62 A TREATISE ON METAMOKPHISM. 



The kinetic energy of a moving body is the product of one-half of its mass 

 into the square of its velocity. When a gas is very dense its molecules 

 are closely crowded, and on account of the molecular attraction there is 

 an appreciable decrease in the theoretical pressure, which is a measure of 

 the kinetic molar energy. Since the kinetic energy of the gaseous molec- 

 ular projectiles increases as the squares of the velocities, this may explain 

 why a slight increase of temperature often greatly increases the chemical 

 reactions of the gases in contact with the solids of the earth's crust, for 

 the likelihood of a chemical union depends, among other things, upon the 

 energy with which the particles of a gas come in contact with the minerals 

 of the rocks. 



SECTION 2. GEOLOGICAL WORK OF GASES. 



The observable geological work of gases is mainly above the level of 

 ground water, or in the belt of weathering. In the belt of cementation, 

 below the level of underground water, the rocks are saturated with water 

 solutions. Gaseous substances, if present, would be in solution in water, 

 and their action would therefore fall under water solutions, treated on later 

 pages. 



In the belt of weathering oxygen and carbon dioxide are immeasura- 

 bly the most important of the mineralizers, because they are present in the 

 interstices of the rocks in this belt throughout the land areas. However, 

 in volcanic districts any or all of the geologically important gases may be 

 present and have a very marked metamorphosing effect upon the rocks. 

 But of these gases that of water is of vastly the greatest consequence. 

 The consideration in detail of the effects of these various mineralizers and 

 of their action in conjunction with other agents properly falls in Chapter VI 

 on "The belt of weathering." 



In the deep-seated zone of anamorphism water itself is maunV above 

 its critical temperature (see pp. 659-661), and is therefore in the form of a 

 gas. On account of the great pressure the gases are dense. Under these 

 conditions most or all of the substances held in solution would also be in 

 the form of gases. The active substances would be solutions of gases in 

 gases. One would expect that the action of water gas holding in solution 

 other gases under such conditions of pressure and temperature would be 

 different from the action of highly heated water, in that its viscosity would 



