It is, perhaps, impossible, in the present state of our knowledge, to account for the origin of these remarkable bodies. Some have supposed them to have been shot out from volcanoes belonging to our earth; but this theory is opposed by the fact that no substance, resembling aërolites, has ever been found in or near any volcano; and they fall from a height to which no volcano can be supposed to have projected them, and still less to have given them the horizontal direction in which they usually move. Another supposition is, that these masses are formed in the atmosphere; but it is almost ridiculous to imagine a body, weighing many tons, to be produced by any chemical or electrical forces in the upper regions of the air. A third explanation is, that they are bodies thrown out by the volcanoes, which are known to exist in the moon, with such force as to bring them within the sphere of the earth’s attraction. This notion was supported by the celebrated astronomer and mathematician La Place. He calculated that a body projected from the moon with the velocity of 7771 feet in the first second, would reach our earth in
about two days and a half. But other astronomers are of opinion, that the known velocity of some meteors is too great to admit of the possibility of their having come from the moon. The theory which agrees best with known facts and the laws of nature, is that proposed by Chladni, namely, that the meteors are bodies moving in space, either masses of matter as originally created, or fragments separated from a larger mass of a similar nature. This view has also been supported by Sir Humphrey Davy, who says, “The luminous appearances of shooting-stars and meteors cannot be owing to any inflammation of elastic fluids, but must depend upon the ignition of solid bodies. Dr. Halley calculated the height of a meteor at ninety miles; and the great American meteor, which threw down showers of stones, was estimated at seventeen miles high. The velocity of motion of these bodies must, in all cases, be immensely great, and the heat produced by the compression of the most rarefied air from the velocity of motion, must be, probably, sufficient to ignite the mass; and all the phenomena may be explained, if falling stars be supposed to be small bodies moving round the earth in very eccentric orbits, which become ignited only when
they pass with immense velocity through the upper region of the atmosphere; and if the meteoric bodies which throw down stones with explosions, be supposed to be similar bodies which contain either combustible or elastic matter.”
This chapter ought not to be concluded without a short notice of that remarkable rain known to geologists as “fossil rain.” In the new red-sandstone of the Storeton quarries, impressions of the foot-prints of ancient animals have been discovered; and in examining some of the slabs of stone extracted at the depth of above thirty feet, Mr. Cunningham observed “that their under surface was thickly covered with minute hemispherical projections, or casts in relief of circular pits, in the immediately subjacent layers of clay. The origin of these marks, he is of opinion, must be ascribed to showers of rain which fell upon an argillaceous beach exposed by the retiring tide, and their preservation to the filling up of the indentations by sand. On the same slabs are impressions of the feet of small reptiles, which appear to have passed over the clay previously to the shower, since the foot-marks are also indented with circular pits, but to a less degree; and the difference Mr. Cunningham
explains by the pressure of the animal having rendered these portions less easily acted upon.” The preservation of these marks has been explained by supposing dry sand, drifted by the wind, to have swept over and filled up the footprints, rain-pits, and hollows of every kind, which the soft argillaceous surface had received.
The frontispiece to the present chapter (p. [156]), represents a slab of sandstone containing impressions of the foot of a bird and of rain drops. This slab is from a sandstone basin near Turner’s Falls, a fine cataract of the Connecticut river in the State of Massachusetts, and is described by Dr. Deane in a recent number of the American Journal of Science. “It is rare,” says that gentleman, to “find a stratum containing these footprints exactly as they were made by the animal, without having suffered change. They are usually more or less disturbed or obliterated by the too soft nature of the mud, the coarseness of the materials, and by many other circumstances which we may easily see would deface them, so that although the general form of the foot may be apparent, the minute traces of its appendages are almost invariably lost. In general, except in thick-toed species, we
cannot discover the distinct evidences of the structure of the toes, each toe appearing to be formed of a single joint, and seldom terminated by a claw. But, a few specimens hitherto discovered at this locality completely developed the true characters of the foot, its ranks of joints, its claws and integuments. So far as I have seen, the faultless impressions are upon shales of the finest texture with a smooth glossy surface, such as would retain the beautiful impressions of rain drops. This kind of surface containing footmarks is exceedingly rare: I have seen but few detached examples; recently it has been my good fortune to recover a stratum, containing in all more than one hundred most beautiful impressions of the feet of four or five varieties of birds, the entire surface being also pitted by a shower of fossil rain-drops. The slabs are perfectly smooth on the inferior surface, and are about two inches in thickness.
“The impression of a medallion is not more sharp and clear than are most of these imprints, and it may be proper to observe, that this remarkable preservation may be ascribed to the circumstance, that the entire surface of the stratum was incrusted with a layer of micaceous sandstone,
adhering so firmly that it would not cleave off, thereby requiring the laborious and skilful application of the chisel. The appearance of this shining layer which is of a gray colour, while the fossil slab is a dark red, seems to carry the probability that it was washed or blown over the latter while in a state of loose sand, thus filling up the foot-prints and rain-drops, and preserving them unchanged until the present day—unchanged in the smallest particular, so far as relates merely to configuration, nothing being obliterated; the precise form of the nails, or claws, and joints, and in the deep impressions of the heel bone, being exquisitely preserved.”
The small slab figured at p. [156] is described as being an incomparable specimen. “For purity of impression it is unsurpassed, and the living reality of the rain-drops, the beautiful colour of the stone, its sound texture and lightness, renders it a fit member for any collection of organic remains.”