146 KEGINALD A DALY: 
proving displacement by the force of crystallization. More 
recently, Professor Shaler has appealed to the hypothesis of 
tensional force to explain the opening of certain vein-fissures, 
the latter not being explicable by the usually accepted idea of 
open fissures." 
In certain of these cases, it may be agreed that the mechani- 
cal force expended seems to have been applied pari passu with 
the process of crystallization ; so far as I have been able to find 
direct statement of the mode of application, each writer signifies 
his belief that the crystal itself did the work of rifting or of 
crowding together. We have seen that what little experimenta- 
tion has already been carried out so far, leaves this interpretation 
decidedly weakened. The question arises as to whether the 
energy is set free in the act of crystallization in ways other than 
-in the form of a push exerted by the growing crystal. An 
answer has suggested itself to me, and I shall briefly out- 
line it, without, I trust,seeming to imply that the idea is any- 
thing more than a somewhat highly specialized working 
hypothesis. 
In the Kettle Point shales, saturation of the underground 
waters by both free and combined carbon dioxide is not hard to 
imagine. An abundant supply of the gas could be found in the 
decomposition of the carbonaceous matter in the shales ;? the 
monocarbonate of lime is supplied in all necessary quantity 
from the calcareous bands in the shale and from the underlying 
Devonian limestones. 
Suppose now that a small fragment of carbonate of lime, 
organic or other, is enclosed in a rock, with a capillary film 
between mineral and rock. This fragment will act as the imme- 
diate stimulus to the decomposition of any sufficiently saturated 
* Bull. Geol. Soc. Amer., 1899, Vol. X, p. 259. 
? The analysis of the gas given off from the “east crater”? among the Mississippi 
mud-lumps of 1871 gave the following result: CO, 9.41 per cent., marsh gas 86.20 | 
per cent., N 4.39 per cent. HILGARD, Amer. Jour. Science, 1871, (1) p. 426. While 
the percentage of CO, is high, we may still regard this analysis as representative 
of the normal gases given off in the decomposition of vegetable matter buried in 
mud. 
