and minute crevices by which it has to pass in adjusting the line of its upper surface, might account for this deviation from the level line which fluids assume, if left to act freely in open spaces, or in large and continuous conduits; Mr. Clutterbuck's repeated observations upon wells, along the line in question, must be considered to have proved the existence of this inclined level. His observations were also very important, as to the floods at Watford raising, in a few hours, the level of the water in deep wells in London, and as to the effect of a steam-engine erected to pump water from a large experimental well near Watford, in lowering the water in smaller wells in that town and the country adjacent to it.

Mr. Dickinson had made very accurate observations upon the absorption of water by the chalk, and was convinced of its being always in a wet state, almost amounting to saturation; but few crevices and fissures exist in the chalk of the district under notice; the rain therefore occupies a considerable time in overcoming the molecular attraction of the particles through which it passes.Wherever fissures exist at a certain depth below the chalk, they become channels, which collect and facilitate the flow of water to maintain the springs; the accumulations of the winter rain sink slowly down in summer, and by a series of vents or springs, furnish a supply for the rivers which run in the deepest valleys of the chalk district; a long cessation of rain lowers the level of the water in the rivers, at an interval of some months after the drought, and any extraordinary demand, by pumping from the wells in the chalk, would lower the water in the wells around, even at a considerable distance.

From experiments with the rain-gauge, buried 3 feet below the surface, he found that but little rain penetrated to that depth until the months of November, December, January, and February -the total quantity per annum was shown to vary between 17 inches and 6 inches, which latter amount sufficed to fill the principal springs. He was induced to believe, that, if a large supply of water was drawn from the chalk, it would eventually have a prejudicial effect in diminishing the water in the rivers of the district.

Mr. Clutterbuck said, that the sphere of his observations extended over a line of wells 20 miles in length, and in the whole of them there was the most perfect accordance between the alterations of level of the water and the indications of the rain-gauge,

allowing the time necessary for the rain to sink into the chalk,— as also there was between the fall and replenishment of the wells at Watford and those in London, whence large quantities of water were obtained by pumping;-he could always tell by measuring the height of water in one well of the series, what would be that of any other well along the line: he therefore was satisfied of the accuracy of the observations in his paper.

Mr. Dickinson observed, that he could not satisfactorily account for the greater amount of variation in the wells at the higher part of the district, when compared with those of the lower part-the alternations of the former amounting frequently to 30 feet, while those of the latter were only 10 feet in the same time. Dr. Buckland believed this fact to arise from the hydrostatic pressure being less interfered with, by friction and capillary attraction in the lower part of the district, than in the upper part.

Mr. Clutterbuck accounted for the alternations of level in the sand springs, being greater than in the chalk springs, by the relative degrees of opposition the water met with, from the friction in passing through the two kinds of strata.

Mr. F. Braithwaite had made many borings and sunk several deep wells into the chalk,-he would instance particularly the wells at Messrs. Meux's and Messrs. Reid's breweries, and that at Greenwich Hospital; in these wells he had used cylinders of iron to shut out the sand springs. He did not find the chalk so spongy or saturated with water as had been stated; he imagined that the supply of water was derived from the crevices in the chalk, and in many instances water had not been arrived at, because one of these crevices had been missed, whilst in a well of less depth, nearly adjoining, in which they had fortunately hit upon the crevice, a plentiful supply of water was obtained. In the first and second beds of flints under London there was very little water; from the third to the fifth bed the quantity increased, and at 30 feet lower down, a continuous fault or crevice was generally found which conveyed a good supply of water; the rise and fall of water in wells in the chalk did not accord with those of wells in the sand beds above the chalk; the alternations in the former amounting to only a few inches in a given time, while those of the latter were as many feet. He placed great confidence in the observations made by Mr. Clutterbuck. That gentleman had told him accurately, from the variations of the well, in the Hampstead Road, all the differences of the quantity of water

drawn from Messrs. Reid's well, arising either from an extra demand or from cessation in the pumping.

The brewers of London could be supplied by the water companies at a cheaper rate than by pumping, but as a large quantity was used for refrigerating the wort, it was important to have the water at a low temperature, they therefore were obliged to pump it up at a great expense. The quantity raised at Messrs. Reid's well, was about 7700 barrels, of 36 gallons each per day, which was calculated to be a sufficient supply for 5000 families,— there was already a decided diminution manifested in the supply from the sand springs, and an extension of these effects might be anticipated from the sinking of any large number of wells into the chalk.

Dr. Buckland ascribed the difference of the supply of water in sand springs, and in those originating in chalk, to the relative extent of surface of the sandy and cretaceous strata in Hertfordshire, by which alone they receive their respective supplies of rain-water, the amount of sandy surface being to that of naked chalk, about as one to twelve.

The rain filters more rapidly through the sand, than through the chalk. In beds of hard and compact chalk, at great depths, the water sometimes finds no passage except through occasional fissures, but where the chalk is soft, loose, and fragmentary, it percolates rapidly.

