DRAINAGE OF ARCTIC SLOPE PROVINCE. 47 



northern part of the Endicott Mountains, near the sixty-eighth parallel and the one 

 hundred and fifty-third meridian, whence it soon makes a large detour to the west 

 and back, and then, in flowing northward to the ocean, traverses both the Anaktuvuk 

 Plateau and the coastal plain. Practically all its tributaries of any importance are 

 received from the right, or southeast. The chief of these — the Ninuluk, Anaktuvuk, 

 and Itvelik — head in the mountains. 



In the inland part of the coastal plain, at the mouth of the Anaktuvuk, as shown 

 by continuous bluffs, the Colville has sunk its bed to a depth of 200 feet (see PL VIII), 

 and at Ocean Point, 40 miles farther north, where it permanently leaves the bluffs, to 

 a depth of SO feet below the surface of the plain. In this downcutting, from a point 

 above the mouth of the Anaktuvuk to the coast, the Colville has migrated laterally 

 westward, into the terranes composing the plain, to such an extent that, while its left 

 or western shore is for the most part lined by steep-faced bluffs, rising from 80 to 

 200 feet above the stream to the level of the plain, into which it is still cutting, on 

 the right or east it is bordered by an expansive waste of low abandoned flats, laid 

 waste by the river, for which the name Colville Flats is proposed. 



These flats occupy a triangular area of probably 2,000 square miles, extending 

 from the mouth of the Auaktuvuk as the apex northeastward to the coast, where, 

 including the Colville delta, they attain a maximum width of probably 50 or 60 

 miles. They are dotted by numei'ous shallow ponds and lakelets. The monotony of 

 their almost dead level is occasionally relieved by low mounds of gravel, rising 10 to 

 ■40 feet above the surface. In fact, from near the mouth of the Anaktuvuk the 

 Colville seems formerly to have flowed more directly northeastward through the 

 area now occupied by the flats and entered the ocean through Gwydyr Bay, from 30 

 to 40 miles east of its present delta, if not Prudhoe Bay, still farther eastward, at 

 the base of Return Reef, as shown b}^ the broken lines on the map forming PI. III. 



At the head of the Colville delta, where the edges of these flats form the stream 

 banks, their surface lies about 10 feet above the river. Here they are composed 

 chiefly of dark mud, muck, and ground ice, while at certain localities farther inland 

 the banks give way to stretches of gravel beach sloping gently to the water's 

 edge. 



The Colville delta at present has a radius of about 15 miles and a width across 

 the front of about 20 miles. It is composed of low islands, which coastward gradu- 

 ally pass into marshes, mud flats, bai's, and expansive shallows, which are continuous 

 with the very gradually deepening sea floor. Near the head of the delta sand dunes 

 have been formed on some of the islands to a height of 60 or more feet. As the 

 "Pelly Mountains" of Dease and Simpson, represented on their map to the west of 

 the Colville delta, do not exist, it seems probable that the features which these men 

 mistook for mountains were merely low sand dunes, similar to those above referred 



