24 COLORADO COLLEGE STUDIES. 



tion along this line. The disintegration of surface rocks by 

 atmosiDheric agencies is very apparent to the eye, and the 

 products of this resolution of the rocks have been the sub- 

 ject of careful study. Carbonic acid from the atmosphere, 

 or that derived from the oxidation of decaying organic mat- 

 ters in the soil, plays a very important part in the disintegra- 

 tion of silicate as well as of carbonate rocks. It produces in 

 the former class carbonates of the alkalies and alkaline earths, 

 and these salts are carried away along with some silica and 

 metallic carbonates, etc., in the percolating waters. It is 

 believed that all rocks, at least to very great depths, are per- 

 meated with Walter which has made its way from the surface 

 downward, and which exerts an action like that shown on 

 rocks near the surface of the ground. As these meteoric 

 waters descend they gradually lose the more active elements, 

 dissolved oxygen and carbonic acid, with which they began 

 their journey — being exhausted in short distances when they 

 percolate slowly through the rocks, and carrying them to 

 great depths when they pass through porous or shattered 

 rocks, especially when they find channels or fissures in which 

 to flow; but as the waters reach more deeply buried zones a 

 new resolvent power and chemical activity is developed in 

 greater and greater degree by the increasing heat and pressure 

 to wdiich they are subjected. Under the influence of these 

 stimuli the metamorphism of rocks proceeds at a vastly in- 

 creased rate, kaolinization, solution, chemical combination 

 and crystallization working a silent, ceaseless change in 

 many kinds of deeply buried formations. Evidence of this 

 heightened action of heated waters is afforded to us in the 

 hot springs of all countries; as a rule, waters which issue 

 from the earth at high temperatures bring with them excessive 

 quantities of dissolved mineral matters. The modern theories 

 of the filling of fissure veins is largely based upon the greater 

 solubility of silicious and calcareous compounds, metallic 

 sulphides and other vein matter, in the heated waters at the 

 deeper parts of the earth's crust to which such crevices 

 extend, or to waters heated by bodies of igneus rocks in 

 process of cooling; although of course at any depth, small or 

 great, the solvent action of water takes place, and solution 



