CLASSIFICATION OK CJIANTS KKTTLKS Zi 



and to ascertain tlie relations of the glacial torrents forming potholes 

 with the hirger glacial hrooks and rivers that produced kames and eskers. 



Classification of Rock Potholes or Giants' Kettles 

 potholes of subaerial waterfalls and r.fpids 



In all parts of tlie world the falls of rivers in cascades or rapids over 

 granitic or other hard and enduring rocks wear portions of their rock 

 hed into beautifully smoothed and gracefully or often fantastically 

 curved forms, among which are frequently found bowl-like or cylindric 

 holes. These range in dimensions from a diameter of a foot or less up 

 to 10 or 15 feet or rarely more, with an equal or often greater depth. 



In a few places such abundantly water-worn rocks, with potholes, are 

 found where no stream now flows nor has existed since a lake hemmed 

 in by the barrier of the departing ice-sheet had its outlet there, flowing 

 over a col of the present watershed between independent hydrographic 

 basins. This is one mode of stream action forming giants' kettles due 

 to the Glacial period ; but these kettles are not filled or covered by 

 glacial drift. 



Good examples of this class occur in New Hampshire at two localities 

 where the watershed dividing the Merrimack and Connecticut River 

 basins is crossed by railroads. The more northern and lower place, at 

 Orange summit of the Northern railroad, had numerous potholes, some 

 of which were partly and others entirely blasted av/ay for the passage 

 of the railroad. The most remarkable one, known as " The Well," was 

 described by Jackson as 11 feet deep, 41. feet in diameter at the top, and 

 2 feet at the bottom. It contained earth and round stones. Another 

 locality of the same character is also reported by Jackson in Warwick, 

 Massachusetts, " on the southern declivity of a bare ledge of gneiss 

 forming the dividing ridge between the Ashuelot and Millers rivers."* 



GIANTS' KETTLES OF MOULINS AND SUBGLACIAL STREAMS 



The class of potholes more particularly considered in this paper de- 

 pended directly on glacial action. They may be called, by way of dis- 

 tinction from those of subaerial streams, glacial potholes ; or perhaps, 

 by usage among geologists, the German and Scandinavian term, giants' 

 kettles, may be restricted to this class of holes, bored in the bed-rock 

 beneath glaciers or an ice-sheet by torrents of water falling through deep 

 moulins. This name, moulin, coming from the French and meaning a 



*C. T. JaeksoQ : Final Report on the Geology of New Hampshire, 1844, pp. 113, 114, 282. Warren 

 Upham, in Hitchcock's Geology of New Hampshire, vol. 3, 1878, pp. 64-GO. 



