DEPOSITION OF OXIDE OF IRON BY INFILTRATION. 
169 
absorbed into the porous beds on each. side. The gradual convergence of the lines, and their 
reappearance below, indicates that the intervening space was not favorable to the absorption of 
the fluid. 
The lines have a dark brown, or iron-rust color, and show distinctly in the white, argillaceous 
strata. Where the oxide has accumulated in quantity, as along the fissure, the earth is closely 
cemented, and, indeed, becomes very hard and unyielding to the weather. The quantity of oxide 
is greatest along the walls of the fissure, and in reality forms a rich iron ore. 
If, as we have good reason to believe, the iron solution is derived from the decomposition of 
pyrites, the lime of the strata plays an important part in the decomposition of the solution. Sul¬ 
phate of lime is undoubtedly formed, and the iron oxide is precipitated, coloring the strata brown 
or red. The solution of lime, thus formed by the decomposition of the sulphate of iron, may then 
descend through the strata until the conditions favorable for its crystallization are obtained, and 
thus produce the beds of gypsum that are found in the same formation. The lime, or other 
substances in the beds, certainly exercise an important influence upon the deposition of the oxide 
of iron, as is sufficiently shown by the fact of the existence of the waving lines in strata below 
others that are free from all stain, and by the peculiar curved and concentric layers, as shown 
in figure 2, which is a faithful sketch of a part of the bank, not far from the point from which 
the first figure was copied. The lines of oxide in this figure resemble the grain of some of the 
gnarled woods, and a decided tendency to the formation of concretions, or balls, with concentric 
layers, is visible. A short distance beyond, the layers are nearly horizontal, and seem to form 
a part of the original stratification. 
The resemblance of these parallel curved lines to the plications and contortions produced in 
soft strata, by pressure, could not pass unobserved. At first, this seemed to be their origin, for, 
to all appearance, the layers of oxide were the result of original deposition, and they formed 
a very considerable part of the strata. It is suggested that many of the apparent instances of 
folding and crumpling in banks of drift, or in beds of the older Tertiary, may be only the result 
of changes produced by infiltration. An example of contorted lines in a stratum of sand, 
included conformably between horizontal beds, is given by Sir Charles Lyell. 1 He describes 
the curves as very complicated, and as sometimes, to all appearance, enveloping a central nucleus 
of chalk, or clay. Similar curved layers occur around large masses of chalk, conforming to 
their surfaces, while the chalk rests upon horizontal layers of clay, or sand, below, without 
any signs of disturbance. All these appearances, as shown in the figures which are presented, 
are similar to those seen in the Ocoya Creek strata. Sir Charles Lyell, however, notes the 
presence of pebbles with the contorted layers, and is of the opinion that the curves result from 
pressure or lateral forces. 
Additional evidence or illustration of the effects produced by infiltrating waters, holding iron 
in solution, was presented in the only deposit of fossil shells which was observed in the strata. 
They were exposed in the bank of the creek about ten feet above its level. The layer was not 
over sixteen inches thick, and was composed mainly of sesquioxide of iron, which formed a firm 
cement to the loose sand in which the shells were imbedded. All the lime of these shells has 
been removed by infiltration or otherwise, and the impressions of their surfaces are all that 
remain. 
These instances of the deposition of oxide of iron in horizontal layers and in veins by infil¬ 
trating waters are exceedingly interesting, as they throw light upon the formation of deposits 
1 Elements of Geology, 5tU edition, p- 154. 
22 F 
