\ GROUND WATER UNIVERSAL. 123 



important factor in the process is the extension of the rock masses from 

 the places of solution to the places of deposition. For instance, in any 

 rock which extends from the belt of weathering to the belt of cementation 

 the water at the places of solution (especially the belt of weathering) 

 would obtain material adapted to the enlargement of the minerals of. the 

 same rock at the place of deposition (especially the belt, of cementation). 

 Consequent upon the two factors above given, rocks in many instances 

 are cemented by minerals like those present before cementation began. 



SECTION 2. CIRCULATION AND WORK OF GROUND WATER. 

 UNIVERSAL PRESENCE OF WATEE IN ROCKS. 



It has already been explained at the opening of this chapter that water 

 is the great dominating ag-ent through which the greatest transformations 

 are accomplished. Free water is present to some extent in all rocks within 

 the zone of observation. That it is abundant in porous rocks is well 

 known. Water has also the power to slowly penetrate the apparently solid 

 rocks. Between the mineral particles there is space sufficient for water to 

 make its way, and a small amount of water is found in the most massive 

 and relatively impervious rocks. 



Besides the free water in rocks, there is always present water in a 

 combined form. The combined water varies from a small fraction of 1 per 

 cent to several per cent. Commonly the combined water does not fall 

 below 0.50 per cent, and seldom is higher than 8 per cent. It therefore 

 appears that all rocks contain water, both in the free and in the combined 

 form. The amounts of each of these are very variable. Bischof many 

 years ago noted the penetration of basalt by water." The permeation of 

 apparently solid rocks by water is well illustrated by the readiness with 

 which agate, chalcedony, and such materials are affected by a staining 

 solution. When agates are boiled in colored solutions, the liquid makes its 

 way through the minute subcapillary spaces so small that the microscope 

 can not detect them, and the bands are differently tinted, the amount 

 of deposited coloring material depending upon the relative sizes of the 

 minute openings. 



° Bischof, Gustav, Chemical and physical geology, translated by Paul and Drumniond, Harrison 

 & Sons, London, vol. 1, 1854, p. 10. 



