236 p. C. SCHRADBR GEOLOGICAL SECTION IN NORTHERN ALASKA 



Where best observed during the past season, principally on the John 

 and Anaktoovuk rivers, a view across the top of the range presents the 

 general appearance of a deeply dissected plateau or baselevel plain, 

 which has probably been uplifted from near sealevel, and whose former 

 surface is denoted by the expanse of closely crowded peaks, which in 

 general rise to an elevation of 6,000 feet, forming an even sky line, as 

 shown in plate 42. The floors of the mountain valleys lie, at about 2,000 

 feet, and the open pass near the northern edge of the range between the 

 John and the Anaktoovuk rivers lies at an elevation of scarcely 2,500 

 feet. For this dissected plateau feature at the top of the range the name 

 Endicott plateau is proposed. 



It seems not improbable that, as our knowledge of the physical geog- 

 raphy of Alaska becomes more complete, it may be found that the 

 Endicott plateau, having probably a considerable extension to the east- 

 ward, may be correlated with similar features, namely, the Chugatch 

 plateau, representing the westward continuation of the Saint Elias range 

 in southern Alaska, whose dissected surface also lies at an elevation of 

 about 6,000 feet.* 



The drainage of this portion of the range is principally southward 

 into the Koyukuk. The master stream is the John river, rising near 

 the northern edge of the range. The main drainage ways are therefore 

 of a transverse character, extending across tlie strike and trend of the 

 rocks as well as across the trend of the range, while the tributaries of 

 these larger streams, being nearly always controlled by structure, flow 

 in general along the strike to enter the master streams, producing a 

 rectangular system of drainage. John River valley may be characterized 

 in general as open, though certain sections are canyonous, because of the 

 character and structure of the rocks. Benching or remnants of old val- 

 ley floors occur at heights respectively of 1,700, 600, and 100 feet above 

 the present stream, and seem to mark stages of comparative rest in the 

 progress of orographic uplift of the land mass from a former lower level. 

 Northward sloping benches at the head of John river denote that a large 

 area of the drainage at the head of this stream, now flowing southward 

 into the Koyukuk, formerly drained northward and entered the Arctic 

 ocean through the Anaktoovuk and the Colville instead of Bering sea 

 through the Koyukuk and the Yukon, as at present. 



COLVILLE Oli ARCTIC SLOPE PROVINCE 



This northern geographic province extends from the northern base of 

 the mountains, in latitude 68° 25', northward to the Arctic coast, a dis- 



*Tlie geology and mineral resources of a portion of the Copper River district, Alaslia. U. S. 

 (Jeologioal Survey, Washington, 1901, 



