ABSTRACT OF VOLUME. XXIII 



Minnosota, tlio Sheyuimu, Klk Valloy, and Pcmbiua deltas in North Dakota, au<l tbe very large 

 delta of the Assinlboine iu Manitoba. 



Chapter VII: Lowek isEAcnES with sooth WAiin outflow. — Below the Herman shore the south- 

 ern part of Lake Agassiz has four shore-lines, which receive names from Norcross, Tintah, 

 Campbell, and McCauleyvilla, in Minnesota. Portions of these shores have been traced with 

 leveling and are hero described. In the northern part of the area of my exploration the Nor- 

 cross and Tintah beaches are double, and the Campbell and McCauleyville beaches are e.ach 

 represented by three. With the seven Herman shores recorded in Manitoba, Lake Agassiz had 

 thus at the north seventeen stages marked by successive beaches during its time of southward 

 discharge by the River Warren. The upper Norcross shore rises from about 1,030 feet above 

 the sea at Lake Traverse to 1,215 feet on the latitude of Gladstone. In the same distance the 

 upper Tintah shore rises from 1,01.5 to 1,150 feet; the upper Campl>ell shore, from 990 to 1,080 

 feet; and the upper and lower McCauleyville shores, respectively, from 970 to 1,035 feet, and 

 from 960 to 1,012 feet, approximately, above the present sea-level. 



Chapter VIII: Beaches for.med when Lake Agassiz outflowed nokthea.stwaku. — Fourteen 

 stages of Lake Agassiz are shown by beaches that were formed after the lake had fallen below 

 its southern outlet. These comprise, in descending order, three successive Blanchard beaches, 

 passing near Blanchard, N. Dak. ; the Hillsboro beach, and two Emerado and two Ojata beaches, 

 named likewise from towns in North Dakota; and the Gladstone, Burnside, Ossowa, Stonewall, 

 and Niverville beaches, the last being double northward, named from places in Manitoba. These 

 shore-lines are as definitely marked by beach ridges, and occasionally by low eroded escarp- 

 ments, as the series belonging to the time of the River Warren. Their northward ascent is 

 gradually diminished, until in the latest-formed Niverville beach it is only about 20 feet iu 

 the distance of more than 200 miles from near Winnipeg and the southern part of Lake Win- 

 nipeg northward to the mouth of the Saskatchewan. 



Chapter IX : Changes in the levels of the beaches. — The rate of northward ascent of the 

 origin.illy level highest beach, within the area of my leveling, varies from about 6 inches per 

 mile near its southern end to about 1 foot per mile along the greater part of its extent to south- 

 ern Manitoba. On the east side of the Red River Valley the old shores are higher than on its 

 west side, the rate of ascent from west to east being about half as mn<-h as from south to north. 

 The direction of maximum ascent of the planes of the former lake levels is therefore toward 

 the north-northeast. Farther north several beaches of the series mapped by Tyrrell along the 

 bases of the Riding and Duck moimtains have a northward rise of 2 to 3 feet per mile. Those 

 changes of level were in progress and were nearly completed during the existence of Lake 

 Agassiz, as is shown by the gradual diminution in the northward ascent of the successive lower 

 beaches, until the latest and lowest differs only very slightly from perfect horizontality. Grav- 

 itation of Lake Agassiz toward the ice-sheet accounts for a small part of the jireseut incliuation 

 of the beaches. Changes in the temperature of the earth's crust due to the Glacial period and 

 its termination produced a still smaller effect, but this tended to give the opjiosite slope, or a 

 descent toward the north. Upward epeirogenio movements, resulting from the unburdening of 

 the land by the departure of the ice-sheet, were the chief element in the causes of the differen- 

 tial changes in the height of this basin. Flow of the plastic inner part of the earth's mass, 

 restoring isostasy, uplifted first the southern half of the area of Lake Agassiz, from Lake Trav- 

 erse to Gladstone ; next it raised the northern half of the lake area, while the region at the south 

 was almost at rest; and finally, during the Recent epoch, afterthe whole basin of Lake Agassiz 

 was passed by this wave-like permanent uplift, it has been elevating the basin of Hudson Bay, 

 where the movement still continues. Pleistocene oscillations of the Land in many other parts 



