LOSSES OF MATERIAL BY SOLUTION. 523 



now soapstone, from Fairfax County, Va., 77.95 per cent; and supposing 

 the silica constant, a Carboniferous limestone from Arkansas has lost 97.635 

 per cent. 



Watson " has calculated the losses of various disintegrated and decom- 

 posed granites from Georgia, including granite, porphyritic granite, and 

 granite-gneiss, and has found that the loss for the entire rock varies in 

 different cases from 7.68 to 71.82 per cent* The losses are in- all cases 

 higher on the assumption that the Fe 2 3 is constant than on the assump- 

 tion that the Al 3 is constant/ 



So far as I am aware, computations have not been made as to the 

 addition of the constituents oxygen, carbon dioxide, and water in the proc- 

 esses of weathering. Until this is done it is impossible to make approxi- 

 mately accurate quantitative statements as to the total amounts of original 

 material and weathered material. It is still less practicable to make quan- 

 titative statements as to the relative volumes of the original and altered 

 materials, since in this matter are involved not only the additions and sub- 

 tractions of materials, but the specific gravities of the original and second- 

 ary materials and their states of aggregation. Undoubtedly the specific 

 gravities of the resulting minerals are less, on the average, than the specific 

 gravities of the original minerals. Also, the state of aggregation is in almost 

 all cases less compact. Therefore, for a given amount of material the 

 volume of the weathered products is greater than that of the original 

 material. But notwithstanding the .addition of material, the lessened 

 specific gravity, and the looser state of aggregation, the losses of the 

 original elements are so great, where decomposition has gone far, that 

 there is no question that the volume of the resultant material is often 

 diminished. 



Among the cases of diminished volume, that of the formation of 

 residual clay from limestone undoubtedly represents the maximum. The 

 dominant constituent of the rock, calcium carbonate, has been almost 

 wholly dissolved and removed. The few feet of residual material at the 

 surface of limestones represents the alteration products of the noncalcareous 



"Watson, Thos. L., Weathering of granitic rocks of Georgia: Bull. Geol. Soc. America, vol. 12, 

 1901, pp. 93-108. 



& Watson, cit, p. 101. 



o Watson, cit., pp. 106-108. 



