Account of a remarkable Cave in the Island of Barbadoes, commonly called "Cole's Cave."
By John Davy, M.D., F.R.S. Lond. and Edin., Inspector-General of Army Hospitals, &c. Communicated by the Author.
It is not my intention, in the present communication, to enter into any minute account of this well-known cave;-it is my wish, chiefly, to point out some of its peculiarities, and, most of all, certain appearances which seem to me interesting in relation to geology.
I may premise, that Cole's Cave is nearly in the central part of the island, on an estate called "the Spring,"-a name derived, it is said, from a spring in the cave, the source of a subterraneous rivulet. It is distant about six miles from the principal town, Bridge-town; and may be about five or six hundred feet above the level of the sea, and about thirty feet deep, measuring from the surface above. The descent to it is steep, but not difficult. The entrance is narrow, and, consequently, the descending rays of light are soon lost, and the interior of the cave is dark within a few feet of its mouth. The cavern may be briefly described as a subterraneous chasm or rent, of variable dimensions, and varying in the most irregular manner, with branches from it. That of greatest extent has never been followed to its termination; and it is yet a problem whether its termination is in the direction of the low coast to the southward, or the contrary, inland towards the hilly part of the island, in a northerly direction. There is a stream on each side, which may be adduced in favour of either hypothesis; but the course the chasm takes, so far as it has been penetrated, favours most the latter. The cavern occurs in a calcareous rock,-an aggregate exceedingly various in different situations,-often abounding in shells and coral, often having the character of freestone. This applies to the formation generally.
Water is plentiful in the cavern; there are few places where there is not a dropping of it from the roof, and, as already mentioned, a spring of water rises in it. This occurs, it may be, about fifty yards from the mouth. It is copious. Its temperature, when I tried it about noon on the 11th July, was 77° Fahr., which, probably, is about the mean annual temperature of the spot. It gushes from the rock with force, and immediately forms a pretty and clear rivulet, which, after flowing some way, is lost, and a little farther reappears, and continues sometimes running sluggishly, forming pools, sometimes rapidly, as far as this the main chasm has been traced. It may be mentioned, that another chasm, communicating with this, is without a running stream. In its bed, however, are some pools of water, and large deposits of clay, which also occur in the first mentioned at intervals; clearly indicating that during floods, the consequence of heavy rains, the cave is liable to be inundated, the clay suspended in the water subsiding on rest; and thus farther indicating, that the outlet of these chasms is very narrow, so as to admit of a small stream only flowing out, and, consequently, of accumulation and rising of the water and of a partial rest within. The clay or mud traces on the walls of the cavern shew that the depth of the collected water, when highest, is many feet.
Though so moist, and though all the other circumstances of the cavern seem favourable to vegetation, excepting one- the exclusion of light,-there is a total absence in it of vegetation, even of the lowest kind; not even a mucor is to be detected, at least I sought for such in vain. The only living things known to be found in its recesses are a few of the freshwater crayfish of Barbadoes in the stream, some insects of the cricket kind on the Walls, and numerous bats, which make its drier parts their roosting-places. I have not been able to learn that any lizard, analogous to the Proteus, has been found in its pools.
Where water is always flowing, and commonly dropping, it is not surprising, especially considering the nature of the rock-formation, that deposited carbonate of lime should abound. Its character seems to me the most interesting circumstance connected with this cave. I have specimens now before me, which I broke off myself, evidently formed from deposition in water, exhibiting a very remarkable variety, not only as regards forms, but also structure; in brief, there is a tolerably complete series, from a kind resembling mountain limestone, to another very little different in appearance from Parian marble. Even in the strata of the smaller stalactites and stalagmites, such and other differences are observable ; thus, one part may be very fine-grained in thin concentric layers, another confusedly crystalline, and a third more regularly so. In one specimen, and that a stalactite, the general structure is radiated, shewing a tendency to the prismatic form of crystallization, accompanied by transverse lines, as it were, of cleavage, denoting the rhomboidal form; the one approximating to arragonite, the other to calc-spar. Moreover, there are, in particular situations, strata formed on the bank of the rivulet very like tufa, or a porous freestone, and somewhat similarly constituted, being formed of carbonate of lime in crystalline grains, acting the part of a cement, and of a portion of sand or a little clay.
I have thought it worth while to examine chemically some of these specimens exhibiting the greatest variety of character ; and I shall briefly notice the results of the trials.
The pure white crystalline specimen resembling Parian marble appeared to consist of carbonate of lime alone; nothing else could be detected in it.
That resembling mountain limestone, of a fawn colour, finely granular, and in part minutely crystalline, besides carbonate of lime, contained a minute quantity of alumine, with a trace of peroxide of iron, and a small quantity of matter in a finely divided state, not soluble in an acid, which, under the microscope, had the granular appearance of particles of clay, with which were intermixed a few grains of excessively fine quartzose sand.
The tufa-like specimen, or that resembling porous sandstone, it has been already mentioned, consisted of crystalline grains of carbonate of lime, and of a little clay or sand. With this carbonate of lime a minute portion of phosphate of lime was detected. The sand that remained undissolved by an acid mixed with a little clay, consisted partly of water-worn particles of quartz, and partly of particles like those of volcanic ashes, being angular with sharp edges;-such was the appearance of both, as seen under the microscope with a high power.
