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Updated: June 6, 2025
The rock a fine-grained, silicious sandstone is disposed in horizontal strata, from six to twelve feet thick, each of which projects about three feet from that above it, and forms a continuity of steps to the summit, which we found some difficulty in climbing; but where the distance between the ledges was great, we assisted our ascent by tufts of grass firmly rooted in the luxurious moss that grew abundantly about the watercourses.
If the silex be derived from the earth, by what vessels is it conveyed to the surface of the plants? and, in addition, if earth be its source, how is it that earth-seeking, and hollow plants, with their epidermis of silex, should arise in soils that are not silicious? being equally predominant, whether the soil be calcareous, argillaceous, or loamy.
In certain parts of the glacial areas, particularly in the region near the margin of the ice sheet, where the glacier remained in one position for a considerable time, we find extensive deposits of silicious sand, formed of the materials which settled from the under-ice stream, near where they escaped from the glacial cavern.
The New Geyser in the same basin is also of quite recent origin. It consists of two fissures in the rock, in which the water boils vigorously. But there is no mound, and the rocks of the fissure are just beginning to get a coating of the silicious geyserite deposited from the water, so that it cannot long have been spouting.
The intervening spaces are indented with a roulette. It apparently belongs to the silicious ware of the north. The shape and ornamentation are somewhat novel. Four large flattish lobes occur about the body, on each of which a figure somewhat resembling a Maltese cross has been made by incising or impressing broad, shallow lines.
They are, however, commonly more sandy, and their substances less penetrated by that decay which goes on very freely in the atmosphere because of the abundant supply of oxygen, and but slowly on the sea floor. Moreover, the marine deposits are generally made up in large part of silicious sand, a material which is produced in large quantities by the disruption of the rocks along the sea coast.
But just as a silicious deposit may be metamorphosed into opal or quartzite, and chalk into marble, so known metamorphic agencies may metamorphose clay into schist, clay-slate, slate, gneiss, or even granite.
Thus, in the whole of the "intermediate zone," the silicious deposit which is being formed there, as elsewhere, by the accumulation of sponge- spicula, Radiolaria, and Diatoms, is obscured and overpowered by the immensely greater amount of calcareous sediment, which arises from the aggregation of the skeletons of dead Foraminifera.
Examine a piece of the shale from one of the oil districts of California, and you will discover that it is a very peculiar rock, for it is made up almost wholly of minute organisms which once inhabited the ocean. Among the forms which you will find are the silicious skeletons of diatoms, the calcareous skeletons of foraminifera, scales of fish, and, rarely, the whole skeleton of a fish.
The continuous deposit of dross contracts the channel, and a less quantity of water overflows, while that close to the edge of the basin evaporates and deposits a quantity of fine silicious earth; whence the upper portion of the cone not only is steeper than its base, but frequently assumes a more cylindrical form, the external surface of which on account of the want of uniformity in the overflow, is ribbed in the form of stalactites.
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