238 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[August, 



bolted throush the flanches, to form one large shuttle, of the entire breadth 

 of the wheel, and its motion was regulateu by radial tie-rods, between the 

 stone apron and the back of the sluice, which could thus be rai^^ed with 

 great facility by racks and pinions, and be regulated by the ordinary gover- 

 nor, the weight of the sluice being in a great degree supported by the water 

 flowing beneath it, on to the wheel. It moved very accurately between the 

 side walls of the pen-trough, and cup-leathers at each side prevented any 

 waste of water. This kind of wheel was less affected by back-water than 

 any other form, and the water acted upon it with its full power of velocity, 

 without any impediment from the air in entering, as there was no sole-plate; 

 the buckets were, therefore, tilled and emptied with great facility. Mr. De 

 liergue was satisfied that this was the best kind of wheel for all falls under 

 8 feet in height; and though the principle differed essentially from that 

 generally taken as the basis of constructioo of water-wheels, he was inclined 

 to prefer it to any other system. 



BUILDING MATERIALS IN PARIS. 



On the Building Materiuls Employed in Paris and in the Valley of 

 the Lou-er Seine. By George Burnell, Esq. — (Paper read at the 

 Royal Institute of British Architects.) 



At the present day, when the attention of the profession has 

 been so powerfully directed to what may be called the physiology 

 of the materials employed in the execution of the works committed 

 to their charge, it may be interesting to examine the practice of 

 the architects in the neighbouring capital. Such an e.xamination, 

 moreover, becomes more interesting from the comparatively supe- 

 rior attention paid by the French architects and engineers to the 

 study of the philosophy of the mechanical parts of their pursuits. 

 ^I'ith the glorious exceptions of Rennie, Tredgold, Barlow, and 

 Hodgkinson, nearly all that we know of the chemical and mechani- 

 cal nature of the materials we have to employ, is derived from the 

 works of tlie French authors. The practical lessons they have 

 drawn from their researches become, therefore, of much more im- 

 mediate importance; and, although the geological nature of the 

 country in which they are applied differs so entirely from that of 

 our own, yet the mode of analysis adopted, and the conclusions 

 arrived at, are as applicable here as elsewhere. 



Building materials may be separated, for the purposes of classi- 

 fication, into the following groups: — 1st, stone; 2nd, bricks; 3rd, 

 limes; 4th, woods; 5th, metals. Under the head of bricks are in- 

 cluded tiles, pottery, and artificial stones; under that of limes are 

 included plaster, cement, sand, stuccos, &c. These materials are 

 to be examined — firstly, as to the nature and qualities of tlieir con- 

 stituent parts; secondly, as to the manner of their use. 



I. Stones. — The stones employed in building are grouped thus 

 — 1st, the argillaceous; 2nd, the calcareous; 3rd, the gypseous; 

 4th, the silicious; 3th, the volcanic and divers natures. 



1st. The Argillaceous Stones. — These are comprised of a base of 

 alumina, generally combined witli silicates and the oxides and sul- 

 l)hurets of iron. They do not effervesce with the acids, and are 

 composed of successive layers, easily separated. The schists and 

 slates are of this class. 



The slates used in Paris are extracted at Angers, in the depart- 

 ment of the Maine and Loire. The quarries are opened in a bed 

 of Silurian argillaceous schist of an enormous tliickness, which 

 outcroj)S for a length of 10 miles, between Avrille and Treluze, 

 jiassing under the town of Angers, where the Mayenne cuts the 

 direction of the formation at right angles. There are eight quar- 

 I'ies opened in a direction from east to west. Immediately under 

 tlie vegetable soil is found a bed of incoherent schist, named in 

 the country "cosse." This is followed by a bed difficult to cleave, 

 and, therefore, used locally as a rubble building stone; and lastly 

 occurs, about 14. or 15 feet from the surface, the useful slate. It 

 is worked in patches about 400 feet wide, leaving underneath an 

 unknown tliickness, though the depth quarried in many cases e.x- 

 tends to 3(I0 feet. 



Tlie ([uarrics of Angers furnish a slate of a very fine grain, re- 

 markably thin and light; although the specific gravity of the slate 

 itself is very great. It is 3-000^ water being 1-000, or 188 lb. per 

 foot cube. Four sizes are worked for the Paris market — viz.: the 

 "grande carre forte," llf long hv ^\ wide, and ^ thick (0™.298 

 X 0"'.217 X 0"'.003); 2nd, the "graiule carre' fine," of the same 

 dimensions as to length and breadth, but of about half the thick- 

 ness; 3rd, the "cartelettes," 8^ long by (iM wide by i thick (0".217 

 X 0"i.l62 X O'".0O3; and 4th, the "cartelette fine, of about half 

 tlie thickness. According to the statistical returns of the In- 

 genieurs des Mines, the value of the slates e.xtracted at Angers in 

 the year 1845, was at the pit's mouth l,420,056f. (56,400/^); and 

 there were employed in the quarries 2,36G workmen. 



