170 THE PEINCIPLES INVOLVED IN EOCK-WEATHERING 



The summary of his investigations he gives as below: 



(1) All the minerals tested were acted upon by the carbonated 



water. 



(2) In this process there were formed carbonates of lime, iron, 



manganese, cobalt, nickel, potash, and soda. 



(3) In the action of the carbonated waters upon the alkaline 



silicates, like the feldspars, a small amount of silica went 

 always into solution, presumably in the form of hydrate. 



(4) Even alumina was dissolved in appreciable quantities. 



(5) Adular proved more resistmg to the action of the acid than 



did the oligoclase. 



(6) The first stage of decomposition in the felijspars was a red- 



dening process; the second, kaolinization 



(7) Hornblende was more easily decomposed than feldspar. 



(8) Increase of pressure on the solution was productive of more 



energetic action than prolonging the time. 



(9) Of all the minerals tested, the magnetic iron was least affected. 



(10) Apatite was readily acted upon, as could be detected by its 



appearance under the miscroscope. 



(11) Olivine was the most readily attacked of all the silicates tested, 



probably twice as easily decomposed as the serpentine. 



(12) Magnesian silicates were attacked by the carbonated waters. 



Hence serpentine cannot be considered a final product of 

 decomposition.^ 



These and similar tests by more recent workers show with ap- 

 parent conelusivenesss that all the ordinary rock-forming miner- 

 als, — silicates, oxides and carbonates — are appreciably soluble 

 in the water of rainfalls and at ordinary temperatures. 



Of all the materials forming any essential part of the earth's 

 crust the limestones are most affected. It is stated that pure 

 water will dissolve lime carbonate in the proportions of one part 

 in 10,800 when cold and one part in 8875 when boiling. 



Since rock-weathering is, as already stated, a superficial 

 phenomenon, we have to do only with waters of ordinary tern- 

 peratnres and under Ordinary conditions of pressure, though 

 this expression must not be taken as necessarily meaning cold 

 waters, since, if we accept the statements of Caldcleugh,'' rain 

 waters falling upon the heated rocks may have their tempera- 

 tures raised as high as 140° F. The enormously destructive 

 effect of carbonated waters on limestone is scarcely apparent 



^Serpentine, however, cannot be properly considered a decomposition 

 product. It is rather a product of alteration. See p. 107. 

 * Trans. Geol. Soc. of London, 1829. 



