46 HISTORY OF GEOLOGY AND PALAEONTOLOGY. 



representing rock formed from a completely molten magma. 

 In spite of Desmarest's mistaken views about the relationship 

 of basalt to porphyry and granite, he was the first clear 

 exponent of the igneous origin of these rocks. He was 

 besides a pioneer in the comparative method of study- 

 ing the igneous rocks. Papers confirming Desmarest in his 

 estimate of the igneous origin of basalt, porphyry, and 

 granite were contributed by Raspe in Hesse, by Professor 

 Arduino in Padua, and by Mr. Strange, the English consul 

 in Venice. 



Faujas de Saint-Fond (1742-1819), Professor in the 

 Museum of Natural History in Paris, brought forward 

 conclusive evidences of the igneous origin of basalt in his 

 famous work entitled, On the Extinct Volcanoes of Vivarais 

 and Velay. The work contains a detailed mineralogical 

 investigation of the ejected material of active volcanoes, and 

 compares them with the rocks present in Vivarais and Velay. 

 In the course of his journeys in Southern France he found 

 a volcanic tuff identical with the Pozzuolo earth, and 

 established the flourishing industry of the preparation of 

 cement. Saint-Fond's descriptions and illustrations of the 

 extinct volcanoes in Vivarais and Velay are excellent, and 

 have scarcely been surpassed in later publications. 



The fearful earthquake which destroyed Lisbon in 1755 was 

 made the subject of a large number of scientific inquiries 

 into the causes of earthquakes. William Stukeley's theory, 

 attributing earthquakes to electrical disturbances, gained a 

 certain amount of support abroad. Another Englishman, Mr. 

 Michell, suggested that the sudden expansion of vapours 

 enclosed in fissures and cavities of the earth's crust caused 

 earthquakes and volcanoes, the upheaval of mountain-systems, 

 and the deformation of the rocks. 



THIRD PERIOD THE HEROIC AGE OF GEOLOGY, 

 FROM 1790 TO 1820. 



The characteristic features of this age, and that which gave 

 it a rejuvenating significance in the development of geology, 

 was the determined spirit that prevailed to discountenance 

 speculation, and to seek untiringly in the field and in the 

 laboratories after new observations, new truths. 



