CHAP. IV.

ON THE CAUSE AND NATURE OF THE INEQUALITIES THAT DIVERSIFY THE SURFACE OF THE EARTH.

In a Letter addressed to Sir HUMPHRY DAVY, by WILLIAM RICHARDSON, D.D.

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SIR,

REQUEST you will be so good as to lay before the Royal Society the following Observations on the Natural History of that part of Antrim, (contiguous to the Giant's Causeway,) which you and I examined so carefully together. I know not any country that deserves so well to have its facts faithfully recorded; from the important conclusions to which they lead.

The basaltic area (taken in its whole extent) comprehends the greater part of Antrim, and the east side of Derry, to a considerable depth.

In a geological point of view, Nature has been very kind to this district; for not content with assembling together in a small space so many of her curious productions, and arranging them with more regularity and steadiness than in any other country described, she has condescended occasionally to withdraw the veil, and lay herself open to view, often exhibiting a spectacle equally gratifying to the admirer of magnificence, and to the curious naturalist, who can here by simple inspection, trace the arrangements which are to be discovered elsewhere, only by penetrating beneath the surface of the earth.

As soon as we enter the basaltic area, we begin to perceive traces of these arrangements; as we advance farther north, they increase; and in the tract near the shore, and especially at the island of Rathlin, which seems to have come fresher from the hand of Nature than the rest of our area; the stratification of the whole is perfectly

* By the word nature, which frequently occurs in the course of this Memoir, I always mean, according to RAY's definition, the wisdom of God in the creation of the world.

visible, and the nature of the several strata laid open to us at their abrupt and precipitous terminations.

To the southward we perceive the distinctive features abate, and wear away; the basaltic stratification indeed remains, but is no longer displayed to us in the same manner; the neat, prismatic, internal construction, of the strata, which occurs so frequently on, and near, the coast, is scarcely to be met with at a distance from it; a rude columnar appearance is all we find, and that but rarely.

It is at the periphery of our area, and especially at its northern side, that every thing is displayed to the greatest advantage; here we have perpendicular façades often continuous for miles, and every separate stratum completely open to examination.

Of these façades, four are more distinguished by their grandeur and beauty than the rest, Magilligan Rock, Cave Hill, Bengore, and Fairhead.

The two former are at the extréme points of the north-west diagonal of our area, and nearly forty miles asunder; they are at the summits of mountains, and accessible by land.

The precipitous faces of Fairhead and Bengore, to which I had the pleasure of attending you, and which are visible only from the sea, are the most beautiful, and the most curious; for the strata, which at Magilligan and Cave Hill, are all nearly similar, at Fairhead and Bengore are much diversified. Of Fairhead I have already published an account in Nicholson's Journal, for December 1801, and I now propose to execute an intention which I have had for some years of giving a minute account of Bengore.

I am aware that it will be extremely difficult to convey a clear and adequate idea of an assemblage of 16 strata, (for such is the number of which our promontory is composed), appearing and disappearing at various altitudes, yet retaining each its own proper place, and forming together a most beautiful and regular whole, though never considered as such before.

But as I have the aid of very correct views of the most important parts of the façade, to the accuracy and fidelity of which I have already obtained your testimony-I shall venture to proceed, for I am anxious to bring into notice the most complete exposure of the internal structure of a district, that I have seen or read of; as there is little likelihood that any other person will enjoy the

opportunities which I have had for so many years, of exploring this interesting part of our coast, through a turbulent sea and rapid tides.

Description of the Promontory of Bengore, and its

Stratification.

This promontory commences at the termination of Bushfoot Strand, where the coast, the general direction of which for several miles had been due east and west, turns to the north-east, and after being cut into several semi-circular bays, deflects to the S. S. E. and near the old castle of Dunseverick, resumes its former rectilineal and nearly eastern direction.

The promontory occupies the interval between Dunseverick, and the Black Rock, at the end of Bushfoot Strand, about four English miles; the façades commence at Black Rock, and increase in height until we reach Pleskin, where the perpendicular part at the summit is 170 feet, and the precipitous part from the bottom of the pillars to the sea 200. As we proceed on from Pleskin to Dunseverick, the height gradually abates, and is finally reduced to about 100 feet.

