i Guettard*s Phy Biographical Geology 29 



the efficacy of moving water in altering the face of the 

 land. At the very beginning of it, he starts with a remin- 

 iscence from the scenes of his infancy, and weaves it into 

 the story he has to tell of the ceaseless degradation of the 

 terrestrial surface. He remembers a picturesque crag of 

 the Fontainebleau sandstone which, perched above the 

 slopes of a little valley, had been worn by the weather 

 into a rudely-formed female figure holding an infant, and 

 had been named by the peasantry the Rock of the Good 

 Virgin. That crag, under which he used to play with his 

 schoolmates, had in the interval of less than half a century 

 gradually crumbled away, and had been washed down to 

 the foot of the declivity. In the same neighbourhood he 

 had noticed at successive visits that prominent rocks had 

 made their appearance which were not previously visible. 

 They seemed, as it were, to start out of the ground, yet he 

 knew that they arose simply from the removal of the 

 material that once covered them. In like manner ravines 

 of some depth were in the course of a few years cut out of 

 ground where there had before been no trace of them. In 

 these striking examples of the general disintegration he 

 sees only the continual operation of "gentle rains and 

 heavy downpours." * 



From illustrations supplied by his own earliest observa- 

 tion, he passes on to others drawn either from his personal 

 researches or his reading, and exemplifying the potent 

 influence of heavy rains and flooded streams. Not only 

 are the solid rocks mouldering down and strewing the 

 slopes below with their debris, but the sides of the hills 

 are gashed by torrents, and narrow defiles are cut in them, 



1 "Des pluies et des averses," op. cit. p. 210. 



