298 On the relative Age of the 



Incontestible geological observations have shewn, that the 

 limestone beds which form the summits of Biiet in Savoy, and 

 Mont Perdu in the Pyrenees, having an elevation of from three 

 to four thousand yards, have been formed at the same time as 

 the chalks of the cliffs on the shores of the English Channel. If 

 the mass of water from which these formations have been precipi- 

 tated had been raised to a height of from three to four thousand 

 yards, France would have been entirely covered by it, and 

 similar deposites would have existed upon all the heights infe- 

 rior to three thousand yards. Now, we observe, on the con- 

 trary, in the north of France, where these deposites appear to 

 have been very little disturbed, that the chalks never attain a 

 height of more than two hundred yards above the present sea. 

 They present precisely the disposition of a deposite, which had 

 been formed in a basin filled with a fluid, whose level had not 

 attained any of the points at present having an elevation of 

 more than two hundred yards. 



I pass to the second proof, borrowed from Saussure, and 

 which seems to me still more convincing. 



The sedimentary formations often contain rolled pebbles of a 

 nearly elliptical form. In the places where the stratification of 

 the deposite is horizontal, the longest axes of these pebbles are 

 all horizontal, for the same reason for which an egg does not re- 

 main on end ; but where the sedimentary beds are inclined at 

 an angle of 45°, the larger axes of a great number of these 

 pebbles also form angles of 45° with the horizon ; and when the 

 beds become vertical, the long axes of many of the pebbles are 

 vertical. 



The sedimentary formations, therefore, as is demonstrated by 

 the observation of the pebbles, have not been deposited on the 

 spot and in the position which they now occupy : they have 

 been more or less raised at the moment when the mountains 

 whose sides they cover issued from the bowels of the earth *. 



• To be convinced, that in the act of the rising of a horizontal bed, all the 

 lone; axes of the pebbles whicli it contains could not have become vertical, 

 one has only to trace lines in different directions on a horizontal plane, and 

 to make it afterwards turn round a certain hinge. In this motion, all the 

 lines parallel to the hinge will remain constantly liorizontal. The perpendi- 

 cular lines to the hinge will, on the contrary, be inclined to the horizon, the 

 whole quantity by which the plane moves ; so that, at the moment when it at- 