Lastly, the clay was found to be very compounded, and to contain carbonate of lime in small quantity, a little carbonate of magnesia, a minute portion of alumine soluble in an acid, and a minute portion of phosphate of lime, besides a portion of sand, and a large proportion of clay not readily soluble in dilute muriatic acid. Its compound nature was also indicated by its fusibility before the blow-pipe. Amongst the specimens I brought with me from the cavern, there were two kinds I have not yet noticed. One was a fragment broken from the wall of the cave: it consisted of incrustation of carbonate of lime, coloured brown, and in part almost black. Its colouring matter I found to be peroxide of magnesia, mixed with some peroxide of iron. The other were small masses, either spherical or oval, the largest not exceeding an almond in size. They were numerous in one part of the bank of the stream. When taken up they were soft and most easily broken; after exposure to the drier open air (the air in the cavern tried by the moistened bulbed thermometer, was found saturated with moisture) they increased in firmness. Many of them when broken were found to have an ochry nucleus, giving the idea that they might be embryo concretions of clay ironstone, that in process of time the proportion of oxide of iron might increase, and that ultimately they might become included in a bed of clay.
What are the influences which are to be drawn from the other specimens? That the material of them, so various, was either deposited from water from a state of solution, in consequence of the separation of carbonic acid, or was a subsidence from water, having been mechanically suspended in it, in a very finely divided state, seems to be unquestionable. The main inference then is, that so many varieties of rock as those mentioned may be formed by deposition and subsidence from water; the pure white crystalline-like marble by deposition of carbonate of lime alone from a state of solution; that like mountain limestone, by a like deposition, with an admixture of a little sediment of foreign matter; and the tufalike kind, or sandstone, from a greater admixture of sediment, and that sediment composed partly of quartz sand, and partly of what I believe to be volcanic ashes.
Now, as the calcareous deposition and the other deposits are constantly increasing in this cavern, judging from what is now to be witnessed, it requires no great stretch of the imagination to conceive a time, and that not very remotely distant in the future, when the fissure may be completely filled up, and its contents be like the contents of a vein, according to the old Wernerian hypothesis ; and which, if broken into and quarried, may exhibit irregular beds of marble in connection with rock having the character of mountain limestone, and other rock having the character of freestone. In parts of the island where excavations have been made, or natural sections occur, phenomena of the kind are to be witnessed at present. The one seem to elucidate the other.
As regards the materials entering into the composition of the rocks now forming in the cavern, it is not difficult to find their source. It is unnecessary to point out whence the carbonate of lime is derived ; the worn honey-comb appearance of the calcareous rocks on the higher grounds, at the surface exposed to the action of rain-water holding carbonic acid in solution, obviously explains it. The clay of the cavern is very like the finest portion of the surface soil; and, doubtless, has been washed out of the soil. The particles contained in the tufa-like deposit resembling volcanic ashes, have also probably been washed out of the soil, and are a portion of the shower which fell on the island at the time of the last volcanic eruption which took place in St Vincent, and of which a thin layer is often now to be seen a few inches below the surface, in spots where the soil has not since been disturbed. Of the manner in which the different varieties have formed, I shall not here speculate. Composition probably will be found to be the most important governing circumstance ; and that one kind has the character of marble, because formed of pure carbonate of lime ; another, the character of tufa, because composed of carbonate of lime, mixed with foreign matter. Nor shall I speculate on the question whether the crystalline stalactites acquired their peculiar structure immediately as they formed, or subsequently after the deposition of the material, in consequence of an internal molecular action and movement, favoured with the presence of water. In alluding to this last, I would express the hope that it may have the attention paid to it which it seems to deserve.
In conplusion, I would remark, that as there are few, if any, objects in this interesting island more deserving of being seen by the casual visitor than " Cole's Cave," if he has any curiosity in such scenes, it is easily gratified. A good carriage road through a pleasant country will bring him to within a hundred yards of the mouth of the cavern; and of a deep ravine contiguous, itself worthy of a visit. In an hour he may reach it from Bridgetown. He will have no difficulty in finding a guide on the spot. If he intends to explore the recesses of the cavern, he should come provided with a change of clothes, and of shoes, and with two or three wax candles. No lantern is necessary, as there is not any strong current of air below. And, however far he penetrate, he need have no apprehension of suffering from the state of the air, which, so far I went, and we were three hours in the cavern, wading and wandering, appeared to be as pure and as respirable as the open atmosphere. This, I specially mention, because the Rev. M. Hughes, in his " Natural History of Barbadoes," published nearly a century ago, states in his account of an excursion he made to this cave, that " near a quarter of a mile from the entrance was his ne plus ultra, being so much fatigued, and wanting air so much, that he durst not, without presumption, proceed any farther," I have recommended wax-lights, because they are greatly preferable to lighted bundles of dried, or partially dried, cane stalks, which, when parties are formed for descending into the cave, are often used to the great discomfort of the company, heating the otherwise cool air, and filling it, otherwise pure, with oppress sive and obscuring smoke.
Barbadoes, 21st July 1846.
The Edinburgh new philosophical journal, Volume 41, pp 355-361.
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