44 Joty—An Estimate of the Geological Age of the Earth. 
We may now refer to a similar table of the sedimentaries: still deriving our 
figures as averages calculated from Rosenbusch’s work :—— 
K,0. Na,0. 
Mean of 16 Sandstones, Quartzites, and Greywackes (p. 391), 1°56 0:92 
», 12 Clays and Shales (p. 420), : : ‘ : ile7/il 0°48 
» 17 Clay-slates (p. 425), 0 : . 6 ‘ 2°68 Lig) 
99 6 Calcareous Clay-slates and Whet-stones (p. 428), 2°69 0:98 
», 16 Phyllite-schists, or Clay-mica-schists (p. 487), . 3°52 1°53 
», 10 Schists (Serecite, Ottrelite, Chlorite, &c.) (p.436), 2°36 1-04 
» 18 ‘ Pelit-gneisse’ (Phyllite-gneisses) (p. 470), . 3°18 1°69 
99 8 ‘ Psammit-gneisse’ (Sandstone-gneisses) (p. 471), 1:95 2°13 
8 Amphibole-gneisses (p. 484), . : : : 1°44 2°65 
% 4 Mica-schists (p. 497), . 0 : : : 3°85 2°07 
Mean of sedimentaries, ; : 2°49 1:47 
We may observe further that the averages afforded by the valuable collection 
of analysis of American rocks, compiled by Messrs. Clarke & Hillebrand, will 
be found to confirm these results.* 
For the original crust, Clarke’s alkali ratio works out—— 
Na,O _ 129 
iGO ~ si 
and Rosenbusch’s, 
NaO 1:22 
iO 1” 
On the other hand Rosenbusch’s sedimentary rocks show that 
Na,O 0°59 
EO ~~ i 
When it is remembered that, age by age, those sediments were being 
deposited, some directly from the parent igneous rocks, and others by denudation 
of former sediments, the great importance to the present hypothesis of this broad 
difference in the alkali ratios, and in the absolute amounts of sodium and potash 
in the original and derived rocks, must be evident. 
If now the inference is right that the missing alkalies were supplied to the ocean, 
we should expect to find on a rough approximation of the bulk of sedimentaries, 
and hence of the original rocks giving rise to them, that such a mass of parent 
rock would be adequate to supply the sodium in the ocean. And this is actually 
the case; we find, in fact, that the estimated amount of sedimentary strata would, 
* U.S. Geol. Survey. Bulletin No. 148, 1897. 
