i6o 



NEW YORK STATE MUSEUM 



in succession and the lower foot or two may be free from the 

 action of water only in exceptional seasons. 



Plate .1 presents a view taken November 7, 1908. The fore- 

 ground is near the water level and the little potholes have been 

 filled by the waves of a moderate sea which was running at the 

 time. The upper portions of this exposed rock area are prac- 

 tically as they were left by the Wisconsin ice sheet. These are 

 the portions rarely covered or covered but a month or two in 

 the year. In the immediate foreground the potholes have become 

 confluent and this represents that portion of the rock surface 

 which is rarely uncovered and which has thus been acted upon 

 more persistently by water, wave and undertow. Plate 2 is a 

 view of a portion of this region near the water level of September 

 27, 1908. The character of the little potholes on the glaciated 

 surface is here better seen as is also their increasing number per 

 unit area, as we reach near the water level of the right-hand lower 

 corner. 



In the bay back of the lighthouse is a very perfect and interest- 

 ing roche moutoneee bearing a record which also testifies to present 

 stability of the water level of Lake Champlain. The position is 

 here much more sheltered and the little potholes [sec pi. 3] do 

 not appear to descend to so great a depth as in the former locality. 

 To the left they occur at a lower level and have become confluent. 

 These little potholes were not cut by pebbles. Not one in 

 several hundreds has a pebble in it and no pebble could 

 "have found a lodging on the steep and smooth glaciated sides 

 of these " sheepbacks." They all contain sand however and 

 were cut by water vortexes carrying sand and finer silt. They 

 rarely exceed 12 centimeters in diameter, unless confluent, and 

 many are very much smaller. They are cut also in very steep 

 sides as shown in plate 4, where they appear as glacial sections 

 of small potholes. The maintenance of a water vortex carrying 

 material which ever cuts back and widens the rock at one side, 

 while the other side of the vortex is not inclosed, and which thus 

 continues to develop the vertical and conical character of the ex- 

 cavation, is of special interest. 



Potholes are said to " often point to the former existence of 

 rapids 'or falls" and the term usually carries with it the idea of 

 much larger excavations than those found on the shores of Val- 

 cour island. The potholes of rivers and glacial streams are not 

 due to wind action on water and are not confined to one level 



