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THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[June, 



vapour at a temperature of 105 to 120 ceutriirrade. Tliey burst 

 forth with violence from fissures ia the ground, and rise in white 

 columns from 30 to C6 feet from the earth. Tljey are accompanied 

 hy a strong odour of sulpliuretted hydrogen; they alter the rocks 

 they approach, and deposit in them crystalline or concreted g)'p- 

 suni, occasionally mixed with sulphur and horacic acid. 



The lagoni are found in groups of from ten to thirty, nearly in 

 a straight line extending from the Mount Cerholi, Castel Nuovo, 

 and .Monte Rotondo; as though they followed the direction of a 

 fault, or dyke whose length is from 20 to 25 miles. The horacic 

 acid they contain is extracted by means of the heat of the lagoni 

 themselves, which are made to evaporate the waters drawn into 

 basins for that purpose. But the most interesting geological fact 

 connected with them is the influence their vapours appear to have 

 in the formation of the sulphate of lime; which accumulates in 

 small crystals, or in crystalline masses in the marls, and the cal- 

 carcerous strata they traverse. 



If such lagoni had acted upon the gulfs or the lakes of salt 

 water, of the tertiary period, it is easy to account for the alterna- 

 tions of the gypsum and the rock salt in the sedimentary deposits 

 of that period. The gypsum, whether crystalline, in small beds, 

 in mamillary, or botryoidal nodules, which are disseminated in the 

 marl beds, would naturally result from the phenomena of affinity 

 of which we find instances in almost every foimation. The gyp- 

 seous strata we may consider as representing the epochs of activity 

 of the vapours, and of the disturbance of the waters; the saliferou's 

 strata would correspond with the epochs of tranquility, during 

 which the evaporating powers of the jets exercised alone their in- 

 fluence. The presence of the borates of magnesia (which are 

 sufficiently common in gypsums) may be explained also by the 

 nature of the lagoni in actiivity at the present day. 



The gypseous formation of Paris difl^ers from all those we have 

 hitherto considered on many accounts. Geologically a very marked 

 distinction is to be made, inasmuch as from the manner of its for- 

 mation, its stratification, and the shells it contains, we are led to 

 believe that it was produced hy mechanical deposition rather than 

 by chemical separation, like the other formations. Tlie rocks now 

 to be examined form a portion of the immense tertiarj' deposits 

 which fill a depression in the chalk, called, from the fact of Paris 

 occupying its centre, the Paris basin. An adventitious interest is 

 communicated to this formation from the fact of its having led M. 

 M. Cuvier and Brogniart to propound the doctrine of the superior 

 importance of the study of organic remains, to that of the litho- 

 logical character of a deposit; a doctrine, it is true, previously 

 propounded by our countryman Smith, but the superior knowledge 

 of the French geologists in comparative anatomy, and conchology, 

 ])laced the question beyond doubt. The Paris basin was the first 

 wliich was distinctly classed as a tertiary formation, and the an- 

 nouncement of this clasification gave rise to the researches which 

 led to the discovery of similar deposits in many other parts of 

 Europe. There is also a chemical difterence between the Paris 

 gypsum and any of the saliferous gypsums hitherto noticed, viz. — 

 that it contains as much as 12 per cent, of carbonate of lime in 

 combination. This appears to communicate to it the much superior 

 jjower it possesses of resisting atmospheric change. Another differ- 

 ence lies in the mechanical structure, for the Paris gypsum is the 

 hardest known, except perhaps that found near CJirgenti, in Sicily, 

 which, according to Rondelet, a most conscientious autliority, is 

 still harder. We do not, however, possess any details on this 

 subject. 



The gypseous deposits near Paris form a very distinct and easily 

 identified group, or subdivision, which comprehends (at the same 

 time as the gypsum) alternating beds of marl, either calcareous or 

 argillaceous. These beds follow an order precisely identical 

 throughout the whole district, from the neighbourliood of Meaux 

 to Meulan. Some beds are absent in particular cantons ; but those 

 which are still to he met with occupy the same relative positions. 



The gyi)sum immediately overlies the calcareous beds Cuvier 

 designated as the "calcaire marin;" and their appearance in the 

 landscape in the neighbourhood of Paris is very remarkable, even 

 in a pictures<|ue point of view. They cap tlie hills of the older and 

 harder formations; and appear to have suffered more severely from 

 the denuding effects of the cataclasms which gave rise to the 

 existing valleys, than the subjacent rocks. They thus form, as it 

 were, a second range of hills (sometimes conical, as at iMontraartre, 

 Les Buttes Dorgeniont ; or elongated, as at Chaumont and Belle- 

 ville, Triel, Ike.) superposed on a first series of hills, bearing all 

 the characteristic marks of the calcareous ranges. 



