18S0.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



269 



so would the circulation of water, in the subterranean range of 

 the lower cretaceous strata, have a tendency to follow under- 

 ground a direction corresponding to that in which it flows on tlie 

 surface, and would indicate that the position of London, with 

 reference to the probability of meeting with such sources of supply, 

 is extremely favourable. 



Til ere are many other points I could have wished to notice, such 

 as tlie fall of rain on the surfaces of the different water-bearing 

 strata — the quantity of free water whicli the masses will hold, &c., 

 but whicli the limits of this paper will not allow me to enter upon. 

 Should the general conclusions be correct, and should there exist 

 beneath London two large and important, and liitherto untouched 

 sources of water supply, it then becomes a question how far such 

 sources are available, and what may prove to be tlie quality of the 

 water. It was not my intention, nor do I feel competent, to go 

 beyond the theoretical part of the inquiry, the impartial discussion 

 of which was the sole object I had in view; there are, however, a 

 few questions of practice, and an analogous case, so strongly in 

 point, that I cannot help making a few observations on them. 

 The great difficulty experienced in sinlting Artesian wells in 

 London has arisen from the circumstance of the water not rising 

 to within many feet (60 to 100) of the surface, in consequence of 

 which it has been necessary to sink shafts through the London 

 clay, as well as through the loose sands and clay below it; a work 

 frequently attended with great difficulty and expense. The chalk 

 once reached, the operation of boring to greater depths has been 

 comparatively easy. As it is, however, probable that the water 

 from the greensands would rise, generally, to above the surface, 

 the whole depth could be bored, and the great expense of sinking 

 the shafts would be avoided. The case in point to which I would 

 refer is the Artesian well at Calais; it presents conditions so 

 strikingly similar to those which would probably be found to exist 

 at London, that I think it may be viewed, although unsuccessful" 

 in furnishing a supply of water, as a fair criterion of the difficulty 

 and expense of a like operation here. 



The tertiary strata presented, probably, even greater impediments 

 than they would at London. The first 80 feet consisted of gravel 

 and loose wet sands; then followed a succession of clays, sands, 

 and pebble beds, of a thickness of 161 feet — the larger part being 

 sands. These beds belong to the lower tertiary series. Below 

 them is the chalk, through the entire thickness of which the bore 

 was continued 762 feet. Then followed 3 feet of a stratum, which 

 may be the equivalent of the upper greensands, and then 24 feet of 

 gault clay, and finally, 17 feet of hard greensand. The total depth 

 at this point was 1047 feet. So far the work, which -.vas begun in 

 1842, had been two years and-a-half in progress, but would have 

 been completed in much less time had it not been for delays in the 

 arrival of the necessary apparatus. The size and number of the 

 flint pebbles, and the hardness of the chalk, also caused delay, by 

 breaking the instruments several times. The total expense, up to 

 this time, amounted to 48,500 francs, apart from the cost of the 

 temporary tubes, which came to 18,471 francs. Had the work been 

 successful, the engineer, M. Mulot, would have been entitled to the 

 latter, together with a further sum of 10,000 francs, consequently, 

 the expense of the work necessary to have obtained the hope for 

 supply of water at this depth would not have exceeded 3000/. A 

 further sum of 12,000 francs was afterwards voted, and the works 

 were carried, still without success, to a total depth of 1 1 50 feet — a 

 depth, 1 believe, sufficient to reach the lower greensand at London, 

 while the depth to which the well was first sunk would here, I 

 think, more tlian suflnce to reach tlie upper greensand. The depth 

 of the Artesian well at Crenelle, in Paris, is nearly 1800 feet, and 

 the yield of water about 1,000,000 of gallons per 24 hours. It 

 rises about 120 feet above the surface, and the water-bearing strata 

 crop out in the country beyond Ti-oyes at an elevation of about 

 300 to 350 feet above the surface level of this well. 



There would, therefore, I conceive, be no practical difficulty in 

 boring through the tertiary strata and the chalk to the upper 

 greensand beneath London. The thinness of the latter at this 

 point renders it, of course, uncertain how far its supply of water 

 may be interfered with by causes which have escaped notice. 

 Should any unforeseen causes occur, which, however, I do not 

 anticipate, then it would be necessary to continue the work deeper, 

 so as to reach the lower greensand, which, as the upper greensand 

 is dose and compact, and underlied by clay only, would not be 

 attended with any unusual difficulty. The great thickness and 

 extent of exposed surface of this formation renders the chance of 

 success much greater than with the upper greensand. 



• This is probably caused by a fault, of which Iheie are iippaiently indications a few 

 lnil?s to the south of Calais. Without a uio;e iiupoi'.uut LoowkUge of ihe disuict, 1 can., 

 'bowevir, only haxoiu this opinion. 



With regard to the quality of the water, the uniform character 

 and mixed calcareous and silicious structure of the upper green- 

 sand are favourable for a supply as good, or probably rather better, 

 than tliat from the chalk — probably not quite so hard. With 

 regard to the lower greensand, although it consists chiefly of pure 

 silicious sands, still many of the beds are ferruginous, and others 

 of very variable mineral character; the quality of the water which 

 would be obtained from this source would therefore be rather 

 uncertain. Admitting that it should not be fit for domestic 

 purposes, still it would be free from organic impurities — it would 

 possess a uniform temperature of from 68^ to 70\ (The water of 

 the Crenelle well contains 14 grammes of solid residue in 100 

 litres, whilst the same quantity of Seine water contains 17^ 

 grammes.) 



For the purposes of stand-pipes for cleansing the streets and 

 courts for safety against fires, for public fountains, and ornamental 

 waters (such as the Serpentine), for irrigation and for baths, I 

 believe that a very large and important auxiliary supply might 

 thus be obtained. Even on a limited application, eight or ten 

 wells of tliis description, yielding from 6,000,000 to 10,000,000 

 gallons daily, sunk in different parts of London, each with a 

 limited distriljutory apparatus attached to itself as a centre, would 

 probably constitute, to a certain extent, an efficient and economical 

 mode of supply for this object, and might prove a measure of 

 public utility and advantage. 



LATERAL STRENGTH OF STONE. 



Sir — Experiments on the lateral strength of wood have already 

 been made in abundance; but on the lateral strength of stone — 

 that is, what weight is required to break it when supported at 

 each end, and the weight laid on the middle of its length, I am 

 not aware of any experiments on record. 



This void is the more remarkable, considering the numerous ap- 

 plications of stone supported at the ends and loaded in the middle 

 — especially in Grecian architecture — for entablatures, lintels, &c.; 

 and in stairs, landings, balconies, platforms, &c., &c. The fol- 

 lowing experiments on a variety of stone and slate were made at 

 the time the Chester General Railway Station was constructed, in 

 March 1848. If you think them worth a place in your Journal, 

 chiefly with a view to engage others to pursue the subject, I beg 

 to ])ut them at your disposal, and vouch for the greatest care 

 having been employed to insure their accuracy; — 

 Bangor Slate. 



Note. — The Batigor Slate io each e.xperiment w-asfractiireii straight across 

 oti top, and splititercd underneath; the Llangollen Slate splintered; the 

 Wingerworth Stone fractured nearly straight and square across; and that 

 from the Red Stone Quatry fractured straight. 



