378 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[December, 



use for 18 or 20 years, were subject to a strain of 31 tons per square inch ; 

 and a sliort time ago he liad occasiim to ascertain their actual performance 

 with reference to this very question, and this not being considered conclusive, 

 he had made a machine in which he had put an incli square bar subjected to 

 a constant strain of 5 tons, and an additional varying strain of 21 tons, 

 alternately, raised and lowered by an eccentric 80 or 90 times per minute, 

 and this motion was continued for so long a time that he considered it equal 

 to the effect of 90 years' railway working, but no change whatever was per- 

 ceptible ; and therefore he was one of those who did not believe in a change 

 from a fibrous to a crystalline structure in iron. He remembered a case 

 where a question having arisen as to the manufacture of a certain shaft, it 

 was agreed to hammer it until it split, as a means of discovering the nature 

 of the manufacture of the shaft : the result was satisfactory ; and the iron 

 appeared still fibrous in texture. 



The further consideration of the paper was then adjourned, and the Chair- 

 man said he wished that more of the members had been present at the meet- 

 ing, and hoped they would attend and assist in the further discussion of the 

 subject. 



The third and last paper read was "On Nasmyth's Patent Girders and 

 Fire-proof Floors," contributed by Mr. S. Lloyd, of Wednesbury. The 

 paper was illustrated by drawings and models. A discussion followed the 

 reading of the paper, and after a vote of thanks to the President, the meeting 

 adjourned. 



SUPPLY OF WATER TO THE METROPOLIS. 



On Monday evening-, the 19th inst., I attended a meeting at 

 the Institute of British Architects, to hear a lecture delivered by 

 the Very Rev. Dr. Buckland, Dean of Westminster, on "Artesian 

 Wells." 



This lecture was for the avowed purpose of proving that it is 

 impossible to procure from the chalk formation, situated beneath 

 tlie London clay, sufficient water to supply the requirements of 

 the inhabitants of London; and that the level of the water in 

 wells under London, deriving their supply from this service, has 

 been lowering for several years past. 



In numerous instances, the lowering of the level of the water in 

 deep wells beneath Loudon, is so well attested, as also the fact, 

 not alluded to by Dr. Buckland, that water thus procured contains 

 a large quantity of alkaline bi-carbonates, and is consequently un- 

 fitted for general domestic use, — that much good may result from 

 widely diffusing this information. 



The explanation offered by Dr. Buckland, and referred to by 

 him to account for this fact, is contained in his Bridyewater Treu- 

 titiP, entitled 'Geology and Mineralogy considered with respect to 

 Natural Theology," — in which it is asserted that floods, evapora- 

 tioii, the support of animal and vegetable bodies, and springs sup- 

 plying rivers, will account for the consum])tion of the rain falling 

 upon the earth's surface, as shown in the following quotation, 

 page 557, edition 1837: — 



" The great instrument of communication between the surface of the seo, 

 and that of the land, is the atmosphere, by means of which a perpetual sup- 

 ply of fresh water is derived from an ocean of salt water, through the simple 

 process of evaporation. By this process water is incessantly ascending in 

 the state of vapour, and again descending in the form of dew and rain. 



Of the water thus supplied to the surface of the land a small portion only 

 returns to the sea directly in seasons of flood tbroagli the channels of rivers. 

 A second portion is re-absorbed into the atmosphere by evaporation. A 

 third portiou enters into the composition of animal and vegetable bodies. 

 A fourth portion descends into the strata, and is accumulated in their inter- 

 stices into subterranean sheets and reservoirs of water, from which it is dis- 

 charged gradually at the surface, in the form of perennial springs that form 

 the ordinary supply of rivers." 



If the above quotation contained a true exjilanation of the con- 

 sumption of rain falling ui)on the earth's surface, it would follow 

 that no water found its way by subterraneous drainage to the sea, 

 and that no large amount of water could be procured at consider- 

 able depths beneath the earth's surface. 



This conclusion is in direct opposition to every day's experience, 

 as likewise to that of all other authorities. In a note at the end 

 of the first proposition, before quoted, from Dr. Buckland's iJ/'/o'^e- 

 vtite7- Treatise, the following remark appears: — 



" It is stated by M. Arago, that one-third only of the water which falls in 

 rain, within the basin of the Seine, flows by that river into the sea : the 

 remaining two-thirds either return to the atmosphere by evaporation, or go 

 to the support of vegetuhle and animal life, or find their way into the sea by 

 subterraneous passages. " — Annuairepourl'An. 1835. 



