Suppose that the melted materials within the earth are forced up against a mass of stratified deposits, the direction of the pressure being perfectly vertical, as represented in Figure 2. Such a pressure, if not too violent, would simply lift the strata out of their horizontal position into an arch or dome, (as in Figure 3,) and if continued or repeated in immediate sequence, it would produce a number of such domes, like long billows following each other, such as we have in the Jura. But though this is the prevailing character of the range, there are many instances even here where an unequal pressure has caused a rent at right angles with the general direction of the upheaval; and one may trace the action of this unequal pressure, from the unbroken arch, where it has simply lifted the surface into a dome, to the granite crest, where the melted rock has forced its way out and crystallized between the broken beds that rest against its slopes. [Illustration: Fig. 4.] [Illustration: Fig. 5.] In other instances, the upper beds alone may have been cracked, while the continuity of the lower ones remains unbroken. In this case we have a longitudinal valley on the top of a mountain-range, lying between the two sides of the broken arch (as in Figure 4). Suppose, now, that there are also transverse cracks across such a longitudinal split, we have then a longitudinal valley with transverse valleys opening into it. There are many instances of this in the Alleghanies and in the Jura. Sometimes such transverse valleys are cut straight across, so that their openings face each other; but often the cracks have taken place at different points on the opposite sides, so that, in travelling through such a transverse valley, you turn to the right or left, as the case may be, where it enters the longitudinal valley, and follow that till you come to another transverse valley opening into it from the opposite side, through which you make your way out, thus crossing the chain in a zigzag course (as in Figure 5). Such valleys are often much narrower at some points than at others. There are even places in the Jura where a rent in the chain begins with a mere crack,--a slit but just wide enough to admit the blade of a knife; follow it for a while, and you may find it spreading gradually into a wider chasm, and finally expanding into a valley perhaps half a mile wide, or even wider.