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the granite, it becomes highly indurated, effervesces slowly with acids, and gives, on analysis, a larger portion of siliceous matter. In other respects, there is no obvious change at the planes of contact; and the union between the granite and limestone is so slight, that the action of the water separates them.' p. 275.

We recommend to our readers, in further illustration of the facts described in this paper, the perusal of a Memoir on the same subject in the Transactions of the Royal Society of Edinburgh (vol. VII. p. 303), drawn up by Lord Webb Seymour, from the joint observasions of his Lordship and Mr Playfair. The authors of that communication differ from Dr Macculloch, in denominating Syenite the compound which he calls Granite; and they appear to consider his quartz-rock as gneiss, a rock which he states not to exist at this place. But these differences of nomenclature are altogether unimportant as to the main object of the inquiry, which relates merely to the irregular interference of a subjacent mass with the strata that rest upon it. Having stated the facts in the language of Dr Macculloch, whose paper is confined to description, we shall add the theoretic deductions of Lord Webb Seymour, which are supported in detail by arguments of great force and ingenuity.

The whole hypothesis may be briefly explained thus:-That the sienite, in a state of igneous fusion, was impelled from below by a violent force, against the strata; that it bent them, broke them, dispersed them, and filled up the intervals which it now occupies; that the fragments of the strata were in some degree softened by the heated sienite, so as to admit of a mutual action; that, while the whole intermixed mass was still soft, some further dislocation took place in it; and that all this occurred under a great confining pressure of incumbent matter.*

This hypothesis coincides, in the main, with that by which Dr Hutton himself explains the structure of Glen Tilt, in a paper read before the Royal Society of Edinburgh in 1790, (Edinb. Trans. Vol. III.); but differs widely from the speculative views, concerning the same phenomena, which have been more recently given by Mr Jameson and Dr M'Knight, (Mem. Wernerian Soc. I. p. 362, &c.) p. 362, &c.) This variance of opinion, between authorities of so much weight, gives additional value to the luminous descriptions of the memoir we have just examined.

The geological publications of Dr M'Culloch have now become so voluminous, as to justify criticism upon their manner as well as their substance; and, in this view, we have two observations to make upon them. The author is too fond, we think, of animadverting upon the clumsiness and insufficiency of systematic geology; and he alludes occasionally to the doc

trines of Werner, in a tone too much like that of sarcasm, Whatever be the errors of Werner, or of his more zealous disciples, the school of Freyberg has produced, unquestionably, some of the most eminent geologists of the present day; and the opinions which proceed from it should always be discussed with respect. A second fault of this accomplished geologist, is, the extreme diffuseness of his papers, with a certain want of unity, in part arising from the introduction of two many collateral statements. The best style for publications, issued under the sanction of a learned Society, is surely that which gives, with clearness, the greatest quantity of information in the smallest compass. We have heard it remarked of the late Mr Tennant's papers,-that it was very difficult to abridge them: and could mention, among the productions of our remaining contemporaries, some admirable examples of the union of perspi cuity with condensation. We expect, and have received so much from Dr M'Culloch, combining, as he does, the qualifi cations of a chemist, a draughtsman, and a geological observer of singular enterprise and activity, that he will forgive our pressing upon his attention a defect, which a little additional labour will very easily remove.

Sketch of the Geology of the South-Western Part of Somersetshire; By Leonard Horner, Esq. F. R. S.-An extensive tract, on the confines of Devonshire, and the west of Somersetshire, is divided into several ranges of hills, running nearly east and west, with lateral valleys, at right angles to their direction; to which the Quantock hills, a group of great beauty, is geologically related, though somewhat detached in position towards the east. The surface of this district is smooth, undulating, and rounded; but the cliffs on the sea-shore exhibit very well its geological structure. The highest point is Dunkery Beacon, 1668 feet above the sea; Will's Neck, the highest of the Quantock hills, is 1270 feet in height. The whole tract is composed apparently of one formation, to which Mr Horner gives the general name of Gray-Wacke; but he mentions, as precluding the connexion of any theoretic inferences with that term, that the compound to which he has applied it, is found to alternate with beds of quartz-rock, of clay-slate, and of limestone full of organic remains:-the clay-slate, in fact, cannot be distinguished from that of a primitive country. The curvatures of the slaty strata, on the shore near Minehead, are very remarkable, resembling those described and represented by Mr Conybeare, in the second volume of the Geological Transactions. The contorted beds, in general, are broken at the angles; but the strata seem, upon the whole, to have a line of bearing about east and

west; and the dip, more generally, is towards the south. A mass of granite was observed in one place only,―at the southeast of the district; but Mr Horner supposes it to be a portion of a vein in the slaty rocks. The limestone of the beds above mentioned frequently occurs in masses, like those of ironstone, embedded in the slate; but there is a regular bed at Allercot, 30 feet in thickness. In some places, the limestone is excavated into miniature caverns; and it contains nests of copper ores, which have been found at Doddington in such abundance as to be worked for some time by mining.

