SIXTH REPORT OF THE DIRECTOR IO/X) 1 73 



depth rarely exceeds 10 centimeters. Where dentpits have not 

 become confluent they may also be found on glaciated surfaces and 

 the markedly slower process of their formation has rarely allowed 

 them to penetrate to a depth greater than I centimeter. Scattered 

 dentpits on an undoubtedly glacial surface may be seen in plate 4, 

 on the smoother surface of the rock and about half way between 

 low and high water. Foreshortening makes them appear as ellipses. 

 A little above this belt and near the extreme right a few more nearly 

 circular outlines may be detected. These dentpits are of precisely 

 the age of the cupholes and both were started on glacial surfaces 

 when the water was lowered to near the present level. Now, just 

 inside of the mouth of Bat cave in the opposite wall of the channel 

 and at the same level, we may also find a few separate dentpits but 

 much better developed than those on the wall outside. Where cup- 

 holes have become confluent they have of course destroyed the 

 glaciated surface. In these regions of greater activity the surface 

 may have been cut away to an average depth of perhaps 20 centi- 

 meters. Likewise with dentpits, where confluent, the vortexes pro- 

 ducing them were the more numerous and stronger and the amount 

 of surface removed may have been as great as '2 centimeters. This 

 is the condition of the cave wall shown in plate 11. Now as this 

 cave is more than a meter wide it follows that in all its essential 

 features it is as old as tlie glaciated surfaces on which the dentpits 

 are cut outside. The recognition of these dentpits and a knowledge 

 of their rate of formation thus enables us to decide a very important 

 question and the answer is evidence of the strongest character for 

 preglacial or interglacial Lake Valcour. 



As dentpits stand in such an intimate relation to solution it will 

 be important to consider next this factor in the formation of the 

 Valcour island caves. : 



Solvent power of Lake Champlain on its limestones. Cystid 

 point, on the southeast shore of Valcour island, seems to be caused 

 by the presence of a fissure, and the little cove just south of it is 

 filled- with movable rock debris to a depth of about 2 meters. On 

 either side of this cove the shores consist of bare rock. Suspecting 

 the eastward extension of a fault here, I have made an examination 

 of the visible lake bottom from a rowboat on a perfectly still day at 

 a time of low water in the fall of the year. The condition under 

 water was much like that noted on the exposed shore. A depressed 

 belt over the fissure was covered with boulders and pebbles of 

 various kinds and sizes while, on either side of this, large areas of 



