462 



THE POPULAR SCIENCE MONTHLY. 



covered with a layer of potter's clay in a pasty condition, the thickness 

 of which varied, according to the experiments, from 35 to 60 mm. It 

 will be seen from the dimensions indicated that pressure would dimin- 

 ish the length of the band of clay by one third. This pressure has been 

 exerted on certain mountains of Savoy. For example, the section 

 which I have given * of the mountains situated between the Pointe- 

 Percee and the neighborhood of Bonneville enables it to be seen that 

 those folded and contorted strata which are shown between Dessy and 

 the Col du Grand Bernard cover a length which is two thirds of that 

 which they had before compression. These mountains, then, have been 

 subjected, like the potter's clay, to a compression indicated by the ratio 

 of 60 to 40. Contortions are not, perhaps, observed over all the sur- 

 face of the globe ; it has not been equally folded in all its extent, but 

 they are found in a great number of countries, and even beneath strata 

 almost horizontal. Sometimes the folds approach the vertical, and are 

 close against each other ; this structure indicates that pressure has 

 been exercised in a stronger manner than I have indicated. 



" These powerful lateral thrusts of the external and solid parts of 

 the globe appear to result from a diminution which the radius of the 

 interior pasty or fluid nucleus has undergone during millions of ages. 

 It may have been sufficiently great to cause the solid crust (v/hich 

 must always have been supported on the interior nucleus, whose vol- 

 ume continually diminishes) to assume the forms which we know, with 

 a slowness equal to that of the contraction of the radius. 



Fig. 3. 



" To return to my experiments. At the extremities of the band of 

 clay are pieces of wood or supports, which accompany it in its move- 

 ment of contraction. The clay is thus compressed at once by its adhe- 

 sion to the caoutchouc and by lateral pressure of the supports. By 



' "Bulletin Soeiete Geologique de France," 1875, t. iii., pi. xxii. A. Favre, " Be- 

 cherches Geologiques," Atlas, pi. ix. 



