226 M. Arago*s Historical Eloge of Joseph Fourier, 



excited a lively interest among educated men, as, supposing it 

 to be perfect, it would throw light on the most minute processes 

 of the arts. In our times, its numerous points of connexion 

 with the curious discoveries of geologists, have made it a pecu- 

 liarly well-timed addition to science. The best way of pointing 

 out the intimate connexion between these two branches of scien- 

 tific research, will be to mention the most important portion of 

 the discoveries of Fourier, and to shew how happily our col- 

 league had made choice of a subject for consideration. 



Those portions of the mineral crust of the globe, which are 

 called sedimentary formations by geologists, have not been 

 formed all at once. The waters formerly covered, at different 

 times, regions at present situated in the centre of continents. 

 They deposited in them different kinds of rocks, in thin hori- 

 zontal beds. These rocks, although immediately superimposed 

 on each other like the layers of a wall, cannot be confounded 

 together : indeed their differences strike the most careless ob- 

 servers. I must also mention this most important fact, that 

 each formation has a distinct and perfectly defined limit, and 

 that no transition connects it with the superior formation. 

 Thus the ocean, the primary source of these deposits^ formerly 

 experienced, in its chemical composition, immense changes, to 

 which it is no longer subject in the present times. 



With some rare exceptions, arising from local convulsions 

 whose effects are otherwise made manifest, the relative order of 

 the antiquity of the rocky beds which form the external crust 

 of the globe, is that of their superposition. The lowest were 

 the first formed. The attentive study of these different forma- 

 tions may assist us in tracing out the chain of events beyond 

 the most remote periods, and enlighten us on the character of 

 the frightful revolutions which periodically buried continents 

 under water or left them dry again. 



The crystalline granitic rocks, on which the sea formed its 

 first deposits, have never exhibited any trace of organic beings. 

 These traces are only found in the sedimentary formations. 



Vegetables appear to have formed the commencement of 

 organic life on the earth. Their debris are the only things met 

 with in the oldest beds deposited by water, and these belong to 