,VV'e find at Montmartre and at Belleville, where the formation 

 exists iu the most perfect development, that there are three masses 



of gypsum of various thicknesses. The lowest mass, situated imme- 

 diately upon the "calcaire marin" is composed of beds of gypsum of 

 feeble thickness, containing a large proportion of selenitous', or crys- 

 tallised gypsum, and alternating with beds of calcareous marl, of a 

 very solid character, or with argillaceous marls in very thin flakes. 

 Sometimes a deep bed of white fresh-water marl is interposed be- 

 tween the gypsum and the upper courses of the " calcaire marin." 

 The number of the beds of gypsum in the lowest mass is five; 

 their total thickness is not more than 7 ft. 7 in. This mass is 

 seldom worked; for the douhle reason, that its extraction is very 

 difficult, and the quality of the plaster it yields is decidedly infe- 

 rior to that of the upper masses. But it is to be borne in mind, 

 that the thickness and the number of the beds in the lowest mass 

 are very variable. Those quoted above are obtained from the 

 quarries called " L'Amerique," at Belleville; at Montmartre the 

 total thickness of the beds of gypsum and the marls is from thirty- 

 three to thirty-six feet, measuring from the upper bed of gypsum 

 to the bed of white calcareous marl. There is, however, some- 

 thing exceptional in the nature of this third mass at .Montmartre, 

 inasmuch as it has never been observed to pass under the others, 

 and it occurs in a detached hillock, rather towards the east. Its 

 beds are not horizontal, but decidedly inclined towards the south- 

 west. 



The second and third masses are separated by a set of beds of 

 marl, whose thickness is about five feet. Like the third mass, it 

 is composed of a series of beds of gypsum, intercallated with 

 marl in variable thicknesses, and without definite order; that is to 

 say, that the marl beds are wanting in some localities, whilst they 

 are very numerous and powerful in others. The greatest thickness 

 which the second mass exhibits is met with in the quarries at 

 Montmartre, where it sometimes attains as much as 33 feet. At 

 Belleville, the height is, however, rarely more than 19ft. 6in.; 

 and it affords eight workable and useful beds: the irregularities in 

 the thickness appear to be, however, more owing to the beds of 

 marl than to those of gypsum, which present a very striking uni- 

 formity. The second mass yields a stone which makes excellent 

 plaster. One bed in particular, found at Belleville, and called by 

 the quarrymen "le gros banc," three feet in thickness, is often set 

 aside for the purpose of making plaster for the exclusive use of 

 statuaries or artists. 



The first mass is the most important, and also the most widely 

 distributed. The lower masses are wanting in many localities, as 

 at Triel, where the first mass rests immediately upon the marls 

 and clays interposed between the first and second masses in Mont- 

 martre and Belleville. At Montmorency there are two masses; 

 but in all cases the relative superiority of the first mass, both in 

 quantity and freedom from mixture of the marl beds, is very 

 remarkable. In some cases, as at Dammartin and Montmorency, 

 this formation occurs immediately under the vegetable soil. At 

 others, as at Belleville and at Montmartre, it is covered by a series 

 of beds of sands, clays, argillaceous and calcareous marls, which 

 attain as much as from 110 to 120 feet in thickness. A somewhat 

 similar set of beds of marls and clays forms the floor, separating 

 the first from the second masses of gi'psum; its thickness is 

 variable, but may be taken as being about 10 feet on the average. 



The upper beds of the first mass are strongly impregnated with 

 marl, and this latter substance even intercallates with the gypsum 

 with sufficient regularity to enable us to follow the respective 

 strata over great distances. They are soft; the workmen group 

 them under the name of "les chiens;" and they yield a very infe- 

 rior plaster if burnt alone. Their united thickness is about 5ft. 

 6 in.; and they are six in number, in some of the quarries at least, 

 never being fewer than five. The intermediate beds whose number 

 and thickness is the most exposed to variations, are divided natu- 

 rally into large many-sided prisms, which have jirocured for them 

 the name of "les hauts piliers" among the quai-rymen. Their 

 united thickness is about 35 feet; the quality of the stone they 

 yield differs somewhat, and care is requisite in the burning to 

 secure a plaster of uniform quality. The bed called "la corraie," 

 about 2 ft. 9 in. thick, is very hard, and it requires to be mixed 

 with the softer beds to make a saleable article. Two others, "les 

 battaillon" and "les rousses," are reserved for the special use of 

 statuaries. The lowest beds of this mass contain much sile.v, 

 which even at times seems to shade off as it were into the gypsum, 

 without our being enabled to say precisely where the one begins 

 or the other ends. The plaster made from them is of ratlier an 

 inferior quality compared with that obtained from the interme- 

 diate beds. 



The lowest mass contains at times, especially in the associated 

 marls, marine fossils, and large crystals of selenitic gypsum. The 



