many thin beds, the broadest of which does not exceed a foot in thickness. Its general colour is of a whitish grey, with a small mix ture of yellow, and it is divided transversely by straight septa or cracks, both sides of which are covered with dendritical figures, of a yellowish brown colour, beautifully representing the objects of landscape. At the western base of the mountain, on a level with the sea by which it is washed, a very extensive stratum occurs, of the same nature as the last described, bearing from north to south parallel with, and dipping towards, the mountain nearly at an angle of 40 degrees. "In some parts of the western slope of the mountain, towards the south are found nests of a dark red shivery clay, in which are imbedded flints of a dirty sap-green colour of those no regular stratum is to be perceived; many of them are unshapely masses; but they, in general, tend to the rhomboidal form, and are from three to four inches long by two or three broad, and an inch and a half thick. They are not incrusted as the flints found in chalk, nor have they the appearance of having been worn by attri bank is perfectly loose and uncombined: one half of it has been levelled into an extensive parade, its surface having been combined by the lime and rubbish from the ruins of the town. The southern extremity of the bank is still to be seen in its natural state, and forms the burying-ground of the garrison. "Upon the east side of the mountain is found another of these banks, of considerable extent, and, as I mentioned before, rising from the Mediterranean in a rapid acclivity, and reaching to one-third of its entire elevation. This bank is composed of small particles of crystallised quartz, of testaceous bodies rounded by attrition, and of a few minute particles of the calcareous rock; the whole has a whitish grey colour. The rain water, which falls from the bare mountain rock above the sand, brings along with it calcareous matter, which is deposited upon the bank, and combines its surface in. to a crust, which in some places is so much indurated as to bear the pressure of the foot. "In other parts of the moun. tain, where this sand is surrounded by the calcareous rock, and covered in and protected from the action of the air, and corrosion of the sea-salts, it is found in a perfect indurated state, combined by stalactitical spar, and forming a minute breccia. A quarry of this arenaceous stone has been opened upon the south-east quarter of the mountain, and is made use of, with great propriety, to line the embrasures of some of the new works belonging to the garrison. Its inaptitude to fly off in splinters, when struck by a ball, gives, in such situations, additional safety to the defenders of the place. "The "The western side of the mountain's base, around Rosia Bay, and the new Mole, is a rock composed of an aggregate of small fragments of every fossil that has been here described, with the addition of two different species of marble that are probably adventitious, as their native beds have not been found in the mountain. The one of those is black, and the other of an olive green colour. The whole of this mixture produces a most beautiful breccia, and is firmly combined by a calcareous cement of a yellow, verging towards an orange colour. It is susceptible of a high polish, except where fragments of the argillaceous strata occur; these can be easily smoothed down, but cannot be brought to a perfect polish. The fragments in this breccia are angular, and none of them have the appearance of being water worn. "It only now remains for me to mention what are generally called the fossil bones, found in the rock of Gibraltar. These have been much talked of, and by some look ed upon as a phænomenon beyond the power of explanation. The general idea, which exists concern ing them, is, that they are found in a petrified state, and inclosed in the solid calcareous rock; but these are mistakes, which could only arise from inaccurate observation and false description. mals, some of which have the appearance of being human. These bones are of various sizes, and lie in all directions, intermixed with shells of snails, fragments of the calcareous rock, and particles of spar; all of which materials are still to be seen in their natural uncombined states, partially scattered over the surface of the mountain, These having been swept, by heavy rains at different periods, from the surface into the situations above described, and having remained for a long series of years in those places of rest, exposed to the permeating action of water, have become enveloped in, and cemented by, the calcareous matter which it deposits. "The bones, in this composition, have not the smallest appearance of being petrified; and if they have undergone any change, it is more like that of calcination than that of petrifaction, as the most solid parts of them generally admit of being cut and scraped down with the same ease as chalk. "Bones combined in such concretions are not peculiar to Gibraltar: they are found in such large quantities in the country of Dalmatia, and upon its coasts in the islands of Cherso, and Osero, that some naturalists have been induced to go so far as to assert, that there has been a regular stratum of "In the perpendicular fissures of such matter in that country, and the rock, and in some of the ca- that its present broken and interverns of the mountain (all of rupted appearance has been caused which afford evident proofs of their by earthquakes, or other convulformer communication with the sions, experienced in that part of surface), a calcareous concretion is the globe. But, of late years, a found, of a reddish brown ferru- traveller (Abbé Alberto Fortis), ginous colour, with an earthy frac- has given a minute description of ture, and considerable induration, the concretion in which the bones inclosing the bones of various ani- are found in that country: and by his account it appears that with regard to situation, composition and colour, it is perfectly similar to that found at Gibraltar. By his description it also appears, that the two mountain rocks of Gibraltar and Dalmatia consists of the same species of