From this it will be seen, that M. Arago, unlike Dr. Buckland, 

 accounts for the disappearance from the eartli of a large body of 



rain by subterraneous drainage into the sea; and all who choose 

 may ascertain the fact that large bodies of fresh water are dis- 

 charged from the fissures of the chalk formation into the shingle 

 and sand that covers the sea-coast, and even into the bed of the 

 sen itself, in the vicinities of Dover, Folkstone, New Romuey, 

 Brighton, AVeymouth, and other places. 



This water may be traced at various places along the coast, 

 issuing in large quantities (doubtless where the greatest fractures 

 in the chalk occur), between high and low tide; and the large 

 amount which must be discharged in this manner will be apparent 

 from the fact, that the chalk formation, when it appears near the 

 surface, is full of small fissures (caused possibly by the action of 

 frost), which, communicating with larger ones, rapidly absorb and 

 carry off all the rain falling upon it. This fact must be familiar 

 to every observing person; Dr. Buckland himself dwelt upon it 

 in his lecture. It is only wlien the surface of the ground is se- 

 verely frozen, and a rapid fall of rain follows, or when a sudden 

 thaw of snow takes place, that a flood is found in rivers fed en- 

 tirely from the drainage of a chalk district ; the heaviest rains, at 

 other times, is absorbed as it fails. This fact is alluded to in 

 Conybeare and Phillips's ' Geology,' where it is stated, "All the 

 rain and snow which fall upon chalk percolate downwards to the 

 base, where the water is stopped by a subsoil of blue clay, and that 

 occasions it to accumulate in the chalk, until it rises to such a 

 height as doth enable it to flow over the surface of the adjoining 

 land." 



In the south of England the area of the chalk formation, almost 

 bare or only slightly covered with porous layers, consists of 4,117 

 square miles, as measured upon Knipe's geological map. The ave- 

 rage annual depth of rain falling upon this area of chalk country 

 will be certainly under than over rated at 20 inches ; and allowing 

 that as much as one-half of this quantity either finds its way to 

 the rivers, or is consumed in supporting vegetation and evapora- 

 tion, still 10 inches in depth remains to percolate down through 

 the fissures of chalk, till arrested by the impervious clay which 

 lies beneath; and it accumulates in fissures, or faults, to such a 

 height as to occasion sufficient hydraulic pressure to cause its exit 

 by subterraneous drainage at the sea-coast. 



This depth of 10 inches of rain per annum percolating through 

 an area of 4.,117 square miles, is equal to a supply of 1,595 (one 

 thousand five hundred and ninety-five) 7nillions nf yallons of water 

 for every day in the year; and this quantity is the least which must 

 find its way by subterraneous drainage to the sea-coast. 



If the amount of water before-named as daily running use- 

 lessly into the sea, could not be clearly demonstrated by an appeal 

 to facts and figures, such a statement would hardly appear credible, 

 yet is nevertheless the case: the largest portion of this water is 

 probably discharged through large fissures, or cavities, which in 

 many places may be distinctly traced. 



Borings in the valley of the Colne, prove that these fissures vary 

 from 2 feet to 12 feet in depth, producing when tapped enormous 

 quantities of water, wliich immediately flow to the surface: and 

 when it is remembered that tlie chalk formation to the north-west 

 of Watford is in some places 900 feet above the sea, or 738 feet 

 above the valley of the Colne, this fact will not appear at all sur- 

 prising. 



From the foregoing, it will be perceived that more water may be 

 expected to be found at some places in the chalk formation than at 

 others, — and this, in fact, is found to be the case: it is necessary 

 to intercept the fissures in the chalk to collect large bodies of 

 water, for solid chalk being almost impervious, will allow but little 

 to pass througli it. Thus it is doubtless owing to the density and 

 closeness of the interstices of the chalk underlying the London 

 clay, caused probably by the weight of the clay itself, that the 

 lowering of the level of the water in many wells in the London 

 basin is to be accounted for. 



It also appears, from chemical analysis, that the water procured 

 from under the London clay is partly replenished with sea-water 

 by means of the fissures of the chalk formation, which to the east 

 of London communicate with the sea, — for the principal constitu- 

 ent of sea-water is found in that procured from under the London 

 clay. 



'I'he above narration will show that the theory laid down by Dr. 

 Buckland, and before quoted, cannot be accepted as the true ex- 

 ])lanatiiin of the falling of the level of the water in so many deep 

 wells in the London basin; but tliat it is to be accounted for 

 simply from the fact that the fissures in the chalk underlying the 

 London clay are not sufficiently large to admit water into the basin 

 as rapidly as it is pumped away. 



It is also clear that by means of a well, or wells, sunk in a suit- 

 able locality, combined with the driving of adits to intercept the 



