consisting altogether of immense masses of black lava, so extremely replete with bladder-holes, and so void of extraneous matter, that it perfectly resembles the scoria of iron, and therefore leaves not the least doubt of its being a volcanic production. This stupendous cliff is situated on the verge of the Atlantic, eight miles north. of Colerain, and six miles west of the Giant's Causeway. The Giant's Causeway is a continuation, indeed, of the lava, the elevation of which is not apparently less than five or six hundred feet above the Atlantic: not one mass, or the effect of one eruption, but of many successive convulsions. The columns are in a vertical position, and of various diameters, from fifteen to twenty inches, and some thirty feet long. They seem all to be prismatical, or equally thick from end to end, though they consist of various regular figures, viz. pentagonal, hexagonal, heptagonal, and probably many other forms. Each column is apparently divided into equal parts, by means of transverse joints; but many bisect the columns partially, leaving five or six inches of the central part solid. In some instances, the joints extend quite through the columns, but they have originally, perhaps, united, and probably separated by water lodging and freezing in them. The articulations are

not

not flat, but convex and concave, exactly fitted together, but not in any order with respect to the convexity or the concavity being upwards or downwards; for in many instances they have been observed in both directions. The columns are of one colour, and of one density, and free from bladder-holes. "As these basaltic columns," says Whitehurst," have assumed a variety of prismatic appearances, the presumption is great, that their various forms are not owing to any property of crystallization, since it is universally allowed, that similar substances, under similar circumstances, invariably assume similar figures. The cause, indeed, is hard to be ascertained. I myself am of opinion, continues Whitehurst, (supposing, as I do, that these basaltic columns were originally in the very heart of the mountain, in a state of fusion, protected by scoria from the external cold) that they received their form from contraction in cooling, from an immense degree of heat, to their present temperature. And that which corroborates the opinion is, that toadstone, channel, cat-dirt, and black clay, found in Derbyshire, are all lava, and flowed from volcanos, whose funnels did not approach the open air, but disgorged their fiery contents between the strata of limestone, in all directions. In the fissures also of limestone they are found. A further

3

A further proof, if necessary, that the limestone must have been first formed, and subsequently broken, ere it were possible for these fissures to be filled up."

In opposition, however, to this opinion, that the basaltic columns do not owe their various forms to any property of crystallization, we have the sentiments of a late ingenious writer,* who has evidently studied his subject with ability and precision." A crude and indefinite hypothesis," says this gentleman, "has been adopted, that the pillars of basaltes, at the Giant's Causeway, were produced by the refrigeration of a liquid body of lava, in consequence of being suddenly plunged into water. Such is the theory of M. Raspe; and such are the sentiments of M. de Luc, who imagines that the ancient volcanos were formed in the ocean, when the sudden cooling of the melted mass (not to count on the presence of the marine salt) might have determined a regularity of figure in the cooling body. But, this ought not hastily to be adopted, for the furious encounter of a river of liquid fire with the waters of the ocean, so far from being suited to form the neat and elegant arrangement of these pillars of basaltes, could only tend to introduce

*Mr. Hamilton.

introduce confusion and irregularity. But, in truth, any argument derived from the particular situation of the Giant's Causeway will be found extremely erroneous, because the circumstances of its standing in the sea is purely accidental; similar pillars being often discoverable on the summit of the highest grounds in the neighbourhood, many hundred feet above the level of the beach. Nay, the Causeway appears to have extended thro' a large tract of country in every direction, insomuch, that many of the common quarries, for several miles around, seem to be only abortive attempts towards the production of a Giant's Causeway. Through a space of more than forty miles in length, and twenty miles in breadth, that is, through above eight hundred square miles, the great cause which generated this species of stone, exerted itself. In kind, this stone seems as perfect as any hitherto discovered. Its component parts are iron in a metallic state, combined chiefly with siliceous and argillaceous earths. Its power of magnetic attraction is proof of this; each fragment of a pillar having its attractive and repellent points. Bergman's experiments shew, that one hundred parts contain, of

Siliceous

Thus, from a knowledge of these elementary parts of basaltæ, we are furnished with an analogy tending to throw some light on the regularity of their form. One of their principles is found to be siliceous earth, and we have numerous proofs, that this substance does, in other instances which come within our observation, frequently affect a regular figure; variable, however, under various circumstances. Thus, rock crystal, which is a very pure flinty earth, is commonly disposed in the form of hexagonal prisms, the denomination of sides, which chiefly prevails among our basaltine pillars. These varieties of crystallizations are found to take place in the metal of glass-houses, where the furnace has been suffered to cool gradually. And though crystals have probably never been produced from any simple substance, precisely answering to the articulated basaltic pillars, yet no very important objection can thence be derived, since it is well

known,