calcareous stone; from which it is to be presumed, that the concretions in both have been formed in the same manner and about the same periods. "Perhaps if the fissures and caves of the rock of Dalmatia were still more minutely examined, their former communications with the surface might yet be traced, as in those described above; and, in that case, there would be at least a strong probability, that the materials of the concretions of that country have been brought together by the same accidental cause, which, in my opinion, has collected those found in the caverns of Gibraltar. I have traced, in Gibraltar, this concretion, from the lowest part of a deep perpendicular fissure, up to the surface of the mountain, As it approached to the surface, the concretion became Jess firmly combined, and, when it had no covering, of the calcareous rock, a small degree of adhesion only remained, which was evident ly produced by the argillaceous earth, in its composition, having been moistened by rain and baked by the sun, "The depth, at which these materials had been penetrated by that proportion of stalactitical matter, capable of giving to the concretion its greatest adhesion and solis dity, I found to vary according to its situation and to the quantity of matter to be combined. In fissures, narrow and contracted, I found the concretion possessing a great degree of hardness at six feet from the sur face; but in other situations more extended, and where a larger quantity of the materials had been accumulated, I found it had not gained its greatest degree of adhesion at double that depth. In one of the caves, where the mass of concretion is of considerable size, I perceived it to be divided into different beds, each bed being covered with a crust of the stalactitical spar, from one inch to an inch and a half in thickness, which seems to indicate, that the materials have been carried in at various periods, and that those periods have been very remote from each other. "At Rosia Bay, upon the west side of Gibraltar, this concretion is found in what has evidently been a cavern, originally formed by huge unshapely masses of the rock, which have tumbled in together. The fissure, or cavern, formed by the disruption and subsidence of those masses, has been entirely filled up with the concretion, and is now exposed to full view by the outward mass having dropped down, in consequence of the encroachments of the sea. It is to this spot that strangers are generally led to examine the phænomenon ; and the composition having here attained to its greatest degree of hardness and solidity, the hasty ob server, seeing the bones inclosed in what has so little the appearance of having been a vacuity, examines no further, but immediately adopts the idea of their being incased in the solid rock. The communication from this former chasm, to the surface from which it has received the materials of the concretion, is still to be traced in the face of the rock, but its opening is at present covered by the base of the line wall of the garrison. Here bones are found that are apparently human; and those of them that appear to be of the legs, arms, and vertebræ of the back, are scattered among others of various kinds and sizes, even down to the smallest bones of small birds. I found here the complete jaw-bone of a sheep; it contained its full complement of teeth, the enamel of which was perfect, and its whiteness and lustre in no degree impaired. In the hollow parts of some of the large bones was contained a minute crystallisation of pure and colourless calcareous spar; but, in most, the interior part consisted of a sparry crust of a reddish colour, scarcely in any degree transparent. "At the northern extremity of the mountain, the concretion is generally found in perpendicular fissures. The miners there, employed upon the fortifications, in exacvating one of those fissures, found, at a great depth from the surface, two skulls, which were supposed to be human; but, to me, one of them, if not both, appeared to be too small for the human species. The bone of each was perfectly firm and solid; from which it is to be presumed, that they were in a state of maturity before they were inclosed in the concretion. Had they appertained to very young children, perhaps the bone would have been more porous, and of a less firm texture. The probability is, that they belonged to a species of monkey, which still continues to inhabit, in considerable numbers, those parts of the rock which are to us inaccessible. "This concretion varies, in its composition, according to the situation in which it is found. At the extremity of Prince's Lines, high in the rock which looks towards Spain, it is found to consist only of a reddish calcareous earth, and the bones of small birds cemented thereby. The rock around this spot is inhabited by a number of hawks, that, in the breeding season, nestle here, and rear their young; the bones in this concretion are probably the remains of the food of those birds. At the base of the rock, below King's Lines, the concretion consists of pebbles of the prevailing calcareous rock. In this concretion, at a very considerable depth under the surface, was found the under part of a glass bottle, uncommonly shaped, and of great thickness; the colour of the glass was of a dark green. "In many parts of the rock I have found concretions, in which there are no bones of any kind; and on the elevated parts of the mountain, where the slopes are rapid, I have found a breccia (if I may so call it), entirely consisting of snail-shells, combined in a mass of opaque stalactitical spar of a yellowish brown colour. The various progressive augmentations of this matter were to be traced in various shades of the same colour, which, like the zones of the antique alabaster, curve round, and follow the form of the shell. The purer matter of this spar has penetrated the shells, and in their interior hollows has formed a lining of small crystals, generally colourless and perfectly transparent. "I have bestowed more time in endeavouring to describe the composition, and the real situation, of this concretion of bones, than the subject, in the estimation of many, |