MORAINES. 187 



ground; but in the middle and lower Alpine regions, where 

 water is frequently converted into ice and again melted, there is 

 is a more active breaking-up of the surface of the mountains. 

 Hence fragments of surrounding rocks fall frequently upon the 

 glaciers traversing these regions, and, remaining on the surface 

 of the glacier, are carried down by it towards the outlet of the 

 valley. 



Regular foci of destruction may be often observed, from which 

 many blocks of rock fall down every year upon a glacier ; and 

 as the glacier advances, the disintegrated fragments will not 

 collect into a heap of rubbish, but those of the previous year 

 will perhaps have been pushed forward some 300 feet, those of 

 two years before 600 feet, and so forth. They will consequently 

 form at the side of the glacier a more or less continuous wall, 

 which may be traced from their place of origin to its extremity, 

 and which will be higher in proportion to the number of points 

 from which it has received accessions. Every one who has 

 visited Swiss glaciers must have been struck with these walls of 

 debris, which are often several miles in length. In the Valais 

 they are called Moraines, in the Bernese Oberland Gandecken 

 and Guffer, and in the Canton of Glaris Firnstdss. Of these 

 popular names, the first, which was adopted by Charpentier, has 

 found general acceptance. 



Moraines are first formed at the edges of the glacier, bound- 

 ing its two sides, and are then called lateral moraines. They 

 rest upon the glacier, and are pushed forward with it. But if 

 the glacier melts at the sides and thus diminishes in volume, 

 the masses of rubbish are left on the slope of the valley-side, and 

 form walls upon the solid ground more or less distant from the 

 glacier, according as its melting has taken place to a greater or 

 less extent. The lateral moraines of the two sides of the glacier 

 remain quite separate on wide glaciers advancing in broad and 

 flat valleys ; but when the valleys become narrower, the moraines 

 approach nearer to each other, the central part of the glacier 

 moves more rapidly on, and the lateral moraines approach the 

 middle of the glacier. A similar effect is produced with timber 

 floating down a river, when the pieces of wood leave the banks 

 and collect in the central current. In the lower parts of the 

 glacier the lateral moraines widen and spread over the whole of 



