A question of speculative interest was determined in a bore made at Kirkland Neuk. A coal-seam passed through had been charred, owing to contact with greenstone (or trap rock); and the question occurred, "Are there any remains of the heat which charred the coal in ancient times; or has it passed off so long ago that the strata are now not sensibly warmer on account of it?" The observations seemed to establish the latter alternative, the bore being colder than its neighbour-that taken at Blythswood.

The observations taken at Kentish Town extended to a depth of 1100 feet, with an ultimate temperature of 70°, giving the mean rate of increase at 0191° per foot, or 1° per 52.4 feet, the mean surface temperature being taken at 49°.

In the case of the Kentish Town bore-hole, notwithstanding the care taken to prevent the influence of the external air affecting the temperature of the water in the well, it was found by Mr. Symons that this influence extended to a depth of nearly 200 feet,-the temperature of the water rising and falling with that of the season of the year down to this depth. The well, however, was no less than 8 feet in diameter.

The experiments undertaken at Rose Bridge Colliery, near Wigan, by the manager, Mr. Bryham, which I have recently communicated to the Royal Society,* deserve special notice, as having been made during the sinking of the deepest coal-pit in Britain. The results arrived at differ so strikingly from those obtained at Dukinfield Colliery, situated near the eastern border of the same coal-field of Lancashire, and only a little less deep, that a discussion of the cause of this discrepancy may not be without interest.

An account of the observations at Dukinfield Colliery, undertaken by Mr. W. Fairbairn, F.R.S. (1848-59), has already been given in the pages of this Journal,† and was originally communicated by Mr. W. Hopkins to the Royal Society. The depth of the shaft is 2151 feet, with an ultimate temperature of 75-5° taken in the seam of coal known as the "Black Mine" of that district. The mean result is a rate of increase of 1o for about every 83·9 feet.

The observations at Rose Bridge, near Wigan (1854-61), were at first extended only to the depth of 1800 feet, giving a resulting temperature in the strata of 80°; but it having been determined by the proprietor to carry down the shafts to the "Arley Mine" coal, which was known to be at a depth of over 600 feet below, operations were commenced in the spring of the year 1868, and in the space of fourteen months the Arley Mine was successfully "won." The total depth reached was 2424 feet, with an ultimate temperature (taken in the coal itself) of 93.5°. Throughout the whole series of experiments from 1650 feet downwards, the increase * Proceedings of the Royal Society,' vol. xviii. (No. 116), p. 173. † Vol. v., p. 17.

Philosophical Transactions,' vol. cxlvii.

appears to have been tolerably uniform, giving the impression that there were no disturbing causes at work. The resulting proportionate increase was found to be 1° for every 54.57 feet; the "invariable stratum" being assumed at 50° of temperature, and at a depth of 50 feet from the surface. The results of the observations at Rose Bridge as compared with those at Dukinfield show a remarkable dissimilarity. The rate of increase in the former case being much more rapid than in the latter: for assuming the same standard of departure in both cases, it will be found that in the case of Rose Bridge the rate of increase is 1°. for about 47.2 feet as against 1° for about 83.2 feet at Dukinfield; an amount of discordance which I am satisfied is to be explained on other grounds than those of error in the observations themselves.

Such a diversity of results cannot be attributed to differences in the conducting powers of the rocks in each locality: for although sections of moderate depth taken at two different parts of the same coal-field would undoubtedly present different proportions of the sandstones, clays, and shales, &c., arranged in a varying manner to one another, which combine to form what is termed the "Coalmeasures;" yet if observations in each case be extended downwards to considerable depths, such as those in the present instance which exceed 2000 feet, the varieties of strata will tend to balance each other, and all cause of discrepancy in the rate of increase of temperature will probably disappear, or be reduced to such a degree as to be immaterial.

Neither is this diversity to be attributed to the presence or flow of water in the strata; for, as I observed on a former occasion,* the percolation of water decreases with the depth, and at variable distances from the surface altogether ceases; or is limited to the very small quantity which appears in some cases to have been locked up in the strata for ages, and which of course takes the temperature of the surrounding strata themselves. We must, therefore, seek for other causes to explain the dissimilarity of results in question.

The amount of inclination in the strata, is a cause of variation in the rate of increase which has not as yet been sufficiently taken into account, but is one which I think ought not to be lost sight of, especially in comparing results obtained at moderate depths. In the case of strata of uniform composition throughout, as the Chalk, or New Red Sandstone formations, the amount of inclination is of comparatively little importance; but where we have to deal with a formation such as the Coal-measures, composed of variable strata alternating with each other, and possessing varying degrees of thermal conductivity, the inclination, or amount of dip of the beds, becomes an element of much importance when the rate of increase

* "Experiments for Ascertaining the Temperature of the Earth's Crust." 'Quart. Journal of Science,' vol. v., p. 18.

of temperature is under discussion. In my communication to the Royal Society I have ventured to suggest that the discordant results obtained at Rose Bridge and Dukinfield are to be attributed to the difference in the inclination of the strata at the two collieries, and I propose to enter a little more fully into the discussion of the question here. I shall now describe in detail the position of the strata in each locality.

