646 General Notes. [June, 
comparative studies of Reusch in Norway and in Corsica, in — 
which similar views are enforced. 
The principal points in the paper are resumed at its close, as 
follows : ie” 
1. The evidence afforded by recent geological studies in Amer- 
ica and elsewhere, of the universality and the antiquity of the 
subaérial decay both of crystalline silicated rocks and of c 
ous rocks, and of its great extent in Pre-cambrian times. } 
u. The fact that the materials resulting from such decay are 
preserved 7 sifu in regions where they have been protected from 
denudation by overlying strata, alike of Cambrian and of more 
recent periods; or, in the absence of these, by the position of the 
decayed rock with reference to denuding agents, as in driltless 
regions, or in places sheltered from erosion, as within the St 
Lawrence and Appalachian valleys. 7 
ur. That this process of decay, though continuous through : 
later geological ages, has, under ordinary conditions, been msig- 
nificant in amount since the glacial period, for the reason that the — 
time which has since elapsed is small when compared with pre- 
vious periods, and also probably on account of changed atmos — 
pheric conditions in the later time. ed 
1v. That this process of decay has furnished the material ps : 
rocks by the more or less complete loss of p 
bases thus separated from crystalline silicate 
the source, directly or indirectly, of all limestones and ca 
rocks, and have, moreover, caused profound secular cha 
the composition of the ocean’s waters. The decomposition 
phuretted ores in the Eozoic rocks has given rise to oxy 
iron ores 7m situ, and to rich copper deposits in various geog 
oon eft in the pr 
drift, but, 
GEOLOGY OF THE CHESTER VALLEY OF Penxsyivania-— Tido 
lowing note from Mr. Chas. Hall further criticizes pot A 
Mr. Rand, which was the subject of a review by Fro! 
in the May number of the NATURALIST: 
