122 DYNAMICAL GEOLOGY. 



Professor A. Corsa subjected the rocks mentioned below, after fine pulverization, to the 

 action of pure water at 05° F. for several days ; the weight dissolved was as follows : — 



Gneiss, from Ragogna, 0-1250 per cent ; porpliyritic retinite, from Monte Sieva, 0-0562 ; 

 perlyte, of Monte Sieva, 0-0024; phonolyte, of Monte Croci, 0-3260; trachyte, of Monte 

 Ortona, 0-0871 ; gx'anite, of Montorfano (Lago Maggiore), 0-0727 ; granite, of Baveno (Lago 

 Maggiore), 0-0966. 



Professors W. B. and R. E. Rogers found in their experiments (Amei: Jour. Sci., 1848), 

 that under the action of carbonated waters, 0-4 to 1 per cent of the whole weight under 

 digestion dissolved in only 48 hours. 



Daubree exposed orthoclase from Limoges in small fragments in a vessel containing 

 twice as much water by weight revolving at the rate of 2550 meters per hour. The water 

 in 8 days, after revolutions equivalent to a flow of 460 kilometers, contained 2-52 grams 

 of potash per liter, along with 0-03 of alumina and 0-02 of silica. In salt water (water con- 

 taining 3 per cent of NaCl) there was only a feeble alkaline reaction, incomparably less 

 than with pure water. 



Water derives its chemical efficiency through the presence of such impurities 

 as are ready to enter into new combinations. The most common of these 

 foreign materials are carbonic acid (COo), humus acids, and alkaline ingredi- 

 ents. When carbonic acid is present one part of calcite will be taken up by 

 1000 of water ; but in this case the material dissolved is not calcium carbo- 

 nate, but calcium bicarbonate. Again, the presence of soda or potash gives 

 increased solubility to silica in its soluble or opal state, — the state charac- 

 terizing organic silica. 



The least effect from moisture in rocks is diminished resistance to 

 fracture or cohesion. Part of this is due to the lubricating effect resulting 

 from the wetting of the grains, in consequence of which they slide over 

 one another more easily than when dry. On this principle a grindstone is 

 wet before using it. But in the case of wet rocks there is often, perhaps 

 generally, a solution of a minute portion of some ingredient of the rock 

 which becomes solid again on drying. For this reason, sand rocks, whether 

 calcareous or siliceous, gradually harden at surface from alternate wetting 

 and drying. 



The more prominent destructive effects of water, consequent on its solvent 

 powers, are : the easy erosion of beds of gypsum ; the rapid removal of beds 

 of salt ; and the injury to animal and vegetable life from encroachments of 

 mineral and marine waters, and to marine life by its concentration on 

 evaporation in shallow basins. The constructive effects are : the deposition 

 of salt and gypsum in large beds ; and also the local superficial consolidation 

 of rocks alluded to above. 



Oxidation and Deoxidation. 



On account of the very strong attraction between oxygen and nearly all 

 the elements, and also because this gas is always at hand in air and water, 

 it is the most prominent agent in the world's destructive and constructive 

 chemical changes. 



