ii Desmaresis Discovery in Auvergne 57 



and observed that they were planted on a bed of scoriae 

 and burnt soil, beneath which lay the old granite that 

 forms the foundation rock of the region. He noticed still 

 more perfect prisms a little further on, belonging to the 

 same thin cake of dark stone that covered the plain which 

 leads up to the foot of the great central puy. 



Every year geological pilgrims now make their way to 

 Auvergne, and wander over its marvellous display of cones, 

 craters and lava-rivers. Each one of them climbs to the 

 plateau of Prudelle, and from its level surface gazes in 

 admiration across the vast fertile plain of the Limagne on 

 the one side, and up to the chain of the puys on the other. 

 Yet how few of them connect that scene with one of the 

 great triumphs of their science, or know that it was there 

 that Desmarest began the observations that directly led to 

 the fierce contest over the origin of basalt. 



That cautious observer tells us that amidst the infinite 

 variety of objects around him, he drew no inference from 

 this first occurrence of columns, but that his attention was 

 aroused. He was kept no long time in suspense on the 

 subject. " On the way back from the Puy de Dome," he 

 tells us, "I followed the thin sheet of black stone and 

 recognised in it the characters of a compact lava. Con- 

 sidering further the thinness of this crust of rock, with its 

 underlying bed of scoriae, and the way in which it extended 

 from the base of hills that were obviously once volcanoes, 

 and spread out over the granite, I saw in it a true lava- 

 stream which had issued from one of the neighbouring 

 volcanoes. With this idea in my mind, I traced out the 

 limits of the lava, and found again everywhere in its thick- 

 ness the faces and angles of the columns, and on the top 



