« AnteriorContinuar »
hand, we are equally at a loss to find an analogue for a quadruped or aligator with a naked toothed bill in place of jaws. Cuvier has rendered it inore than probable that the Maestricht animal was an inhabitant of the sea; we are inclined to suspect that the originals of our aligators frequented the same element, as their remains are accompanied with the briarean pentacrinite, shells, and even sometimes fish. The lowest bed of the lias contains a vast assemblage of palates and joints of the pentacrinus, with teeth and fragments of bone, and is visible at Westbury cliffs, near the Severn. Beneath the beds of lias are twenty-four feet of a fertile blue marle.
From the above abstract of this part of Mr. Townsend's work, our readers will be enabled, in some degree, to judge of the value and precision of his inforination concerning these strata ; and we do not hesitate to assert, that not only 110 account has hitherto been published which bears a comparison with his description of them, but that no district of equal extent with that surrounding Bath, which our author has illustrated, has yet been examined with such patient industry and philosophic impartiality. Mr. Townsend candidly refers part of his information to Mr. William Smith, of Midford, who appears to have led
the way in exploring this stratified portion of our island. Mr. Farey had previously acknowledged him as his tutor, and the unqualified praise bestowed by all geologists who have occasion to mention his discocoveries, cannot but excite an eager wish that he would soon present the public with the results of his long and laborious exertions. These observations of Mr. Townsend's are alone sufficient to render the work before us of no ordinary importance to the geologist, and he deserves additional praise for having explained the subject in a manner perfectly intelligible even to those who are not initiated into the phraseology of modern systems. That this perspicuity is the result of an experimental acquaintance with his subject, the writer of this article is convinced, from having had an opportunity of verifying Mr. Townsend's observations on the spot, in a very considerable number of instances.
Our author's remarks on the red ground, coal strata, and mountain limestone, are interesting and valuable, but either too widely dispersed, or too partial, to afford those general results which may be derived fronì his observations on the oolite strati. fication. The red ground in the vicinity of Bristol appears to differ considerably from that of Shropshire, Cheshire, &c. Indeed we are not convinced that Mr. Townsend is correct in accounting them the same stratum. The Somersetshire red ground appears immediately below the lias, and upon the top of the coal strata it does not generally exceed 100 or 180 feet, and contains marle beds, grit rocks, mill-stone, and pennant flag-stone; its
fossils are the remains of aquatic plants, which Mr. Townsend has, probably by a slip of the pen, termed marine plants, and which are precisely the same as those found in the coal and grey sandstone strata of Yorkshire and Derbyshire.
Among the productions of the red ground in the neighbourhood of Bristol, the sulphat of Strontian deserves notice; according to Mr. Townsend it occurs at Wickwar,“ hoth stratified and in veins.'
Our author gives a comprehensive sketch of the coal geography of England, and indicates the principal coal fields in different parts. The Gloucestershire and Somersetshire coal district has been very imperfectly investigated, but appears to contain several distinct coal-fields. The best defined of these is in the vicinity of Puckle-Church.
• It consists of two elipses, external and internal, which are nearly concentric. In the external range the coal is not so considerable as in the internal. The beds are numerous but small. Yet even in the external range at Siston, one out of ten beds of coal discovered in sinking fourscore fathom, is three feet in thickness. All these are separated by either argillaceous or silecious strata, and all dip towards one common centre, but flatten as they descend, so as to assume not a conical form, but that of a wide bowl dish. In Somersetshire, the coal district is distinctly bounded to the south by the lime. stone of Mendip hills, near to which the general dip of the coal beds is to the north, whilst the surface of the country dips south and south-east. On the northern limits of this coal field, the beds dip south. Forty-six beds appear on Stratton Common, all workable, besides many others of inconsiderable value ...
• Between the wide extremes of these Gloucestershire collieries and those of Mendip, we have others whose limits are not well defined at Radstock, Camerton, Newton, Hanham, Bedminster, and Kingswood, in which the beds dip in every possible direction. These last are separated by deep vallies, and covered by the red ground, but although in the deepest of these mines they have sunk 120 fathom, they have not penetrated to the mountain limestone.
