ii Desmarest on Volcanic History 71 



trial mammals. But to Desmarest they were proofs of the 

 former presence of the sea over the heart of France. He 

 inferred that the pebbles of various lavas which he found 

 among these strata denoted former volcanic eruptions, 

 before the accumulation of the marine deposits. But he 

 noticed also indications of the discharge of lava during the 

 sojourn of the sea over this region. He believed that his 

 third epoch must have lasted some considerable time, so as 

 to permit the deposition of 600 or 900 feet of horizontal 

 sediments above the lowest lavas. 1 



He remarks that from ignorance of this method of 

 following the sequence of eruptions and the effects of con- 

 tinuous waste, naturalists had failed to detect the existence 

 of lavas of the second and third epochs in districts where 

 eruptions of the first epoch were no longer to be recog- 

 nized. These observers, he contended, had misread the 

 evidence of nature, referring what were undoubtedly 

 volcanic rocks to deposition from water, to schists, and to 

 pierre de corne, and on the other hand mistaking for 

 volcanic craters what were only hollows dug out by run- 

 ning water in the lavas of the second, or even of the first 

 epoch. 



The sagacity of these generalizations has been amply 

 sustained by the researches of later times. Alike in 

 volcanic geology and in the doctrines of denudation, the 

 labours of Desmarest marked the rise of a new era in the 



1 In the article " Auvergne " in his Geographic Physique, p. 882 (pub- 

 lished in 1803), he briefly summarises his three epochs thus " I have 

 distinguished three kinds of volcanoes in Auvergne, first, ancient vol- 

 canoes; second, modern volcanoes; and third, submarine volcanoes." 

 Probably most of the lavas of his third epoch are rather of the nature of 

 intrusive sills. 



