STAGES OF GROWTH SHOWN BY MORAINES. 213 



Lake Agassiz theu expanded beyond the limit of the international boun- 

 dary, reaching probably to Winnipeg and Birds Hill (PI. XX). The 

 entire area of this lake in North Dakota had become uncovered from the 

 ice, a lobe of which, however, remaining on the Pembina Mountain pla- 

 teau, closely bordered the shore along a distance of 50 miles south from 

 the Manitoba line. In northwestern Minnesota the lake washed the base 

 of ice cliffs that formed its eastern shore, beginning about 40 miles north 

 of Lake Itasca and running north-northwesterly, as I have supposed, to an 

 angle of the ice front at Birds Hill, from which a similar long, high coast of 

 ice appears to have stretched southwestward to the Pembina Mountain in 

 the vicinity of Thornhill, being the northwestern barrier of the widening 

 and deepening lake. The water surface was about 290 miles in length, 

 110 miles in maximum width, and approximately 16,000 square miles in 

 area; and the depth of water above St. Vincent, Pembina, and Emerson 

 was about 450 feet, while its maximum above the site of the city of Win- 

 nipeg was not less than 550 feet. The extent of the portion of the lake in 

 Manitoba at this time was probably about 3,500 square miles. 



Once more the margin of the ice-sheet recedes, and next halts at the 

 eleventh or Mesabi moraine (p. 177), having relinquished the whole of its 

 area in North Dakota, but still lingering on a large tract of northern Min- 

 nesota, from Red Lake and Lake Winnebagoshish eastward to Lake Supe- 

 rior near the intei'national boundary. The great glacial lake has now 

 extended north to the south end of Lakes Winnipeg and Manitoba, attain- 

 ing a length of about 325 miles, a maximum width of 130 miles from the 

 east end of the south half of Red Lake to Larimore, and an area not far 

 from 26,000 square miles, of which fully one-third was comprised in Mani- 

 toba (PI. XX). Its maximum depth, lying over the present mouth of the 

 Red River, was about 650 feet, and its depth above the south end of Lake 

 Manitoba was 525 feet, very nearly. 



These estimates of depths, it is to be noted, are derived from the 

 determinations of the height of the shore-lines formed during the highest 

 Herman stage, with allowance for the known north-northeastward differ- 

 ential elevation of the basin since the old plane of the lake sm-face was 

 marked by the waves of storms. This earliest and highest level of Lake 



