NOETHWAED ASCENT OF THE BEACHES. 475 



northward rise of the hind and subsidence of the lake had their maximum 

 increase from south-southwest to north-northeast or nearly in that direction. 

 Therefore the more western course of these beaches in the northern part of 

 the area examined compensates approximately for the additional distance 

 between the third and fourth of these groups of observations. 



The letters abed represent successive beaches along the northern 

 part of Lake Agassiz, which are merged in a single beach toward its south 

 end. Several of the beaches thus noted in a preliminary report '^ are found 

 to become double in some parts of their northward extent, and a corre- 

 spondence in notation is here preserved by designating subordinate stages 

 by double letters, as aa, hh. There are also added the two stages of the 

 Tintah lieaches which were discovered after the publication of that report. 



The lake shore belonging to the highest or Herniau stage a has now a 

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

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

 third distance of 74 miles to the international boundary. Its whole ascent 

 thus in 224 miles is 175 feet by a slope which increases from slightly less 

 than a half of a foot per mile in its southern third to slightly more than 1 

 foot per mile in its northern third. Tlu'ough six lower stages represented 

 by separate beaches northward, which seem to be united in the single 

 Herman beach along the southern third of the lake, the northward ascent 

 is gradually diminished to approximately 30, 40, 60, and 70 feet in the four 

 portions of the obseiwed course of these shore-lines, amounting thus to 200 

 feet in about 300 miles. On the international boundary the lowest Herman 

 stage, dd, is about 55 feet below the Herman stage a, while the probable 

 erosion of the outlet and consequent lowering of the south end of the lake 

 between these stages appears not to have exceeded 1 feet. 



Between the series of Herman beaches and the series of Norcross 

 beaches the River Warren eroded its chaimel about 15 feet; and the upper 

 Norcross shore ascends northward in these successive distances about 25, 

 35, 55, and 70 feet, amounting to 185 feet in the entire distance of 308 

 miles. In the most southern quarter its ascent is a third of a foot per 

 mile, and this gradually increases to nearly 1 foot per mile in the most 



' U. S. Geol. Survey, BuUetin No. 39, p. 20. 



