WEATHEKING OP BASALT 





62.44% of the deeomposed. The large percentage of soluble mat- 

 ter in the last case, it shonld be noted, is due mainly to the 

 iron oxide. The region is one of a mean average temperature 

 of 56.9° Fahr., and recorded extremes of — 6° and +102'', 

 with a rainfall of 42.85 inches. The ground, as a rule, freezes 

 in winter to but a slight depth, and remains so but a few days 

 at a time. 



Weathering of Basalts. — Eesearches on basalts in Bohemia 

 and France yielded Ebelman^ results of similar import, although 

 in neither ease had decomposition gone so far as in that de- 

 scribed by Dr. Watson. 



In the case of the Bohemian basalt, the decomposition com- 

 menced with the formation of boulders, which, when the 

 process had not gone too far, still showed fresh, unchanged 



Analyses of Fresh and Decomposed Basalt from Bohemia 









I 



II 



III 



IV 



y 



VI 



Constituents 





 a 







^^ 

 < m 



if 

 p3s 



S a 

 02 



Percentage Lobs 

 FOB Ehtibb 

 Rook 



Percentage of 

 Each Constit- 

 uent SATED 



Percentage op 

 Each Constit- 

 uent LOST 



Silica (SiOa) .... 



43.61 



0/ 



/o 

 -43.00 



% 

 43.27 



% 



15.04 loss 



•y 



/o 



67.01 



% 

 32.99 



Alumina (AI2O3) 







12.26 



13.90 



18.13 



0.00 " 



100.00 



0.00 



Ferric iron (Fe208) . 

 Ferrous iron (FeO) . 







3.61 

 12.16 



5.40 \ 

 8.30 J 



11.70 



9.10 ** 



49.83 



60.17 



Lime (CaO) . . 







11.37 



12.10 



2.60 



9.60 " 



64.47 



84.53 



Magnesia (MgO) . , 







9.14 



'7.30 



3.40 



6.83 *' 



25.90 



74.10 



Soda (NasO)' . . . 

 Potash (K2O) . , . 







2.72 1 

 0.81 j 



0.60 



0.20 



3.39 " 



38.31 



61.69 



Water (H2O) . . . 







4.42 



9.50 



20.70 



0.00 



100.00 



• • • « 









100.00 % 



100.00 % 



100.00 % 



43.96 







■ • • * 



basalt interiorly, but became more and more altered toward 

 their peripheries. The first stage of decomposition (column II), 

 it will be noted, consists, aside from hydration, in a slight appar- 

 ent loss of silica, a considerable oxidation of the iron magnesia 

 minerals, accompanied by a slight loss of both constituents, and 



^Ann. des Mines, Yol, YII, 1845. 



