BAND, SILTS. AND GRAVELS. 

 [NLAND REGION. 



The deposits mentioned in this heading are all represented on the map by the 



same color. 



Along John River and the Kovukuk the color represents recent stream gravels, 

 together with alluvial sands, silt with ground ice, mud flats, and areas of till too 

 small to be represented on the scale of the accompanying map. 



Along Anaktuvuk River the color denotes recent stream gravels, while along 

 Colville River it includes, besides the recent stream gravels, a large, triangular area 

 of flats extending from the mouth of the Anaktuvuk to the coast and eastward along 

 the coast a distance of thirty or more miles to beyond Gwj^dyr Bay. This large area, 

 as noted, is regarded as ground abandoned by the Colville in its lateral migration 

 westward since Tertiary time, as the river is supposed to have formerly flowed more 

 directly northeastward from the mouth of the Anaktuvuk, and to have entered the 

 sea through Gwydvr Bay, following the course indicated by the broken lines on the 

 map. (PL III.) 



Though to the eye this area of flats seems a dead level the surface probably 

 rises very gentty from the Colville eastward. It is dotted by numerous ponds and 

 lakelets. The monotony of the waste is somewhat relieved by occasional low mounds, 

 as shown in PI. XVI, B. These are composed, in part at least, of gravel and sand. 

 Some of them rise as much as -±0 feet above the flats. In shape they are low and 

 rounded. Some have a tapering train on the lee side toward the coast. Their 

 surface is usually scantily clothed with grass and other vegetation. 



The origin of the mounds is not known. Only one of them was visited. Perhaps 

 the most plausible hypothesis is that they are remnants of beds belonging to the Ter- 

 tiary Colville series, which, chancing to be capped with some hard stratum, were not 

 worn down by the river to the level of the flats, and so formed nuclei favorable for 

 accumulation of gravel, and subsequently became bars, and, later still, islands in the 

 Colville, until the river abandoned its bed about their bases. 



Along the Colville the edge of the flats often terminates in gravel bars, descend- 

 ing to the water's edge, or in low, steep-faced banks of frozen black muck and ground 

 ice, showing that at least the surticial portion of the flats consists in the main of 

 recent stream deposits and the decayed products of marsh vegetation. The banks 

 decrease in height toward the coast, and finally vanish as the land surface passes into 

 the bars, reefs, and tidal mud flats at sea level. 



The geologic work now being done by the river in its lateral migration shows 

 that the processes by which the flats were formed were essentially those of planation. 

 In the inland region, as the shifting stream, in its very gradual down-cutting and 

 relatively very rapid lateral cutting, sawed its way westward into the coastal plain, it 



