104 



NATURE 



\_Dec. 5, 1878 



tion in the length of the radius of our globe, and yet 

 there result elevations of the ground in the midst of this 

 general depression. 



The cause of lateral crushing, M. Favre goes on to 

 say, is owing to the cooling of the earth. It is, in fact, 

 very probable that our globe is at the stage when, 

 according to Elie de Beaumont, " the mean annual cool- 

 ing of the mass exceeds that of the surface, and exceeds 

 it more and more." It must follow that the external 



strata of the globe, tending"ahvays to rest on the internal 

 parts, are wrinkled, folded, dislocated, depressed at 

 certain points, and elevated at others. 



"The experiments," M. Favre continues, "which I 

 have made at the works of the Geneva Society for the 

 manufacture of physical instruments, resemble much 

 those of Sir James Hall ; they differ notably, however, 

 in two points : — i. The celebrated Scotchman caused the 

 matter which he wished to compress to rest on a body 



Fic 



which itself could not be compressed, while I placed the 

 layer of clay employed in these experiments on a sheet 

 of caoutchouc, tightly stretched, to which I made it 

 adhere as much as possible ; then I allowed the caout- 

 chouc to resume its original dimensions. By its con- 

 traction the caoutchouc would act equally on all points 

 of the lower part of the clay, and more or less on all the 

 mass in the direction of the lateral thrust. 2. Hall com- 

 pressed, by a weight, the upper surface of the body 



which he wished to wrinkle, which prevented any deform- 

 ation, while by leaving that surface free, I have seen,;, 

 during the experiment, forms appear similar to those of' 

 hills and mountains which may be observed in various- 

 countries." 



" The arrangement of the apparatus is very simple. A 

 sheet of india-rubber 16 mm. in thickness, 12 cm. broad,, 

 and 40 cm. long, was stretched, in most of the experi- 

 ments, to a length of 60 cm. This was covered with a. 



Fig. 2. 



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

 of which varied, according to the experiments, from 25 

 to 60 mm. It will be seen from the dimensions indicated 

 that pressure would diminish 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-Percde and the neighbourhood of Bonneville 



' Bullet. Society G{ologiqiie de France, 1S7S, 

 Recherches Gfologiqncs, Atlas, pi. i.\. 



pi. xxii. A. Favre, 



enables it to be seen that those folded and contorted strata 

 which are shown between Dessy and the Cal du Grand 

 Barnaud 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 surface 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 



