174 NEW YORK STATE MUSEUM 



bed rock were free from loose material. At some distance from 

 the shore the material covering the belt was such as we should 

 fcx;pect to find in a region of washed till. The belt was here neither 

 so wide nor so thickly covered as it was on the exposed shore. 

 Wave action had evidently assorted and built up the shore de- 

 posit but the deposit under deeper water seemed to have suffered 

 little if any movement. 



Under about a meter and a half of water we noticed a pebble 

 about the size of a cobblestone which was resting with its bedding 

 planes in vertical positions and which appeared to show the results 

 of differential solution in a rather interesting manner. The ar- 

 rangement of its alternating layers of very fine silicious and cal- 

 careous sediments seemed strikingly like that of a peculiar bed 

 found on the island only in the weakest part of the Camarotoechia 

 shales. Its calcareous layers had been dissolved or eroded to con- 

 siderable depths, leaving the projecting silicious layers as an index 

 of the former size ajid shape of the pebble. One aspect of this 

 specimen is shown in plate 15. 



When broken from its bed, during the last glacial period, or when 

 separated from the larger block of which it may have formed a 

 part, it evidently had the form oi a four-sided prism with faces of 

 unequal area. In our figure it is resting on the remaining portions 

 of the largest of these former faces, which is much foreshortened 

 in the view, and it has what is now left of its former smallest face, 

 at the lower front. The latter face has been wholly lost from the 

 softer portions of the stone and these now possess an acute angle 

 in place of it. This prismatic form was considerably modified, 

 during its movement with the till, but was not wholly lost. Glacia- 

 tion seems also to have added a few facets. 



Any marked wave or water action on this specimen must have 

 been absent during the existence of Lake Vermont and the Hochel- 

 agan sea, for those were times of deposit in this locality. When 

 Lake Champlain began work at nearly its present level it had first 

 to remove these later deposits and wash out the finer material of 

 the till before it could begin to work on what then must have been a 

 smooth glaciated pebble. The cutting out or the dissolving of the 

 softer portions of this stone must therefore be purely the work of 

 Lake Champlain and oif no older body of water. Its study should 

 yield testimony of great value as to the ability of this lake to have 

 formed the series of caves which now lie along its Valcour island 

 shores. 



