Now, in this case the earth-movements caused great cracks, or splits, doubtless attended by fearful earthquakes. We find here a series of nearly parallel fractures, hundreds of miles long, and fifteen to thirty miles apart. These traverse the entire region, dividing the rocks into long narrow blocks. There is evidence to show that the whole region was once much more elevated than it is now, and has subsided thousands of feet. During the subsidence along these lines of fracture, or faults, the blocks were tilted sideways; and the uptilted blocks, carved by denudation, form the isolated ranges of this very interesting region (see illustration, chap. viii., p. 273, Fig. 1). The faults are indicated by arrows pointing downwards; and the dotted lines indicate the erosion of the uptilted blocks. But this must be regarded as a very exceptional case, for we do not know of any other mountain-range formed quite in the same way. Why the strata, although only slightly bent, should have snapped so violently in this case, while in other mountain-ranges they have suffered much more bending without so much fracture and displacement, we cannot tell, but can only suggest that possibly it was because they were not buried up under an enormous thickness of overlying rocks, which would exert an enormous downward pressure, and so tend to prevent fracturing. There are many other deeply interesting questions with regard to the upheaval of mountains which at present cannot be answered. We have already learned to alter our preconceived ideas about the stability and immovable nature of the earth's crust, and have seen that it is in reality most unstable, and is undergoing continual movements, both great and small. But here we have an equally startling discovery, which quite upsets all our former ideas of the hard and unyielding nature of the rocks composing the earth's crust; for we find that not only can they be bent into innumerable folds and little puckerings, but that in some cases they have been drawn out and squeezed as if they were so much soft putty. The imagination almost fails to grasp such facts as these. Of late years geologists in Switzerland and in Great Britain have discovered that in some parts of mountains rocks have been enormously distorted and crushed, so that they have assumed very different states from those in which they were made, and curious mineral changes have taken place under the influence of this crushing.