ii Desmarest on Volcanic History 67 



developing still further the ideas of denudation and suc- 

 cessive eruptive periods which had been briefly sketched 

 in his first communication. The scope of this new effort 

 may be judged of from its full title : " On the Determina- 

 tion of Three Epochs of Nature from the Products of 

 Volcanoes, and on the Use that may be made of these 

 Epochs in the Study of Volcanoes." This essay was laid 

 before the Academy in the year 1775. An extract from it 

 appeared after the lapse of four years, 1 but the full paper 

 was not published until the year 1806 2 no less than 

 thirty-one years after its original preparation. During this 

 long interval the controversy about the origin of basalt 

 had extended over most of the countries of Europe, and 

 had involved the very subjects of which Desmarest treated. 

 He himself, keenly as the matters in dispute interested 

 him, took no part in the warfare. In his memoir he ignores 

 the combatants and their strife, but quietly repeats and 

 strengthens statements which he had published a genera- 

 tion before, and which, had they been properly considered 

 and verified, would have prevented any controversy from 

 ever arising. I shall have more to say about this dispute 

 in my next lecture. In the meantime let us consider the 

 character of Desmarest's long-delayed contribution to the 

 literature and theory of geology. 



The progress of his investigations had led him to 

 perceive the necessity of correlating the various pheno- 

 mena connected with ancient volcanoes, and especially 

 with reference to the questions of their relative age and 

 of the alterations they have undergone from exposure to 



1 Journal de Physique, tome xiii. (1779), p. 115. 



2 Mem. de VInstit. des Sciences Math, et Phys. tome vi. (1806), p. 219. 

 It was read again on 1st Prairial, An XII (20th May 1804). 



