1839.] 



THE Cn^IL ENGINEER AND ARCHITECT'S JOURNAL. 



145 



ARTESIAN WELLS. 



[This subject is, once again, exciting a good deal of attention. The oUl schemes 

 liave been revived, for supplying considerable districts, indeed whole parishes, ot 

 this thirsty metropolis, with water, by sinking wells througli the London clay. 

 When the project was heretofore under discussion, we brought together such evidence 

 as appeared to as conclusive against it. But as the importunate appealers to our 

 breeches pockets are not easily to be got rid of, we tliought, under these circumstances, 

 that our readers might desire to hear the opinion of a geologist ; and as Mr. Webster, 

 who is at present delivering a course of lectures on Geology at the Russell Institution, 

 fully considered the question last week, in a lecture on the tertiary formations, we 

 present an abstract of so much as referred directly to this subject..) 



Mr. Webster observed, that an Artesian well is pvoiUiced by boring 

 through strata impervious to water, down to another stratum eontaining 

 water, and so placed that this fluid will rise up tlu-ougli the bore by hydro- 

 static pressiu'e; that is, by tlie pressure of anotlior part of the water on a 

 higher level. He then pointed out what he considered to be the true source 

 from whence the water found below the London clay is derived. We must 

 first imagine a geat depression in the chalk stratum that co-vers the chief 

 part of till' south-east of England, the boundaries of mIucIi depression or 

 basin is marked by the Nortli Downis, Marlborough Do\ra.s, and the Chilton 

 Do^\-ns, wher« the chalk is on the surface. Within this depression, we 

 must, then, conceive a great stratum of sand, lying in the chalk, but less 

 extensive, — or ratlier several strata of sand alternating with several beds of 

 coarse pipe-clay, but in a very irregular manner. This bed is named the 

 sand and plastic clay; and this sand contains a large quantily of water, so 

 as to be. in some places, almost of the nature of quick sand. Over these 

 last strata lies a very thick one of dark blue clay, called the London clay, 

 which being less extensive still than the sand, leaves a portion of the latter 

 exposed in a belt or outcrop all round the basin. Now when rain falls upon 

 the chalk do-mis, it descends the slopes in streamlets towards the centre of 

 the basin ; and when it meets with the sand uncovered, it sinks info it, 

 passing do\rawards below the London clay. In course of time, from this 

 cause, the whole of the sand stratum lias become full of water, and must 

 continue tn be so, except the latter should be drawni out ; and it is evident 

 that this water si ra turn can be exhausted only by raising tnit of it a quantity 

 of water greater than the supply it receives from the hills all round. The 

 rain which fiills upon the London clay cannot add to the water beneath it, 

 since this clay is impervious; and, therefore, landsprings only arc found on 

 the top. If a boring be made anywhere through the blue or London clay, 

 down to the stratum of sand containing water, the latter will rise in the 

 bore with considerable force, to the same height or level as the outcrop of 

 sand between the London clay and the chalk. If this boring be made at a 

 spot which is on a lower level than this source, the water will spout up like 

 a fountain; but if the boring be made in a place where the surface of the 

 ground is higher than the source, then the water, though it will rise, will 

 not reach the surface ■ and this accoimts for the various heights to which 

 the water ascends in various Artesian wells. (We omit the description of 

 the mineralogical characters of these strata, and of the fossils they contain, 

 and confine ourselves to the circumstances connected with the water.) 

 During the last twenty years, a great many perforations have been made 

 through the London clay, from it,s having been found that simple boring 

 witJi an anger is sufficient when a small supply only is required : and 

 enough has been done, fully to establish the truth of the geological principle, 

 that the sand stratum bearing water extends all under the London clay; 

 and that the metropolis stands upon a chalk basin containing an immense 

 quantity of pure soft water, sulficient for the supply of many breweries, and 

 numerous private houses, &c. But now comes the question : is this pure 

 soft water sufficient in quantily, not merely for the consumption just men- 

 tioned, but for the supply of the whole metropolis, or of several parishes, or 

 of a single parish? With respect to the actual quantity of water in the 

 basin, it is impossible to calculate it with any certainty; for althongh we 

 can estimate the extent of the sand and water stratum from the map, yet 

 ■n'e cannot ascertain its thickness, since this varies in ditferent places. In 

 by far the greater number of borings the thickness has not been taken ac- 

 count of, because the work generally ceases at the top of the sand, when 

 water ajipears : to say nothing of the impossibility of knowing the propor- 

 tions of water and sand. Mr. Webster went on to prove that the stratum 

 of sand and water is extremely in-egular, and that we cannot have a clear 

 idea of its actual nature, except a much more accurate account of the 

 borings were kept than had been the case. The sand stratum is subdivided, 

 in all probability, by band.s of clay: and it is incorrect to assert, as has 

 been done, that it is possible to predict success in sinking in one place, 

 because a successful boring has been made in another ; or that the supply 

 of water will be the same in all places. All mention has been omitted, 

 when speculating on this project, of the wcll-knowni failure of many -Ar- 

 tesian wells ; and it is certain that, in several cases, one well has taken the 

 water from another, proving that the supply in that locality was limited. 

