132 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[April, 



of four millions litres (880,387 gallons) per 2 J hours, being nearly a gallon 

 for each individual in Paris. — The waterworks of Gros Caillou Chaillot and 

 the engine near the bridge of Notre Darae supply at the most, double this 

 quantity ; the well at Crenelle consequently, notwithstanding its first cost of 

 250,000 francs (.t'10,000), affords a cheap supply of water, more particularly 

 if we bear in mind that this kind of fountain requires no repair. 



Some persons are already raising doubts as to the continuity of the supply, 

 resting their argument on the fact of some of the wells at Tours yiehiing loss 

 water at present than when first ojjened. They may, however, lay aside all 

 uneasiness — if some of the wells at Tours have undergone a diminution, a 

 greater number have increased in abundance, their supply having augmented 

 by nearly one-tlnrd — ami this discrepancy as it apjjcars at first sight, is easily 

 accounted for, by those who enter into all the facts of the case, being found 

 to depend upon the more or less perfect lining of the borings. In the Pro- 

 vince of Artois where Artesian wells which have existed upwards of .100 

 years arc found, no diminution of the quantity of water produi ed has ever 

 been observed — which by the way is (pute natural, the sheet of water which 

 supplies these having an almost unlimited extent — stretcliing as it does over 

 a space of several hundred square leagues (1 square league = 5 square miles), 

 the outlets to which (being these bore-holes) are almost unappreciable. This 

 also shows us that greater numliers of wells may be sunk into the same stra- 

 tum without affecting one another in the least. The outlay is however too 

 great ever to lead us to expect nuich competition, and the perforation of the 

 strata under Paris leaves us easy as to the future. 



From an analysis made by ]M. Pelouze the water of the Puits de GreneUe is 

 of a verv good quality, and far purer than that of tlie Seine or of Arcueil, 

 100 litres oidy gave \i grammes of extraneous matter (100 cubical inches 

 gave 3i grains,) whilst a similar quantity of water from Arcueil, or from the 

 Seine, yielded 17 grammes in suspension, and 46 in chemical combination, 

 (100 cubical inches yielded 43 grs. troy mechanically suspended, and 11-6 

 grs. troy of chemical impurities). 



.\n important question, anil one the solution of which will not be com- 

 pletely attained for a few months, is the height to which the water will rise- - 

 referring to the levels where this water first percolates into the strata, we may 

 hope that it will reach higher than the " Plateau " of the Pantheon — if this ex- 

 pectation be realized, all the vario\is districts of Paris can be attained, and 

 the improvements which the municipal council of Paris have long contem- 

 plated of supplying every habitation will be effected in a simple and economical 

 manner, as it will only be necessary to make two or three other wells like 

 that of GreneUe. 



We cannot however be certain of the ascentional power of the water until 

 the boring rods are withdrawn from the well, and the lining completed — 

 some time is therefore still necessary before we know all the advantages 

 which the perseverance of the municipality will have procured — a courageous 

 perseverance which we cannot sufficiently praise, and which has had to en- 

 counter the lively attacks of many persons who fancied it impossible, that 

 flowing water could ever be obtained by the means brought into play. The 

 council however placed the gieatest confidence in M. M. Eymery and Marie, 

 the engineers charged by the " Fonts and Chaussees," with the superintendance 

 of the supply of water to Paris, and who had first originated the proposal of 

 an .\rtesian fountain — It was also supported by the opinions of MM. Elie de 

 Beaumont and .\rago, who never for a moment doubted of the final success 

 of the undertaking, their confidence being based on analogy, and on a com- 

 plete acquaintance with the geological conformation of the Paris basin. 



We will endeavour to explain the reasons upon which they grounded their 

 opinion : — 



Paris occupies the centre of a basin, bounded on the west by the hills of 

 Brittany and of La Vendee, on the south by the range which traverses the 

 centre of France, and on the east by the Chain of the Vosges ; this basin is 

 filled up by successive layers, moulded as it were upon it, and fitting one into 

 the other like those sets of cups we sometimes see inclosed in each other in 

 order to occupy less room. 



It will be clearly seen that each of these layers exposes its edges or outcro|i 

 to the day at greater or less distances from the centre. Those filling up the 

 basin of Paris form three successive kinds of strata. The first or upper one 

 called the tertiary formation consists of gravels and sands as foimd at Fon- 

 tainebleau, of the gypsum which yields the plaster of Montmartre .ind St.Chau- 

 mond (plaster of Paris), of the limestone of Vaugirard and Montrouge, which 

 supplies building materials for Paris, and lastly, of the plastic clay em- 

 ployed in all the potteries of the capital. — This last layer contains the sheet 

 of water of St. Denis and St. Ouen. The second formation which immedi- 

 ately follows is the chalk which may be seen on the banks of the Seine from 

 near Paris to Havre. 



I he third consists of various limestones connected with the Jura moun- 

 tains, and consequently called the Jura formation (in England the oolitic). — 

 The second water hearing stratum that of Tours and Elbouf occupies the 

 lower part of the chalk : it consists of a thick bed of sand inclosed in two 

 very considerable layers of clay. The sand forms a kind of sponge which 

 imbibes the water, and the beds of clay are as it were the sides of a ]iipc con- 

 fining it, and whence it escapes whenever a perforation occurs. This stratum 

 then, if it be continuous under the basin of Paris, if it exactly represent the 

 cups we have described, must crop out at a certain distance from Paris, and 

 form a kind of circle round it more or less regular in shape. This is actually 

 the case. M. EUe de Beaumont has ])resented to the .Vcademy a collection 

 of samples of the sands belonging to this bed, and obtained at Cap la lUve 



near Havre, in the neighbourhood of la Fleche and Bonne Etable in the Sarther 

 from Chateau la Valicre in the Department of Indre et Loire, and from AUi- 

 champs near Vassy in the Haute Marne. .Ml these are identical, and resemble 

 the sand brought up with the water of the Puits de GreneUe. It is then 

 evidenc to every one, as it long has been to geologists, that this sand forms a 

 continuous basis to the Paris basin. Similar in shape to the bottom of a boat 

 its sides rise to the day, whilst the centre is at a great depth from the sur- 

 face. The waters falling on its edges or outcrop filter in and have for.nied a 

 subterranean sea, occupying the entire width of the basin, (jeology is thus 

 cstaldished by the Puits de (irenelle as a positive science in the eyes of the 

 whole world, and the conformation of the Paris basin made known with cer- 

 taintv. — Le Cottsliliitionnel, March 4. 