Sections showing relative positions of the strata at Rose Bridge

Rose Bridge Colliery.-That part of the South Lancashire Coalfield known as "the Wigan Coal district," is traversed by a series of parallel faults, ranging in a north-westerly direction, with occasionally very large displacements of the strata. These faults divide the coal-field into sections or "belts ;" and where the strata are let down between two faults, a "deep belt" is produced; on the other hand, where the strata are thrust 66 up, a shallow belt" is the result. The

same coal-seam being thereby placed at a less depth from the surface than in the case of the "deep belt."

Between these faults the strata incline at small angles, generally dipping gently to the eastward.

Nearly in the centre of one of these "deep belts," Rose Bridge Colliery is situated; the belt being bounded on the west by the "Standish fault," along which the strata are let down on the eastern side about 150 yards; and on the east, by the Kirkless Hall fault, along which the strata are let down on the west about 600 yards. At the colliery itself the strata are almost horizontal; consequently all the strata, except those comparatively shallow, are broken off by the large faults above described before they reach the surface.

Dukinfield Colliery.-The circumstances of the strata at this colliery are very different from those of Rose Bridge. The pits are situated on the Cheshire side of the river Tame, near Ashtonunder-Lyne, and in this district the beds rise and crop out to the eastward at high angles. At the colliery, the dip is west at about 35°, and the "Black Mine" (or coal), which was reached at a depth of 2151 feet, crops out at a distance to the eastward of little more than 1000 yards.

From this account it will be seen that we have very different stratigraphical conditions in each locality, and to this I attribute in a great measure the difference in the rate of increase of underground temperature in these localities respectively. For purposes of comparison we may assume a constant supply of heat from the interior of the earth, tending to travel towards the surface. In its progress it meets with strata of different conducting powers, the thermal conductivity of each stratum in the same locality being in the inverse ratio of the rate of increase, as shown by Mr. W. Hopkins, F.R.S.,* in other words, where the rate of increase is rapid the conducting power is small.

But whatever may be the conducting power of a series of strata, it seems probable that it is impeded when the heat has to travel in a direction perpendicular to the planes of bedding. On the other hand if the heat can find its way towards the surface partly along the planes of bedding, the thermal conductivity is increased, and the rate of increase is proportionally lessened; for in this way it may be conveyed by strata which have high conducting powers, and escape along the outcrop of the strata themselves.

If this view be correct, we can at once account for the difference in the results at Rose Bridge and Dukinfield collieries. In the former, owing to the horizontality of the strata, the heat can only find its way outwards directly across the planes of bedding. We may, therefore, suppose that the resistance to its motion is increased thereby; the conductivity is lessened, and, in consequence, the rate * 'Philosophical Transactions,' vol. cxlvii.

of increase of temperature is rapid. In the case of Dukinfield it is inferred that, owing to the high inclination of the strata, some of the heat travels along the planes of bedding, and escapes along the outcrop with greater rapidity than it would if it were obliged to travel solely across the strata themselves.

It has been suggested that in the case of Dukinfield Colliery the escape of the underground heat may have been facilitated by the formation of vapour at certain depths, the vapour making its escape along the planes of bedding by the aid of the fissures and porosity of some of the rocks. It is questionable, however, whether the elastic force of the vapour would be sufficient, at the comparatively low temperature of the strata, to overcome the enormous pressure to which it would be subjected at depths much below the surface.

VI. MR. BRUCE'S MINES REGULATION BILL.

MODERN legislation in this country in reference to industrial employments tends more and more to impose on the Government the duty of caring for the health and safety, and at least the elementary education, of those who, owing either to weakness or to ignorance, are unable to care for themselves.

In our Factory Enactments, foreign countries have followed gradually in our footsteps; in the regulations affecting the mining population, on the other hand, we shall probably never attain the completeness of supervision, be it for good or for evil, which prevails in States such as France, Belgium, and Prussia, where the minerals are the property of the nation.

Mr. Bruce's Bill for the Regulation and Inspection of Mines, a réchauffé of his Bill of last Session, consolidates the existing laws; but is in other, respects as modest a measure as the opponents of Government interference could desire.

It continues to forbid females to work in mines, and, at the urgent request of the operatives, limits, though not to the full extent of their desires, the time during which youths from twelve to sixteen years of age may be employed below ground. Recognizing the failure, in the case of young children working in mines, of the attempt made to combine work and elementary instruction, it forbids entirely their employment underground before the age of twelve. It places women, young persons, and children employed on the surface under the provisions, as regards the hours of labour and education, of 'The Workshops Regulation Act of 1867,' which, however, owing to its administration being in the hands of local