SOLUBILITIES OF CHEMICAL CONSTITUENTS OF ROCKS 111 
column II and called “surface rocks.” These figures are assumed 
to represent the composition of the rocks leached by drainage 
waters, and, compared with the mean composition of the latter, 
column I, give the average relative solubilities of the abundant 
constituents of the earth’s crust. 
The latter values are represented by the ratios between the 
constituents in the water and the corresponding constituents in 
the rocks. These values appear in columns III and IV, in the 
latter recalculated to a basis of lime= too, lime having the highest 
relative solubility, being an abundant constituent, and readily 
determined with accuracy. 
The constituents are written in the order of relative solubility 
beginning with CaO. 
I II III HIV Ac 
Corkes aiean Surface Rocks | Rel. Solubilities. | Re, gglubbities 
(Ca@r ees one 48.34 joe Ounle7, 100.0 
INBADS Rae are 14.61 1.69 8.64 96.1 
WANS OSs aiarecleear 9.55 2.86 3.34 36.3 
USAO a avalon 3.09 2.84 1.09 I1.g 
‘SiO)ag arene eos 19.7 58.88 - 0.34 3.7 
RO ere etiscartose 4.65 19.35 0. 22 2.6 
Thus, assuming the accuracy of the figures in columns I and II, 
it follows that the abundant oxides of the crust are dissolved at 
relative rates represented by the figures of columns III and IV, 
Lime and soda appear to be dissolved at about the same rate, 
magnesia at about one-third this rate, potassa again about one- 
third as fast as magnesia, silica about a third as fast as potassa, 
and the sesquioxides about two-thirds as fast as silica. How far 
these figures may be trusted depends, obviously, upon the reliability 
of the estimated composition of river waters and of surface rocks. 
That these estimates will be modified in future is beyond question, 
and any change will, of course, affect the values of the relative 
solubilities. But it is believed that the figures given are a fairly 
close approximation to the true values, indicating, at least, the 
proper orders of magnitude. The most questionable figure is that 
for soda, since it is this constituent that is largely retained in the 
ocean and least likely to be accurately estimated in sediments, 
