T. 8S. Hunt—The Decay of Rocks. 193 
ness of 120 feet.” This process is evidently due to a simple 
solution of the carbonates of lime and magnesia in meteoric 
aters, 
$9. A similar decay is conspicuous along the outerop of the 
Auroral limestones and their associated schists in the Appa- 
lachian valley, as will be noticed farther on, in $27, and may 
also be seen at several points in the Trenton limestone and the 
Utica shale of the St. Lawrence valley. One of these localities, 
described by Dr. J. W. Dawson, is at Les Eboulemens, on the 
north shore of the St. Lawrence, below Quebec. ere, at t 
southwest base of the high Laurentide hills, the Post-pliocene 
clays, enclosing marine shells and large gneiss bowlders, are 
found resting upon a mass of Utica slate, deprived of its calea- 
Teous matter, and so soft as to be readily mistaken for the 
newer clays of the region but for its stratification and its 
organic remains. This, according to Dawson, had been changed 
to a great depth by sub-aérial action previous to the period of 
10. It may be said that with the exception of Darwin, who 
had observed the decay of rocks in Brazil and conjectured that 
the process might have been sub-marine, all observers have cor- - 
rectly regarded it as sub-aérial. The chemistry of the process 
was discussed, among others, by Fournet in the paper already 
cited, and later by Delesse in 1853; also very fully by Kbel- 
men, who considered the question of rock-decay in its relations 
to the atmosphere, in two memoirs in 1845 and 1847." The 
same subject was further considered at some length by the 
present writer in 1880." Ae ea ne 
$11. Having thus briefly indicated some of the points in its 
to this, as we have seen, it had been recognized that the process 
of rock-decay had been in operation not only in pre-glacial — 
ut in pre-Tertiary times, and that the resulting material had 
en the source of Tertiary clays and sands, and even, in certain 
cases, of glacial drift and bowlders. Py 
$12. In a review of Hartt’s volume on Brazil, in 1870, the 
present writer said: “The great wasting and wearing-away of 
crystalline rocks in former geological periods, of which we have : 
,, Geological Survey of Missouri; Iron Ores and Coal Fields, p. 8. ee 
* Dawson: Notes on the Post-pliocene Geology of Canada; from Canadian 
Naturalist, vol. vi, 1872. - . 
z Bull. Soc. Geol. de France, x, 256. 
Annales des Mines [4], vii, and xiii, 
This Journal, xix, 349; see also his Chem. and Geol. Essays, p. 100 
Jour, rye Series, VoL. XXVI, No. 153,—SeEpr., 1883. 
