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ANNALS

OF

PHILOSOPHY.

FEBRUARY, 1815.

ARTICLE I.

An Essay on the Shapes, Dimensions, and Positions of the Spaces, in the Earth which are called Rents, and the Arrangement of the Matter in them. By Mr. John B. Longmire.

SIR,

(To Dr. Thomson.)

I COMMENCED in the year 1812 to write an essay on rents, which I advertised in the beginning of the year 1813 as a work "the object of which was to prove, that metallic veins, dykes, slips, and all other rents, in the internal part of the earth, were formed when it was passing from a fluid to a solid state, and are owing to the unequal contraction of its matter; and that the phenomena of stratification, and formations, in some points of view, as well as the features of the earth at its surface, are effects of the same cause." This work I intended to publish in the beginning of the present year; but since advertising, I have extended it much beyond what I originally intended; and as I purpose to make considerable additions to it, perhaps a few years may elapse before I publish it; but as some of my friends and correspondents have requested its early publication, I have determined, with your permission, to give an abstract of it in the Annals of Philosophy. In doing so, I will commence with that part which relates to rents. I am, Sir, with great respect,

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Of Rents in General.

There are numerous spaces existing throughout the earth, many of which extend further from its surface towards its centre than man has hitherto penetrated. These spaces contain irregularlyshaped tabular masses of earthy and metallic matter, which have a position very different from that of the matter filling up the other parts of the earth. A close examination of all the phenomena presented by these spaces convinces the observer that they have been formed when the matter of the earth changed its state from fluidity to solidity, and are owing to its contraction unequally. The most of these spaces, or those which were formed the earliest, were filled by some of the matter which is contiguous to their sides being forced into them, from portions of it still nearly in a fluid state, by the weight of the matter incumbent on these portions; the rest of them, or those which were formed when every portion of the matter contiguous to their sides was so far advanced to its present state of solidity as to resist the incumbent weight, were filled with matter that entered them at the earth's surface, in either a fluid state, as the matter of green-stone, basalt, &c.; or a solid state, as gravel, sand, and clay. These spaces, therefore, are rents; and may be called, according to their shapes, the bended-tabular, the straighttabular, the ovalar, and cylindrical, rents.

Of the Bended-Tabular Rent.

In treating of this rent I will, in the first part, describe its common names, its shape, dimensions, and position; the difference in the appearance and position of the strata, between where they are contiguous to it, and at given distances from it; and, lastly, the forming cause of the rent. In the second part, I will describe the arrangement of the matter in rents of this shape; dividing them into such as contain matter which proceeded from that on their sides, and such as have been filled from above.

seams,

1. The Names common to this Rent.-Bended-tabular rents which contain only earthy tabular masses, and metallic and earthy crystals, are known by the appellations of slips, dykes, shifts, lodes, troubles, and faults. They are denominated slips by some geological writers, because the strata on one of their sides have slipped from those on the other, and fallen below them. They are known at Whitehaven by the names of dykes, because they divide the or bands of coal, as they are there called, into fields. They also call them up-throw and down-throw dykes; up-throw dykes, when the strata are higher on the side opposite to that on which the observer is standing; and down-throw dykes, when they are lower on the former than on the latter side. They are called shifts in some parts of England and Scotland, as they are considered by the majority of miners in these parts to have shifted the strata on their sides. In Cornwall they are denominated cross lodes; and in some

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