392 Transactions of the South African PhilosopJiical Society. 



into the lower half of the vessel, the water becomes vapourised and 

 exerts a pressure of several atmospheres in endeavouring to escape, 

 yet it is apparently not able to find its way out through the sandstone. 

 This is another reason for rejecting Prof. Suess' theory of the water 

 in hot springs having come by transudation from the interior of the 

 Earth. 



Having now cleared the way for the statement that water per- 

 meates all rocks down to the zone of permanent potential fusion, 

 it remains to examine how this water helps on the deformation of 

 rocks. To get some idea of the nature of the solvent action of water 

 under great temperatures and pressures we have to go to the 

 experiments of Carl Barus" in America, though Hannayi to a certain 

 extent clea.red the ground. 



Barus found that water under pressure at a temperature of 180° C. 

 contained in capillary tubes of glass, decreased very markedly 

 in volume, and this decrease went on at a fairly uniform rate 

 the longer the conditions were maintained. On examining the 

 tubes, he found that a considerable quantity of glass had been 

 dissolved and redeposited in a crystalline condition. As the 

 crystalline state is one of a closer packing of the molecules as 

 compared with glass, the apparent decrease of volume in the water 

 was thus explained. Below 180° C. this effect did not take place, 

 but above it the solution and crystallization went on very much 

 more rapidly, far more so than proportional to the increase of 

 temperature. The control of experiments of this kind at enormous 

 temperatures is extremely difficult ; as the critical temperature of 

 water is 773° F., above which it cannot exist as a liquid and the 

 molecule already becomes unstable, it is probable that the power 

 of dissolving silicates goes on at an increasing rate with increase 

 of temperature, till it reaches a maximum at 773° F. ; at this point, 

 if not before it is reached, it is very probable that all known rock- 

 . substances are soluble in water. 



The effects of solution on deformation are very remarkable. To 

 begin with carbonates which are soluble in water containing 

 carbonic acid. The effects in this case are to remove the carbonates 

 bodily from points where there is pressure and to deposit it else- 

 where. Some beautiful examples of this are given by Chapman 

 from the oolitic limestones of Ilfracombe.:[: We see here the 

 original rounded grains of the oolite pressed upon one another 

 and flattened normal to the direction of pressure, not only so, 



* Bull. Geol. Survey, U.S.A., No. 92, 189-2, pp. 78-84. 



t Nature, July 15, 1880. 



+ Geol. Mag. x., 1893, p. 100, pi. 5, especially Fig. 2. 



