1867.] Ice Marks in North Wales. 43 



difference of opinion among geologists about referring such pheno- 

 mena as I have hitherto been considering to the action of ice, 

 even though the countries where they occur no longer produce 

 glaciers. But on the question of the origin of Alpine Lakes, which 

 we have now to consider, there is no such unanimity. 



6th. Alpine Lakes. — It is only about five years since Pro- 

 fessor Eanisay propounded the startling theory that almost all the 

 lakes which form one of the greatest charms of our mountain 

 districts, were actually produced by that comparatively recent 

 irruption of thick-ribbed ice over a great part of the temperate 

 zone, which we can hardly contemplate without a thrill of horror ; 

 and that during the preceding warm tertiary epochs they were so 

 scarce as to form no important feature in the scenery of Europe. 

 A short and simple statement of this theory is as follows. In 

 all districts where glaciers have been proved to exist there are 

 numerous lakes. In exactly similar districts where there is no 

 trace of there having ever been glaciers, there are few or no lakes. 

 This holds good all over the globe. Glaciers wear away their beds, 

 as proved, — first, by the immense quantity of sediment in all glacial 

 streams ; secondly, by the existence of " roches moutonnees " where- 

 ever glaciers have passed. It can almost always be shown that the 

 old glaciers have passed over the exact spots where the lakes now 

 are, and the size of the lakes bears a general proportion to the 

 proved size of the old glaciers. This theory of the glacial origin 

 of Alpine lakes is now the great battle-ground of physical geologists. 

 In this country Eamsay, Jukes, Geikie, and Tyndall are its chief 

 supporters ; Sir Eoderick Murchison and Sir Charles Lyell, its chief 

 oj)ponents. Every year brings fresh evidence and new combatants ; 

 and as it is a question of such great interest, and at the same time 

 one rather of physical than of purely geological science, I shall 

 endeavour to give such an outline of the subject as may enable 

 the general reader to understand the question at issue and form his 

 own judgment upon it. 



The first point to be considered in explaining the origin of 

 lakes, is to form such a theory as shall not only show how such 

 and such particular lakes were or might have been formed, but shall 

 also account for then present actual distribution over the surface 

 of the earth. This may be learnt from good maps as well as by 

 personal observation, and is highly peculiar. In our own island 

 we all know that it is only in three mountainous districts that 

 lakes abound; in Wales, in Scotland, and in Cumberland. The 

 lakes of these districts amount to some hundreds. In Europe the 

 best known lake district is that of the Alps, which contains hundreds 

 of lakes and many of very large size. In the Scandinavian 



