The name of the Giants’ Causeway arose, probably, from an idea of the supernatural power, entertained in times of ignorance and superstition. And yet it is demonstrated that vast masses of rock are to be traced to causes strictly natural. Basalt is of very frequent occurrence on the surface of the globe, and is frequently detected in a variety of volcanoes, both extinct and active. The greatest mass of basalt hitherto observed is that in the Deccan, which constitutes the surface of many thousand square miles of that part of India. In other instances, it occurs in horizontal tabular masses, and is columnar. Sometimes, the basaltic columns are curved, and of this there is a beautiful example in the island of Staffa. Now basalt is not a crystalline substance, for as it is not capable, as all crystals are, of cleavage in the line of its planes, or at some angle with them, it is concretional. Its structure resembles an onion, or any bulbous root, for, in the centre, is a solid mass, about which are others just like the parts of the vegetable products already mentioned. These portions of basalt are at first of an oval form, and then they gradually become rudely hexagonal. Some non-columnar basalts show no trace of any particular arrangement of parts, while others have a globular structure, so that when the rock becomes much decomposed, it has the appearance of numerous bomb-shells and cannon-balls cemented together. Here, then, we have an extraordinary effect of heat. Mr. Gregory Watt took seven hundred weight of the substance named rowley rag, kept it in fusion more than six hours, and cooled it so gradually, that eight days elapsed before it was taken from the furnace. The shape of the mass was uneven and while the thinner portion was, in consequence of more rapid cooling, vitreous, the thicker was stony; the one state passing into the other. Numerous spheroids were also formed, some being two inches in diameter. They were radiated with distinct fibres, the latter also forming concentric coats, when circumstances were favourable to such an arrangement. When the temperature had been sufficiently continued, the centres of the spheroids became compacted before they had attained the diameter of half-an-inch. When two spheroids came into contact, no penetration ensued; but the two bodies became mutually compressed and separated by a plane, well defined, and invested with a rusty colour. When several met, they formed prisms. In reasoning on these facts, Mr. G. Watt observes: “In a stratum composed of an indefinite number in superficial extent, but only one in height, of impenetrable spheroids, if their peripheries should come in contact in the same plane, it seems obvious that their mutual action would form them into hexagons; and if these were resisted below, and there was no opposing cause above them, it seems equally clear that they would extend their dimensions upwards, and thus form hexagonal prisms, whose length might be indefinitely