206 | T. 8. Hunt—The Decay of Rocks. 
ferric oxide in sediments into massive limonite imbedded there- 
in, is thus a-two-fold process, involving first, the intervention 
change of this latter, through peroxidation and hydratation, into _ 
limonite. 
It is evident that the first stage of the process thus indicated 
by Rogers as taking place'in sediments as yet unconsolidated, 
may also be set up in the disintegrated ferriferous materials 
Seenlenie from the sub-aérial decay of rocks, and still undis- 
turbed; that is to say, that the infiltration of waters holding 
dissolved organic matter may give rise in the decomposed mass 
to concretions of ferrous carbonate, which are eet 
changed into limonite. In this way, a concentration may 
effected, through which rocks oueinely < containing a small ie 
tion of diffused iron-oxide come to include masses of limonite 
Illustrations of this process are Se canes seen in the decay of 
some ferrous carbonate, in the residuum of which we find the 
upon the serpentine- -rock of the region, into which it eee 
and from the sub-aérial decay of which it has evidently been 
derived, the lower portion of the earthy nite still preserving 
the peculiar jointed structure of the underlying serpentine. 
This decomposed material, though including err aidid crusts, 
sane and concretionary grains of limonite, with occasional 
ruses of _shaieolepy and of quart crystals, retains considera 
ble coher 
The achibe of this limonite seems to have been the iron- 
oxide liberated by the decay of the ferriferous serpentine, and 
the proportion of ore in the superjacent mass shows a direct 
relation to the color and apparent Eaionion of bona in 
the serpentine beneath. This limonite, which is now mined to 
a considerable extent, contains, as several analyses have shown, 
from one to two-hundredths of chromic oxide, which is ae 
known to be present in small amount in the serpentine. 
impure argillaceous specimen containing only 59°63 of Ken 
oxide yielded the writer 2°81 of chromic oxide in a condition 
readily soluble in chlorhydric acid. 
~ $88. Dr. N. L. Britton, of the School of Mines of Columbia 
snus eee yielding supersaturated solutions, which inclose vessels er y 
taneously de posit, after many hours, a large part of the carbonate in a 
