402 THE GLACIAL LAKE AGASSIZ. 



water from 1,057 to 1,063 feet above tlie sea, shows that this large lake was 

 first separated from the dimiuishing expanse of the ghicial Lake Agassiz 

 between the times of formation of the Tiutah and Campbell beaches. 



WESTEKN TINTAII SHORES IN NORTH DAKOTA. 



(PLATES XXVII-XXX.) 



In the northeast corner of South Dakota, two beach ridges, belonging 

 to the upper Tintah shore of this glacial lake, run north-northwestward 

 across the northeast part of section 6, township 128, range 47. The east- 

 ern ridge is 20 to 30 rods wide, consisting of gravel and sand on the west- 

 wardly ascending surface of till. It has a height of 1,014 to 1,018 feet 

 above the sea, with a descent of about 15 feet on the east and of 3 to 6 

 feet on the west. A smaller parallel gravel ridge, rising 5 feet from its 

 eastern base and falling 1 to 3 feet toward the west, with crest at 1,015 to 

 1,021 feet, lies a quarter of a mile farther west. The eastern beach, curving 

 northwestward, was traced several miles into North Dakota, to the northeast 

 quarter of section 22, township 129, range 48, where its elevation is 1,015 

 to 1,018 feet. Thence it is probably continuous to two small beach ridges 

 that were observed, without determination of their height (known, however, 

 to be approximately 1,015 feet), in or near the north edge of section 34, 

 township 130, range 49, on the south side of a, little creek which there 

 emerges from the sand area of the Sheyenne delta. 



The Tintah shore-lines cross the eastern portion of this delta, Ijut are 

 seldom traceable, even on its smooth areas, and still less among its frequent 

 tracts of dunes. The altitudes of the Northern Pacific, Fergus Falls and 

 Black Hills Railroad show that they cross this line 1 to 2 miles east of 

 Barney. Along the northern border of the delta they coincide with the 

 escarpment and slope descending from its plateau, which pass close north 

 of Leonard and thence extend 8 miles westward to the Maple River. On 

 the Fargo and Southwestern Railroad the upper Tintah level of Lake 

 Agassiz eroded an escarpment in the delta sand and gravel whose top has 

 an altitude of 1,034 feet above the sea; and the lower Tintah shore bears 

 three beach ridges, 5 to 7 feet above the intervening hollows, with their 

 crests at 1,017, 1,016, and 1,014 feet. 



