242 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[JULT, 



and it shows that iron ought to be entirely rejected in the construction of 

 ascensional tubes. Tubes of oak or chn arc certainly those to which pre- 

 fcrtnce is always given ; but the thickness which is indispensable for tlieiu, 

 ivoiild diminish the interior diameter too much in the Crenelle well. Copper 

 lubes of a thickness of two or three niiUiui. (about -^ of an inch), not only 

 possess a suthcient resistance, but also the property of being indestructible. 

 It is with these latter, therefore, tliat the Grenellc well is to be tubed. 



Independently of the importance of M. Mulot's undertaking for the useful 

 purposes to which it may be ajiplied, it is also of great interest for the geolo- 

 gical study of the strata tlirough which it traverses with regard to the central 

 heat of the globe. Taking as our starting point the constant temperature of 

 the cellars of the Observatory, which are 28 metres (91 feet) deep, the tem- 

 perature would present a unijform increase of a degree centigrade for every j2 

 metres (105 feet) in depth. The temperature of the water of this well has 

 leen calculated at about 27'C Cent. (8-17 I'ahr.) 



The cretaceous formation, passed through by the well of Crenelle, has liecn 

 deposited in successive layers in an immense basin, formed by the forma- 

 tions anterior to this part, of the secondary formation ; the borders of the 

 inferior strata of the chalk formation, crop out in many places, some on the 

 edges of the basin and others a little below the sod; they not only receive 

 the infdtrations of the rain water, but also those of rivers that flow over the 

 exposed strata. A complete identity has been found to exist between speci- 

 mens of lirown free stone ami green sand ol)tained in very different places, and 

 very far one from another, and specimens from M. Midot's boring. At Lisieux 

 in isorniandy, the inferior part of the cretaceous formation reposes on the Jura 

 formation ; — the limit of w liicb fonnation extends towards Mans and La Flechc, 

 and receives in this part considerable infiltratious from the Loire, which flows 

 direct upon it X. E. of Angers. The Loire ought also to furnish water to 

 the lower part of the formation near Saumur ; the boundary then passes 

 south of Paris liy Louduu, Chi'itellerault, to the north of Bovjrges, and then 

 to Sancerre. In all these difierent localities it receives the waters of the 

 Vienne, Creuse, Indre, Clier and Loire ; at Sancerre this limit takes a north- 

 east duection passing near .\iixerre, Joiguy, and Troves, and receiving the 

 waters of the Yonne, Seine, Aube, and a great many other rivers of less 

 importance. Near Troyes,* at Lusigny, and at the Abbey of Monster-Rancey, 

 at four leagues south-east of Troyes, the brown free stone and the green 

 sand crop out. In its northern direction through Sainte-Menebould this 

 boundary receives the waters of the Aisne very considerably. Lastly, this 

 formatioii. forms the bottom of the tertiary formation of Belgium, where it 

 receives other infdtrations that feed the Artesian wells of Picardv and Artois, 

 &c. 



All these waters filter freely enough through the sand of the cretaceous 

 formations, and from thence pass and accumulate at the bottom of the basin, 

 continuing to be in direct communication with the points of infiltration. As 

 these points are so much elevated above Paris, the waters rise, and will rise 

 still more in the Crenelle well when it is completely tubed, to a height which 

 will be a measure of the amount of pressure exercised ou the layer which 

 forms as it were the roof of the bottom of the basin. 



ON THE GIVING WAY OF EMBANKMENTS. 



The following remarks on the giving way of embankments, by M. Colin, 

 principal engineer of the bridges and embankments of one of the largest 

 canals in France, are the results of many years practical acquaintance with 

 the subject. 



The first appearance presented by a slope that has given way is that of an 

 alteration more or less complete of its primitive form, whether natural or 

 artificial. On examining the facts wluch strike the eye of the observer it 

 nmst be at once admitted that the cause of the fall of a mass of moving earth 

 must have operated either at a certain depth, or near the surface of the slope ; 

 therefore it is requisite, in all cases, to distinguish the superficial sUps of 

 cartli from those that have a deeper origin. 



When a mass of homogeneous earth is composed of argillaceous matter, 

 which is liable to give way, the strata may be more or less inclined to the 

 liorizon. Mhen the slip occurs on a pre-existing surface, the following con- 

 siderations will not be applicable ; the slips of this kind are very rare, and are 

 only accidental occurrences, which we should be careful not to confound with 

 the general facts examined by M. Colin. 



The mass of fallen earth whether natural or artificial, could not have been 

 in a state of equilibrium in relatiou to the cohesion of its particles, which on 

 the one hand tended to hold it together — and to gravity, which, on the other 

 hand, tends to destroy the cohesive attraction. When this equilibrium is 

 destroyed it must happen that the slope, or a part of it, will experience a 

 spontaneous fall. 



When by the action of the fall the moving mass is detached at such a depth 

 that it ])reserves its central cohesion notwithstanding the fracture, which has 

 destroyed the cohesion only on the surface of the slip, and notwithstanding 

 that relative alteration in the angle of the striita which compose that mass, — 

 in such case the cause of the slip must be pronounced to have proceeded from 



' The specimens from Lusigtiy were presented by M. A\)lfardric, who ob- 

 serves ihni the height of the well aboye the level of the sea is 130 metres, 

 whilst thai at Paris is ouly 31 metres. 



below, in contradistinction to that fall which occurs when the moving mass 

 is detached nearer the surface, and when the cohesion of the mass is more or 

 less destroyed by the action of external agents. It often happens, however, 

 that both tlicse kinds of slip occur at tlie same time. 



nds characteristic difl'erence depends on the chemical nature of the soil, 

 so tliat the same kind of slope may in one case experience a falling away 

 from the surface alone, wlu;n iu another case the cause of the slip may be 

 more deeply seated. 



