22 PROCEEDINGS OF BROOKLYN MEETING. 



complexity, the shorelines of the glacial predecessors of the Laurentiaii lakes were 

 uplifted with varying gradients, so that now, in connection with the history of the 

 successive channels of outlet opened by the retreat of the ice, they record the wave- 

 like northeastwaixi advance of a permanent uplift of that region from its Glacial 

 and Champlain depression. 



Ancient high Shorelines in the western Part op the Basin of Lake Superior. 



The upper limit of lacustrine action in Dulu,th and its vicinity, at the west end 

 of lake Superior, is marked by discontinuous beach deposits on the upper part of 

 the steeply ascending bluffs at an altitude of 535 to 540 feet above the lake. Another 

 shore terrace of beach gravel and sand is at 515 to 505 feet, approximately. Next 

 below these shorelines is the most definite and persistent beach of the entire series, 

 both of the Western Superior lake and the ensuing lake Warren. This was gen- 

 erally represented along the bluff face by a narrow beach terrace or slight shelf 

 carved and built up by the waves acting on the drift which thinly overlies the bed 

 rock, less steep than the slopes below and above it, so that its contour line, 470 to 

 475 feet above the present lake, has been used as the course of a driveway, known 

 as " the boulevard," which has been graded and is much used for pleasure driving, 

 along an extent of four miles, above the principal part of the city of Duluth, from 

 Millers creek to Chester creek. Beyond these limits the boulevard is planned to be 

 extended for distances of four miles more both to the southwest and northeast, fol- 

 lowing the same altitude and shoreline, giving a total length of 12 miles. Its 

 height is only a few feet above the water divide in the old channel of outflow from 

 the Western Superior glacial lake past the head of the Bois Brule river to the Saint 

 Croix river;* but, if we make due allowance for the partial filling of that channel 

 with postglacial alluvium and peaty swamp deposits, it seems probable that this 

 latest shore of that glacial lake has now an ascent of 15 or 20 feet in the distance of 

 about 25 miles from its outlet north-northwest to Duluth. The earlier and higher 

 shores here were made when the erosion of the outlet lacked successivelv about 65 

 and 30 or 35 feet of its final depth ; but a certain part of its earliest erosion had 

 been done before the retreat of the ice extended the lake to this northwest coast. 



Between the neighborhood of Duluth and mount Josephine, on the north coast of 

 lake Superior, near Grand Portage, no definite observations of these three early shore- 

 lines have been obtained, although there can be no doubt that they extend contin- 

 uously along this distance, which is about 130 miles in a nearly direct north east ward 

 course. When the woods of this high coast shall be cleared off', as will probably 

 some time be done in many places for farming and pasturage, the old lake levels 

 will be observed, especially the highest and lowest of these three noted at Duluth. 

 Attempting to'correlate these beaches with those found by Dr A. C. Lawsonf on 

 mount Josephine, I identify the 535 feet and 515 to 505 feet Duluth shores as repre- 

 senting his 607 and 587 feet shores; and the 475 to 470 feet beach of the Duluth 

 boulevard becomes apparently the conspicuous 509 feet beach of mount Josephine. 

 The total differential uplifting of the two upper shores between these localities has 

 been about 70 feet, of which about half had been accomplished previous to the time 

 of the Boulevard beach. 



* Proc. Am. Assoc. Adv. Sei.. vol. xxxii, for 1883, p. 230 ; Geology of Minnesota, vol. ii, 1888, p. 642 ; 

 Bulletin Geol. Society of Annerica, vol. ii, 1891, p. 258. 

 fGeol and Nat. Hist. Survey of Minnesota, Twentieth An. Rep., for 1891, pp. 251-253. 