In the deep well now sinking near Southampton, through London and plastic clay into hard and solid chalk, it would probably be necessary to continue the boring or excavation down into some loose and more permeable stratum below the chalk, before any very large supply of water would be obtained.

Mr. Palmer directed the attention of the meeting to the account of the wells in the London Basin, given in Conybeare and Phillips' Geology, (book 1, chap. iv., sect. 11.) It is there stated, that at Tottenham, which is about 70 feet above highwater mark, after boring through 123 feet of clay, and 2 feet of calcareous sand-stone rock, the water rose to within a short distance of the surface in a few hours. At Epping, where the summit of the well is 340 feet above high-water mark, the extreme depth of the bore was 420 feet, but it was abandoned because no water was found; at the end of five months, the water rose to within 26 feet of the surface, and it has so continued, at 314 feet above high-water mark.

These recorded facts induced him to receive, with much caution, the statements in Mr. Clutterbuck's paper, especially since he doubted the ready flow of water through the chalk, by which the sympathy between the various wells was demonstrated. He had found, that chalk might be used as a good puddle for holding water, and therefore, as it was certainly more compact when in situ than when it had been worked, unless the water flowed along the faults and the beds of flint, he could not understand how it passed so rapidly as had been stated. The chalk, no doubt, contained some water, but if it was saturated, why did not the water in all the wells assume one uniform level, instead of heights varying between 20 feet and 314 feet above high-water mark?

Mr. Clutterbuck contended that the main points of his statement were borne out by Mr. Braithwaite's experience at Messrs. Reid's well. A clear distinction must be drawn between the water derived from strata, above the clay, and that from the chalk; in some elevated spots near London, situated like Hampstead, the clay is capped with gravel, which, on being tapped, yielded a supply of water: at Stanmore, the water from the gravel at the top of the hill is used; and in a well, sunk through the clay, at the bottom of the hill, the water stood at 140 feet below the surface. He could not understand why, at Epping, there should exist any variation from the usual observed facts; the case deserved very careful examination, as it might arise from some local cause. In the course of his observations, upon the levels of the wells in London, he found on one occasion that no depression occurred on the Thursday, which had hitherto always been the case, he therefore sought for the cause and found that the Elstree reservoir had been opened on Wednesday, June 1st, which satisfactorily accounted for what had occurred, as from the dry state of the water-course not more than half the quantity of water which passed from the reservoir, reached the river Colne, the rest sank through swallow holes down into the chalk; this showed the attention to collateral circumstances, which was demanded in investigations of this kind.

Mr. Frederick Braithwaite presented and explained a model of a well, sunk by him in the year 1841, at Messrs. Reid's brewery, in order to obtain water from the chalk, which had become indispensable, in consequence of the decrease of the supply of water from the sand spring.

VOL. XXII.

P

On examining the lower part of the well, which had collapsed in 1814, he found that the dimensions of the cast-iron cylinder to be introduced, must be limited to 5 feet 3 inches by 3 feet 2 inches; it was commenced at the depth of 87 feet from the surface, and carried down 135 feet, to within 1 foot 6 inches of the face of the first bed of flints in the chalk.

Being desirous of retaining all the water from the sand spring, he inserted an internal cylinder, which was sunk into the chalk at a depth of 138 feet from the surface, thus effectually shutting out the sand spring from that of the chalk, but permitting the former to flow to its accustomed level in the space between the two cylinders; and to make this supply available in case of need, cocks were inserted in the internal cylinders at convenient depths.

He then proceeded with the excavation in the chalk, increasing the dimensions at every foot in depth, until at 178 feet from the surface, the diameter was 16 feet 6 inches; the excavation was continued at that diameter to a depth of 202 feet from the surface.

In the progress of the work, water was found under the second, sixth, eighth, and tenth beds of flints, and the total supply at this period was two thousand barrels or seventy-two thousand gallons per day of twenty-four hours.

At 196 feet from the surface, the first tunnel was driven 91 feet N. W. in the direction of another well, which only increased the supply four hundred barrels, or fourteen thousand four hundred gallons in twenty-four hours.

The eighth bed of flints, at 154 feet from the surface, yielding the largest quantity of water, (three hundred barrels or ten thousand eight hundred gallons per day,) he drove a second tunnel, 6 feet high by 5 feet wide, for 16 feet E. to W., and then N. and S. for 108 feet, by which he obtained an increase of fifteen hundred barrels or fifty-four thousand gallons per day.

Having ascertained, by boring, that a further supply of water could be obtained at 20 feet below, he continued the excavation 22 feet deeper by 7 feet diameter, when he found water flowing from two horizontal fissures in the chalk without flints; at that depth he drove two tunnels, one N. W., connected with the first tunnel 91 feet long, by which he obtained an increase of three thousand one hundred barrels or one hundred and twenty-one thousand six hundred gallons per day; the second tunnel, in a S. E. direction, was driven for 24 feet, when he obtained a further increase of eight hundred barrels or twenty-eight thousand eight hundred gallons per day.