Mar. 28, 1872J 



NATURE 



433 



tion, the water in these fissures circulates freely. This line of 

 saturation is governed in this as well as in all other permeable 

 formations, by the level of the lowest natural point of escape, 

 which is either the coast-line if near, or the nearest river- 

 valley. Below these levels permeal>le strata are always 

 charged with water ; consequently under London the chalk 

 is everywhere water-bearing ; but as the Lower Chalk is more 

 compact than the Upper, and is less fissured, especially when 

 covered by other strata, and as the more compact water-logged 

 chalk delivers its charge with extreme slowness, it is not until a 

 fissure is met with that a free supply of water is obtained. 

 Further, as there is no law regulating the position of the fissures, 

 the depth to which the chalk has to be traversed before meeting 

 with a free supply of water is quite uncertain. It is a question 

 of probability depending upon meeting with a fissure sooner or 

 later — lo to 15 feet have sufficed in some of the deep London 

 wells, whereas in others it has been necessary to sink to a depth 

 of from 100 to 200 feet or more before hitting on the necessary 

 fissures. Large as this supply is, the same causes which have 

 operated in the case of the sands have told also on the chalk 

 supplies (and, no doubt, there is some community between tbe 

 two), and the great demands on it have occasioned a similar 

 lowering of the water-line. At the same time this line also re- 

 mains unaltered at a distance from London, and as witli Tertiary 

 Sands the mass of the chalk beneath intersecting the level of 

 the river valleys remains constantly charged with water. Ordinary 

 wells, therefore, sunk below this line of saturation into the chalk 

 where it comes to or near the surface, are capable of yielding 

 very large quantities of water. More than seven million gallons 

 daily are in fact now so obtained from the chalk on the south- 

 east of London. 



Numerous and useful as the London Artesian wells are, they sink 

 into insignificance when compared with the application of the same 

 system in Paris. Our deepest wells range from about 400 to 500 feet, 

 and the water comesfromthechalk hills at a nearest distance of from 

 15 to 25 miles from London ; whereas in Paris the well of Crenelle 

 is 1,798 feet deep, and derives its supplies from the rain-water fall- 

 ing in the Lower Greensands of Champagne, and travelling 

 above 100 miles underground before reaching Paris. The well 

 of Passy, sunk also through the Chalk into the Lower Green- 

 sands at a depth of 1,923 feet, derives its supplies from the same 

 source. The level of the ground above the sea at the outcrop 

 of the Lower Greensands in Champagne averages about 350 feet, 

 and the water at Crenelle well rises 120 above the surface, which 

 is nearly the level of the Seine, there 89 feet above the 

 sea-level. The water-delivery is large and well maintained. 

 These results were considered so encouraging, that in 1865 the 

 Municipality of Paris decided on sinking two Artesian wells of 

 unexampled magnitude. Hitherto the bore-holes of such wells 

 have been measured by inches, varying from 14 to 4 inches, that 

 of Passy alone having been 4 feet at the surface and 2 feet 4 

 inches at bottom. But it was resolved to exceed even the larger 

 dimensions of this well. 



One of these experimental wells is in the north of Paris, at 

 La Chapelle, St. Denis, 157 feet above the sea-level. A shaft, 

 with a diameter of of 6.V feet, was first sunk through Tertiary 

 strata to a depth of 1 13'feet. At this point the boring was com- 

 menced with a diameter of 5! feet, and carried through difficult 

 Tertiary strata to a depth of 450 feet, when the Chalk was 

 reached. A fresh bore-hole was here commenced in August 1867, 

 which in September 1870 had reached the depth of 1,954 feet. 

 The works were stopped on account of the war until June 1S71, 

 when they were resumed, and the bore-hole has now reached the 

 great depth of 2,034 feet, with a diameter still of 4 feet i,\ inches. 

 It is now in the Grey Chalk, and it is calculated that the Lower 

 Greensands will be reached at a depth of about 2,300 feet. 



The other Artesian well is at the Buttes-aux-Cailles, on the 

 south-east of Paris, at an elevation of 203 fc. above the sea. 

 The Tertiary strata are there only 205 ft. thick. This well is 

 not quite on so large a scale as the other, and is still, at the depth 

 of 1,640 ft., in the White Chalk. 



The discharge from these great wells will probably be equal to 

 that of a small river. At Passy, notwithstanding some defective 

 tubage, and the circumstance that the surface of the ground is 

 there 86 ft. above the Seine, the discharge at the surface is equal 

 to 3 J millons of gallons daily ; and it has been above 5 millions, 

 or enough for the supply of a town of 150,000 inhabitants. 