The Grey-wacke district is surrounded by conglomerate and red sandstone, which occur in all the valleys, and constitute the whole of the great one on the western side of the Quantock hills; but the relative position of these compounds does not appear to be uniform. The greatest height at which they were found by Mr Horner, was near the summit of the Quantock group.-Besides these rocks, a red argillaceous sandstone, containing calcareous matter, but characterized principally by spots and strips of a greenish colour, belongs to this series. It is the same rock that, under the names of Red ground, Red marl, &c. covers a great portion of the midland counties of England, and which contains the gypsum of Derbyshire and Staffordshire, the salt mines of Cheshire, and the brine springs of Worcestershire. -Mr Horner states, that few of the English strata present a greater variety of aggregation, or have given rise to so many contradictory opinions: and he considers the determination of its relative place, as a point of great interest, not only to Geologists, but, in an economical view, from its intimate connexion with the coal formations. In the district under examination, this red marl appears to be connected, by insensible gradation, with the conglomerate and sandstone above mentioned, and here always occurs above the former; but this does not appear to be the case in any other part of England where it is found. It is most prominent in the district now under consideration, on the shore near Watchet, where there is great confusion in the stra tification; and near the same place, it is found to contain gypsum in great abundance, in veins and detached masses,—but no rock-salt has been found there,

The rocky shore between Minehead and the mouth of the river Parret, is composed of the lyas limestone and the red marl; but the disturbances of the strata render it difficult to ascertain their relative position: Mr Horner is of opinion, however, that they do not alternate. The lyas limestone occurs here in very regular strata, seldom exceeding a foot, and often not more than four inches in thickness, which are separated by beds of slate

clay. It varies much, however, in its qualities: one variety, of a light blue colour, which is called by the quarriers blue lyas and building lime, yielding a lime remarkable for setting under water; the other principal variety, black lyas or ground lime, gives a fetid smell on being struck or burnt, and abounds in organic remains; among which Mr Horner found those of an ammonite, of a pecten or lima, a pentacrinite, terebratulites, a large shell of the genus Nautilus, and slight remains and traces of of some unknown pinnated vegetable converted into coal.' The fossils of the slate-clay beds appear to be the same; but the ammonites, which in the limestone preserve their usual form, appear to be flattened in the clay. The limestone strata are, in several places, formed of columnar concretions; and a similar structure has been observed in the red rock also. The appearances of disturbance in the strata are very remarkable in some places on the shore; but on the north of the Quantock hills, the lyas appears, in all distinct cases, to repose upon the red rock. The lyas strata are found in the vicinity of the quarries at East Lynch near Porlock; and this appears to be the most western point of England where they occur.

The south-western part of Somersetshire appears, therefore, to have furnished the following rocks. 1. Granite, probably in a vein; 2. The grey-wacke formation, containing beds of limestone; 3. & 4. Conglomerate and sandstone, of doubtful relations; 5. Red marl; 6. Lyas: But the relative position of all the beds above the grey-wacke appears still to demand investigation. Mr Horner mentions the detached hills of conglomerate at Torweston, and those near Tone and Vellow, as deserving of particular examination; and is of opinion, that the obscure relations of the lyas and red marl may be very well investigated on the Somersetshire coast.-In the eastern part of the district, near the river Parret, there is an insulated hill, called Connington Park, 230 feet above the sea, which is totally different in structure from all that has been described. It is composed of highly crystallized limestone, of a pearl grey colour, and very close grain; and is entirely destitute of organized remains. The mass is evidently stratified, but exceedingly shattered: the beds, however, seem to be nearly vertical, and to run from north to south.

One of the most remarkable features of this coast occurs about three miles west of the Parret, where the remains of a forest, considerably below the level of the sea, are visible at low water. They continue for three quarters of a mile along the shore; and, after an interruption of two miles, are resumed again for a short

space.

Here there are seen, at intervals, patches of various dimensions, raised six or eight inches above the sand; and upon digging into these, they are found to consist of a dark brown matter, resembling peat, or decayed vegetable substances, mixed with a plant, in which the structure is entire, with twigs and small branches of wood, in a soft state, and containing here and there a few nuts. This brown matter rests upon a light-blue very stiff and unctuous clay, and is of various thickness, in general from a foot to eighteen inches; but in one place I observed it two feet and a half, without coming to the blue clay. Trunks of trees, of a very large size, (some of them supposed to be oak and yew), are found at different intervals, surrounded by the brown matter, and with them roots diverging as they grew, and fixed in the blue clay. The smaller twigs and branches in the brown matter, which look like the roots of underwood, also penetrate the blue clay; and the clay contains a great deal of that particular plant which appears the least decayed in the brown matter. In order to ascertain whether the species of any of the plants contained in the brown matter could be made out, I sent specimens of it to my friend Mr Brown, of the Linnean Society, whose eminent skill in Botany is so well known, requesting him to examine them. He informs me, that the plant which was best preserved was the only one upon which he could pronounce with any degree of probability, the rest being too much decayed. It resembles the common Sea Grasswrack; but the leaves are so much broader, that he considers it more probably the Zostera Oceanica of Linnæus.' (Caulinia Oceanica of De Candolle). It is worthy of remark, that Dr Smith, in his Flora Britannica, when speaking of this plant, says, • Zostera oceanica Linnæi, sui generis planta, nostras nunquam oras attigit." p. 380, 381.

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There is an evident resemblance between the submarine forest here described, and that on the coast of Lincolnshire, observed by Sir Joseph Banks and Mr Correa De Serra. (Phil. Trans. 1799.) The trunks, however, at the latter place, were flattened, which Mr Horner did not find to be the case in Somersetshire. We also have observed similar remains on the shore between the town of Swansea and the Mumbles Point, where the roots of trees are visible beneath low-water mark in a bed of stiff blue clay; and similar remains, we believe, are found in several other places on the coast of Wales and of Lancashire. The most obvious cause of these phenomena is the encroachment of the sea; but Mr Horner mentions several circumstances, which render it not improbable that, in Somersetshire, the land itself may have subsided.

We regret that we have not space for an abstract of the two remaining papers on the Geology of England.-Outlines of the Geology of Cambridgeshire, by the Reverend J. Hailstone, Wood

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