There is .loother important difl'erence between slips of earth proceeding 

 from the surface and from below, which is, that the extent of the former is 

 immediately known, wliile that of the latter may go ou gradually increasing, 

 according to the influence of rain, frost, and tliaw. In every ease, however, 

 it is the action of gravity which causes the disturbance of the equilibrium ; 

 for the destruction of cohesion by the external agents is only an action emi- 

 nently statical ; the force of gravity alone causes tlie movement. It is there- 

 fore natural to infer, that as the princi])al cause of tlie destruction of the 

 eqnilibrinm is the same in all cases, the dynamical results nmst also be the 

 same. Consequently the surfaces of shps, whether they proceed from below 

 or from the superficies, ought, tlieoretically speaking, to be of the same kind, 

 and to present, as regaids their material points, a striking resemblance. 



On examining with great care the general facts concerning these two kinds 

 of spontaneous slips of earth, the angle of inclination of the failing earth, and 

 that of the surface on which it falls, and comparing them with a great num- 

 ber of facts collected in various places, with different kinds of soU, and under 

 different circumstances, by other engineers, as well as by M. Colin himself, 

 he thinks he has established as a principle the following proposition : — 



" When masses of earth nearly homogeneous, whether natural or artificial, 

 are composed of such materials that the action of gravitation may, under the 

 influence of certain physical circumstances, overcome the cohesion of their 

 molecules, the results are spontaneous movements, which are called slips. 

 These movements are independent of the height of the slopes on which tliey 

 occur ; they always present, nearly in the same degree, tlie character which 

 appertains to them ; lastly, and above all, the natural surface of separation, 

 or the surface of the slip, has no pre-cxistence, and possesses a constant and 

 regular form, which approaches more or less exactly, according to different 

 circumstances, to a surface of a cycloidal shape, which brings the causes of 

 its formation essentially v\ithin the domain of mechanical science." — Inven- 

 tors' Advocate. 



HEREFORD CATHEDRAL. 



The public are already aware that very extensive improvements have for 

 some time been going on in this beautiful edifice imder the superintendence 

 of Mr. Cottingham, the celebrated architect. M'e have already described the 

 various restorations in the choir. Lady Chapel, kc, but all the interest ia 

 these (and it has been veiy great) is altogether lost in the discovery by the 

 architect that the tower of the cathedral, with its immense superincumbent 

 weight, is in imminent danger of falling, and crushing the mighty fabric in 

 one general ruin. Before entering into a somewhat technical description 

 (which may perhaps be understood only by a few) of the appearances tliat 

 lead to this conclusion, we may observe, that we have examined the present 

 state of the tower most minutely, and the fissures in the masonry at the 

 angles of the Norman arches of the transepts arc truly frightful. In some 

 places the workmen may insert a piece of wood or any implement to the depth 

 of two feet; and we particidarly noticed that one of the stones forming the 

 masonry had given way, not at the joining, but in the solid part itself, being 

 literally s])lit in two. It appears that some cracks in the chief wall of the 

 tower led Mr. Cottingham to examine into the cause. He accordingly pro- 

 ceeded first to ascertain the state of the main piers below in the body of the 

 church, and these he found to be all soUd. He next explored the masonry 

 of the unsightly piers tmder the Norman arches of the north and south trau- 

 septs, and ascertained that the arch was quite independent of this enormous 

 body of masonry; that is, that the Norman arch had " stuck firmly to its 

 work," and that, as has long been suspected, tlie piers were no support what- 

 ever. Mr. Cottingham next examined the string course round the bell cham- 

 ber, which supports the 52 solid stone columns above that chamber, and he 

 found that this course (or wall, as we should call it) was rounded in the cen- 

 tre, and dipping down at the angles of the tower. This proved that the 

 ancient Norman arches were still in their original position, and that the frac- 

 tures which now exhibited themselves in every direction were occasioned by 

 some defect in tlie main piers of the tower. On taking up the bell-ringers' 

 floor, Mr. Cottingham found the stone groining (which was put up about the 

 time of Edward IV.) also pressing upon the four angles of the tower. It is 

 singular that the " jiockets," or angtilar spaces of this groining, were filled up 

 to the level of the floor with solid rubbish. On removing this, a most extra- 

 ordinary failure in the masonry fully developed itself. At each end of the 

 four angles was a hollow chamber running diagonally through the main wall, 

 which, from the pressure of the enormous stone piers above alluded to, was 

 crushing in in every direction. All the bond of the interior ashlering was 

 ascertained to be broken, and the stones fractured into innumerable pieces; 

 indeed, the failure is awful to contemplate, and we may congratulate the 

 public that the discovery was made previously to any further pressure, which 

 mu?t have occasioned the total destruction of this magnificent tower, together 

 with the choir, the transepts, and the eastern portion of the nave. When, ot 



