l6o NEW YORK STATE MUSEUM 



because soon after it was filled, and before the central portion had 

 become cold, the fissure walls sprang wider apart and a new filling 

 rushed up from below. Before its arrival, however, and under the 

 low pressure of the newly opened walls, the bubbles near the older 

 lava surfaces expanded and by that expansion further chilled their 

 walls. They thereby saved their bubbles from obliteration by the 

 new filling. A view of this dike is given in figure 7. 



There seems to be evidence that these fissures never reached the 

 ancient surface of the land. This evidence will be given in a forth- 

 coming paper on the " Geology of Valcour Island." If the con- 

 clusions there given are supported by further study, we may hold 

 that after this dike was injected into its fissure, some 3000 feet 

 thickness of deposits have been removed from over its present 

 exposed portion. The dikes of the Champlain valley have not yet 

 been given the attention they deserve. 



