2 



glacier. Still further north the glacier re- 

 treated and formed an ever enlarging sheet 

 of fresh water, which at length found for 

 the time being its outlet southward down the 

 channel described, and deposited from the 

 grinding up of the old Silurian limestones, 

 and also ot the hard Laurentian rocks of the 

 east, the drift clay and the boulders in its 

 vast moraines. It is to this wide sheet of 

 water that in memory of the late Prof. Louis 

 Agassiz, the first great upholder of the theory 

 "that the drift was produced by land ice," 

 the name has been given of the glacial "Lake 

 Agassiz." 



ITS B0L'NDAEIE3. 



Figure 1, gives the limits of the ancient lake 

 at its greatest extent, and it will be seen that 

 Lakes Winnipeg, Manitoba and Winnipeg- 

 oosis now occupy the bottom of the basin 

 which was then of so great size. At the time 

 when this wide expanse was pouring its waters 

 down the Mississippi valley the depth of the 

 lake where Winnipeg now stands was about 

 500 feet, and the waters laved a coastline high 

 up the steep of Pembina Mountains, Tiger 

 Hills and Riding Mountains to the weist. To 

 the east Lake Agassiz extended including the 

 present Lake of the Woods, and spread even 

 to the height of land bounding Rainy Lake. 

 The northern limit was the great ice barrier 

 itself, which was from year to year and cen- 

 tury to century slowly receding. While the 

 surplus waters were thus pouring from the 

 southern outlet this place of exit was being 

 gradually deepened, and thus standing for a 

 few years at one level along the coast line one 

 beach was outlined, and then as it receded an- 

 other at thf lower level was formed, and so 

 on. At the the same time in the period of 

 highest water there seems to have been a grad- 

 ual elevation of the coast line as well, arising 

 from inner motions of the earth's crust, and 

 from other causes. No less than 



SEVENTEEN BEACHES 



have been traced in Manitoba, formed during 

 the time when Lake Agassiz was emptying 

 southward. We have not time to name and 

 describe all of these, but may notice one or 

 two of the most remarkable. At the time 

 when Lake Agasssz formed its first beach, its 

 outlet was 85 feet above the present surface 

 of Lake Traverse, or 1,055 feet above the sea, 

 and itp v^uannel was cut through the height of 

 laud about 50 feet deep. The beach 

 has been called by Mr. Upham 

 the Herman beach. It is divided into 

 several levels in Manitoba, but at one point 

 its greatest height is attained on the road over 

 Pembina Mountain between Morden and 

 Thornhill in bouthern Manitoba where it is 

 1,258 feet above the sea. Thu second division 

 of this highest or Herman beach is found on 

 Tiger Hills about one mile south of the vil- 

 lage of Treherne, and again appears in the 

 well marked sand and gravel ridge one eighth 

 of a mile north of the court house in the city 

 of Brandon, while the same beach is seen 

 some three miles west of the town of Neepa 

 wa. Thus from this winding coast line east- 

 ward extended the watersoftheice cold lakeheld 

 in along the northern side by the great glacier 



mass itself (fig. 1) The next lower beach 

 formed when the waters of the lake had low- 

 ered about 25 feet, no doubt by the cutting 

 down of the outlet at Lake Traverse. This is 

 known as the Norcross beach ; and so we 

 might give the elevations and features of the 

 fifteen other beaches whose existence as ter- 

 races on the slope of Pembina Mountains has 

 been often pointed out to the writer by the 

 farmers in the several western regions. 



DIFFERENCE OF BEACH LEVEL. 



One of the most remarkable features of the 

 upper beaches of Lake Agassiz is the gradual 

 ascent in the level of each beach. It is plain 

 that if the lake theory of the formation of 

 these beaches is correct, each beach should 

 have the same|normal level. But if raising a 

 horizontal bar pointing north and south, 

 greater upward pressure is exerted at the 

 north end than at the other, the bar will slant 

 upwards toward the north. Some earth pres- 

 sure seems thus to have raised the north end 

 of these beaches. In the highest or Herman 

 beach it is found that taking its level at Lake 

 Traverse, when Lake Agassiz emptied there, 

 the beach line was from 1055 to 1045 feet 

 above the sea, while at the international 

 boundary line a point 224 miles further north, 

 it was actually 1230 feet above the sea or 175 

 feet higher. But this elevating tendency in 

 the north was very far from being a constant 

 or steady rise. In the stages of the Herman 

 beach toward its northern limit the elevation 

 varied so that four fairly well marked stages 

 of the Herman beach are traceable. Thus 

 while the Herman beach only differed at the 

 outlet of the lake between i055 to 1045 feet 

 above the sea, its lowest stage was 1175 feet 

 above the sea at the international line i. e. 

 1.30 feet above the outlet level. Ten feet thus 

 marks the variation at the outlet while no less 

 than 45 feet is the difference caused by the 

 northern elevation at the boundary line. 



CAUSES OF BEACH ELEVATION. 



There has been much discussion as to the 

 causes of this upward motion in the northern 

 end of Lake A.gassiz. Probably no one cause 

 entirely accounts for this. The following are 

 the agencies suggested : 



(1) The tendency shown by Mr. R. S. 

 Woodward, of the U.S. Geological Survey, of 

 the waters of a glacial lake to gravitate toward 

 the ice sheet. In the case before us the ice 

 sheet probably extended for 1000 miles north 

 and north-eastward, and being from Ig to 2 

 miles in depth would have an enormous at- 

 tractive power. This would raise the waters 

 of the northern end of the lake, and in this 

 way perhaps one quarter of the elevation that 

 took place in the northern beach levels is 

 accounted for : 



(2) The re-elevation of the land as the ice 

 belt receded to the north. The pressure from 

 one to two miles' depth of ice would be so 

 great, that according to some geologists a 

 considerable sinking in the underlying earths 

 crust must take place, and then as the glacier 

 mass melted the re elevation of the depressed 

 crust would result. 



(3) At this period ^n the history of our 

 earth there were great oscillations taking 



