burat's geologie appliquee. 135 



sionally bituminous. The beds are numerous (amounting to 13 in 

 number), and the total thickness is as much as 60 yards. The 

 district of the Pyrenees, however, is more remarkable in this 

 respect than Eastern France ; and in the valley of Cardona there 

 are two extensive and thick masses of rock-salt, united at their 

 bases, one of which is worked as a quarry on the steep face of a 

 hill. It is composed of eight beds, separated by red marls, and 

 extends for about 130 yards by 250, with an unknown depth. 

 The other is not worked. M. Bur at, referring to the saliferous 

 gypsum of Yolterra in Tuscany, offers a few speculations with re- 

 gard to the possible origin of these singular masses, and considers 

 the latter to be connected with the lagoni, which are eruptions of 

 aqueous vapour at a considerable temperature (105° to 120°), 

 mixed with sulphuretted hydrogen gas. The singular beds of 

 Seyssel and elsewhere, so remarkable for the quantity of bitumen 

 they contain, are considered by M. Burat to be due to a similar 

 agency. 



The subject of iron ore bedded among stratified rocks next occu- 

 pies our author's attention. Few of the French coal basins contain 

 the carbonate of iron (the common ore of England) in any abun- 

 dance, although small quantities, in nodules, are not rare. The 

 basin of Aubin (Aveyron) is that which contains the most valuable 

 seams of this mineral. Pisolitic ores of iron are common, and 

 sometimes valuable, in some of the Oolitic beds of the Jura ; and in 

 several places they have been found worth working. 



Having thus considered the various circumstances under which 

 valuable mineral produce occurs in masses in stratified rocks, or 

 actually embedded and alternating with the regular strata, the 

 next subject introduced is that of the metallic ores contained in 

 mineral veins. The meaning of the term vein, the nature of the 

 cracks and fissures that contain ores, the particular appearances 

 observable in, and the composition of, veins, occupy, as might be 

 expected, a considerable space, and are very carefully and instruc- 

 tively shown. Nowhere, perhaps, is this difficult subject more 

 simply explained and better illustrated than in these pages ; and 

 some beautiful engravings speak to the eye in a manner which can- 

 not fail to be highly useful. A description of metalliferous districts 

 next follows, from which it appears that in France there are four 

 principal mining regions — that of Brittany, resembling the opposite 

 coast of Cornwall, that of the Vosges, rich in argentiferous lead ore, 

 the plateau of Central France, abounding in the same valuable 

 mineral, and the chain of the Pyrenees, in which the ores of iron 

 are of chief importance. Much valuable local and statistical inform- 

 ation concerning these districts is given in the chapter now under 

 consideration. 



The mechanical contrivances made use of in actually obtaining 

 the discovered ore, and reducing it to a state in which it is saleable 

 to advantage, are next treated of, and occupy a considerable space ; 

 and a very detailed account is given of the contrivances by which 

 the whole mineral produce may be best obtained with safety to 



K 4 



