134 NOTICES OF NEW BOOKS. 



coal at Mons, near Valenciennes, and thence to Douai, where, so 

 long ago as in 1734, mines were opened, though unsuccessfully. 

 The proprietors, in after years, followed the known direction of the 

 axis of the basin in which the coal was lying ; and although the cre- 

 taceous rocks covered up and hid the coal measures, yet as there 

 appeared from the structure and condition of the associated old 

 rocks that no great disturbance was to be feared, the search was 

 pursued, and at length rewarded by the discovery of the mines of 

 Anzin, after an expense of about three millions of francs (120,000Z.) 

 had been incurred. M. Burat then remarks : 



' Guided by the principle of the direction of the beds of coal and the strata 

 containing them, as in this example, we may advance in our explorings of the 

 carboniferous formation, if not with certainty, at least with a high degree of pro- 

 bability afforded by Geology ; but in searching a priori for the carboniferous 

 rocks, under the vast superficial area covered up by secondary and tertiary rocks 

 which may happen to rest upon them, science can furnish no more than very 

 indirect indications.' 



The curious position of the coal in some of the Continental 

 localities is next alluded to, and the structure of coal, the varieties 

 of its appearance and inclination, and the occurrence of faults, are 

 dwelt upon practically and usefully. 



The origin of coal had already formed the subject of a Memoir 

 by the author ; and he here again alludes to the proof of its being 

 due to the accumulation of large masses of decomposing vegetables, 

 and that the leaves and stems preserved in the accompanying 

 shales and sandstones are the only records remaining of the kind of 

 vegetation at that early period. 



The extraction of coal in France is greatly limited for want of 

 ready and cheap communication ; and this is so much the case, that 

 five-eighths of the whole quantity extracted is obtained from four 

 of the very numerous basins (not less than seventy) in different 

 parts of the country. A large quantity of lignite and turf is an- 

 nually obtained from different parts of France, and foreign coal is 

 imported to a very considerable extent. 



The supplies of rock-salt and of gypsum extracted from the 

 earth are from very different geological formations in different 

 countries. In England, as is well known, the beds of the New 

 red sandstone contain rock-salt in great abundance ; and so also do 

 the variegated marls of cotemporaneous origin in the east of 

 France. At Bex, in Switzerland, the same mineral occurs in the 

 lias ; in the Austrian Alps and the Carpathians it is found in the 

 upper oolites and greensand ; and in Poland in tertiary rocks ; 

 while in Catalonia and the Pyrenees it is sometimes in the cre- 

 taceous, and at others in the tertiary, beds that the salt-springs and 

 salt occur. The presence of gypsum is almost invariably asso- 

 ciated with the salt in some form or other ; and coloured clays or 

 marls are also so generally met with, that they seem to be almost 

 necessary conditions for the presence of large masses of salt. 



In the east of France the most common rock-salt is generally of 

 a dirty-grey or blue colour, and when mixed with salzthon is occa- 



