16 



found in the Mountains," 1740, showed the effects of volcanic 

 action in elevating strata, and causing faults. Vallisneri had 

 studied with care the marine deposits of Italy. Donati, in 

 1750, had investigated the Adriatic, and ascertained by sound- 

 ings that shells and corals were being imbedded in the deposits 

 there, just as they were found in the rocks. 



John Gesner's dissertation, u De Pei/rifioaUs" published at 

 Leyden in 1758, was a valuable contribution to the science. 

 He enumerated the various kinds of fossils, and the different 

 conditions in which they are found petrified, and stated that 

 some of them, like those at Oeningen, resembled the shells, 

 fishes, and plants of the neighboring region, while others, such 

 as Ammonites and Belemnites, were either unknown species, or 

 those found only in distant seas. He discusses the structure of 

 the earth at length, and speculates as to the causes of changes in 

 sea and land. He estimates that, at the observed rate of reces- 

 sion of the ocean, to allow the Appenines, whose summits are 

 filled with marine shells, to reach their present height, would 

 have taken about eighty thousand years, a period more than 

 " ten times greater than the age of the universe." He accord- 

 ingly refers the change to the direct command of the Deity, 

 as related by Moses, that, " The waters should be gathered 

 together in one place, and the dry land appear." 



Voltaire (1694-1778), discussed geological questions and the 

 nature of fossils in several of his works, but his published 

 opinions are far from consistent. He ridiculed effectively and 

 justly the cosmogonists of his day, and showed, also, that he 

 knew the true nature of organic remains. Finding, however, 

 that theologians used these objects to confirm the Scriptural 

 account of the deluge, he changed his views, and accounted for 

 fossil shells found in the Alps, by suggesting that they were 

 Eastern species, dropped by the pilgrims on their return from 

 the Holy Land ! 



Buffon, in 1749, published his important work on Natural 

 History, and included in it his " Theory of the Earth," in 

 which he discussed, with much ability, many points in Geology. 



