Giant's Causeway, in Ireland. - The following account is taken from notes of a mineralogical excursion to the Giant's Causeway, by the Rev. Dr. Grierson, as published in the Annals of Philosophy.

The Giant's Causeway, A Stupendous Collection Of Natural Columns Of Basalt, On The Coast Of Ireland.

"I left (says the Doctor) Colerain on the morning of Sept. 17, in company with a gentleman of that place, whose obligingness, intelligence, hospitality, and kindness, afforded me a most agreeable specimen of the Irish character, and proceeded to Giant's Causeway. The day was charming; and it is not easy for me to express the gratification I felt, as we made our way through a fine and gently varied district, at the idea of having it in my power soon to contemplate in favourable circumstances one of the most stupendous and interesting natural phenomena, that are any where to be seen. From Coleraine to the Causeway is eight miles in a northerly direction, and I could observe no rock on our way, but the trap formation. On crossing the river Bush, at the village called Bushmills, the country begins gradually to rise, and we descry, about two miles before us, a ridge of considerable height, seeming to terminate quite abruptly on the other side. What we perceive is the land side of the precipice of the Giant's Causeway. It seems to have been a hill of basalt, with nearly perpendicular columnar concretions, cut in two, as it were, by a vertical section, and the half of the hill next the sea carried away. On getting in front of this precipice, which you do by a pass on the west side of it, a most stupendous scene presents itself. The precipice, extending for a mile or two along the shore, is in many places quite perpendicular, and often three hundred and fifty and four hundred feet high, consisting of pure columnar basalt, some of the columns fifty feet in perpendicular height, straight and smooth, as if polished with a chisel. In other parts the columns are smaller, inclined, or bent; and a less length of them strikes the eye. From the bottom of this precipice issues, with a gentle slope of about one foot in thirty towards the sea, an immense and surprising pavement, as it were, consisting of the upper ends of the fragments of vertical columns of basalt, that have been left when the seaward half of the basaltic hill was carried off. The ends of these columns are in general fifteen or twenty inches in diameter, some of them of three sides, some four, five, six, seven, eight, or even nine. Five or six sides seem to prevail most. From the bottom of the precipice to the sea at low water, along this pavement or causeway, which, from the artificial appearance it puts on, has doubtless, in a rude age, given name to the place, is a length of seven hundred and thirty feet. It has been observed to proceed into the ocean as far as can be traced by the eye in a calm and clear day. To any person who has seen both this place and Staffa, the idea naturally enough suggests itself, that they are parts of the same once continuous immense bed of columnar basalt.

"There are properly three pavements proceeding into the sea, distinguished by the names of the Great Causeway, the Middle Causeway, and the West Causeway. These are three large gently sloping ridges of the ends of basaltic columns, with depressions between them, covered with large blocks or masses, that seem to have been from time to time detached, and rolled from the precipice. I had no opportunity of perceiving with what rocks the basalt of the Giant's Causeway it connected. I am told conchoidal white lime-stone meets it on both the east and west sides. There is in one place, near the east side of the Great Causeway, a green-stone vein, eight or ten feet wide, intersecting the basalt from north-west to south-east.

"There was now pointed out to us by the guides a very rare and curious phenomenon, and which is particularly interesting, as it has been thought, by those who hold the igneous origin of basalt, to be a confirmation of their doctrine. Nearly opposite to the West Causeway, and within about eighty feet of the top of the cliff, is found to exist a quantity of slags and ashes, unquestionably the production of fire. On ascending to this spot, which can be easily done, I found the slags and ashes deposited in a sort of bed about four feet thick, and running horizontally along the face of the basaltie precipice twenty or thirty feet. The ashes are in general observed to lie undermost, and the slags above them. They are covered with a considerable quantity of earth and stones, which all consist of basalt, are of a large size, some of them three or four feet or more in diameter, and the ashes likewise rest on the same sort of materials. What struck me here was, that these ashes and slags are entirely unconnected with any rock or formation which seems to be in situ, or in its original position. They are therefore, in my opinion, distinctly artificial, and nothing more than the remains of some large and powerful fire, which had been kept burning for a long while on the top of this precipice, used either as a signal, or for some other purpose which we cannot now ascertain; and that, owing to the part of the cliff on which the ashes were lying having given way and tumbled down, they have been thus buried beneath the ruins, and there remain.

"A considerable way from the repository of the ashes and slags, and to the east of the Great Causeway, is another curi-cus appearance. Here, in the pure basalt, seventy or eighty feet from the top of the cliff, is a horizontal bed of wood coal, eight feet thick. The coal to all appearance rests immediately on the basalt below, and the ends of perpendicular basaltic columns are seen distinctly to rest on it above. The basalt is not in the least changed by the contact of the coal, nor the coal by that of the basalt. The coal is very beautiful and distinct, and in one place is seen a coalified tree, (if I may use the word,) ten or twelve inches in diameter, running directly in below the basalt.

"Within sight of this spot, and about three hundred yards to the east of it, are the beautifully conspicuous basaltic pillars, forty-five feet long, and vertical, with the longest ones in the middle, and others gradually shortening towards each side, like the columns of an organ. From this appearance they have received the appropriate name of The Organ.

"At the bottom of this cliff, by examining and breaking the loose columnar pieces of the rock that have fallen down, we found many fine specimens of calcedony, zeolite, and semi-opal. These occur in cavities in the basalt. Sometimes the cavity is not completely filled with the calcedony or opal; and when that is the case, the empty space is observed to be always the upper part of the cavity, while the rock is in situ. Moreover, the surface of the calcedony or opal, next to the empty space, is always found to be flat and horizontal, which would show that the substance must have been filtered into its situation in a fluid state, and afterwards consolidated."