568 



A TREATISE ON METAMORPHISM. 



A fuller table, showing the relations of temperature and pressure 

 between 225° and 365° C, at intervals of 5° C, is given below." 



Relations of temperatures and pressures of water. 



From these tables it is seen that the hydrostatic pressure at various 

 depths is normally far in excess of that required to hold the water in the 

 form of a liquid, or, looked at in another way, for any given depth the 

 temperature is not sufficiently high to allow the water at that depth and 

 pressure to exist in the form of a gas. 



It therefore appears perfectly clear that where the increase in tempera- 

 ture with depth is normal the water remains as a liquid to its critical 

 temperature, i. e., 365° C, and that the depth of the zone of water circu- 

 lation is, therefore, about 10,000 or 11,000 meters. In another place (pp. 

 189-190), it has been shown that this approximates to the greatest depth 

 at which continuous crevices and cracks can long exist in the earth. It 

 therefore follows that in the belt of cementation the water is normally in the 

 form of a. liquid to the bottom of the zone. Where magma is intruded in 

 the lithosphere the temperature may become so high that this statement 

 will not hold. But this is the exceptional, not the usual case. Furthermore, 



"Preston, Thomas, The theory of heat, Macmillan & Co., London, 1894, p. 385. 



