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county of Cheshire. This plain is subdivided into three; the bason of the Dee on the west, of the Mersey on the north, and the Weaver in the middle. In this middle district, which may be compared to a sector of a circle, having its centre at the point where the Weaver falls into the Mersey (the circumference stretching along the borders of Flintshire, Shropshire and Staffordshire), are found the salt mines, generally not far from the banks of the Weaver and its branches. « The salt rock was • first discovered at Marbury, near Northwich, about a llun• dred and forty years ago, in searching for coal. After this 6 bed of rock had been worked for more than a century, a se• cond and inferior stratum was met with, separated by a bed
of indurated clay from the one previously known. This lower • stratum was ascertained to possess, at a certain depth, a great
degree of purity and freedom from earthy admixture; on
which account, and from the local advantages of Northwieh • for exportation, the fossil salt is now worked only in the vicinity of this place. Trans. p. 45.
The thickness of the upper bed of salt varies from twenty to thirty yards: that of the lower bed has never yet been ascertained. It is a certain fact, that no marine exuviæ or organic remains are found in the strata situated over the rock-salt of Cheshire. The occurrence of gypsum in connexion with beds of fossil salt, is a fact generally observed; and it occurs in Chen shire, as well as in the salt rocks on the Continent.
“ One of the most striking facts connected with the internal structure of the Northwich rock-salt, is the appearance observable in the horizontal sections of the rock, of various figures, more or less distinctly marked, and differing considerably in the forms which they assume ; some appearing nearly circular, others perfectly pentagonal ; and others again having an irregular polyhedral form. The lines which form the boundaries of these figures are composed of extremely pure fine salt, forming a division between the coarse red rock exterior to the figure, and the equally coarse rock included within its area. It had been stated to me, that their form is a pyramidal one, the area enlarging by a determinate ratio of increase, as they are traced downwards: But I consider this statement as a very doubtful one, and certainly founded upon
On this subject, it happens that we ourselves can state, from observation, that this pyramidal form is quite inconsistent with what we have seen. In a perpendicular wall of the mine pear the roof, where the miners had been recently working, the section of the coats above described appear
ed as segments of circles, which succeeded one another like waves, when traced horizontally along a vertical section. They have that appearance of concentric layers which Dr Hutton has described in his Theory of the Earth, and from which he has inferred the original fluidity of these rocks.
The comparative commercial value of the English and Po lish mines is best ascertained by the fact, that many thousand tons of rock salt are usually sent ftom Cheshire to the parts of the Prussian coast most nearly adjacent to the salt mines.
The fourth paper in this collection relates to a very interesting object, the Pitch-lake of the island of Trinidad.' Dr Nugent, who had himself an opportunity of visiting this singular spot, tells us, that, on approaching it, he perceived a strong sulphureous and pitchy smell, like that of burning coal; and soon after had a view of the lake, which, at first sight, appeared to be an expanse of still water, frequently interrupted by clumps of dwarf trees, or islets of rushes and shrubs; but, on a nearer approach, was found to be in reality an extensive plain of mineral pitch, with frequent crevices and chasms filled with water. The surface of the lake is of the colour of ashes, and at this season was not polished or smooth so as to be slippery; the hardness or consistence was such as to bear any weight; and it was not adhesive, though it partially received the impression of the foot: it bore us without any tremulous motion whatever, and several head of cattle were browsing on it in perfect security. In the dry season, however, the surface is much more yielding, and must be in a state approaching to fluidity, as is shown by pieces of recent wood and other substances being enveloped in it. Even large branches of trees, which were a foot above the level, had in some way become enveloped in the bituminous matter. The interstices or chasms are very numerous, ramifying and joining in every direction ; and in the wet season being filled with water, present the only obstacle to walking over the surface. These cavities are generally deep in proportion to their width ; some being only a few inches in depth, others several feet, and many almost unfathomable: The water in them is good and uncontaminated by the pitch; the people of the neighbourhood derive their supply from this source, and refresh themselves by bathing in it. Fish are caught in it, and particularly a very good species of mullet.'
This extraordinary lake is bounded on the north and west sides by the sea ;- on the south by a rocky eminence of porcelain jasper ;-and on the east by the usual argillaceous soil of the country. The main body may, perhaps, be estimated at three miles in circumference :-- the depth cannot be ascertained;
and no subjacent rock or soil can be discovered. Where the bitumen is slightly covered with soil, there are plantations of cassava, plantains, and pine-apples, -athe last of which grow with luxuriance, and attain to great perfection.
A bit of the pitch, held at a candle, melts like sealing wax, and burns with a light flame, which is extinguished whenever it is removed; and, on cooling, the bitumen hardens again. From this it is evident, that it may be converted to many useful pur: poses; and it is universally used in the country wherever pitch
is required. The reports of the naval officers who have tried it, - are extremely favourable: It only requires to be prepared with a proportion of oil, tallow, or common tar, to give it a sufficient degree of fluidity. In this point of view it is an object of great national importance, especially to a maritime power like Britain. It is, indeed, singular, that the attention of Government should not have been more forcibly directed to a subject of such magnitude. The attempts that have hitherto been made to render it extensively useful, have, for the most part, been only feeble and injudicious, and have consequently proved abortiye.
