THE PEMBINA DELTA. 357 



and lowest Herman beach, of .similar form with the last, liut larger, running- 

 a few degrees west of north through the west edge of section 33, 1,173 to 

 1,175 feet, with depression of 1 to 5 feet on its west side and descent of 

 25 feet within 30 or 40 rods east. 



Tongue River, at bridge near the center of the soutli half of section 28, 

 township 161, range 56, about 1,110 feet; bottom land, 10 feet higher; top 

 of the bluffs, about 1,150 feet. Gavins reek, in the south half of section 

 20, about 1,140 feet; valley, 40 feet deep, a sixth of a mile wide. 



The lowest Herman Ijeach forms a massive ridge of sand and fine 

 gravel in the northeast quarter of section 29 and the east part of sections 

 20 and 17, township 161, range 56, with its crest at 1,175 to 1,180 feet. 



DELTA OF THE PEMBINA RIVER. 

 (PLATE XXX.) 



The largest tributary to the Red River in North Dakota is the Pembina 

 River, which has cut a valley about 400 feet deep and a mile wide in the 

 plateau of the second Pembina Mountain. During the reces.sion of the ice- 

 sheet this stream was much larger than now, being for a time the outlet of 

 g-lacial lakes in the basins of the Souris and Saskatchewan rivers.^ The 

 delta deposited in tlie margin of the glacial Lake Agassiz by the Pembina 

 River, swollen by a great affluent from the melting ice-fields at the north- 

 west, beyond the present limits of its basin, extends about 16 miles from 

 south to noi-tli and lias an average width of about 5 miles, with a maxinumi 

 width of 7^ miles and a maximum thickness exceeding 200 feet. Its mean 

 thickness is probably not less than 150 feet, giving for its volume about 2J 

 cubic miles, spread upon an area of <S0 square miles. Four-fifths of this 

 delta lie south of the Pembina River, reaching nearly to the Tongue River. 

 Fig-. 15 shows a section across this delta from east to west about 3 miles 

 soiith of Walhalla. 



Its elevation in the northwest part of section 17, township 161, range 

 56, is 1,200 feet; thence northward it ri.ses slowly in 2 iniles to 1,225 feet 

 in the east part of section 6; and in sections 31 and 30, township 162, range 



' Pages 267-274, foregoing. Geol. and Nat. Hist. Survey of Minnesota, Nintli Annual Report, 

 for 1880, p. 342. Hind's Reiiort of tlie Assiniboine and Saskatchewan Exploring Expedition, 18.">9, pp. 

 118 and 168. 