The question may arise, and has arisen, why, with a like geo- 

 logical structure, should not like results be obtained at London 

 as at Paris ; and, to a certain extent, it has been answered. At 

 Kentish Town an Artesian well ,was, in 1 85 Si carried through 



324 feet of Tertiary strata, 645 ft. of Chalk, 14 ft. of Upper 

 Greensand, and 130ft. of Gault. Instead of then meeting with the 

 water-bearing Lower Greensands which crop out from beneath 

 the Chalk, both on the north and south of London, unexpected 

 geological conditions were found to prevail, to which we shall have 

 occasion to refer presently ; and not only were these Green- 

 sands found to be absent, but likewise all the Oolitic and Liassic 

 series. The bore-hole passed at once from the Gault into a 

 series of red and grey sandstones, probably of Palaeozoic age, 

 and not water-bearing. The Chalk has more recently been 

 traversed at Crossness, near Plumstead, where its base was reached 

 at a depth of 785 ft., and the bore-hole carried 159 ft. deeper 

 into, but not through, the Gault, when, owing to difficulties 

 caused by the small size of tiie bore-hole, the work had to be 

 abandoned. Although we were mistaken in our anticipations as 

 to the results of the first of these works, still it is evident — as 

 the Lower Greensands, with a thickness of 450 ft., pass beneath 

 the Chalk and the Gault in a line from Farnham, Reigate, to and 

 beyond Sevenoaks — and they again occupy the same position 

 north of London, on a line from Leighton Buzzard to Potton — 

 that it is only a question of how far they may be prolonged 

 underground towards London. They have as yet been followed 

 only 4 miles from their outcrop under the Gault in Buckingham- 

 shire, and I mile in Kent ; and no attempt has been made to 

 follow them under the Chalk. It is therefore quite possible that 

 they mry extend to under Croydon, or even to Sydenham, or 

 still nearer London ; but this depends upon the width of the 

 underground ridge of Palaeozoic rocks, which has not been deter- 

 mined. It is a matter for trial. As the sands are from 20D to 

 500 ft. thick, and show no sign of an immediate approach to the 

 old shore-line, there is every probability that in Kent and Surrey 

 they extend at all events some miles northward, and in Bucks 

 some miles southward, before they thin off against the under- 

 ground ridge of old rocks, so that they might still be found avail- 

 able, as a supplementary source, for the water-supply of London. 



Such is the geological structure of the ground on which this 

 large city is dependent for its first and immediate water-supply 

 by means of wells. The highest seam of water, that in the 

 drift-gravel, extends almost everywhere under the streets and 

 houses of London, at depths of from 12ft. to 25ft., forming what 

 is called ground-springs. The Lower Tertiary sands, with their 

 greater thickness, and their larger and distant area of outcrop, 

 contain the second and larger underground body of water be- 

 neath I^ondon. The third underground reservoir is the Chalk, 

 which, from its large dimensions — 500ft. to i, 000ft. thick — and 

 extensive superficial area, forms a still larger reservoir, and 

 source of water-supply. 



With the increase of population, however, the, need for larger 

 quantities necessitated the recourse to river-supply ; and this 

 supply, equally with the other, is regulated by geological con- 

 ditions, only that in this case the question concerns those con- 

 ditions which affect the strata throughout the catchment-basin of 

 the river itself above the town which needs its supply. 

 ( To be conlinued. ) 



PROF. SCHIAPARELLVS RESEARCHES 

 "T^HE following address was delivered by the president of the 

 Royal Astronomical Society, Mr. William Lassell, Feb- 

 ruary 9, 1872, on presenting the Gold Medal of the Society to 

 Signor Schiaparelli :— 



You will have learned from the Report just read, that your 

 Council have awarded the Gold Medal this year to Signor Schia- 

 parelli ; and I regret to have to inform you that we shall be 

 deprived of the pleasure of presenting it to him in person ; as by 

 a letter received from him a few days ago, I learn that his duties 

 of Professor and Director of the Observatory at Milan will 

 prevent his being able to undertake so long a journey. 



The first notice I find of Signor Schiaparelli's labours is his 

 discovery of the minor planet Hcspcria, at the Observatory of 

 Milan, on April 29, 1861, an indication that, besides his mathe- 

 matical attainments in Theoretical Astronomy, he possesses in- 

 dustry and practical skill as an observer. 



In the .■Istroiiomische Nachrichten of August 13, 1S64 (No. 

 1487), |is a purely mathematical paper by him, entitled 

 " Theoremes sur le mouvement de plusiers corps qui s'attirent 

 mutuellement dans I'espace." Of this paper, not bearing imme- 

 diately upon those labours of Signor Schiaparelli which have 

 more especially called forth the award, I will only express the 

 opinion of a friend of high mathematical attainments, who 



