Giants' Kettles ?iear Christiania and in Lucerne. — Uphani. 295 
The largest pot-hole of Lucerne, on the northwest border 
of the group, has a diameter of 26 feet and depth of 31 feet. 
Its southern side overhangs, probably because the northwardly 
flowing current of the overlying glacier carried the moulin 
slightly forward while the rock erosion was taking place. The 
movement was least at the base of the glacier, and increased 
differentially upward. The moulin therefore became inclined, 
and discharged its torrent somewhat backwardly into the rock 
kettle, hollowing it thus with an overhanging wall. The same 
feature is observable in several others of these pot-holes, and 
many of them display spiral wearing. In some instances the 
pot-holes have irregular and composite forms, showing ap- 
parently that successive and independent moulins, probably 
of different years, contributed to their erosion. They range 
in size from the largest to others 9 or to feet deep and 4 or 
5 feet in diameter, and to small cylindric or hemispherical 
kettles only one or two feet deep. 
It is also to be noted that the rock at two or three places 
is waterworn in broad and somewhat crooked grooves, vary- 
ing in depth to six or seven feet, and extending 20 or 30 feet 
in length, where the moulin torrent was less concentrated and 
more variable than usual; or, more probably, these grooves 
may have been made by a very inclined and powerful englacial 
and subglacial stream there impinging on the rock floor. Per- 
pendicular pot-holes of the usual form, but of small size, occur 
occasionally in the grooves. It is especially noteworthy, both 
here and in other localities of Europe and America, that gen- 
erally the edge or lip of the giants' kettles, whether large or 
small, is abruptly cut in the rock surface, perhaps sometimes 
because of their partial removal by glaciation subsequent to 
the moulin erosion. They seldom have a flaringly curved 
mouth, such as more frequently characterizes pot-holes seen 
at the present time in the process of erosion by cascades in 
brooks and rivers. 
Rock exposures adjoining giants' kettles are often un- 
marked by other waterwearing; but in every present stream 
having falls and eroding pot-holes, larger spaces are irreeularly 
worn and channelled. The rock kettles of moulin formation, 
found where no stream now exists nor can be supposed to 
have ever flowed except when the country was ice-enveloped. 
