SIXTH REPORT OF THE DIRECTOR I909 1 77 



in the depth of the cutting is clue purely to a difference in the 

 action of the environmental forces. When this specimen was 

 first taken from its resting place no attention was given to its 

 position on the bottom other than that its bedding planes were 

 vertical. In other words it was not noted which side was upper- 

 most. The two distinct types of erosive action we have been 

 discussing have, however, enabled us to very positively determine 

 this matter some years after the date of collection. Not only 

 have they done this but they also have strengthened the con- 

 clusion, drawn from the thin edged laminae, that this stone had 

 never been moved by the action of heavy seas but had remained 

 with its dentpitted surface down for several thousand years. 



It may here be noted that this pebble yields information of 

 yet another variety. That the floors of many of our caves are 

 a .meter or more below the present lowest water level of the 

 lake would in itself be evidence that this lake did not cut them 

 unless it had for a long time been at a lower level than the 

 average of the last hundred years. Now it could not have been 

 that meter lower without having brought the specimen we have 

 been discussing so near to the surface that the waves of storms 

 would have used it as a plaything, deprived it of its thin edges, 

 destroyed the remaining evidences of its former angular out- 

 lines and made of it a simple beach pebble. Its fellows would 

 also have been so changed in position as to bear witness of the 

 segregating power of wave action. Our pebble thus yields evi- 

 dence that goes to prove that the surface of Lake Champlain 

 has never been materially lower than it was in November 1908, 

 and never before perhaps so low. 



The old benchmark in Shelbourne harbor made in 1827 marks 

 the exceptionally low water reached that year. Not till 1881 

 was this mark passed and a new record established. In No- 

 vember 1908 this was again passed by about 2 inches. As the 

 pebble we have discussed is in itself testimony that the lake 

 has never been lower since the period of the Hochelagan sea and 

 as it bears on its surface an index of the work accomplished 

 only since the present lake waters were low enough to uncover 

 this pebble, it becomes in itself a timepiece showing the age of 

 Lake Champlain. In other words this pebble presents clear evi- 

 dence which goes to show that on the melting of the ice sheet, iso- 

 static balance was quickly restored in this region and a position close 

 to a former water level, that of Lake Valcour, was rapidly recov- 

 ered and has since been held. 



