Thus in the geological history of the Scottish Highlands we may trace the successive phases through which many other elevated tracts have passed. The Scandinavian plateau, and many of the mountains of middle Germany--such, for example, as the Harz, the Erzgebirge, the Thüringer-Wald, etc.--show by their structure that they have undergone similar changes. First we have an epoch of mountain-elevation, when the strata are squeezed and crushed laterally, fractured and shattered--the result being the production of a series of more or less parallel anticlines and synclines, or, in other words, a true mountain-chain. Next we have a prolonged period of erosion, during which running water flows through synclinal troughs, works along the backs of broken and shattered anticlines, and makes its way by joints, gaping cracks, and dislocations, to the low grounds. As time goes on, the varying character of the rocks and the mode of their arrangement begin to tell: the weaker structures are broken up; rock-falls and landslips ever and anon take place; anticlinal ridges are gradually demolished, while synclines tend to endure, and thus grow, as it were, into hills, by the gradual removal of the more weakly-constructed rock-masses that surround them. Valleys continue to be deepened and widened, while the intervening mountains, eaten into by the rivers and their countless feeders, and shattered and pulverised by springs and frosts, are gradually narrowed, interrupted, and reduced, until eventually what was formerly a great mountain-chain becomes converted into a low-lying undulating plain. Should the region now experience a movement of depression, and sink under the sea, new sedimentary deposits will gather over its surface to a depth, it may be, of many hundreds or even thousands of feet. Should this sunken area be once more elevated en masse--pushed up bodily until it attains a height of several thousand feet--it will form a plateau, composed of a series of horizontal strata resting on the contorted and convoluted rocks of the ancient denuded mountain-chain. The surface of the plateau will now be traversed by streams and rivers, and in course of time it must become deeply cleft and furrowed, the ground between the various valleys rising into mountain-masses. Should the land remain stationary, its former fate shall again overtake it; it will inevitably be degraded and worn down by the sub-aërial agents of erosion, until once more it assumes the character of a low-lying undulating plain.