324 PICTURESQUE SKETCHES 



more regular, more widely spread, and more cha- 

 racteristic beds of gravel than the Alpine rocks > 

 whose range is, in every respect, more limited. 



The whole subject of the distribution of gravel is, 

 however, one abounding in difficulties which have 

 as yet been only partially explained. Besides as- 

 suming the action of great waves acting for a very 

 short time immediately after an earthquake shock, 

 and propelling a mass of broken rock with irresist- 

 ible power at a rapid rate for a short distance, some 

 geologists have called in the aid of marine currents. 

 The action of the waves on an ordinary coast-line is 

 also itself sufficient to account for many even of the 

 more striking phenomena. While these causes, ana- 

 logous to those now in action, are thought by some 

 geologists sufficient to explain the facts, others again 

 have resorted to ice in some form as the only agent 

 capable of solving the problem. One theory connected 

 with ice is indeed only more improbable than it is 

 bold and ingenious, its author and supporters as- 

 suming the whole of that part of the earth on which 

 gravel is now found to have been once actually be- 

 neath a frozen surface, and to have been traversed by 

 glaciers, such as those which in the Alps produce 

 very similar and analogous appearances. There are 

 certainly, however, no sufficient grounds for believing 

 that true glaciers have ever covered Europe, since 

 there is no evidence of the existence of mountain 

 chains from which they could have proceeded. 



Although these authors, misled by partial observa- 

 tion, have thus limited the action of ice to glaciers, 

 or frozen streams descending from mountain sides 

 and moving along on the plains, simply from the 



