« EdellinenJatka »
to affording the inquirer any information on the subject. From what I could collect, the beds of coal are very numerous, and several of them upwards of six feet in thickness; but, if the different accounts were correct, great changes must take place, both in the thickness of the different beds, and the distances between them in different parts of the field. Mr. Heath, of Kidcrew, was kind enough to give me a section of the Hurecastle tunnel, in which a total thickness of upwards of three thousand feet of coal measures was cut through, containing twenty-eight beds of coal, whose thickness was altogether between sixty and seventy feet, and in which section neither the highest nor the lowest known beds are included. As, however, no mention is made of the occurrence of faults, I think there must probably be some mistake, and that some faults must have been unobserved by which a repetition of some of the beds was occasioned, producing this apparently enormous thickness of mea. The position of the beds in this coal-field is highly remarkable. Along the whole of the eastern portion, from Biddulph, through Burslem and Hanley, to Lane End, the beds dip west at an angle of 33°, on the average; but on proceeding two or three miles in that direction the beds are found to rise again, and in the country between Newcastle and Kidcrew they dip to the east at a similar angle. On the extreme western boundary of the district, however, they again recover their westerly dip, and plunge under the new red sandstone plain of Cheshire. About Kidcrew and Talk-o'-theHill the beds are greatly broken and shattered, one portion lying horizontal, perhaps, whilst its immediate neighbours dip E. or W. at the rate sometimes of eleven inches in twelve, or nearly 45°.* The direction of the chief line of fracture coincides with that of the ridge of hills called Mole Cop, Congleton Edge, and Cloud; and on examining these we find still stronger evidence of the action of the disturbing power. Along the W. side of Mole Cop, the upper beds of the mountain limestone begin to shew themselves near the base of the hill, and are worked at one or two points, having the shale above them, which is capped by the millstone grit. These two latter rocks compose the remainder of the ridge, their beds dipping to the E. and forming a clear escarpment to the W. Along this part of its course, then, the elevating force has not merely tilted the beds into a highly inclined position, and left them leaning against each other, as it were, for support, but has broken them clean through
* The workmen call the E. and W. inclinations "the Staffordshire dip" and "the Cheshire dip" respectively.
and lifted those on the E. side up into the air, while those on the W. remain buried at an unknown depth below the plain of Cheshire. If we compare the position of the rocks (such as it appears from even these brief notices) on the western side of the Penine chain,* with that of the same beds on the eastern, we shall be struck with the remarkable preponderance in the magnitude of the faults and dislocations of the former over those of the latter. This violently fractured state of the rocks on the western side of the district, and their comparatively undisturbed condition over the eastern portion, is true for the whole of this great range, and the ridge of Mole Cop is but a minor representation of Cross Fell.
In deducing from the examination of its structure a geological history of the district, the same remarks will apply to N. Staffordshire as to Derbyshire. We have, however, in Staffordshire, more striking evidence of the period intervening between the formation of the carboniferous system and the upper part of that of the new red sandstone, and of the great forces, both of dislocation and degradation, which were at work in the interval, than can be seen in Derbyshire. The fact of the new red sandstone running up the valley of the Dove and lying for several miles along that of the Churnet, following their windings, and resting with its horizontal beds against their broken and eroded banks, shews in the most striking manner that the carboniferous rocks had been elevated and disturbed, and these very valleys had been scooped out in them, before the deposition of the new red sandstone. The valleys seem, indeed, as if they had been arms of the sea running, like some of the Scotch lochs, into the dry land,† during the new red sandstone period, before which they must have been deeper than they are at present. During this period they were filled with new red sandstone up to a certain height, which at some subsequent period has itself suffered from an eroding cause, and the beds of the present rivers have been thus formed. These facts are important, as teaching us to look to a very ancient period for the beginning, at least, of those deep dales and ravines which cut through the mountain limestone and other hard rocks, and whose erosion seems impossible by any forces with
The Penine chain is a term given by Phillips and Conybeare to the great central ridge of hilly country that runs from Derbyshire and Staffordshire to the borders of Scotland.
It is by no means meant positively to assert that the hills of Staffordshire and Derbyshire were dry land during this period, though several arguments might be brought forward to render such an idea probable.
which we are acquainted, unless acting through very long periods of time.
Concerning the very important practical question of the extension of the coal-measures beneath the new red sandstone districts, I am not at present prepared to offer any thing farther than was stated in the last number, except that some facts I met with tended to confirm me in the opinion of the present boundaries of the coal-fields, when ending abruptly against the new red sandstone, having been formed by denuding and eroding forces acting before the deposition of that rock, rather than by direct fractures and dislocations having marked them out, either before or since. If this opinion should be correct, the existence of coal measures beneath any part of the new red sandstone can only be determined by direct experiment, since we have no means of inferring to what depth eroding forces may have acted. It is, at all events, a circumstance well worthy of cautious examination before entering into an expensive undertaking in search of coal beyond the present fields.
OBSERVATIONS ON THE NATURE OF HEAT.