This vast colleetion of bitumen might, in all probability, afford an inexhaustible supply of an essential article of naval "stores ; and, being situated on the margin of the sea, could be wrought and shipped with little inconvenience or expense. It would, however, be great injustice to Sir Alexander Cochrane, not to state explicitly, that he has, at various times, during his long and active command on the Leeward Island station, taken considerable pains to insure'a fair and proper trial of this mineral production, for the highly important use of which it is generally believed to be capable.
To frame any satisfactory hypothesis on the origin of this singufar mass, would require an exact examination of the neighbouring country. Immediately to the southward, the face of the coun try is broken and rugged, which Mr Anderson (Phil. Trans. Vol. 79.) attributes to some convulsion of nature from subterranean fires ;-in which idea he is confirmed, by having found sem veral hot springs in the neighbouring woods. The production of all bituminous substances has certainly, with plausibility, been attributed to the action of subterraneous fire on beds of coal, Dr N. was particular in his inquiries with regard to the existence of beds of coal, but could not learn that there was any certain trace of that substance in the island ; and though it may exist at a great depth, it is not indicated, the Doctor says, by the strata that are in sight. *** The examination of this tract of country (he adds) could not fail to be highly gratifying to those who embrace the
Hattonian Theory of the Earth for they might behold the numerous branches of one of the largest rivers of the world (the Orinoco), bringing down so amazing a quantity of earthy particles, as to discolour the sea in a most remarkable manner for many leagues distant ;-they might see these earthy particles deposited by the influence of powerful currents on the shores of the Gulf of Paria, and, particularly, on the western side of the Island of Trinidad ;--they might there find vast collections of bituminous substances, beds of porcelain jasper, and such other bodies as may readily be supposed to arise from the modified action of heat on such vegetable and earthy materials as the waters are known actually to deposit. They would, further, perceive no very vague traces.of subterranean fire, by which these changes may have been effected, and the wbole tract ele vated above the ordinary level of the general loose soil of the country - as, for instance, hot springs, the frequent occurrence of earthquakes, and two singular semi- volcanic mounds at Point Icaque; which, though not very near, throw light on the gene ral character of the country. Without pledging myself to any particular system of Geology, I confess, an explanation, similat to this, appears to me sufficiently probable, and consonant with the known phenomena of nature. A vast river, like the. Orie poco, must, for ages, have rolled down great quantities of woody and vegetable bodies, which from certain causes, as the influence of currents and eddies, may have been arrested and accumulated in particular places ;--they may have there undergone those transformations and chemical changes, which various vegetable substances, similarly situated, have been proved to suffer in other parts of the world. An accidental fire, such as is known to Oce cur frequently in the bowels of the earth, may then have operu ated in separating and driving off the newly-formed bitumen, more or less combined with silicious and argillaceous earths ; which, forcing its way through the surface, and afterwards becoming inspissated. Sy exposure to the air, may have occasioned such scenes as I have ventured to describe. The only other country, aecurately resembling this part of Trinidad, of which I recollect to have read, is that which borders on the Gulf of Taman in Crim Tartary. From the representation of travel bers, springs of naphtha and petroleum equaly abound, and they describe volcanic mounds precisely similar to those of Point Icaque.
The next Geological paper is on the physical strueture of Devonshire and Cornwall, by J. F. Berger, M. D. of Genera
No part of the Island of Great Britain affords more interest ing matter of mineralogical observation than Cornwall
. Its chaQ4
racter, as belonging to the primary or intermediate strata; the abundance of mineral veins; and the various points in which these veins and the adjoining rock have been cut into, or perforated, are all circumstances that render Cornwall a subject of curious and important inquiry. Dr Berger's attention was therefore very properly directed to this spot; and his survey (though, doubtless, imperfect) has furnished a great deal of valuable information. He is a mineralogist of the Wernerian school; and not only adopts the language of that school, but has been guided by its principles in his observations. He seems sensible, however, that the language which he employs is too theoretical ;-and, in his use of the word formation, though he gives a definition of the term in which nothing theoretical is implied, he allows, that the idea of time or of epoch is involved. We might add to this, that not only is epoch involved, but the agent is likewise indicated; and an identity, in the order of time and the order of position, is certainly understood.
The general remarks on what the author calls the Low Mountain Chain of Cornwall,'convey a very good idea of the disposition of the rocks in this western promontory, or the ridge of hills that divides the country lengthwise. The chain begins in the centre of Devonshire, where it spreads out into the elevated, or, as it is here called, the mountain plain of Dartmoor Forest. • Like all primitive chains, he says, it stretches from N. E. to S. W.; or, more correctly, from E. N. E. to W.S. W. for the length of 115 or 119 miles. Its direction is pretty accurately represented by a line passing through the following places: Two Bridges, Lanceston, Bodmin, Redruth, &c. to the Land's End. The centre and highest part of the chain is of granite; it is formed into a mountain plain at the N. E. extremity, and, as it approaches the S. W., gradually contracts into a ridge, and is flanked on the right and left by grauwacke. The outline of the range is not altogether continuous: several of the rounded summits which compose ii, are separated by small valleys, or ravines, of various depths. The whole chain may be said to be formed of downs, and to be in some places interrupted, but no where entirely broken off. On this
passage, which, we believe, contains a correct general view of the rocks in the Cornish promontory, we cannot but remark, that the assertion that all primitive chains stretch from N. E. to S. W., seems to us much too general. The Riphean, or Ural mountains, which are undoubtedly priinitive, stretch nearly from south to north. The great range of mountains in Norway has the same direction; and this is also true of the great