How rapidly some of these great earth-movements took place it is impossible at present to say; but in several cases it can be shown that they were quite slow, as indicated by the testimony of the rivers. Thus, the rise of the great Uintah Mountains of the Western States was so slow and gradual that the Green River, which flowed across the site of the range, so far from being turned aside as they rose up, has actually been able to deepen its cañon as fast as the mountains were upheaved. So that the two processes, as it were, kept pace with each other, and the river went on cutting out its gorges at the same time that the ground over which it flowed was gently upheaved; and as the land rose the river flowed faster, and therefore acquired more power to cut and deepen its channel. This is a valuable piece of evidence; but in this case we have only a few big broad folds, instead of the violent folding seen in the Alps. However, certain Pliocene strata lying on the southern flanks of the Himalayas show that the rivers still run in the same lines as they occupied before the last great upheaval took place. We have seen how the substance of the mountains was slowly manufactured by means of such quiet and gentle operations as may be witnessed at the present day; how the rivers of old brought down their burdens as they do now, and flung them into the sea; how the sea spread them out very slowly and compacted them into level layers, to form, in process of time, the hard rocky framework of the plateaux, hills, and mountains of the world; how vast marine accumulations were also slowly manufactured through the agency of countless generations of humble organisms, subtracting carbonate of lime from sea water to form the limestones of future ages; how by slow earth-movements these marine deposits were reared up into dry land; how they have frequently been penetrated by molten rocky matter from below, which occasionally forced its way up to the surface and gave rise to various volcanic eruptions, by means of which the sedimentary rocks were often considerably baked and hardened, and new fissures filled up with valuable metallic ores and precious stones; how lava-flows and great deposits of volcanic ash were mingled with these sedimentary rocks. Then we endeavoured to follow the history of these rocky layers after their upheaval, and learn how they are affected by the ceaseless operations of rain and rivers and other agents of destruction, so that finally the upheaved ridges of the lands are carved out into all those wonderful features of crag and pinnacle and precipice that give the mountains their present shapes and outlines. All this we were able to account for, without the aid of any imaginary or unnatural causes.