SHORE-LINES AND DELTAS. 27 



height of these steep, wave-cut slopes varies from 10 to 30 feet, which is 

 indeed a very sUght elevation in comparisonwith the cliffs of similar origin 

 on some portions of the shores of Lake Michigan and others of the Lau- 

 rentian lakes. No portions of the beach ridges, nor of these low, eroded 

 escarpments marking the margin of Lake Agassiz, are noteworthy objects 

 in the view from points so far away as 2 or 3 miles, but nearer at hand they 

 appear sufficienth' impressive when the mind reverts to the receding ice- 

 sheet and this great glacial lake by which they were made. 



Sand and gravel deltas, so extensive as to be important features in the 

 topography, were formed in the edge of Lake Agassiz during its earliest 

 and highest stage by several of its tributary streams. Such deltas were 

 brought into the east side of the lake by the Buffalo and Sand Hill rivers, 

 and into the west side by the Sheyenne, Pembina, and Assiniboine rivers. 

 They all consist for the greater part of modified di'ift, derived directly from 

 the ice-sheet in which it had been held; and another delta of this lake, 

 extending south from the Elk Valley, in North Dakota, was deposited by a 

 large glacial river, flowing where no river exists now. 



The delta of the Buffalo River is well seen from the Northern Pacific 

 Railroad, on which the traveler going westward enters the delta area at 

 Muskoda and passes through it in the next 2^ miles. Its eastern border 

 bears a massive beach ridge, 15 feet thick, of coarse gravel and sand, which 

 marks the highest level of the lake; but the chief mass of the delta, 

 attaining a thickness of 25 to 75 feet, is stratified sand, with occasional 

 layers of fine gravel, as exhibited in the railroad cuts. 



The Pembina River intersects the highest part of its delta, whicli rises 

 200 to 250 feet above the stream. Its eroded eastern border, carved in a 

 steep escarpment by the waves of Lake Agassiz while this lake fell to suc- 

 ces.sive lower stag-es, forms the "First Pembina Mountain," passing from 

 south to nortli and northwest by Walhalla as a very conspicuous wooded 

 bluff 100 to 175 feet above the flat prairie of the Red River Valley at its 

 base, with its crest 1,100 feet to nearly 1,200 feet above the sea. 



