42 The Founders of Geology LECT. 



means shared by the people themselves, for they refused 

 to believe that the Puys, which they had known from 

 infancy as quiet, well-behaved hills, had ever been anything 

 else, and they looked upon the learned doctor's descriptions 

 of the former eruptions as mere speculation of his own 

 manufacture. 



In taking leave of Guettard's scientific labours, I must 

 refer to one further essay of his, on account of its connec- 

 tion with his work among the old volcanoes of Auvergne. 

 Eighteen years after his memoir on these hills had been 

 read to the Academy, he published a paper " On the Basalt 

 of the Ancients and the Moderns." * The furious war over 

 the origin of basalt, of which I shall give some account in 

 another lecture, had not yet definitely begun. Various 

 writers had maintained that this rock is of volcanic origin, 

 and we might have supposed that Guettard's experience in 

 Auvergne would have led him to adopt this correct opinion. 

 So far from doing so, however, he entered into an elaborate 

 discussion to show that basalt could not be a volcanic rock. 

 He admitted that it is found among volcanic masses, but 

 he accounted for its presence there by supposing that in 

 some cases it was already in that position before the erup- 

 tions, in others that it had been laid down upon the lavas 

 after they had consolidated. " If a columnar basalt can be 

 produced by a volcano," he asks, " why do we not find it 

 among the recent eruptions of Vesuvius and other active 

 volcanoes ? " After reviewing all that had then been 

 written on the subject, he concludes that "basalt is a 

 species of vitrifiable rock, formed by crystallization in an 



1 Mtmoires sur differentes parties des Sciences et Arts, tome ii. p. 226 

 (1770). 