 Mr. Webster next adverted to an experiment which had been made by the 

 New River Company, in endeavouring to avail themseh'es of the water 

 below the London clay, by sinking a large shaft or well at their reservoir 

 ill the Uampstead Road. At a depth of 170 feet they came to the stratum 

 of sand and water, which rose up together, as is usual, into tlii; well ; but find- 

 ing that they could not sufficiently separate "the water from the sand, which 

 is the chief difficulty in forming wells on a great scale in the London clay, 

 they passed through this rumiing or quicksand, by means of cast-iron 

 cylinders, at an expense of 4,0UU;., independent of the 8,UU0/. wliich the 

 well cost, hoping to obtain water by sinking into the chalk below. They 



foiuid water in that stratum, but in quantity too inconsiderable for their 

 object ; and hence this well has been represented as a failure. Mr. Webster 

 stated, that, considering tliis experiment as an important one, he applied to 

 Mr. Mylne, engineer to the New River Company, for inforaiation respecting 

 it, and received from him all the information he required. A remarkable 

 discrepancy had appeared in the public statements respecting this well ; on 

 one side it having been termed a failure, whereas information was given to 

 the vestry of St. Pancras by one of the workmen who had been employed, 

 that water had been obtained at the rate of 6,.350,400 gallons weekly; this 

 Mr. Mylne explained by stating that the ievm failure had been used, not aS 

 implying that they had not got water, but that they had not procured it in 

 suiBcient quantity to answer their purpose as matter of trade : the actual 

 quantity being only 6.50,0(10 gallons per week, instead of 6,.350,400, less 

 than one-ninth part of what had been reported ! Mr. Mylne likewise stated 

 that, so far was the supply from being constant, they were able to work 

 the pump in raising the water only ono-tliird of their time; because, when 

 they had procured what water trickled in slowly through the chalk, they 

 were obliged to wait until a sufficient quantity was again collected. Mr. 

 Webster seemed to consider the idea of a certain supply of water in the 

 chalk, independently of that in the sand stratum, as a fallacy, or at least 

 extremely problematical; and that the water found there had proceeded 

 from the sand stratum resting upon it, and which had forced its way down- 

 wards through numerous minute lissures in the chalk. He observed that 

 the procuring much water at a number of points considerably distant from 

 each other, by no means demonstrated, as had been asserted, the certainty 

 of raising the same quantity by means of a single large well; and he further 

 observed, that since it was a manifest and great advantage which the in- 

 habitants of London now possessed, and which was imkno-wn formerly, that 

 they can have numerous supplies of fine spring water only by boring, ii Avas 

 well worth con.sideration whether the sinking large shafts, and employing 

 powerful machinery to raise water, might not disturb the sand and water 

 stratum to some distance, so as to destroy or injiu-e the subterranean chan- 

 nels by wliich water reaches those wells, which are already the property of 

 individuals; wliile at the same time no reliance can be placed on the con- 

 tinuance, without inteiTuption, of a supply on so great a scale as is con- 

 templated from this source. Upon the whole, Mr. Webster gave it as his 

 opinion, that proper and sufficient data had not yet been collected, to 

 establish, upon good authority, the existence of water in sufficient abundance 

 to afford a constant supply to the metropolis, or even a considerable district, 

 by raising it in a single place from below the Ijondon clay, notwithstanding 

 borings or Artesian wells, dispersed through London, fulfil their object in 

 fiu-nishing manufactories and many private houses with water. 



With respect to the present supply of water to the metropolis. Mr. 

 Webster obseiTed, that although the subject did not come properly within 

 the scope of his lecture, lie would just state, that a considerable degree ot 

 misapprehension still existed on the subject. The Thames water is often 

 represented as of bad quality. There is no doubt, that in its progress through 

 the capital, it is rendered very impure; but it has been abundantly proved 

 by the accurate analysis of the most eminent chemists, that when the sup- 

 ply is taken sufficiently high up the river, and conducted into the to\m in a 

 proper manner, it is of gi'eat purity. At present the parishes of Marylebone, 

 St. George's, St. James's, are supplied from parts of the river much beyond 

 the influence of the London drainage. Possessing this, and other excellent 

 sources, we cannot be said to be unfavourably situated by nature respectiiif 

 a necessai7 of life of the first importance. — Athenaum. 



PROCEEDINGS OP SCIENTIFIC SOCIETIES. 



INSTITUTION OP CIVIL ENGINEERS. 



Feb. 12, 1839.— The President in the chair. 



The following gentlemen were elected : — Robert Hawthorn, Nichohss 

 Harvey, and William West, as Members ; J. R. M'Clean, as a Graduate ; 

 E. W Brayley, as an Associate ; and General Sir John F. Burgoyne, R. E., 

 as an Honorary Member. 



" On the Properties and Composition of the Peat and Resin Fuel." By 

 C. Wye Williams, A. Inst. C. E. 



The nature of the fuel being of great importance in the manufacture of 

 iron and the arts generally, it is interesting to inquire into the value of peat 

 for these purposes. Peat may also be used for railroad engines, and with 

 peculiar advantage, being free from many of the impurities of gas cokes : 

 it may also be used in combination with resin, or other bituminous sub- 

 stances, as a fuel for long voyages. The bogs of Ireland Avere, nearly 

 thirty years ago, designated by a Mr. Griffiths as mines above ground ; 

 who remarked, also, that the iron founders in Dublin might probably, ere 

 long, be supplied with turf-charcoal, which is superior to every other for 

 their pui'pose. The attention of the author was dii'ected to the use of peat 

 for the steamers on the Shannon, where coal is necessarily dear, and peat 

 was at first used only for economy ; the impediments to its use, from its 

 bulk and dampness, being great. The property of holding and absorbing 

 moisture is also a great impediment to its luc, particularly in wet season^, 

 the only remedy for which is great care during the process of drying and 

 in its subsequent preparation, any care being amply repaid by the dimi- 

 nished consumption. The evils of its bulb and low specific gravity may 

 be obviated by compressing it when diy ; when compressed perfectly dry, 



