Ch. XII.] MORAIXIC LAKES. 171 



where we behold proofs that the glacier, by the aid of sand and peb- 

 bles, can grind down, polish, and plane the bottom ; bnt it seems in- 

 capable of doing more, although the fundamental rocks must in dif 

 ferent places, be of very unequal hardness. It is also well known that 

 at certain points in the course of some of the principal glaciers of the 

 Alps, transverse rents in the ice, or crevices, several feet wide and of 

 great number and depth, occur, which are referred by geologists to 

 inequalities in the ground below, over which the icy mass is pushed. 

 In such instances, though the ice moves on and the old crevices close 

 up, others of precisely the same form and dimensions are renewed 

 every year, century after century, in the same place, implying that 

 even where the declivity is very great, and the propelling force from 

 behind enormous, the ice cannot saw through and get rid of the ob- 

 stacles which impede the freedom of its onward march. 



When we are endeavoring to form sound opinions as to the rela- 

 tion of the frequency of lake-basins to an antecedent glacial period, 

 we must not forget that such basins, large and small, are met with in 

 all latitudes, and that there are lacustrine deposits of all geological 

 epochs, attesting the existence of lakes at times when no one is dis- 

 posed to attribute them to the agency of ice. In Central France, for 

 example, in the Miocene and Eocene periods, there were lakes of con- 

 siderable dimensions when the climate, like that of the preceding 

 Cretaceous era, was sub-tropical. It would, indeed, be the most per- 

 plexing of all enigmas if we did not find that lake-basins were now, 

 and had been at all times, a normal feature in the physiognomy of the 

 earth's surface, since we know that unequal movements of upheaval and 

 subsidence are now in progress, and were going on at all former geo- 

 logical periods. 



It needs but little reflection on this subject to discover that, when 

 such changes of level are in progress, some of the principal valleys can 

 hardly fail to be converted in some parts of their course into lakes of 

 considerable magnitude. To escape such a result we should have to 

 assume that the greatest elevatory movement always conforms to the 

 central axis of every chain, or, what would be still more singular, 

 that it concides in direction with every water-shed. Occasionally, no 

 doubt, there would be such a coincidence, and if so, the upheaval, in- 

 stead of interfering with the drainage and damming back the rivers, 

 would, by increasing the fall of water, tend even to obliterate such 

 lakes as preexisted. But sometimes upheaval will be in excess in the 

 lower part of the valley, and at other times (which would equally pro- 

 duce lake-basins) there would be an excess of subsidence in the higher 

 region, the alluvial plains below sinking at a less rapid rate, or being, 

 perhaps, stationary. 



When controverting, in 1863, in the first edition of my " Antiquity of 

 Man" (p. 316), Professor Ramsay's hypothesis of the scooping out by 

 ice of long and deep cavities like those containing the Swiss and Ital- 

 ian lakes, I proposed to substitute for his ice-agency the theory of 



