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evaporation, and we are therefore justified in assuming that the quantity which descends upon the surface of the chalk finds its way, with very slight diminu tion, into the fissures below. The lower beds of the cretaceous group, and the gault which immediately succeeds it, again present an impermeable stra tum of clay, causing the water to accumulate through the lower regions ot the more porous chalk. An enormous natural reservoir has thus been formed and the level up to which it may be considered as quite full of water is the lowest point where it can find a vent and overflow, therefore, as the chalk communicates under the coasts of Norfolk, Suffolk, and Essex with the ocean, this level, in the present case, may be considered to be the same as the mean height of the sea. That there is, however, an extensive accumulation of water above this level will be obvious, when it is considered that the friction, which from the na ture of the small fissures and pores must exist, will necessarily prevent the water from exerting rapidly its hydrostatic pressure, and as for this reason it cannot flow off with sufficient velocity, the higher parts of the chalk belt which surround the London clay being saturated, will allow of its escape to the surface wherever it can find a nearer and more ready vent than its sub terranean one. The greater or lesser facility, which from lines of fissures soft strata and pores, the water may encounter in flowing towards the centre of the basin, will also govern its surface, and cause it to assume an inclination, the angle of which will represent the friction, and in this manner we may readily ac count for the different levels, which often appear anomalous, at which the water will be found to stand in wells. The foregoing remarks will now enable me, I think, to show that the pro posal of perforating the tertiary clays for the purpose of obtaining the water for the general supply of the inhabitants of London, would not have been at tended with the advantages which at first sight it would appear possessed of: it may indeed be urged that a reference to the section, shews us London situated nearly over the centre of the basin to which it gives its name, and that we may consequently infer, that wells sunk through eocene strata into the chalk, will derive their supply immediately from that portion where the greatest accumulation of water exists by my own shewing. But it will be found that this very circumstance throws a material difficulty in the way of any attempt to supply the inhabitants of the Metropolis from this source, and one which has been found frequently confirmed, when private individuals have sunk deep wells in London. The objection is, that whenever a large quantity is extracted, the wells in the vicinity, which derive their water from the same strata, are very sensibly affected ; and, for this reason, that although a constant supply will always, as I have shown, find its way down, to take the place of whatever water we may pump away, this cannot flow in so quickly from the obstructions of the stratification, but that the level, for some dis tance round this focus, will be temporarily reduced. In other parts of the district, as will be readily understood, this would not be the case ; or if so at least in an inferior degree, as a well would not here derive its share from every side of the basin at once, but only from that portion situated immedi ately above it. At Watford, for instance, a well would only be fed from the chalk which intervenes between that place and the great outcropping Chiltern ridge, and so in any other part of the belt. I may also here add, that the sheet of water in the deeper part of the chalk, can only be affected to an in sensible degree by such a well, which at most would merely deprive it of the supply from a very trifling part of the great circle which every where else would remain untouched. The company which had been based on the Artesian project, probably soon obtained facts which proved that their proposal could not be established without such interference with private interests, as they undoubtedly fore saw, would have great weight with the House of Commons ; and they must also have taken into account the expense of forcing the requisite quantity of water to the elevation necessary for the high services, in addition to which, it must be borne in mind, that after perforating say two hundred feet of clay, the water under London by no means rises to the surface. As might have been readily foreseen, this idea was after some time, abandoned ; and it is not surprising, that its originator, Mr. R. Paten, should have turned his at tention to other endeavours. The abundance of the springs which overflow into the Colne valley, above Watford, and the apparent purity of the water, had long attracted his atten tion, and now led him, in connexion \yith some other gentlemen, to make various experiments to ascertain w'hether a sufficient quantity for the de mands of the Metropolis, could be obtained in that neighbourhood, at a small depth beneath the surface ; and whether this might be effected without in juring the existing interests in the vicinity. When it was found that the re sult more than confirmed their most sanguine wishes, I was requested to examine whether the experiments were well grounded, and to advise as to the means of carrying the plan into effect. I had for a length of time been acquainted with the various proposals which have been submitted to the public, and was aware of the objections which could with justice be urged against them. It was therefore not without plea sure that I undertook the examination of a plan, which I at once saw might be possessed of advantages, which were not before contemplated. It will be ray endeavour, in the remainder of this Report, to show how far the hope of obtaining the necessary quantity of water at Watford is well founded ; to describe the experiments which have been made for the purpose of acquiring practical data, to explain the proposed method of procuring the water and conveying it to London; and