346 GLACIAL GEAVELS OF MAINE. 



The lateral moraines form large ridges or terraces -upon the momatain sides. 

 The glaciers from the west side of the valley were much larger than those 

 from the east. It is possible that at one time a broad glacier occupied the 

 whole Arkansas Valley, but my own observations leave the matter in doubt 

 as to the last glacial period. A good place for observing these phenomena 

 is in the valley of Box Creek, and its tributaries, Willow Gulch and Har- 

 rington Gulch. They originate on the eastern slopes of Mount Elbei't and 

 flow southeastward and eastward into the Arkansas River near Hayden 

 station, on the Denver and Rio Grande Railroad, about 12 miles below 

 Leadville. Near here, on both sides of the Arkansas River, are well exhib- 

 ited two types of valleys, the broad U-shaped valleys that were occupied 

 b}" glaciers while their margins were being piled high with morainal and 

 sedimentar}^ drift, and the narrower valleys, generally V-shaped, due to 

 recent erosion of a once continuous mass. The Arkansas River is here 

 bordered by a rather level plain of glacial sediments about a mile wide. 

 Extending west from this plain is the plain-like valley of Box Creek and its 

 tributaries, from one-fourth mile to near a mile in width. Near the 

 Arkansas they are bordered by mesas of glacial sediments ending in steep 

 bluffs 150 to 250 feet high, while as we near the mountains they are bor- 

 dered by bluif-like lateral moraines. These moraines prove conclusively 

 that the upper portions of these valleys were filled by glaciers that origi- 

 nated in the large cirques of Mount Elbert. If the glaciers had stopped at 

 the base of the mountain they ought to have deposited terminal moraines. 

 Instead, a U-shaped valley of the same character as those bordered by 

 lateral moraines extends continuously to the Arkansas Valley, which is also 

 free from moraines at this place. The conclusion follows that three glaciers 

 originated on Moimt Elbert and united near its base to form a single tongue, 

 and it in turn united with a glacier which filled the bottom of the Arkansas 

 Valley for many miles below Leadville over a varying breadth of one-half 

 mile to somewhat more than a mile. This main glacier received many 

 tributaries from the adjoining mountains. Between the successive lateral 

 valley glaciers and the main glacier that extended along the axis of the 

 Arkansas Valley there were open spaces bare of ice into which the subgla- 

 cial streams of the lateral glaciers poured and deposited overwash aprons 

 of glacial sediments. Sometimes these alluvial mesas end next the river 

 bluifs in sand or fine clay and rock flour, proving that here were glacial 



