In all these wells, the water undoubtedly flows on the same bed of clay which appears under the chalk in the higher parts of Wiltshire.

These wells are sunk in chalk, and the well-diggers find water before they get through the bed, that is, when the pressure of water upwards overcomes the resistance of the chalk to its ascent. This perfectly accords with the well-known laws of Hydrostatics.

The well at Dover Castle was sunk three hundred and sixty feet through the cliff, and contained twenty-one feet of water in September, 1784. Lord Spencer's well, at Maidstone, is the same depth.

I have no doubt, therefore, that the whole thickness of the chalk stratum is more than four hundred feet. My valuable friend, Mr. Parkinson, states the upper bed at six hundred and fifty feet.'

The sand-beds, taken together, are supposed to be not less than 300 feet in thickness; the superior oolite, in some places, 20, and in others 40 feet; the calcareous grit and the coral rag seem to vary from 8 to 30 feet, each; the Kelloway rock, from 3 to 6; the corn-brash, near Bath, does not exceed 12; the forest marble is at least 40; the great oolite, in its thickest portions, 140; the inferior oolite, about 40, and its subjacent sand not much less; the lyas (blue and white) has in some places been penetrated through 60 feet, though some of the upper beds are wanting; the red ground, comprehending its marl-beds, gritrocks, &c., has been found of various thicknesses, from 100 to 180 feet, or even more.

Beyond the limits (says Mr. T.) which I have traced, it is not easy to ascertain the thickness of the several strata which remain hereafter to be noticed. First, because, being hard, they have not, to the same degree as the preceding strata, been subject to attrition. Secondly, because the spirit of adventure, on which deep perforations must depend, has been chiefly confined to districts, where either coal strata or the precious metals have been found.'

The natural dip of the superior strata is to the S. E., which is the prevailing inclination in almost every part of Europe: but the coal-strata dip in various directions; and, beyond them, in proceeding westward, the schistose strata either dip to the N. W. or assume a nearly vertical position. The author enters into various particulars relative to the rapidity of the dip in the several strata, as far as he has been able to determine it by accurate admeasurement; and with his domestic data he compares appearances in different parts of the world. The range or direction of the strata, as discovered by the horizontal section, is found, in this country, to be generally N. E. and S. W.; and the same observation seems to be applicable to other regions that have been geologically explored. In the more specific illustration of this latter position, the British strata again pass in review; and the coal-fields, or elliptical

basins of coal and mountain lime-stone, are enumerated and delineated with a considerable degree of interest and minuteness. A section is next devoted to the bassetting and dislocations of -the strata. The basset or crop of a stratum is its termination at the surface; and this termination, if bold, elevated, and abrupt, is called the scarp. The crop, owing to the weathering of the materials, the mouldering of an elevated scarp, the deficiency of the superior portion of a bed, &c., is not always easily detected. In mountainous countries it is remarked, that every ridge, or chain, has on one side a gentle slope, whilst the opposite is either steep or even precipitous. The angle (which) these slopes inclose depends on the tenacity of the materials which originally composed the scarp. If these are hard, the angle will be acute; if soft, it will be proportionably obtuse. Hence it is, that even in countries which are new to him, the skilful observer will, at the greatest distance, judge what substances compose the hills and mountains which present themselves to view.'

From these and other general observations, Mr. Townsend passes to the indications of the bassetting of several of our native strata, the various peculiarities attending them, and some of those striking appearances for which several writers conveniently account by the term dislocation. A register of such appearances is, at all events, desirable; and, as Mr. Townsend usually employs the provincial terms applied to the substances described, his work may prove a very valuable guide to mineralogists who have an opportunity of surveying the tracts to which he refers. Moreover, as several of the localities specified occur in the neighbourhood of Bath and Bristol, they are readily accessible to contemplation, and may furnish agreeable occupation to the geological visitants of those much frequented places. Numerous faults in collieries are also here pointed out, and attributed to tie dislocation and disruption of strata; as are the fissures and caverns in mountain lime-stone, detached bowlders of granular quartz, fragments of granite, &c. Mr. Townsend is particularly sollicitous to prove that such blocks have not been detached by common land-floods, or torrents: but may they not have resulted from the decomposition of the softer matters in which they were originally involved? That precipitous mountains and abrupt cliffs are the effect of some violent disruption of their former continuity may, or may not, be consistent with fact: but we can also conceive that their present appearance may be that of their original formation, whether they proceeded from volcanic fire, or from other causes which our limited faculties are inadequate to explain. Even the cir cumstance of encrini, and the relics of corals which now

affect

affect the tropical latitudes, being found in the lime-stone of northern Europe, is no unequivocal proof of extensive and stupendous catastrophes; since the phænomena in question may, with at least equal plausibility, be ascribed to changes in the' constitutional temperature of our planet.

That portion of the work, which describes the extraneous fossils of our own and other countries, will be found highly deserving of perusal; especially by those who are strangers to the writings of De Luc, Pallas, Saussure, Parkinson, &c. Among the relics belonging to the inferior oolite, the Madrepora cinerascens is thus specified:

The coral bed contains the Madrepora cinerascens, which is found recent in the Indian seas. One of these curious petrifactions. was standing upright more than five feet high, and expanding nearly six feet, with a double cup, much fractured, but no fragment is scattered to a distance. It was, A. D. 1802, examined by several gentlemen. The remains are to be seen near Midford, in the lane leading from thence to South Stoke. In its cavities it contains numerous coated mytili, with their cables covered by a crust, on some of which corals have begun to build.'