THE MAPLIN LIGHTHOUSE. 



Ix the second volume of the Journ.il, page 38, we gave a description of 

 the foundations of a Lighthouse to be constructed on a novel principal, by 

 direction of the Trinity Board, under the superintendance of Messrs. Walker 

 and liurges, the eminent engineers ; the spot selected was the Southerly 

 point of the MapUn Sands, which form the northern extremity of the Swin 

 Channel, at the entrance of the river Thames. The foundations, as we before 

 described, consisted of nine of Mitchell's patent mooring screws, with shafts of 

 wrought iron .5 inches in diameter and 26 feet long, one was fixed in the 

 sands in the centre, and the remaining 8 at the angles of au octagon 40 feet 

 diameter, the screws were turned into the sand to the depth of 21 ft. 6 in., 

 the top being then within 4 feet of the low water mark of a spring tide. 



.\fter the screws were fixed in August 1838, it was determined to leave 

 them for a few months; from that period to June 1839, every change in the 

 surface of the sand was observed, and notwithstanding that in the early part 

 of 1839. there were several storms of more than ordmary violence, yet 

 the screw piles stood firmly, and the sand at no time was lowered more 

 than 3 feet. .Vs a )>recautionary measure the engineers had constructed 

 an open platform or raft of timber in two thicknesses, crossing each other at 

 right angles, and bolted together at their intersections, which covered the 

 whole site within the piles, and also extended some distance beyond them ; 

 round the exterior was raised a curb 1 8 inches high ; over the platform was 

 laid bnishwood, and then about 200 tons of rough stone which sunk the raft 

 on to the sand and prevented it being displaced, between the spaces of the 

 platform and the brushwood the sand was allowed to work its way up, which 

 soon fiUed the interstices of the stone. Very shortly after the whole of the 

 platfonu and stone was embedded below the surface of the sand, which gave 

 considerable support sideways to the screw piles, and formeii a solid body for 

 the water to wash upon. Nothing farther was done on the spot till the 

 framing for the construction of the lighthouse was ready to be fixed in .\ugust 

 1840, when upon a careful examination it was found that the raft had com- 

 pletely settled down, and the piles as firm as the first day they were screwed 

 in — it was then determined to proceed with the erection of the super- 

 structure, which we shall now proceed to describe. The lower part consists 

 of eight cast iron pillars 18 feet long, 11 inches diameter externally, and 9 

 internally, they are fixed at the angles of tlie octagon, and in the centre there 

 is a similar pillar 22 feet long ; the lower part of the pillars forms a socket, 

 and is fitted over the top of the shafts of the screw piles to the extent of 4 

 feet, to which they are attached by adjusting screws of wrought iron ; the 

 U]iper part of the pillars also forms a socket 12 inches clear diameter, and 4 

 feet deep, into which are fixed the principal posts of the timber framing — 

 these pillars are fixed inclining towards the centre. The pillars are tied to- 

 gether at top and bottom with wrought iron horizontal bars 2 J inches dia- 

 meter, fitted with collars and screw bolts ; similar bars are fixed on the same 

 level in a raking position to the centre pillar, by the aid of which the whole 

 are firmly tied and braceil together — the top of the pillars stands about 4 feet 

 above high water mark of a spring tide. The timber framing was commenced 

 by first fixing the centre post 21 feet long and 14 inches square, and subse- 

 quently those of the angles, 30 feet long, 12 inches square at the base, and 

 10 inches square at the top ; they are tied together at the bottom by double 

 horizontal tie beauis, 12 by .'), and 27 feet long, and at the top 10 by 4, and 

 21 feet long ; the ends are secured to the angle posts by wrought iron nut 

 and screw bolts aiui iron knees. There are also raking braces from the angle 

 posts to the centre lOJ by 9, and \f> feet long; upon the tie beams are laid 

 the flooring joists 9 bv 3, the principal posts of the carcase framing are 6 

 by 4. 



The interior accommodation consists of a li\ing room 22 feet long, and a 

 store-room in the ujipcr part, and store-rooms for coals and water in the 

 lower part. Thus far the erection was completed in October 1840, within a 

 period of three months. 



Above the living-room is fixed the lantern with a gallery all rounil — it is a 

 polygon of 16 sides. 12 feet diiuueter internally, and 10 feet high from the 

 floor to the roof; tbr principal ])art of the framing is of cast iron — the roof, 

 the interior lining ami floor are covered with copper. In the centre, raised 

 upon a pedestal, is the beautiful apparatus of a second order of Dioptric light, 

 made and fitted up, together with the iron work of the lantern, by Messrs. 

 Wilkins and Son, of Long .\crc. The height of the hght above the mean 

 level of the sea is 4.") feet, and may be clearly seen from the deck of a vessel, 

 in fine weather, upwards of 10 miles off in all directions. The light was first 

 exhibited on the evening of the 10th of February last. 