• To the west of these collieries we have another coal field at Nailsea and Kenn.... They have here already discovered ten seams.' pp. 159-161.
Our author has collected much information respecting the coal fields of the forest of Dean, of South Wales, of Shropshire, Leicestershire, Nottinghamshire, Derbyshire, Flintshire, Lancashire, Westmoreland, Cumberland, Durham, and Northumberland, which all contribute to prove the great diversity existing in different places, and to shew how much is yet required to afford us a distinct idea of the actual state of these curious formations. At Puckle Church they sunk sixty feet through lias, one hundred and fifty-three through red ground, six feet in duns: when they found coal, and beneath the coal one hundred and eight feet of red ground, without either coal or limestone. At Clydash, in Monmouthshire; argillaceous and silecious strata have
been found beneath the coal to the depth of 360 feet, and in the forest of Dean these strata measure from 12 to 1800 yards in thickness. In the present state of the geology of this island our knowledge of the succession of strata between the lias and the mountain limestone, is extremely confused and uncertain. The mountain limestone, however, is stratum which may be readily ascertained by its fossils. It appears in Somersetshire and Gloucestershire, to the north of Bristol, forming St. Vincent's rocks, but is devoid of the intermediate beds of toadstone, basalt, or amygdaloid, which occur in Derbyshire, nor does it appear to be equally productive of metals , yet the stratum may be perfectly identified from Torbay, through the Mendip hills, by the side of the Malvern hills to the Peak in Derbyshire, to In- * gleborough, Whernside, and Pennigent, in Yorkshire, and into Durham and Northumberland. Our author remarks that this stratum is not by any means regular, but seems to form basins of vast extent, in which the coal formations are deposited, and in proof of it adduces numerous observations. The dip of the beds appears to be towards the centre of these basins, and the dip of the coal conforms to the limestone beneath ; on the contrary, the dip of the whole succession of lias and oolite strata, together with the incumbent chalk, is uniformly to the south east, and so rapid that they would be lost in a much shorter space than is actually the case, were it not for a succession of faults which throw them continually up again. The total dip of the chalk, from Devizes to London Bridge, is about one thousand feet; while the mountain limestone at Wick, near Bath, makes an angle of 45" to the horizon, dipping N. W. and at Caerphilly, in Wales, the same angle to the south.
Our author has a very interesting section, marked by great accuracy of observation, on the crop and dislocation of the strata, a proper knowledge of which is the foundation of geological science. Our limits do not permit us to enter into an investigation of the subject; but the following passage may serve to shew such as have studied systems of nature what difficulties occasionally occur.
• In the quarries at the summit of Anthony Hill, near Bath, we meet with a very interesting dislocation. Here are seen only the bottom beds of the great oolite rock, which are...1. A bed of rubble six feet; 2. Beds of ragstone, nearly horizontal, 21 feet in thickness, lying perfectly flat on a smooth face of the subjacent beds ; 3. Pure oolite, with its beds dipping S. W. in an angle of 45°. Its beds are all truncated at the upper surface, in one straight feather edge, and the whole lies with a smooth truncated face on a bed of ragstone, which like the upper ragstone, is nearly horizontal. The same dipping beds, enclosed between two horizontal beds, are to be seen at Burnthouse-gate, and on the Gloucester road. But what is still more remarkable, is to find... in the parish of Mells, rhon
boidal beds of the ragstone truncated, ... and confined between two horizontal beds of clay, of which the uppermost is yellow and the undermost is blue. We can scarcely conceive that such dipping beds were ever horizontal, as the laminæ make it probable that they were. If they were once horizontal, in what state or condition were they when this dislocation, producing their angular position, took place ?. Were they soft? Why then did they not subside, and again assume an horizontal position? Were they indurated ? By what agent then were the horizontal sections made, so as to leave a flat, rhomboidal, and perfectly smooth surface, incumbent on and covered by soft beds of clay?" p. 200.