Mr. Townsend's descriptive catalogue of animal and vegetable remains is, however, far more extensive and minute than the purpose of his argument required. His suggestions concerning lime-stone, that is generally reputed primitive, are not unworthy of consideration:

In no part of Great Britain have I seen a primitive lime-stone, that is, such a lime-stone as in none of its beds contains extraneous fossils. I have indeed seen many rocks which do not readily exhibit the fossils (which) they contain, unless these have been brought to light by polishing. Alternating with such beds, we find others, in which shells and corals are extremely rare, or which seem to be composed entirely of calcareous paste, as in our lyas, whose fossils are confined principally to its intermediate beds of clay.

In the most perfect of Italian marbles, we have indeed no extraneous fossils, but it does not therefore follow that such rocks are primitive. They are in the vicinity of granite. They border on basalt, and other volcanic productions. They have not the least resemblance to our mountain lime-stone, or other calcareous rocks, formed evidently by subsidence in water. They are semi-pellucid, and in their fracture have a crystalline appearance.

These circumstances have long since made me suspect the agency of fire, and now the experiments of Sir James Hall confirm my suspicions. He has had the goodness to shew me some of his marble, produced by fusion under pressure, equal in its appearance to the Italian. The term primitive lime-stone seems therefore to be improper, and the reason why no extraneous fossils are to be found in the Carrara' marble may be, that the whole mass of this carbonate has been in fusion.'

Mr. T.'s main object, in exhibiting a copious enumeration of organized remains in a petrified state, is to prove that our present continents were, for ages, covered by the waters of the ocean; a position which few intelligent naturalists will be disposed to controvert: but that the shifting of the channel of the sea, and its diffusion over its present beds, constituted the phænomenon of the deluge recorded by Moses, may not be so readily conceded either by the geologist or the divine. It is true, indeed, that the term days has been construed into periods of indefinite duration, so as to allow ample time for the consolidation of the strata: but, if we make thus free with the pointed and precise language of Scripture where are we to stop, or how shall we draw the line between literal and figurative interpretation? Again, the ark seems to have quietly reposed on known ground; while the olive-leaf, plucked by the dove, and the vineyard planted by Noah, would indicate a return to the former physical condition of things. In short, if the flood universally prevailed over our planet, and to the height of fifteen cubits above the highest mountain, we must believe it as a miracle, and not vainly attempt to explain it by any reference to the known and established laws of nature.

From the section on Springs, we learn that they follow the courses of their containing strata; a doctrine of much practical import to landholders and engineers, but which seems to have. no immediate connection with the Mosaic account of the Deluge. Vallies are represented as the effect of subsidence, and not erosion; consequently, as originating in the debacle of the Deluge, and not in the slow but incessant waste produced. by the attrition of rivers. Yet the converse of the proposition is, perhaps, equally tenable.

Under the article Consolidation of Strata, the attention is principally directed to the process of petrifaction, which Mr. Townsend is particularly sollicitous to ascribe to aqueous deposition, and not to igneous fusion. Now, we are not certain that either hypothesis will satisfactorily explain all the phænomena; and, perhaps, the idea of chemical conversion, suggested by Patrin, is less chimerical than we might, at first sight, suppose. At any rate, we must believe that, in many instances, the process of silification, whatever it may be, takes place with great rapidity. Some specimens of wood-stone, for example, exhibit not only the most entire organization, with the shades of each fibre, but worms, which are themselves converted into agate, with their external surface whitish and opaque, and their interior characterized by waving zones, of different tints, pourtraying the intestines. The annual circles of the wood, and the medullary prolongations from the centre to

the

the circumference, are distinctly traceable; and it is particularly worthy of remark that the only unsilicified parts are precisely. those which had suffered decomposition. At Naufle, near Grignon, have been found morsels of agatized wood, which contain a multitude of the larvæ of insects, retaining their natural form. In others, the caterpillars are observed to be moveable in their cavities; a circumstance which is not easily reconcileable to the infiltration of aquatose fluid that would have consolidated the mass. Saussure informs us that the cabinet of M. Annone, at Basil, includes a fossil crab, of which even the ova, under the tail, are petrified. Some petrified fruits might likewise be quoted, on the present occasion; particularly the fossil walnuts of Lons-le-Saunier, which were found at the depth of 180 feet, in an old salt-brine pit. The shell and rhind retained the ligneous texture, while the kernel was converted into silex. În Davila's catalogue, mention is made of similar specimens, found in Piedmont: of which the colour and appearance are so little changed, that a person would be tempted to eat them, though the inner part of the shell presents not the smallest vestige of infiltration. The case of Trajan's bridge over the Danube, which Mr. Townsend cites with perfect complacency, needs not to be regarded as an exception to this view of the subject; for we can easily conceive siliceous incrustation or deposition taking place very slowly, and being, in fact, a very different process from the transmutation of large trunks of trees into stony matter, by the union of aeriform fluid with the elements. of an organized body. Or, if the petrifying progress must be measured by that of the incrustation just mentioned, its extreme tardiness would denote a higher degree of antiquity than the author had probably contemplated, or than would suit the exigencies of his theory.

The operating causes of the dislocation of strata are here attributed to the joint agency of fire and subterranean currents of water. That the first of these has exerted more powerful and extensive influence than many have imagined will be readily admitted: but every candid inquirer will be disposed to have recourse to some cause of more uniform and simultaneous operation, in order to account for the inclination of strata which pervade whole countries. The effects produced by subterraneous currents of water are thus explained:

A different species of dislocation, wholly unconnected with the preceding, has been noticed on the northern extremity of Lansdown and at Derry Hill. Such dislocations are extremely common. To understand their nature, we must call to mind, what has been said of strata, and of springs, and must consider, what is passing at the present moment in the bosom of the ocean.

• We