In the caves in the limestone, owing to a thread of water having found its way in a particular direction through the porous stone of the roof, a drop falls age after age on one spot on the cave-floor, accurately directed by the stalactite which it is all the time creating. The water contains a certain proportion of carbonate of lime, which is deposited as stalagmite as the water evaporates, and thus a ring-like crust is produced at a little distance from the spot where the drop falls. When a ring is once formed, it limits the spread of the drop, and determines the position of the wall bounding the little pool made by the drop. The floor of the cave gradually rises by the accumulation of sand and travertine, and with it rise the walls and floor of the cup by the deposit of successive layers of stalagmite produced by the drop percolating into the limestone of the floor which hardens it still further, but in this peculiar symmetrical way. From the floor and sides of the cup the water oozes into the softer limestone around and beneath; but, as in all these limestones, it does not ooze indiscriminately, but follows certain more free paths. These become soon lined and finally blocked with stalagmite, and it is these tubes and threads of stalagmite which afterwards in the pseudo-fossil represent the diverging rootlets.
[Illustration: A STALAGMITE CAVE.]
Sometimes when two or more drops fall from stalactites close to one another the cups coalesce (Figs. 2, 3, and 4); sometimes one drop or two is more frequent than the other, and then we have the form shown in Figs. 3 and 4; sometimes many drops irregularly scattered form a large pool with its raised border, and a few drops more frequent and more constant than the rest grow their “palmetto stems” within its limit (Fig. 5); and sometimes a number of drops near one another make a curious regular pattern, with the partitions between the recesses quite straight (Fig. 6).
I have already referred to the rapid denudation which is going on in these islands, and to the extent to which they have been denuded within comparatively recent times. The floors of caves, from their being cemented into a nearly homogeneous mass by stalagmitic matter, are much harder than the ordinary porous blown limestone; and it seems that in many cases, after the rocks forming the walls and roof have been removed, disintegration has been at all events temporarily arrested by the floor. Where there is a flat surface of rock exposed anywhere on the island, it very generally bears traces of having been at one time the floor of a cave; and as the weather-wearing of the surface goes on, the old concretionary structures are gradually brought out again, the parts specially hardened by a localized slow infiltration of lime resist integration longest and project above the general surface. Often a surface of weathered rock is so studded with these symmetrical concretions, that it is hard to believe that one is not looking at the calcified stumps of a close-growing grove of palms.