390 THE JOURNAL OF GEOLOGY. 



opment of this uplift, it will be needful to consider it first for the 

 southern half and afterward for the northern half of the glacial 

 lake area. 



About thirty successive levels of Lake Agassiz have been 

 recognized by its beaches.. A considerable number were due to 

 the gradual erosion and lowering of the outlets, and to their 

 changes of place and direction, first toward the south and later 

 toward the northeast ; but probably more than half of this whole 

 series of lake levels are distinctly exhibited only upon the cen- 

 tral and northern portions of the lacustrine area, being due 

 chiefly to its differential uplift increasing from south to north, 

 and in a small degree to the decrease in the gravitative attraction 

 of the waning ice-sheet. The five well defined beaches near the 

 south end of this ancient lake, named in descending order the 

 Herman, Norcross, Tintah, Campbell, and McCauleyville beaches, 

 formed at the successive levels of southward outflow as the chan- 

 nel was deepened, are each found to be represented, when they 

 are followed northward, by two, three, or more, so that near the 

 international boundary and in Manitoba, they become subdivided 

 into no less than seventeen beaches, marking the stages of the 

 subsidence of the lake and in larger proportion of the differen- 

 tial elevation of the land. Nearly as many other lower shore 

 lines record the stages of the lake while it outflowed northeast- 

 ward. My surveys of these shores, with exact mapping and 

 leveling, extend more than 300 miles from the south end, to 

 lakes Winnipeg and Manitoba and the Riding Mountain. ^ 



In this southern half of the whole extent of Lake Agassiz, 

 the shore of its highest or Herman stage, as represented at the 

 north by the uppermost of its divided beaches, has now a north- 

 ward ascent of about 35 feet in the first 75 miles north from 

 Lake Traverse, which lies in the old channel of southward outlet, 

 about 60 feet in the second 75 miles, and about 80 feet in the 



'Geological and Natural History Survey of Minnesota, Eighth An. Rep., for 1879, 

 pp. 84-87 ; Eleventh An. Rep., for 1882, pp. 137-153, with map; Final Report, Vol. i 

 (1884), and Vol. 2 (1888). U. S. Geol. Survey, Bulletin No. 39 (1887), pp. 84, with 

 map. Geol. and Nat. Hist. Survey of Canada, An. Rep., new series, Vol. 4, for 

 1888-89, Part E, pp. 156, with maps and sections. 



i 



