WEATHERING- OP CALCAEEOUS ROCKS 



217 



laid by a capping of chert, which reduced to a minimum the 

 possibility of any admixture of foreign matter. The materials 

 were dried at a temperature of 110° to 115° C before analyzing. 



Analyses of Fresh Limestone and its Residual Clay, Batesville 



Arkansas 



CONSTITtlENTS 



Silica (SiOa) .... 

 Alumina (AI2O3) . . 

 Terric iron (^6203) 

 Manganic oxide (MnO) 

 Lime (CaO) .... 

 Magnesia (MgO) . . 

 Potash (K2O) . . . 

 Soda (Na20) .... 

 Water (H2O). . . . 

 Carbonic acid (CO2) . 

 Phosphoric acid (PaOs) 



o 



4.13% 



4.19 



2.35 



4.33 

 44.79 



0.30 



0.35 



0.16 



2.20 

 34.10 



3.04 



100.00 % 



11 



5 



hi 



o 



» 



w 



33.69% 

 30.30 



1.99 

 14.98 



3.91 



0.26 



0.96 



0.61 

 10.76 



0.00 



2.54 



100.00 % 



III 





DO W 

 K GO U 



woe? 



0.00^ 



0.47 



2.11 



2.49 

 44.32 



0.27 



0.23 



0.085 



0.95 

 34.10 



2.73 



87.755% 



IV 



o S 



100 00 % 

 88.65 

 10.44 

 42.41 



1.07 

 10.62 

 33.63 

 46.74 

 58.37 



0.00 

 10.24 



O H 



s ^ 



H O 



U H 



« ■< 



0.00% 

 11.35 

 89.56 

 57.59 

 98.93 

 89.38 

 66.37 

 53.26 

 41.63 

 100.00 

 89.76 



These analyses have been recalculated in the same manner as 

 before, excepting that silica, instead of alumina, is taken as the 

 constant factor. It is believed that one is safe in assuming little 

 or no silica is lost here through the action of alkaline carbonates, 

 since the alkalies are almost wholly lacking in the fresh rock, 

 and a large portion of the silica doubtless exists as free quartz. 

 Eecalculating, then, in the same manner as before, but on a silica 

 constant basis, we obtain the matter in columns III, IV, and V. 



These columns bring to light some unexpected features, not 

 the least interesting of which is the fact that the residual clay, 

 in spite of its highly hydrated condition, in reality contains 

 scarcely half the amount of water it would, had the small amount 

 (2.26%) in the original limestone been allowed to accumulate 

 without loss. A more important, though perhaps more to be ex- 

 pected, feature is the entire removal of that portion of the lime 

 which existed as carbonate, as indicated by the absence of car- 



