INTRODUCTION. 39 



areas. One of the most notable workers was the versatile 

 Guettard, 1 who travelled through France, England, Germany, 

 and Poland, and whose great desire it was to reproduce his 

 scientific observations on maps. 



Guettard's mineralogical map of France and England r 

 naturally cannot compare with the present Geological Survey j 

 maps ; but it certainly gives so much accurate information j 

 regarding the local occurrence of rocks and minerals, and the ' 

 position of mines, quarries, fossil localities, mineral springs, 

 hot springs, coal, etc., that it can still be used with advantage. 

 The map is not coloured. The accompanying text refers only 

 in a very meagre and unsatisfactory manner to the strati- 

 graphical succession of the rocks. 



It was a pet scheme of Guettard's to publish a mineralogical } 

 atlas of the whole of France. This gigantic plan was never \ 

 completed; Guettard, in collaboration with his colleague, the 

 chemist Lavoisier, published twenty-nine parts, and Monnet, 

 in 1780, added thirty-one farther sheets. Indirectly, this idea 

 of Guettard's was productive of very important results, for the 

 preparation of the maps demanded an energetic search in the 

 open field for the necessary data. The enthusiasm of Guettard 

 inspired others, and there rapidly appeared a large number of 

 scientific papers on the mineralogical features of different 

 French terrains. One very interesting paper gives an enthusi- 

 astic account of the neighbourhood of Paris, its rocks, its 

 minerals, and a large number of fossils. 



Guettard described the processes of land denudation effected 

 by the solvent and destructive agency of rain and rivers, and 

 by the abrasion of the waves. This is probably the first paper 

 in which a systematic account of denudation is given in its 

 relation to changes in the configuration of the earth's surface. 

 But the most brilliant of Guettard's achievements was his 

 discovery of the volcanic rocks in the Auvergne region. 



In 1757 he was journeying to Moulins and Riom, when he 

 observed that black stones were very common on the roads 

 and in buildings. Recognising that these were fragments of 

 volcanic lava, Guettard, accompanied by his friend Malesherbes, 



1 Jean Etienne Guettard (1715-86), son of an apothecary, while still a 

 boy displayed a passion for natural history, especially for botany ; studied 

 medicine in Paris, afterwards accompanied the Duke of Orleans on his 

 travels, and was made keeper of his natural history collections. In 1734 

 he was elected a member of the French Academy. 



