100 HISTORY OF GEOLOGY AND PALEONTOLOGY. 



and basalt rock; but as Hall's experiments had shown that 

 basalt when melted could again solidify in crystalline form, he 

 supposed that the lavas of Vesuvius represented a pre-existing 

 basalt of aqueous origin which had been melted in the 

 earth's crust and ejected as lava. In other cases, for example 

 at Solfatara, the lava might not be basaltic in character, and 

 might have some other origin- In the same letter he gave a 

 description of the definite sequence in the eruptive phenomena 

 of Vesuvius. The eruptions, he said, begin with earthquakes, 

 radial fissures form on the slopes of the mountains, and lava 

 wells out; then the pent-up steam and vapours burst forth 

 from the central vent with explosive force and noise, throwing 

 into the air enormous masses of ashes and fragmentary scoriae 

 amidst dust and smoke. After the crater is emptied, quiet is 

 regained, the exhalations of injurious gases marking the final 

 stages of a spent volcanic outburst. 



While our scientific knowledge of volcanoes was derived in 

 great measure from Italy, that country also was the scene of the 

 series of earthquake shocks which convulsed Calabria in 1783. 

 Great importance is attributed to the Calabrian earthquake 

 in scientific literature, from the circumstance that many of 

 the observers present in Calabria during the disturbance, or 

 immediately after it, were experienced men of science, and 

 their vivid descriptions and accurate observations and drawings 

 afforded the first circumstantial scientific account of earthquake 

 phenomena. 



D. France, Belgium, Holland, and the Iberian Peninsula. 

 During the eighteenth century France had fallen behind 

 Great Britain, Germany, and Italy in the pursuit of geology 

 and palaeontology, but the influence of Buffon revived a 

 warmer interest in these studies. Scarcely any other country 

 in Europe offers such a fine field for geological studies as 

 France. Apart from the Pyrenees, Alps, Brittany, and the 

 Ardennes, the stratigraphy of French districts is comparatively 

 simple, and the strata abound with a wealth of well-preserved 

 fossil remains. In addition, there is the wonderful Auvergne 

 district, with its groups of extinct volcanoes, discovered by 

 Guettard in 1752. 



Desmarest was the French geologist whose genius disclosed 

 the full significance of these extinct volcanoes and made 

 Auvergne famous. In 1763 he observed on the plateau of 