THE word heat, as used in common language, expresses a cause and its effect; it expresses the sensation of heat and the cause of that sensation: hence philosophers, to avoid looseness of speech, have determined to strip the word of its two-fold meaning, and to confine it to the sensation, while, for the cause, they have framed a new word, viz. caloric. This distinction, I conceive, will appear sufficiently important to adopt it in the following remarks.
When the attention is first drawn to this subject, it may possibly be thought an easy matter to determine the nature of a principle so universal as caloric; but that men of the greatest fame in science differ in opinion upon its nature, will be ample refutation of the simplicity of the question. At present there prevail two opinions: the one is, that caloric is a subtle fluid, capable of entering into bodies and of being emitted from them; the other, that it is merely caused by the motion excited among the particles of matter; or, in other words, the one holds that caloric is material, while the other, that it is merely a property of matter. In entering upon this inquiry, it
will be necessary to consider how far caloric corresponds with our ideas of matter; then, which of the hypotheses gives the most plausible explanation of the phenomena dependent upon caloric.
If we adopt the opinion, as many do, that whatever is capable of acting upon our senses is material, the question is at once settled ; but, to give greater scope to the argument, it will be better to fix upon some characteristics common to all matter, and then to find if there is any thing in caloric resembling or approaching to these. Extent and impenetrability are chosen as the indisputable characteristics of all material objects. The first implies, that every atom of matter must occupy space; the second, that no two atoms can occupy the same space in the same precise instant of time. "Were this latter proposition otherwise," says Sir John Leslie, "each body or atom might be successively absorbed into the substance of another till the whole frame of the universe, collapsing into a point, were lost in the vortex of annihilation."
Does this general and common characteristic of matter, extent, apply to caloric, or does caloric occupy space? It decidedly occupies space for most bodies, by an increase of density, give out caloric; or it is a general law, with a very few exceptions, that bodies passing from a larger to a smaller bulk evolve caloric; or the reverse, bodies passing from a smaller to a larger bulk necessarily absorb, or take in, caloric. Thus, according to the experiments of Mr. Watt, water, by conversion into steam, is enlarged about 1800 times. It may be urged that this is all very plain when caloric is viewed in connection with matter; but does it occupy space unconnected with matter, as we can conceive an atom or a number of atoms of any elementary substance to do? This question certainly cannot be answered with the same clearness as that respecting caloric in connection with material objects. That it can, however, be answered in the affirmative, will be abundantly evident to any unbiassed mind who considers the following fact: the transmission of caloric in vacuo, as shewn by Pictet, by placing a thermometer in the exhausted receiver of an air-pump; and by Count Runiford, by placing the same in a Torricellian vacuum, the most perfect that can be found. Now, whatever passes through a complete void naturally occupies a portion of that, unless it be analogous to mental phenomena, which few would be willing to admit of caloric. Therefore, with the idea that caloric is material there is nothing preposterous in saying that extent is one of its essential properties.
The other essential property of matter is impenetrability, or that
VOL. IX., NO. XXVI.
no two bodies can occupy the same space in the same moment of time. For example, if a piece of wood or metal be plunged into a vessel filled to the brim with water, a portion of the water will overflow, exactly equal to the bulk of wood or metal immersed. To apply the same experiments to caloric, with our present knowledge of its nature, would be impossible; but there is evidently something very analogous, as is shewn in the following experiment by the distinguished chemist Berthollet:-"He took pieces of gold, silver, copper, and iron, equal in size, and submitted them to the stroke of a coining press when he ascertained the heat produced by each stroke, by throwing the pieces into water, the relation between the degree of heat given to the water, and the heat previously in the metal having been found by experiment." So he was able to ascertain how much the temperature of each piece had been raised; and the conclusions are these each piece gave the greatest quantity of caloric out at the first stroke, less at the second, and still less at the third; besides, there was a close connection between the caloric produced by each blow and the reduction in size of the metal. Now, from these facts, I think, we may fairly infer the point at issue. Each piece of metal underwent the greatest diminution, and gave off the greatest quantity of caloric at the first stroke; there was less diminution and less caloric, at the second stroke; and still less of these at the third stroke. The particles or atoms of the metal would, on the first stroke, approach nearer to each other, whereby something, if any thing existed between the particles, must be thrown out, and that something may be caloric, which the increase of temperature seems to support. After the first stroke, the distance between the particles would be less, consequently there must be less of any thing between them; hence less contraction and less of anything to thrust out on the second stroke; and so with the third stroke. This argument may be met by saying, that there is no caloric in cold metal, at least not so much as to explain the quantity that can be produced in percussion. Our senses, or the most delicate thermometer, indeed, cannot inform us of the actual quantity of caloric in any body. The information these give us is only relative, and our knowledge of the subject has been compared to a person knowing a few links in the middle of a chain, while the extremities are removed from his view. So in the metal there may be much caloric, not to be detected by our senses or our instruments, capable of being evolved on compression, as the latent heat of steam is evolved on the condensation of the same. I am aware that, in hazarding this remark,