298 THE GLACIAL LAKE AGASSIZ. 



DELTA OF THE SAND HILL RIVER. 



(PLATES XXV AND XXVI.) 



Wlien Lake Agassiz stood at its greatest height, the Sand Hill River 

 lirouglit into its margin a delta G miles long from south to north and 3 

 miles wide, reaching from the upper beach to the west side of Gai-field and 

 Sundal townships (fig. 12). This deposit of stratified gravel and sanjd has 

 about an equal area and thickness with the delta of the Buffklo River at 

 Muskoda. Its surface descends slowly westward and is crossed by the 

 lower Herman and the Norcross shores, though these lake levels are not 

 generally traceable. The Tintah shores pass along its western margin, 

 which in some portions was worn away to a low escarpment, steeper than 

 its original frontal slope, while the eroded sand and gravel, after being 

 carried some distance southward, but not wholly beyond the delta, were 

 deposited in beach ridges. Upon the delta plain many dunes of small and 



Herman Seac^ 



FiQ. 12 — Section acrosa the delta of the Sand Hill Kiver. Uurizoutal scale, one-half mile to an inch. 



large size, seen from a distance of 10 or 12 miles across the lower expanse 

 at the west, have lieen heaped up l)y the winds, ^jrobably mostly before 

 vegetation had spread over this area after the withdrawal of the glacial lake. 

 As was stated on page 291, in the description of the Bufi'alo delta, 

 both these river deposits in the edge of Lake Agassiz seem attributable to 

 conditions of the recession of the ice-sheet. Their gravel and sand were 

 doubtless mainly englacial drift and were brought into this lake by streams 

 which had gathered their freight upon the ice surface during the time of 

 formation of terminal moraines. One of these glacial rivers, supplying a 

 part or perhaps nearly all of the Sand Hill delta, flowed from an angle of 

 the ninth or Leaf Hills moraine in a cliannel which has been traced IG 

 miles to its junction with the Sand Hill River, as described on page 164. 

 Its sand and fine silt were carried more than 30 miles by the strong current 