The quarries of Charleville, in the department of the Ardennes, 

 are worked upon a larger scale for the supply of slates for the east 

 of France, Holland, and the Low Countries; but the e.xpensive 

 land carriage prevents them being employed in the capital. The 

 value of their |)roduce is about l,793,945f. (72,000/.); they employ 

 2,843 men. The slates are somewhat softer than those of Angers, 

 consequently they decayed rapidly in the damp countries where 

 they were usually emjiloyed. M. Vialet, Ingenieur des Ponts et 

 C'haussees, overcame this objection by roasting the slates until 

 they assumed a red tinge; their durability was doubled by this 

 process. In the neighbourhood of St. L6, in the department of 

 Calvados, are some slate quarries in the Cambrian strata, which are 

 used to a considerable extent in the neighbourhood, and which, if 

 the land carriage were not so ruinous, would doubtlessly be for- 

 midable rivals to those of Angers. The cathedral of Bayeux is 

 covered with the former; but even there, the price of the Angers 

 slate is so much inferior to that of St. L6, as to ensure the preference 

 for general use, in spite of the superiority of the latter. The 

 value of the slates extracted in the department of the Calvados in 

 1845 was 10,360f. (414/.) 



The usual practice in Paris and in the departments of the 

 Lower Seine, is to nail the slates with two nails upon battens half 

 an inch thick, and from 4^ inches to 7 inches wide, that is to say, 

 either of deals cut in two, or of battens. Sometimes these 

 "voliges," as they are called, are of poplar or sycamore, but they 

 decay very rapidly. The slates lap over one another two-thirds of 

 their length, leaving a "pureau" of one-third, when the inclination 

 of the roof is not above 33°: at 45° the pureau is one-half of the 

 slate; at 60' two-thirds. The battens are rarely laid close, for the 

 slates are found to decay more rapidly if there be no circulation of 

 air. Tlie usual space between the battens is about Ig inch. Hips, 

 ridges, valleys, and gutters are executed as in England, with the 

 trifling exception, that step-metal flashings are unknown; the slates 

 are made good to the Pignon walls by merely covering the meeting 

 angle with plaster. 



2nd. The Calcareous Stones. — The formations which furnish tlie 

 building stones of this class occur in the neighbourhood of Paris, and 

 of the basin of the Lower Seine, in vast deposits. The ease with 

 which they are extracted, and the proximity of the quarries to the 

 places in which tlie stone is to be used, render their employ almost 

 imperative; and it is to the use of these materials that the monu- 

 mental character of Paris is in a great measure to be attributed. 



The nature of this class of stone is too generally known to ren- 

 der it worth while to dw ell upon it at present. Our geological ob- 

 servations will therefore be merely confined to an enumeration of 

 the great sources of supply. These are, for Paris itself, the vast 

 tertiary formation, which nearly covers the wliole of the depart- 

 ments of the Seine, Seine and Oise, Seine and Marne, I'Oise, and 

 extends into those immediately around. Rouen, and some of the 

 small towns above and below it, use large quantities of an indu- 

 rated chalk met with on the banks of the Seine, whilst Havre and 

 the intermediate towns derive their building stones principally 

 from the oolitic formations of the department of Calvados. 



Nearly the whole of the department of the Seine in which Paris 

 is situated, may be considered as capable of furnishing calcareous 

 stones for building purposes. The excavations which have been, 

 and still continue to be made, in and around Paris, ai-e immense. 

 About one-sixth of the town is built over the abandoned quarries, 

 which are known under the name of the catacombs. Tlie quarters 

 St. Marcel, St. Jacques, St. Germain, and Chaillot, are in this con- 

 dition; and it is calculated that the mass of materials extracted 

 tliencefrom is not less than 385 million cubic feet. At present the 

 bulk of the superior stimes furnished by the department, comes 

 from the quarries of Arceuil, Bagneux, Montrouge, and St. Cloud, 

 tthich lie to the south-west of Paris. 



The department of the Seine and Oise, is rich in quarries. 

 Amongst them may be cited those of Saillancourt and Conflans, 

 near Pontois, of Poissy, St. Nom, St. Maure, I'lle Adam, and 

 Cherence near Mantes, and upon the borders of the Chalk. The 

 department of the Oise furnishes the lias of Seiilis, and the 

 Vergelee of St. Leu. The Seine and Marne furnish the very beau- 

 tiful stone called the Chateau Laudon. 



This stone of the Chateau Laudon is the hardest, densest, and, 

 consequently, heaviest, employed in Paris. It is nearly a pure 

 carbonate of lime, containing in 1,000 parts 18 only of magnesia, 

 and 18 of silicate of alumina. Its colour is a grey, slightly tinged 

 with yellow; it is subcrystalline, resists the action of the atmo- 

 sjihere, and bears a kind of polish. The quarries from w hich it is 

 extracted are about C3 miles from Paris; yet the great superiority 

 of the stone causes it to be ])referred wherever great solidity is 

 desired. It was first employed in the erection of the bridge of 



