Another striking feature of many glacial valleys is a very marked want of continuity in the slope of the main valley. Not only do the side valleys "hang" over the main valleys, but, further, this main valley itself often consists of relatively level reaches alternating with rocky bars, through which the river has sometimes later cut a gorge. Examples of this are very frequent. The famous gorge of the Aar above Meiringen is a river gorge cut through a rocky bar of this kind. The Pyrenees are somewhat less familiar, both to tourists and in the form of pictures, but there, also, the same thing occurs. Above the health resort of Cauterets lies the little Lac de Gaube, whose mouth is blocked by a rocky bar through which the little torrent is cutting a tiny gorge. If the tourist crosses the lake in a boat and begins to walk up the valley above it, he will find that it has the form of a staircase, the huge steps being separated from one another by broad plateaux, which are flat and swampy, and have obviously been occupied by lakes not long ago. Above each plateau there is a rocky wall, almost precipitous, down which the stream flows in cascades. In other parts of the Pyrenees the same phenomenon occurs, and the lakes sometimes persist, lying one above the other in a series. [Illustration: Fig. 9.--Profile of the Maderaner thal in Switzerland, to show the staircase arrangement peculiar to recently glaciated valleys. (From Garwood.)] The phenomenon is so common that it markedly affects human life in the Alps. The "landings," as the French call them, usually afford good pasture ground, while those which lie at no great elevation can be cultivated. Further, as the ground is level there is room for houses or even for a considerable village. The intervening region or step is too rocky to give level ground for human habitations or for pasture and cultivation. Where the river has had time to cut a gorge, the road must leave the stream, and can often be constructed only with difficulty. The result is that an Alpine valley often consists of a chain of villages, linked together by a difficult mule track or path. The abundant water-power, however, makes mechanical traction relatively easy, and we have sometimes the curious condition that a mule track is replaced by a railway, without the intervention of a road fit for wheeled traffic.