In this whole space, wherever the precipice is accurately perpendicular, the several strata are easily distinguished from each other, but where the slightest obliquity prevails, a grassy covering is formed that effectually conceals all beneath it; hence the face of the precipice seems much diversified; the columnar strata in some places only exhibiting detached groups of pillars, while in others they form extensive colonnades.

I shall now state the appearances as we approach, and coast the promontory from the westward, noticing in this first view of the precipice, every thing that may be considered as general, and reserving for my return in the contrary direction, a detailed account of the strata taken separately.

The first circumstance, that occurs to the attentive observer on his approach, is, that, although both the promontory itself, and the strata composing it, ascend to the northward, yet it is not in the same angle, the strata being more inclined to the horizon than the line tracing the surface of the promontory, a fact which I shall account for afterwards.

From the Black Rock to the Giant's Causeway (about a mile)

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the materials, and their arrangement, are similar to those of the coast to the westward, viz. strata of table basalt, generally separated by thinner strata of a reddish substance.

At the Giant's Causeway a new arrangement commences, by the aggregate of which our coast is formed; nature having changed her materials, or their disposition, or both, every two or three miles. To the system of strata comprehended between the Giant's Causeway and Dunseverick I now limit myself, as all the strata composing it emerge between these two points.

As we proceed along the coast from the Giant's Causeway eastward, we perceive the whole mass of strata ascend gradually, culminate at the northern point of the promontory, and then descend more rapidly, as the land falls away to the south-east, until having traced them across the face of the precipice we see them immerge separately at and beyond Portmoon Whyn Dykes.

The western side of the promontory is cut down perpendicularly, by eleven Whyn Dykes; the intervals between them are unequal, but they all reach from the top of the precipice to the water, out of which some of them again emerge in considerable fragments; they are all constructed of horizontal prisms, which are strongly contrasted with the vertical pillars of the strata through which they pass.

One of the dykes at Port Cooan, on Bengore, half a mile from the Giant's Causeway, is very beautiful; an insulated rock about 160 feet high, and 20 in diameter, stands perpendicular in the middle of a small bay; the main body of the rock is similar to the contiguous consolidated masses but on the east side a singular whyn dyke is joined to it, composed, (as they often are) of several walls agglutinated together, with wall-like fragments of other parts of the dyke emerging at their base; the solid mass of dyke is seen cutting down the precipice to the southward at 150 yards distance.

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Depressions of the Strala.

Soon after we have passed the last of our whyn dykes at Port Spagna, (a name derived from a vessel belonging to the Spanish Armada having been driven ashore in that Creek), we discover a new and curious circumstance, viz. that the western half of the promontory has sunk or subsided between thirty and forty feet,

without the slightest concussion or derangement of the parallelism of the strata.

Two other depressions appear as we proceed onwards, one at Portmoon, and the other at the angle where the promontory begins to project from the rectilineal coast; these however are far less considerable in thickness than the preceding, neither of them exceeding five feet.

Such depressions occur at the collieries near Ballycastle, and generally on one side of a whyn dyke, We have also at Seaport, two miles west from the Giant's Causeway, a dyke, oblique and undulating, with a depression of the strata of about four feet on one side: but on Bengore promontory our dykes are unaccompanied by depressions of the strata; and where we have depressions, we do not find a trace of a dyke.

The portions of this extensive façade, which I have selected for explanatory views, are Portmoon, in or near which most of the strata emerge, and Pleskin, where the strata culminate. Each of these views too, exhibits one of our depressions; but in that of Pleskin, the first apparent depression is purely an optical effect arising from the position of my friend Major O'Neal, of the 56th, who took his view from the water.

Enumeration of the sixteen Strata that compose the Promontory of Bengore, taken in their regular Order, and counting from above.

The country immediately to the southward of Bengore is, like the Promontory itself, a stratified mass, accumulated to the summits of Craig Park and Croaghmore, the first five hundred and the second seven hundred feet high; but with these strata I have nothing to do, limiting myself to those alone of which the promontory is formed, and which are exhibited in its façades.

The uppermost of these commences near half a mile to the eastward of the angle, where the coast, deflecting from its due east and west course, turns to the north-west, and begins to form the promontory.

So far the course of this stratum is to appearance perfectly horizontal; for the strata all ascending to the north, the intersection of their planes with the plane of the sea, must run east and west, that is, in the present case it coincides with the direction of the coast,