40 HISTORY OF GEOLOGY AND PALEONTOLOGY. 



followed the traces of the lava, and was thus guided to the ex- 

 tinct volcanoes in Auvergne, which had up to that time been 

 unknown in mineralogical science. His famous paper, entitled 

 "Sur quelques montagnes de la France qui ont ^te Volcans," 

 was presented at the Royal Academy of Sciences in 1752, and 

 published in 1756. His paper on basalt was published in 

 1770. 



Giraud Soulavie, abbot at Nimes, investigated the extinct 

 volcanoes in Vivarais, Velay, Auvergne, and Provence. His 

 chief book, Histoire naturelle de /a France mendionale (Nimes, 

 1780-84), gave an accurate description of the rocks of the 

 neighbourhood. In it Soulavie strongly advocated the vol- 

 canic origin of basalt, and described minutely the physical 

 peculiarities and the divisional planes of basalt rock. He also 

 made an attempt to determine a chronological succession of 

 the volcanic eruptions upon the basis (i) of the position of 

 the basaltic flows above or below rocks of other composition 

 and origin, (2) of the preservation of the scoriaceous and 

 slaggy surfaces, (3) of the variations in the height of the 

 extinct craters. Even although the succession drawn up by 

 Soulavie could not be other than faulty, owing to the ele- 

 mentary state of stratigraphical knowledge at that time, it was 

 a remarkable piece of work, and fully justifies for him a high 

 place amongst the geologists of the end of the eighteenth 

 century. His own contemporaries were inclined to see rather 

 the weaknesses than the excellences in the work of the country 

 abbot. Many of Soulavie's conceptions and observations have, 

 however, proved themselves to be eminently fruitful and valu- 

 able. 



Rouelle, a lecturer on chemistry, seems to have been an 

 exceptionally acute thinker. In a short introduction to a 

 series of lectures on chemistry, Rouelle touched on the origin 

 of the earth and the composition of its crust. He distinguished 

 "an old and a new earth." To the first he reckoned granite, 

 in the latter he placed all calcareous, argillaceous, and arena- 

 ceous rocks, together with the fossils contained in them. The 

 fossils were, he said, distributed in the succession of rocks in 

 a definite order of development, and these extinct forms had 

 differed in the different lands according to environment and 

 climate, just as the existing faunas and floras differ in different 

 localities at the present day. Rouelle further explained the 

 coal seams as accumulations of plants; the rough limestone 



