320 VAN HISE—METAMORPHISM OF ROCKS AND ROCK FLOWAGE. 
capillary tubes in 42 minutes and 18 per cent in an hour. This shows 
that solution continued during the later stages of the experiment at 
about the same speed as during its earlier stages, for 13:42 about as 
18:60. This is apparent when the first terms of the ratios are made 1, 
for the proportion then stands 1:3; about as 1:33. From this propor- 
tion it appears that the action was apparently slightly more rapid during 
the last few minutes. Reasons which may be suggested for an increased 
rate of action, supposing the pressure, temperature, and composition of 
the glass to remain constant, are (1) the smooth glass at the beginning 
of the process was less readily attacked than the roughened surface pro- 
duced by solution ; (2) the roughening during the process gave the glass 
increased surface for action as the experiment continued. However, the 
apparent change of rate is so slight as to be possibly attributed to errors 
of observation. 
During the experiment, unless hydrous minerals were produced, the 
water remained a constant quantity, and continued work. This could 
~have been continued so long as the temperature and pressure were suffi- 
cient and glass was available for crystallization through solution, as a 
result of which the material is condensed. If no hydrated minerals are 
formed, there is no reason why a small amount of water cannot omiunas 
the process indefinitely. 
If in this experiment we suppose the condensation of recrystallization 
to be 10 per cent, the amount of condensation in diabase in passing from 
the glassy to the crystalline conditlon, as shown by Barus,* this would 
mean (neglecting the condensation of the water) that in one hour, in 
order to have given an apparent voiume contraction of 18 per cent, the 
water had dissolved 1.8 times its own volume of the glass, and depos- 
ited crystallized material. with 10 per cent less volume. Therefore, for 
the water to dissolve a volume of glass equal to that of the water and 
deposit it in a crystallized form would require 333 minutes, or approx- 
imately one-half hour. 
This illustrates the fact that the activity of water is amazing at a very 
moderate temperature, and one need not be surprised at its potency in 
the alteration of rocks deep below the surface of the earth. Temper- 
atures higher than 180° C. exist at moderate depth, and therefore it is 
reasonable to suppose that a small amount of water may be the medium 
of rapid and most profound modification of the rocks. 
We have already seen (pages 299, 300) that during the process of de- 
formation the material, if not dissolved, may be strained even to the 
point of granulation by the mechanical processes; also it has been 
seen that, so far as strain occurs, or the particles are small, the minerals 
* The contraction of molten rock, by C. Barus: Am. Journ. Sci., vol. 42, 1891, pp. 498, 499. 