lastly, to submit such remarks a a will enable you, in my opinion, to present the project before parliament, with a confident reliance that it cannot but deserve its attention and support. As I have already described at some length the geological features of the country surrounding London, I am not called upon to add much to my former explanation on this head, and shall confine myself here to stating, that as re gards the more immediate object now in view, we may look upon the Colne valley as marking in a great part of its length, on the one side the escarp ment caused by the outcrop of the plastic clay, whilst on the other, the coun try rises gradually to the north-western boundary of the chalk strata, the Chiltern Ridge. An attempt to fix positive quantities, by any line of argument, is naturally attended with considerable difficulty ; nevertheless, the following considera tions will give some idea of the volume of water that can be derived from the chalk of the Colne valley. The surface of country which has its drainage into the Verulam and Colne above Watford, maybe taken at 113 i square miles. If, then, we assume that the annual fall of rain amounts to twenty inches, which you will find a low average, the result will be 14.1 millions of cubic feet of water per twenty-four hours, falling on the surface. Of this quantity, Mr. Telford found that the Colne carried off at Watford, thirty cubic feet per second, or about 2A mil lions per twenty-four hours ; as this was however in a dry season, it will be safer to assume Dr. Thompson’s calculations, with respect to the annual quantity of water flowing off by streams and springs, which he w r as led to fix at four inches, and this would give us for the area drained by the Colne, not quite three millions per day. There remain then 11* millions of cubic feet per twenty-four hours, either to be again evaporated, or to find their way into the earth. In an earlier part of this Report, you will remember that I showed that the porous nature of the soil, in a chalk district, prevents the evaporation to a great extent; nevertheless, if we assume that with the portion which enters into animal and vegetable life, one-third of the entire quantity falling, disappears in this man ner, we still shall have upwards of 6* millions of cubic feet, or 42 millions of gallons per twenty-four hours, supplying the sheet of water under that por tion of ihe chalk surface. Mr. Telford’s examination of the body of water flowing off by the Colne river, having been made at a period of unusual drought, when the surface water might be considered to have nearly disappeared, we shpll, I think, be correct in assuming that two millions at least of the quantity he measured, had issued from springs. In order therefore to represent the total subter ranean flow, we should add these two millions to the former 6£. These in deed would form no part of the supply to the deep, but would designate that supply which has been already explained, cannot find its way to the lower depths, owing to friction, and other impediments, and therefore seeks a readier vent at a higher level. It was important that this should be set in its proper light, as the evident inference we may draw is, that we cannot, by pumping from a lower level, a quantity small in comparison to the accumulation of water, produce any visi ble effect upon the springs which feed the Colne. I am quite confident that my views as regards the manner in which the water finds its way into the strata of the chalk, will not for a moment he called in doubt by any scientific person, but that whicli may by such a one be considered in the light of a received axiom, and proved by numerous cor responding facts bearing thereon, with which he will be already acquainted, will require more lengthened demonstration to the general public, with wlioin an appeal to experience will have far greater weight than any abstract rea soning. To these then the experiments which have been made, will aflord far more conviction than any argument however well founded. The alluvial bed, which covers the bottom of the Colne valley, rather ex ceeds twenty feet in thickness, after which we reach the chalk : proceeding about five feet lower, abundant springs of water are encountered, which in crease in magnitude and force as we continue to descend. It was therefore in the first place necessary to ascertain that these did not derive their supply directly from the river, which, had it been the case, would have affected the various mills in the vicinity ; and it was also desirable to have direct proof of the quantity which might be calculated on being obtain ed. In order to obtain positive evidence on both these points, a well was sunk in Bushey Hall meadows, near the Colne, to a depth of about 34 feet. Two small steam engines were then set up temporarily, for the purpose of working four pumps, of which two were 13 inches in diameter, with a length of stroke of 20 inches, and the others were 13& inches in diameter, with a 30 inch stroke. One of the engines might be calculated to produce from 27 to 30 strokes of the smaller pumps per minute, the other between 17 and 20 strokes of the larger pumps. The water of the well was now r repeatedly pumped out, as low as the power of the engines admitted, and the height of the Colne at those times carefully noted, and it soon became obvious that the height of the springs could in no degree be said to affect the level of the river, thus shewing that all direct communication between the two might be considered as cut off by a bed of puddle or clay. The next object of enquiry was as to the supply which a well might be expected to yield, and the result of a careful experiment, made under my direction, and confirming those pre viously conducted by Mr. Paten, satisfied me that after the water had for 24 hours been kept at the lowest level to which the power of the pumps would reduce it, (about 26 feet below its surface when undisturbed,) it rose in the well with a velocity equal to 2 02 feet per second, thus yielding 174,500 cubic feet, or 1,091,000 gallons per 24 hours. As this was obtained in a
