TIIK IXTKKSTATK TARK, TAVI.OIJS FAl,I.S, MINNKSOTA 20 



exactly at the foot of a great and very deep moulin ])y its powerful 

 descending torrent. 



Potholes of suhglacial erosion, whether bored just beneath a moulin 

 or in or l)eside the pathway of a rapid stream flowing from it, may suh- 

 sequenth' have become partly or wholly filled by till, the direct deposit 

 of the ice-sheet, unmodified by water action, or such potholes may be 

 completely concealed under a later general sheet of glacial drift. On 

 the other hand, too, they may remain nearly or quite empty, having been 

 so left, without drift accumulation, while the overlying ice disappeared. 



Localities of Surglacial Potholes 

 interstate park of the saint croix dalles 



The northern part of this park and the adjoining southern part of the 

 town of Taylors Falls are mapped on plate 1. The potholes are mostl}'^ 

 on the western or Minnesota side of the Saint Croix, occurring plentifully 

 on certain areas between Trap Rock street (the road to the steamer land- 

 ing) and the river. These areas of their abundant development are 

 comprised within a length of 50 rods from north to south and about 

 12 to 15 rods from east to west. With other tracts where single examples 

 or a few occur, as west of this street, again on the Wisconsin side of the 

 river, and again on a low rock hill in the valley about a mile north of 

 Taylors Falls, not less than a hundred potholes are known in this vicinity. 

 Many of them, however, are small, as a foot or less in diameter and one 

 to five feet deep. The greater number were originally left empty, or 

 with only a partial filling of rounded grinding stones, silt, mud, or peat, 

 differing much in their contents. Others, mostly of small size, were 

 found completely filled, and some were covered and hidden by a hard 

 deposit of glacial drift, almost typical till. 



The chief area of large potholes, worthy to be called giants' kettles, 

 reaches from the steamboat wharf about 15 rods east-northeastward to 

 Angle rock and about 20 rods northward, comprising only an acre and 

 a half, within which space are all the very large and deep potholes known 

 in the entire district. Counting the small and large holes, I found 30 

 on that area, including several so remarkable for their great diameter 

 or depth, unusual form, or contents that they deserve to be separately 

 described. The rock, like that of all the places having potholes in and 

 near the Interstate park, is the ver}'' hard diabase trap of Keweenawan 

 age, which here forms extensive outcrops, everywhere much divided by 

 vertical and oblique systems of joints. Under the glacial and river ero- 

 sion there has resulted a very ruggedly broken surface of rock cliffs and 

 dells. Little or no drift and only few boulders have been left on the rock 



