Wadsworth.] 
92 
[November 17, 
I hold that all, or nearly all, rocks are permeable by water to a 
greater or less extent and rapidity, which permeability may be 
indeed impaired by materials deposited by the percolating waters ; 
that all volcanic (eruptive) rocks after consolidation, and all 
derivative ones, are subject to more or less alteration, according 
to the stability of the compounds forming the rocks, in the con- 
ditions to which they are subjected; that these alterations are 
chiefly molecular and brought about through the medium of the 
percolating waters, which may or may not be thermal; that amyg- 
daloidal and pseudo-amygdaloidal structure, the filling of segre- 
gated veins, and the secondary deposition of mineral matter in 
beds of rock, have all been brought about through the same 
medium, the material deposited being in general derived from 
the adjacent rock. 
If I understand Professor Dana aright, he holds that water will 
penetrate the rocks spoken of only a short distance, “ in some not 
an inch ” ; that all the alterations in them, the filling of the veins 
and amygdaloidal cavities, took place before the rocks had lost 
their original heat ; and that these changes were brought about 
by means of the moisture inclosed at the time of the eruption, 
acting generally in the vaporized state. (See extract near the 
end of this article.) 
That water will penetrate rocks, it seems would follow from 
the general properties of matter ; the known absorption of water 
by rocks ; the well-known fact of the “ quarry water ” before a 
rock is raised from its bed; the experiments of Daubree, Hunt, 
C. Lang, and others ; the facts cited by Bischof (Lehrbuch der 
Chemischen und Physikalischen Geologie, Zweite Auiiage, I, 203- 
213) ; the methods of preparation employed in the case of cer- 
tain decorative stones ; etc., etc. Furthermore, it seems to me 
that the method of filling veins by infiltration or segregation, as 
described by Professor Dana, admits this percolation (Manual of 
Geology, 1862, p. 713 ; 1874, p. 732; 1880, p. 775 ; Text Book of 
Geology, 1863, p. 317; 1874, p. 324). 
In order to arrive at any decision whether the amygdules and 
veins were formed or not before the rocks lost their original heat, 
it is necessary that we understand the mode in which the beds were 
laid down in the district in question. The eastern sandstone and 
