684 THE POPULAR SCIENCE MONTHLY. 



exactly like an ancient fortification. The characteristic features 

 of moraines are their position in valleys where there are other 

 indications of glacial action, their steep slopes and often level 

 tops, but especially their composition of earth, stones, and gravel, 

 with large fragments of rock irregularly scattered through them 

 from top to bottom without any sign of stratification, while usu- 

 ally one or more large blocks rest upon their summits in positions 

 where they could only have been left by the retreat of the glacier, 

 or possibly stranded from floating ice. Where extensive glaciers 

 have covered large areas of nearly level ground, the moraines 

 form great sheets extending for many miles, often concealing the 

 original contours of the country, and then receive the general 

 name of drift. The composition of drift is usually the same as 

 that of well-marked moraines, large blocks of stone being dis- 

 tributed throughout its mass. It is this which mainly distin- 

 guishes drift from alluvial or shore deposits, in which the ma- 

 terials are always more or less assorted and stratified ; but the 

 angular forms of many of the contained blocks and the striated 

 surfaces of others are also characteristic. Besides the terminal 

 moraines of extinct glaciers, lateral moraines are also left along 

 the slo^Des of open valleys from which glaciers have retreated. As 

 a whole, moraines are well distinguished from all accumulations 

 formed by water, and it has not been shown that any other 

 agency than glaciers is capable of forming them. In all recently 

 glaciated countries they are to be found more or less frequently, 

 and thus afford an excellent first indication of the former exist- 

 ence of glaciers. 



2. Smoothed and rounded rocks, called in Switzerland " roches 

 moutonn^es,^' from their supposed resemblance at a distance to 

 sheep lying down, are perhaps the most general of all the indi- 

 cations of glacial action. Every glacier carries with it, imbedded 

 in its under surface, numbers of rocks and stones, which, during 

 the slow but unceasing motion over its bed, crush and grind down 

 all rocky projections, producing in the end gently rounded or 

 almost flat surfaces even on the hardest and toughest rocks. In 

 many of the valleys of Wales, the Lake District, and Scotland 

 every exposed rock has acquired this characteristic outline, and 

 the same feature can be traced on all the rocky slopes, and often 

 on the summits of the lesser heights ; and the explanation how 

 these forms have been produced is not a theory only, but has been 

 observed in actual operation in the accessible portions of many 

 glaciers. Rocks and stones are to be seen imbedded in the ice 

 and actually scratching, grooving, and grinding the rock beneath 

 in their slow but irresistible onward motion. The rocky islets in 

 Windermere, Ullswater, and other lakes, as well as the Thousand 

 Islands of the St. Lawrence, are thus ice-ground ; and the amount 