Intimately connected with the crop and dislocation of the strata is the rising of springs, which often convey information to the experienced eye, by a line of rushes, where distance or the cover of vegetable earth render an examination of the substratum impossible This subject seems to be a favourite with Mr. Townsend, and he renders it instructive and amusing. It deserves remark, and may be placed among the numerous proofs of the wisdom of Providence in accommodating inert matter to specific purposes, that every porous stratum of rock has its corresponding bed of tenacious clay or marle beneath it, which holds up the water filtrating through the rock above; dislocations of the strata occasion these beds of clay to deliver the water in the form of springs, which would otherwise be conducted along their regular declivity into the abyss.
Mr. Townsend's remarks on the geology of foreign countries are unavoidably of a more desultory nature, but they form a very interesting collection. Many are original; and his readers are under great obligations to him for having extracted the rest from the mass of matter, often unimportant and perplexing, with which they were blended in the descriptions of travellers. In examining the systems of the moderns, he does ample justice to the accuracy and industry of the venerable De Luc, and adds several new facts to those produced in contradiction to Hutton and Playfair; but we must defer any observations which we had intended to inake on this part of his work, to an opportunity which we shall shortly take of noticing, though later than we wished, the travels of the former gentleman.
In a section entitled “ Geological Conjectures, Mr. Townsend seems to be desirous of giving credit to Plato's story of the immersion of the island of Atlantis, and attributing to this cause the depression of the sea which produced the flat ground of Egypt and China. We are however at a loss how to explain a depression of the sea by an event which appears calculated to have directly the contrary effect; nor do the arguments brought forward in support of the eruption of the Black Sea, seem sufficiently conclusive. Our author then mentions the hypothesis, that the earth has shifted her axis, and adduces in proof the cir
cumstance, that shells peculiar to warm countries are discovered petrified in the colder regions of the north ; but we apprehend that he has taken the identity of recent and petrified species upon the authority of others, rather than from his own observation ; at least in referring the reliquia of elephants found in Britain to the Asiatie species, he forgets that Cuvier has indicated a most decided difference between them. Mr. Townsend's third conjecture' intimates the probability that the term days in the Mosaic account of the creation, simply implies periods. In the fourth, relating to the formation of the nodules of flint, which occur in the chalk stratum, we think he unnecessarily multiplies causes, by admitting that some may have been produced by fusion. Infiltration appears to us quite sufficient to produce all the appearances under which they are found.
The concluding section discusses the importance of geology, to gentlemen of landed property---to civil engineers---to builders---to commissioners of the highways---to brickmakers, statuaries and marble masons---to cloth manufacturers---to coal adventurers and mineral adventurers of all kinds---and lastly to all who are interested in establishing the credibility of a divine revelation. The first series of points he proves by numerous apposite anecdotes of the needless expence incurred, and useless precautions taken, for want of a little geological information. Thus coal pits, or pits intended to reach coal, have been sunk from the foot of the chalk stratum, and even in the chalk stratum, some of which have reached the top of the great oolite, while others have never even got into the sand; circumstances which a slender acquaintance with this science would have enabled the adventurers to foresee. Drains have been dug and wells sunk, in an equally preposterous manner. Materials have been fetched ten miles to mend sandy roads, though excellent'stone for the purpose might have been got within a few feet of the surface over which it passed. Gypsum was procured from Paris, and the exportation of fuller's earth made felony; though we have abundance of the former, and the latter regularly attends the great oolite. The last consideration, that the evidence of geology tends to confirm our belief in the truth of scripture, brings us safely back again, after an excursion of somewhat more than 300
pages, to the place where we left Moses. We must however confess, that, notwithstanding an attentive perusal of Dr. Townsend's work, we are not quite certain whether he attributes the stratification of the superior part of the earth's surface to the flood, to the successive periods indicated by the expression duys in the Mosaic record, or to a time antecedent to the chaos mentioned by the inspired historian; or whether he thinks the flood the cause of the change of situation of the strata from an borizontal position, in which they must have been formed, to their