T.S. Hunt—The Decay of Rocks. 203 
will generally serve to distinguish the sideritic from the pyritic 
limonites.” *° 
In the paper just quoted I have also considered the change of 
volume which should accompany the conversion of pyrites into 
limonite, a process generally complicated by the loss of a part 
of the iron as a soluble sulphate. 
30. Portions of the contorted and often highly inclined 
schistose strata enclosing the limonite ores in the Appalachian 
valley, are still found but partially decayed, and while some 
are converted to depths of 100 feet or more into white or vari- 
ously colored clays, others‘retain more or less of their original 
texture. From the presence in some of these of considerable 
quantities of a hydrous micaceous mineral, having the compo- — 
the outlying or western’ valleys of the Appalachian region, 
ors “3 Pennsylvania and in Alabama.” 
the Shenandoah valley had been washed into it from or across 
the Blue Ridge,” This Lesley properly get ig as an “ab- 
“plain 
or more to the west of the Blue Ridge; and declares that had 
- 8S, M. Jackson continued his geological studies, “he would 
have published a satisfactory refutation of this surface-drain- 
age theory of the brown hematites.’ 
% The Genesis of certain Iron Ores, read before the Amer. rere 
see (i 
Boston, 1880 - i : 
Adv. Science, 
nadian Naturalist, for Dec. 1880, vol. ix, p. 434. 
as : of a 
t + 
_ Portion of the ancient deca yed strata of the valley, are of comparatively ine 3 
Sconomic importance. (See H. C. Lewis, Proc. Acad. Nat. Sci. Philadelphia, Oct. 
= : “Second Geol. Survey of Penn., Report A, p. 83. 
