JjLm 



EOGK DISINTEGRATION AND DECOMPOSITION 



in his analyses of tlie decomposed basalts of the Haute Loire, 

 which are given on p. 206. 



A varietal form of this rock occurring near Fostoria in Fair- 

 fax County, the same state, is thoroughly decomposed throughout 

 nearly the entire area to a depth of twenty or more feet. The 

 fresh rock is composed mainly of a light greenish, almost white 

 talc, with sporadic patches of chlorite some five or more milli- 

 metres in diameter, and scattering granules of iron ores. The 

 decomposed material is dull brownish or gray, and when washed 

 and submitted to microscopic examination is found to consist 

 almost wholly of brown and yellow-brown scales of talcose 

 material, intermingled with an impalpable silt, composed so far 

 as determinable of talcose and chloritic shreds. It is wholly 

 without grit, and with a decided soapy or greasy feeling. 

 Analyses of fresh and decomposed material, and calculations as 

 already given, yielded results as shown in the accompanying 

 xaDie. 



Analyses of !Presh and Decomposed Soapstone, Fairfax County, 



Virginia 





I 



II 



III 



IV 



Y 



CONSTITlTENTa 











02 



g 



M 



P5 



Percentage op 

 Lobs for Entire 



Percentage of 

 Each Constit- 

 uent SAVED 



Percentage op 

 Each Constit- 

 uent LOST 



Silica (Si02) 



Alumina (Al^Og) . . . 

 Iron oxides (I'eO and ^'6203) 



Lime (CaO) 



Magnesia (MgO) . . . 

 Alkalies (K2O and Na20) 

 Ignition (H2O) .... 



58.40% 



1 7.44 



0.00 



29.19 



0.00 



4.97 



64.84% 



33.75 



0.00 

 4.36 

 0.00 

 7,05 



46.31% 

 0.00 



28.23 



* « « • 



3.41 



20.70% 

 100.00 



3.29 



31.28 



79.30% 

 0.00 



96.71 

 68.72 





100.00% 



100.00% 



77.95 % 







THE WEATHERING OF SEDIMENTARY ROCKS 



The principles involved in the decomposition of fragmen- 

 tal and crystalline stratified rocks are not so different from 

 those we have been discussing as to call for detailed considera- 



