122 THE WONDERFUL CENTURY. CHAP. xn. 



mit of a moraine, or, in the case of lateral moraines, on 

 the very edge of a precipice in positions where no known 

 agency but ice could have deposited them. These are 

 called " perched blocks." Drifts or glacial gravels are 

 deposits of material similar to that forming the moraines, 

 but spread widely over districts which have formerly 

 been buried in ice. These are often partially formed of 

 stiff clay, in which are embedded quantities of smoothed 

 and striated stones; but the great characteristic of all 

 these ice-products is that the materials are not stratified, 

 that is, sorted according to their fineness or coarseness, 

 as is always the case when deposited by water, but are 

 mingled confusedly together, the large stones being 

 scattered all through the mass, and usually being quite 

 as abundant at the top as at the bottom of the deposit. 

 Such deposits are to be found all over the north and 

 northwest of our islands, and are often well exhibited in 

 railway cuttings; and wherever they are well developed, 

 and the materials of which they consist differ from those 

 forming the underlying rocks, they are an almost in- 

 fallible indication of the former existence of a glacier or 

 ice-sheet. 



(2) The smoothed and rounded rocks called in Switzer- 

 land roches mouionnees, from their resemblance at a dis- 

 tance to recumbent sheep, are present in almost all 

 recently glaciated mountainous countries, especially 

 where the rocks are very hard. They are to be seen in 

 all the higher valleys of Wales, the Lake District, and 

 Scotland, and on examination are found to consist often 

 of the hardest and toughest rocks. In other cases the 

 rock forming the bed of the valley is found to be planed 

 off smooth, even when it consists of hard crystalline 





