The walls of the cave above these shells, are of a deep slate colour. The pillars which compose them, are on the average about three feet in diameter, and they are fitted so close together that you cannot get a penknife in between them. If separated at certain intervals, they break short off, and leave a remarkably level surface without the least splinter. Between these joints they break roughly and irregularly. Here is a view of the inside of the cave. It is supposed that these wonderful pillars are formed by the cooling of a melted mass, and that this and other basaltic spots, are the remains of streams of lava from a volcano long ago extinct. In some of the lava streams of Mount Vesuvius, there has been noticed an approach to this structure, though not quite so regular as what we have been describing. You may understand in some measure how it may come about, by examining starch, which always hardens into little columns or pillars; and if you look at the little sketch of a portion of the pavement of the cave which I have given you above, you will see that nearly all the pillars have six sides, the same as the pieces of starch. It is remarkable what pains the basalt seems to have taken to get into a six-sided form. I should think about two-thirds of the columns have six sides, though sometimes one side is little more than a sharp edge blunted, because it seems to have been prevented by its neighbour making a similar effort to get its six sides complete. None of the remaining third of the pillars, have more than nine, or, of course, less than three sides. You might look a long time before you would find two pillars exactly alike. All this you will find occurring just in the same manner in starch, except that the edges of the basalt pillars are quite even, while those of starch are more or less waved or twisted. Near the side of the cave there is a little rock formed by pillars into a pretty regular cone, which you may see in the plate. It has a very striking appearance as you approach the island. Close by the rock there is a little cave, the mouth of which is formed by bent pillars, in this manner. [Illustration] The water in this is not very deep, but it was deep enough to give one of my companions a good ducking as he was trying to reach a shell which one of the ladies of our party wanted to possess. You will also often see something like these bent pillars in starch. THE GIANT'S CAUSEWAY. On the north coast of Ireland, the Giant's Causeway is a collection of similar pillars of rather a smaller size. They stretch far into the sea, and at low water you may walk a long distance upon the tops of them. The pillars get higher as they approach the cliff, and in the cliff itself, just above them, is a remarkable layer of fossil wood in the state called lignite, which closely resembles charcoal.