THEORY OF THE EA&TH. 169 



results to the public ; and though these only con- 

 tain a very small portion of the phenomena con- 

 nected with the immediately preceding period of 

 the history of the earth, they yet connect them- 

 selves most intimately with the rest. It was hard- 

 ly possible to avoid endeavouring to examine these 

 phenomena in the country immediately round 

 Paris ; and my excellent friend M. Brongniart, led 

 by other studies to have similar views, associated 

 himself with me in the investigation, by which we 

 laid the foundation of our Essay on the Mineral 

 Geography of Paris. That work, however, al- 

 though it bears my name, has become almost en- 

 tirely the work of my friend, in consequence of 

 the infinite care he has bestowed, ever since the 

 first conception of our plan, and during the exe- 

 cution of our several surveys and researches, in 

 the thorough investigation of all the objects of our 

 research, and in the composition of the Essay itself. 



The Essay on the Mineral Geography of the 

 Environs of Paris, affords the most complete and 

 satisfactory evidences of the principal facts and 

 circumstances which I have endeavoured to esta- 

 blish in this discourse. It contains a history of 

 the most recent changes which have taken place 

 in one particular basin, and leads us as far as the 

 chalk formation, which is infinitely more extended 

 over the globe than the formations composed of 

 those materials which are found in the basin of 

 Paris. The chalk formation, which was before 



22 



