56 The Founders of Geology LECT. 



basalt and lava, and this opinion was general in his time. 

 The basalts of Central and Western Europe were usually 

 found on hill tops, and displayed no cones or craters, or 

 other familiar sign of volcanic action. On the contrary, 

 they were not infrequently found to lie upon, and even to 

 alternate with, undoubted sedimentary strata. They were, 

 therefore, not unnaturally grouped with these strata, and 

 the whole association of rocks was looked upon as having 

 had one common aqueous origin. It was also a prevalent 

 idea that a rock which had been molten must retain obvious 

 traces of that condition in a glassy structure. There was 

 no such conspicuous vitreous element in basalt, so that this 

 rock, it was assumed, could never have been volcanic. 1 As 

 Desmarest afterwards contended, those who made such 

 objections could have but little knowledge of volcanic 

 products. 



We may now proceed to trace how the patient and 

 sagacious inspector of French industries made his memor- 

 able contribution to geological theory. It was while travers- 

 ing a part of Auvergne in the year 1763 that he detected 

 for the first time columnar rocks in association with the 

 remains of former volcanoes. On the way from Clermont 

 to the Puy de Dome, climbing the steep slope that leads 

 up to the plateau of Prudelle, with its isolated outlier of a 

 lava-stream that flowed long before the valley below it 

 had been excavated, he came upon some loose columns of 

 a dark compact stone which had fallen from the edge of 

 the overlying sheet of lava. He found similar columns 

 standing vertically all along the mural front of the lava, 



1 See for instance Wallerius' Mineralogia, (1773) i. p. 336, replied to 

 by Desmarest, Mtm. Acad. Roy. Sciences (1774), p. 753. 



