general aspect and structure, are usually so analogous to the facts which prevail in similar formations in other regions, that we may be excused for treating this paper with much more brevity than it would otherwise deserve.

The granite of this territory, which approaches to that which the Wernerians conceive to be of more recent origin than the primitive, is either granular or porphyritic; the former sometimes containing small reddish garnets as an accidental ingredient, and the latter more commonly crystals of hornblend. More than two thirds of the mica-slate, which prevails in the primitive district, may be termed talcose; and the rest is of the common sort: but both varieties, it is presumed, are destitute of garnets: the remainder is granular and micaceous lime-stone, of different colours, usually subordinate to the mica-slate, but sometimes alternating with it. The primitive traps here enumerated and described are common hornblend-rock, hornblend-slate, green-stone, greenstone-slate, and hornblend with mica. Of the green-stoneslate, it is remarked that attempts have been made to quarry "it for the purpose of roofing; and that, if the works were conducted with spirit, they might supply as good slate as that which is imported from Wales. The remaining members of the primitive series are porphyry and syenite.

The transition-rocks which are particularized are graywacke, gray-wacke-slate, lime-stone, trap, (including three modifications of green-stone,) and the old red sand-stone. This last has its station assigned in this division rather than among the secondary rocks, because, in one instance at least, it appears to alternate with gray-wacke. It is mentioned

that Lord Londonderry has caused this formation to be bored to the depth of 500 feet, in the fruitless search for coal on the east side of Strangford Lough near Mount Stewart; if to this depth the height of the sand-stone on Scabro hill be added, it will give from 800 to 900 feet as the known thickness of this formation. The greatest length of this district of sand-stone does not exceed six or seven English miles. It appears to rest on gray-wacke.' We are informed, however, in a note, that the sand-stone-formations of this territory are arranged in a most problematical manner. - In some parts of the gray-wacke-formation, have been found flinty and drawing slate, and lead and copper ores.

Of the floetz-rocks, the designations are, lime-stone, underlying the coal-formation, coal-formations, sand-stone-formations, lias, green sand-stone, or mulattoe, and chalk. Their courses are analyzed with considerable minuteness; and the account of the lias-clay is supplied from the joint observations

of Mr. Buckland, and the editor, Mr. Conybeare. We purposely omit, however, any farther notice of these detailed descriptions, as far as they correspond with known appearances in the coal-districts, or in the chalk-formations of England. The ensuing particulars are probably less notorious, even to some of our geological readers:

• The average thickness of the chalk-formation in Ireland may be estimated at between two and three hundred feet; the upper beds seem to have been partially re-dissolved before the basaltic mass was deposited upon them, since along the line of junction a confused aggregation of chalk-flints exists, imbedded in the lowest member of the trap-deposit, which is usually a bed of ochreous bole: the flints so imbedded have usually themselves acquired a red tinge, apparently by percolation, from the oxidated iron of the stratum in which they lie.

This aggregation of flints, bedded in red ochreous bole, forms at Macgilligan a stratum thirteen feet thick. It may be observed, also, near Larne and near Belfast, and seems indeed of almost universal occurrence.'.

The chalk is frequently traversed by basaltic dykes, and often undergoes a remarkable alteration near the point of contact; where this is the case, the change sometimes extends eight or ten feet from the wall of the dyke, being at that point greatest, and thence gradually decreasing till it becomes evanescent. The extreme effect presents a dark-brown crystalline lime-stone, the crystals running in flakes as large as those of coarse primitive lime-stone; the next state is saccharine, then fine grained and arenaceous; a compact variety having a porcellanous aspect and a bluish-gray colour succeeds: this towards the outer edge becomes yellowish white, and insensibly graduates into the unaltered chalk. The flints, in the altered chalk usually assume a gray yellowish colour: the altered chalk is highly phosphorescent when subjected

to heat.'

Under the head of floetz-trap are comprized tabular and columnar basalt, green-stone, gray-stone, clink-stone, porphyry, bole, or red ochre, wacke, amygdaloidal wacke, and wood-coal. The simple minerals imbedded in some of the rocks of this series are granular olivine, augite, calcareous spar, analcime, mesotype, stilbite, chabasite, iron pyrites, glassy felspar, and chalcedony, which occasionally passes into semi-opal,

The magnificent colonnades of Fairhead and Crosshill are of green-stone, and are destitute of the regular articulations and neatness of form which distinguish the pillars of the Giant's Causeway but they exhibit enormous prismatic masses, often quadrilateral, and these latter appear to be formed of a congeries of smaller prisms, aggregated in a manner which brings to the mind the clustered assemblage of

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shafts

shafts forming a Gothic column: the greatest length of these columns is not less than 250 feet; the green-stone is highly crystallized, the concretions being distinct and large, and contains augite. Slievemish, a remarkable mountain, which lies like a colossal land-mark in the middle of the county, is from its basis to its summit composed entirely of green-stone, thus forming a mass of nine hundred feet in thickness.'

Wood-coal occurs in seams which vary in thickness, from two inches to upwards of five feet; alternating with traprocks, in the centre of the basaltic area, and along the eastern shore of Lough Neagh. The ligneous texture, which is often remarkably distinct, seems to appertain to a species of fir. At Portnoffer, the external surface of some of the fragments of this substance is penetrated, to a certain depth, by small groupes of imperfectly crystallized augites. It is somewhat remarkable that a porphyritic district occurs in the midst of the great area of basalt: but the rocks which compose it, and which are specified in the Addenda, are reported to be of doubtful formation.

