THE FORMATION OF MOUNTAINS. ■ 465 



band of claj, and at the same distance from each other. Before com- 

 pression the surface of the clay and the strata were completely hori- 

 zontal. Pressure gave rise at the top of the half-cylinder, a, to a val- 

 ley, c, formed by a twisting of the beds to the right, and by a little 

 mountain, d, to the left. But I do not believe that it has ever been 

 thought to assign to a valley an origin of this nature. 



" On the other semi-cylinder, &, is produced an enormous elevation 

 which has carried the ground to e, with such a rupture that the left 

 lip, f, g, has suifered a complete reversal by turning, as on a hinge, 

 around the horizontal line which passes by the point h. It follows 

 that the four upper strata of clay designated by the figures 1, 2, 3, 4, 

 being in a normal position before compression, are, after that, so ar- 

 ranged as to show the succession represented by the following arrange- 

 ment of figures : 1, 2, 3, 4, 4, 3, 2, 1, 1, 2, 3, 4, making the section of 

 this formation by a line drawn from x to z. If the left lip should dis- 

 appear we should then have between the points x and z the section 1, 

 2, 3, 4, 5, 1, 2, 3, 4, 5. Sections analogous to these, presenting inver- 

 sions in the order of strata, are known to geologists. 



" The forms assumed by the clay depend on several circumstances 

 which it is difficult to describe, such as the strength and the rate of 

 compression, the thickness and the greater or less plasticity of the 

 clay, etc. Why have accidents of tlie upper surface of the clay, whicli 

 are intimately connected with those of the interior of the mass, so 

 small an extension that they are not even similar in the two sides of a 

 band of clay ? This small continuity is owing to causes which we can 

 neither foresee nor appreciate. Is it not the same in nature ? Why is 

 the chain of the Alps not a true chain, but a succession of masses often 

 oblique with respect to each other? Why, in the Jura, do we see 

 chains which have for their prolongation plains and valleys? It is 

 always the case that the forms and structures obtained in these experi- 

 ments have an incredible resemblance to those which are found on the 

 surface of the globe. But it must be admitted that many of the latter 

 have not been reproduced by these artificial crushings. 



" It appears probable that, by pressures more powerful and more 

 variedly eraploj'ed, we might obtain again very different structures. 

 But I have not thought it necessary to multiply these experiments, 

 thinking that the varied forms which have resulted show sufficiently 

 the effects of crushing:." — Nature. 



