GLACIATION OF WRANGELL MOUNTAINS 43 



For some distance above Camp Creek, and between Copper and 

 Stone creeks, there are gravel terraces which stand 30 to 50 feet 

 above the stream. 



Extent of earlier glaciers. — ^As shown in Fig. i, the Nabesna 

 Glacier was formerly of much greater size than it is at present. The 

 glaciers from the Wrangell Mountains, moving northward, were 

 unable to override the opposing Nutzotin Mountains, but sent their 

 ice across this range through the two great troughs through which 

 the Nabesna and Chisana rivers now flow. In the Nabesna Valley 

 the ice extended to the north base of the Nutzotin Mountains, and 

 there spread out into a broad, spatulate lobe. The outlines of this 

 lobe have not been traced, but there is reason to believe that its 

 northern edge was 40 or 50 miles below the existing ice-edge. The 

 ice filled the valley to a depth of 2,000 to 3,000 feet, and its erosive 

 power was enormous. It truncated the lower ends of the rock spurs on 

 either side of the valley and developed the broad U-shaped trough 

 through which the river now flows. There is a notable absence of 

 craggy outcrops and of ridge-like spurs along the valley-sides. 



At the time of the maximum ice-advance each tributary valley in 

 the Wrangell and Nutzotin mountains sent down a glacier to join 

 the main lobe so that only the highest peaks and crests of the moun- 

 tains projected above the ice. With a change in climatic conditions 

 came a gradual contraction of the glaciated area. The ice in the 

 large trunk valley slowly melted back and left separate the small 

 glaciers which occupied the side gulches. These in turn retreated 

 toward their heads, and although many of them have now disappeared 

 entirely, their former presence is shown by the U shape of the stream- 

 troughs, and by the moraines which the ice left. 



CHISANA VALLEY 



Chisana Glacier.— The Chisana Glacier, locally called the Shu- 

 shana, Hes on the northeast slope of the Wrangell Mountains, between 

 the Nabesna and White valleys. Its heads reach westward to the 

 Nabesna divide, and in many of the cirques the ice is continuous 

 across the divide with the easternmost heads of the Nabesna. To 

 the south the ice is continuous over the divide with the Rohn and 

 Nizina glaciers on the south slope of the mountains (Fig. 4). There 



