Joty—An Estimate of the Geological Age of the Earth. oT 
residual material from the most diverse rocks are very similar in compo- 
sition. 
The full tables should be consulted.* 
K,0. Naz20. 
Residual soil from Limestone, Wisconsin, 4°5 feet from surface, 1°61 2°19 
Same, 83 feet from surface, . ; : : 6 : : 0:93 0°80 
Residual soil from Limestone, Wisconsin, 3 feet from surface, 0°83 1°45 
Same, 43 feet from surface, . ‘ ; 5 : : ; 1°60 TLOSsY/ 
From Dolomite, Alabama, 5 : 3 ; : , : 2°32 0°17 
From Diabase dike, N. Carolina, . : : : é 0 trace. trace. 
A Gabbro-soil, Maryland, : j : 3 : ; j 0:86 0°40 
Subsoil from Trenton Limestone, Maryland, . 5 : : 4°41 0°29 
Soil from Triassic Sandstone, Maryland, 0 6 : : 4°08 0:79 
Trenton Limestone, unaltered, : : ; ; 6 ‘ not det. not det. 
Residual soil from same, F : ; : : ; ; 2°50 1:20 
Gneiss, Virginia, . ; ; : 5 : : 5 ; 4°25 2°42 
Soil from same, . : 6 6 . : : ; ; 1:10 0:22 
Diorite, Virginia, . : : : : ‘ , : : 0:55 2°56 
Soilfrom same, . 5 5 : : : : : é 0:45 0°56 
In the above it appears that the soils derived from the igneous rocks—more 
especially the more basic ones—show a greater poverty in alkalies than those 
derived from Limestones and Sandstones. This probably arises, in part, form 
more soluble alkali constituents being present, but in many cases doubtless from a 
more resistant parent rock leading to the more complete weathering of the soil. 
On the other hand, the more soluble Limestones rapidly concentrate their siliceous 
materials to a soil rich in very fine felspathic and other particles. 
In short, the daily and yearly action of the weather upon such soils would not 
show a yield of alkali greater in the case of those residual from igneous rocks than 
from those residual from sedimentary rocks. The attack on the rock beneath 
must furnish a very minute supply of alkalies contrasted with what is proceeding 
from the soil. Merrill refers to a calculation in reference to one of the ‘Trenton 
Limestone soils that, in every cubic foot of soil, “158,000 square feet of sur- 
face are exposed to the action of water and air as well as to the roots of growing 
plants.” 
It is, too, a fact of common observation and comment, that igneous and 
eruptive rock masses are more slowly denuded than the majority of sediment- 
aries. Whether in regions of Limestone or Slate the higher and more abrupt 
surface features are generally the granitic or igneous masses; and this obtains 
* Loe. cit., pp. 305, 806; also, pp. 358, 359. + Loe. cit., p. 307. t Loe. cit., p. 808. 
K2 