The notes on the alluvial depositions are scanty, and probably imperfect: but they apprize us of the occurrence of disseminated pieces of bituminous wood, of which the fissures are penetrated by silex, and even sometimes lined with quartzcrystals. It was once the general opinion that the waters of Lough Neagh had the property of petrifying, and that the quartz contained in the bituminous wood of Sandy Bay had been deposited from them. The experiments, however, made by Mr. Tennant during his stay at Belfast, appear to discountenance that belief, since he found no traces of silica whatsoever in the water of the lough.'

To Dr. Berger's communication are appended Descriptive Notes referring to the Outline of Sections presented by a Part of the Coasts of Antrim and Derry, collected by the Rev. W. Conybeare, M.G.S. From the joint Observations of the Rev. W. Buckland, M.G.S. Reader in Mineralogy to the University of Oxford, and Himself, during a Tour in the Summer of 1813. As this paper is also accompanied by a tabular view of the heights of several stations, calculated from the level of the sea by barometrical measurement, the whole article may be regarded as an interesting geological delineation of a tract of country which cannot fail to invite the contemplation of every scientific observer.

On the Dykes of the North of Ireland. By J. F. Berger, M.D. Member of the Geological Society.-Some of the most important facts deducible from Dr. Berger's observations on

sixty-two dykes are, that they seldom occur singly, but several within a comparatively short distance of one another; that their uniform bearing is from S. E. to N. W.; that they all cut the planes of the strata through which they pass at very considerable angles; that they rarely exhibit shifts in their direction; that they differ very much from one another in respect of width, which varies from a few inches to several hundred feet; that they sometimes rise to a very considerable height above the strata which they intersect; that their depth is unknown; that they are nearly vertical; that they are composed of the following substances, recited in the order of their most frequent occurrence, viz. trap and green-stone, with their associates, lydian-stone, flinty-slate, gray-stone, and wacke; that they are formed either of a number of diminutive and aggregated pillars, or of square rhomboidal pieces, piled on one another; that the mean specific gravities of the different sorts range between 2.45 and 3.14.; that they traverse both primitive and secondary rocks; that they have often had the effect of indurating the latter to some little distance from themselves; that they seem to be of a very different constitution from metallic veins; and that the mineral matters which they contain imbedded, in a greater or less quantity, are augite, in angular fragments, olivine, in disseminated grains, crystallized glassy felspar, compact felspar, in distinct rounded concretions, radiated zeolite, green soft steatite, in distinct concretions, iron pyrites, calcareous spar, carbonate of lime, mixed with the trap, glassy quartz, in distinct concretions, sulphate of barytes, and plates of mica. It is observed that, "whatever date and whatever agents we are disposed to assign to the origin of dykes, their uniformly vertical and nearly parallel positions evince that both they and the mountains which they intersect have not undergone any modern disturbance beyond superficial abrasion, but that they remain in the same situation as at the remote period at which they were formed.'

From the appendix to this article, extracted from the correspondence of the late Rev. George Graydon, it should seem that a considerable analogy obtains between the dykes of Monte Somma, in Italy, and those of the north of Ireland.

Some Remarks upon the Structure of Barbadoes, as connected with Specimens of its Rocks. By Joseph Skey, M. D. Physician to the Forces. - Dr. Skey bears ample testimony to the almost uniformly calcareous character of the composition of Barbadoes; which is unlike, in this respect, to the constitution of most of the West-India islands. A great part of the

island seems to consist of stages or terraces of coral rock; and the specimens to which he refers are chiefly madrepores.

Outlines of the Geology of Cambridgeshire. By the Rev. J. Hailstone, F.R. and L.S. Woodwardian Professor in the University of Cambridge. — The upland parts of this county consist of chalk-hills, being a portion of the great chalkformation which traverses the island from Dorsetshire to the Yorkshire coast. On some of the highest hills, near Cambridge, horizontal layers of gravel and loose stones, resting immediately on the chalk, have been lately discovered. Their prevailing material is a pale blue, or light gray variety of flint, with numerous traces of the alcyonium or other similar bodies in its substance. The details of this deposition are succeeded by a mineralogical analysis of Harston-hill, by Mr. Warburton. By far the greatest part of the hills of the county are composed of the lower beds, or gray chalk, which contain no flints: but dispersed masses of radiated pyrites, in a globular or kidney form. It is considerably harder than. the common chalk, is provincially denominated clunch, and is the material from which the best lime is burnt. As it endures heat, it is also used for the backs of grates, &c. It seems to pass, by degrees, into the gault, or stratum of blue clay on which it rests. At Ely, a concrete bed of siliceous sand, with small rounded fragments of iron-stone and quartz-pebbles, varying in thickness from eight to twelve feet, overlies the gault, and is conjectured to be an alluvial deposition. The organic remains, found in the chalk and clunch beds of Cambridgeshire, are generally analogous to those which occur in the other districts of the chalk-formation.

Some Observations on a Bed of Trap occurring in the Colliery of Birch-hill, near Walsall, in Staffordshire. By Arthur Aikin, Esq. Secretary to the Geological Society. - From such an examination as circumstances permitted him to institute, Mr. Aikin infers, first, the existence of a bed of green-stone interposed between the usual strata of the coalformation, but not co-extensive with them; and secondly, that the coal and bituminous shale, where they are covered by the green-stone but protected from actual contact with it by an indurated sand-stone a yard in thickness, differ materially in many respects, but chiefly in being deprived of bitumen, from those parts of the same beds where they are not covered by the green-stone.'

A Geological Description of Glen Tilt. By John Mac Culloch, M.D., &c. &c. &c. As the perplexing rocks of this Highland-valley have proved the source of some sharp tilting matches among our northern geologists, the President of the

Society