44 THE WORLD'S LUMBER ROOM. 



can come to the surface, and the water remains locked up 

 in its subterranean reservoirs; and where there are no 

 springs there are neither brooks, nor streams, nor rivers, 

 and the inhabitants must either sink wells, or catch and 

 store the rain as it falls. 



But it is as dust-makers that we must now consider the 

 springs, and in this capacity they are often very active. 



As they flow underground they tear up and carry away 

 in the form of mud some of the clay, &c., over which they 

 pass, thus undermining the rocks above, which in course 

 of time sink down or subside. But if the bed over which 

 the water flows be, as it often is, a sloping one, something 

 else is very apt to occur ; for if the upper beds be of sand, 

 chalk, or any other porous rock, they become so heavy 

 after much rain that large masses often slip down over the 

 greasy clay beneath, which, instead of offering any resistance, 

 helps them down just as the tallowed planks help to launch 

 a ship. 



Landslips of this kind have occurred at various places 

 along the English coast, and not long ago one took place at 

 Crich Cliff, near Matlock. The limestone of which the hill 

 consists rests upon a sloping bed of soft clay, which was 

 rendered softer and more slippery still by unusually heavy 

 rain. Cracks opened in the hill-side and in some cases 

 grew from a few inches to yards in width. Soon after, the 

 cliff was seen to be in motion, and great masses of lime- 

 stone, many tons in weight, dashed down the hill, with 

 a roar like thunder, and swept away the trees in their path 

 as if they had been so much grass. Many million tons of 

 rock were carried down in this way ; but though a landslip 



