208 The Founders of Geology LECT. 



mations of the Paris basin suggested to Guettard the first 

 idea of depicting on maps the geographical distribution of 

 rocks and minerals. The same region and the same features 

 of topography and structure inspired long afterwards a 

 series of researches that contributed in large measure to 

 the establishment of the principles of geological strati- 

 graphy. No fitter birthplace could be found in Europe 

 for the rise of this great department of science. Around 

 the capital of France, the Tertiary and Secondary forma- 

 tions are ranged in orderly sequence, group emerging from 

 under group, to the far confines of Brittany on the west, 

 the hills of the Ardennes and the Vosges on the east, 

 and the central plateau on the south. Not only is the 

 succession of the strata clear, but their abundant 

 fossils furnish a most complete basis for stratigraphical 

 arrangement and comparison. 



Various observers had been struck with the orderly 

 sequence of rocks in this classic region. Desmarest tells 

 us that the chemist Eouelle was so impressed with its 

 symmetry of structure that, though he never wrote any- 

 thing on the subject, he used to discourse on it to his 

 students at the Jardin des Plantes, of whom Desmarest 

 himself appears to have been one. He would enlarge to 

 them upon the significance of the masses of shells im- 

 bedded in the rocks of the earth's surface, pointing out 

 that these rocks were not disposed at random, as had been 

 supposed. He saw that the shells were not the same in 

 all regions, that certain forms were always found associ- 

 ated together, while others were never to be met with in 

 the same strata or layers. He noticed, as Guettard had 

 done before him, that in some districts the fossil shells 



