144 JOURNAL OF THE [JunCj 



New Hampshire,'* of the apparent conditions by which the car- 

 bon dioxide was actually formed in the cavities of the granyte at 

 that locality, /. e., by expulsion from a limestone in contact with 

 silicic acid. This was the same effect as that which we now see 

 in the effervescence of carbon dioxide produced when any free 

 acid is dropped upon calcium carbonate. 



The general investigation of the fluid-cavities is by no means 

 exhausted, and it may lie within the reach of members of this 

 Society to gather new facts which may throw great light upon 

 the conditions of metamorphism to which the rocks and miner- 

 als inclosing such cavities were subjected. 



"Geol. of N. H., Vol. III., Pt. IV., p. 207. 



