Page:Popular Science Monthly Volume 14.djvu/480

464 ("Transactions R. S. E.," vol. vii., 1813), and to that of the Petit Bernard in Savoy (Favre, "Recherches," pi. x.); at b is a valley open at one of its ends and almost closed at the other; at e is a vault almost straight, the prolongation of which is very level; at g, h, and l are vaults twisted and a little broken, while at i is a broken fold, the curves of which are almost vertical. All these accidents of the ground recall those which have been so often observed in the Jura, the Alps, and the Appalachians.

Fig. 2 represents a band of clay whose thickness was about 40 mm. before compression and 65 after. We remark contortions similar to those of the preceding figure, among others a vault a, very exactly formed. At distances are seen vertical slices, on which the pressure appears to have acted in a particularly energetic fashion, and which may be called "zones de refoulement"; the strata are there broken in an exceptional manner, often separated from each other. One of these vaults is replaced by a single vault on the opposite side of the band of clay.

Before compression, in the band of clay in Fig. 3, were seen the two divisions which are seen there now—that in the right was 33 cm. long and 25 mm. thick at a, and 35 at b; the left division was 25 cm. long and 65 mm. thick. A gentle slope united the part c to the part b. After compression, the mean height of a b was 45 and that of c 75 mm. All the layers were spread horizontally.

"In this experiment I have sought to imitate the effect of crushing at the limit of a mountain and a plain. The height of the mountain c has been notably increased, the five or six upper layers have advanced on the side of the plain; they encroach on it. The plain has, however, offered a resistance sufficiently great to cause the strata of the mountain to be strongly inflected at the bottom. From this struggle between the plain and the mountain there resulted a cushion, d, which is the first hill at the foot of the height. It also resulted that the strata of the plain assumed an appearance of depression at contact with the mountain in consequence of the vault which is formed at b; they plunge underneath the mountain. This resembles what is often seen in the Alps at the junction of the first calcareous chain and the hills of 'mollasse'; in fact, the strata of the latter rock seem to plunge under those of the neighboring heights. In consequence of the pressure, there are formed several ranges of hills in the plain between b and a.

"In Fig. 4 the band of clay had, before compression, a thickness of 45 mm.; after that the culminating point was more than 10 cm. I have here sought to represent what must happen when terrestrial pressure is exerted on horizontal strata still moist, deposited at the bottom of a sea where are two mountains already solidified. For this purpose I placed in the caoutchouc and under the clay two bare cylinders of wood, a and b, of about 35 mm. radius, at 20 cm. from the ends of the