CHAP. XV. THEORY OF THE ORIGIN OF LAKE-BASINS. 309 



and small ones of limestone and serpentine, which, have been 

 brought down from Monte Eosa, through the gorge of Ivrea, 

 after having travelled for a distance of 100 miles. Confining 

 my attention to a part of the moraine where pieces of lime- 

 stone and serpentine wei'e very numerous, I found that no less 

 than one-third of the whole number bore unequivocal signs 

 of glacial action; a state of things which seems to bear some 

 relation to the vast volume and pressure of the ice which 

 once constituted the extinct glacier, and to the distance which 

 the stones had travelled. When I separated the pebbles of 

 quartz, which were never striated, and those of granite, mica- 

 schist, and diorite, which do not often exhibit glacial mark- 

 ings, and confined my attention to the serpentine alone, I 

 found no less than nineteen in twenty of the whole number 

 polished and scratched; whereas in the terminal moraines of 

 some modern glaciers, where the materials have travelled not 

 more than ten or fifteen, instead of a hundred miles, scarce 

 one in twenty even of the serpentine pebbles exhibits glacial 

 polish and striation. 



Theory of the Origin of Lake-hasins by the erosive Action of 

 Glaciers, considered. 

 Geologists are all agreed that the last series of movements 

 to which the Alps owe their present form and internal stx'uc- 

 ture occurred after the deposition of the miocene strata; and 

 it has been usual to refer the origin of the numerous lake- 

 basins of Alpine and sub-Alpine regions, both in Switzerland 

 and Northern Italy, to the same movements; for it seemed 

 not unnatural to suppose that forces capable of modifying 

 the configuration of the greatest European chain, by up- 

 lifting some of its component tertiary strata (those of marine 

 origin of the miocene period) several thousand feet above 

 their former level, after throwing them into vertical and 



