444 THE GEOSPHERES 



temperature higher than at the surface. It is a well-known 

 property of water to dissolve certain substances, and its efficiency 

 in dissolving many rock-substances is greatly increased when 

 the substances are subjected to pressure and heat; and, under 

 these conditions, it also ionizes complex substances — i. e., sepa- 

 rates them into their simple components or ions. Accordingly 

 when moist rocks are subjected to strong pressure at high tem- 

 perature, as is frequently the case deep in the earthcrust, the 

 rock-matter is dissolved at the points and planes of greatest 

 pressure and precipitated or redeposited at neighboring points 

 and planes of less pressure; so that, for example, a crystalline 

 cube of wet and hot rock -matter may be permanently distorted 

 by long-continued pressure on opposite faces, the crystals grad- 

 ually yielding to the stress in the direction of pressure and 

 elongating themselves in the orthogonal directions. Through 

 its property as a dissolving and ionizing agent, that portion of 

 the hydrosphere which penetrates and suffuses the lithosphere 

 has determined the texture and structure of most of our rocks ; 

 it has transformed the muds and sands and slimes of original 

 deposition into shales, sandstones, and limestones; in some 

 instances it has reconverted or metamorphosed these rocks into 

 schists, quartzites, and marbles ; still more significantly it has 

 aided in rem etamorphosing deep-seated rocks into lavas and 

 other crystallines. This extreme effect of water is peculiarly 

 instructive in that it reveals something of the character of the 

 centrosphere, whose dense materials are brought within reach 

 of observation only by water as a solvent and sublimant in the 

 form of lavas, vein-stones, and other rocks of hypogean origin. 

 There is reason for regarding the atmosphere as a differentiating 

 and dissipating factor, and the hydrosphere as a unifying and 

 conserving factor, both interacting with the centrosphere in such 

 manner as to develop the lithosphere and convert , it into the 

 terrestrial home of humanity,; but this relation need not be 

 pursued for the present. Yet it is worth while to note a curious 

 relation between lithosphere and centrosphere which is appar- 

 ently controlled' by the waters both of the surface and the 

 depths : The two inner geospheres are in unstable equilibrium-; 

 this is shown by the occasional escape of the deep-seated ma- 

 terials from the foundation of the lithosphere (if not from- the 

 centrosphere itself) in the form of extruded lavas and subli- 

 mated vein-stones ; it is shown also by the interminable heav- 

 ing of the centrosphere manifested in continental oscillation 



