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Updated: August 19, 2024
In former times a long spit of this nature seems to have become consolidated by the percolation of calcareous matter, and afterwards to have been gradually upheaved; the outer and loose parts during this process having been worn away by the action of the sea, and the solid nucleus left as we now see it.
With this they fill up the pans of sugar that are sunk 2 or 3 inches below the brim by the draining of the molasses out of it: first scraping off the thin hard crust of the sugar that lies at the top, and would hinder the water of the clay from soaking through the sugar of the pan. The refining is made by this percolation.
From the facts now given we may conclude that castings ejected on our Chalk Downs suffer some loss by the percolation of their finer matter into the chalk. But such impure superficial chalk, when dissolved, would leave a larger supply of earthy matter to be added to the mould than in the case of pure chalk.
Now, the percolation of water may increase the porousness of that body which it pervades, but never can thus change it from a porous to a perfect solid body.
Some of the beds of this limestone are between six hundred and seven hundred feet above the sea; but part of this height may possibly be due to an elevation of the land, subsequent to the accumulation of the calcareous sand. The percolation of rain-water has consolidated parts of these beds into a solid rock, and has formed masses of dark brown, stalagmitic limestone.
This interspace caused by the melting of ice becomes filled with water and forms a lake, the drainage of which usually takes place by percolation through the porous parts of the moraine, and not by a stream overflowing that barrier. Such a glacier-lake Dr. Hooker actually found in existence near the head of the Yangma valley in the Himalaya.
But even the percolation of water through the strata deposited at the bottom of the sea, necessarily required, according to the supposition of naturalists, must be refused; for, the interstices of those strata are, from the supposition of the case, already filled with water; consequently, without first removing that stagnant water, it is in vain to propose the infiltration of any fluid from the surface.
It is of course possible that the Leadville porphyries are only phases of rocks rich in silver, lead, and iron, which underlie this region, and which have been fused and forced to the surface by an ascending mass of deeper seated igneous rock; but even if the argentiferous character of the porphyry shall be proved, it will not be proved that such portions of it as here lie upon the limestone have furnished the ore by the descending percolation of cold surface waters.
Beds of rock of any thickness, crammed full of organic remains, may yet, either by the percolation of water through them, or by the influence of subterranean heat, lose all trace of these remains, and present the appearance of beds of rock formed under conditions in which living forms were absent.
Homogeneous sandstone preserves its perpendicularity better than other rocks, one reason being that it does not invite percolation, and usually offers, for a considerable distance on each side of the canyon, barren and impervious surfaces to the rains. Where strata rest on exposed softer beds, these are undermined from the front, and in this way recession is brought about.
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