26 W. UPHAM — giants' kettles eroded by MOULIN TORRENTS 



but either the common English term, potholes, or the German and Scan- 

 dinavian designation, apparently alluding to mythical giants, seems 

 preferable. 



These potholes, occurring most numerously near the steamboat land- 

 ing of Taylors Falls, Minnesota, at the central part of the Upper Dalles, 

 and within a distance of 50 rods northward, are unsurpassed by any 

 other known localit}'' in respect to their variety of forms and grouping, 

 their great number, the extraordinary irregularity of contour of the 

 much jointed diabase in which the}^ are eroded, and the difficulty of 

 explanation of the conditions of their origin. 



In view of the late Glacial confluence of ice currents there, known by 

 the occurrence of drift on all the country eastward derived from the 

 northeast and largely from the basin of lake Superior, while all the 

 region westward is enveloped by drift from the northwest, with gravel 

 and large masses of limestone from Manitoba, it is evident that the sur- 

 face of the ice-sheet at its time of departure sloped downward from each 

 side toward this area. The superficial line of boundary between the 

 northeastern and northwestern drift, mapped for the Saint Croix Dalles 

 area by Doctor Charles P. Berkey,* passes from south to north in coin- 

 cidence with this part of the Saint Croix river. Beneath the ice-sheet 

 during its later accumulation here, after the Buchanan interglacial stage, 

 a subglacial brook flowed in the summers along the course of the inter- 

 glacial Saint Croix. It probably ceased while the ice of that time at- 

 tained its greatest area, depositing the Illinoian and lowan drift; but 

 when the ice was finally melting away, remaining here with only a depth 

 of a few hundred feet, the same subglacial stream course doubtless re- 

 ceived torrents })lunging vertically down through crevasses and moulins. 

 Such glacial waterfalls and the subglacial streams flowing rapidly away 

 to a more deeply channeled avenue of discharge southward along the 

 valley seem to have been the chief agencies of erosion of the })otholes in 

 the Interstate park and its vicinity. 



A consideration of the diverse classes of streams which are capable of 

 eroding potholes shows two modes of their origin dei)endent on glacia- 

 tion. The purpose of this paper is to describe these " giants' kettles " 

 at the Dalles and elsewhere near Taylors Falls, Minnesota; to compare 

 with these, for aid in their explanation, other examples of their kind in 

 many localities of North America and Europe, which are unquestionably 

 of subglacial origin ; to inquire what conditions were necessar}^ for this 

 result, and in what parts of a stage of glaciation they were apt to occur; 



*Am. Geologist, vol. 20, pp. 355-309, with maps and sections, December, 1897. Compare my paper, 

 " Changes of currents of the ice of the last Glacial epoch in eastern Minnesota," Proe. Am. Assoc. 

 Adv. Sci., vol. 32, for 1883, pp. 231-234, and Geology of Minn., Final Report, vol. 2, 1888, pp. 409-417. 



