256 ANNUAL OF SCIENTIFIC DISCOVERY. 



west, and then partly west, scooped out the hollow of the Lake of 

 Geneva most deeply in its eastern part, opposite Lausanne, where 

 the thickness and the weight of ice, and consequently its grinding 

 power, were greatest." 



The lakes of Thun and Brienz lie in the course of the great Aar 

 glacier, those of Zug and the Four Cantons in that of Altorf, the 

 Lake of Zurich lies in that of the Linth, the Lake of Constance in 

 the course of the prodigious glacier of the Rhine valleys, the numer- 

 ous little rock-basin lakes near Ivrea in the line of the glacier of the 

 Val d'Acosta, and those of Maggiore, Lugano, and Como, in the 

 courses of the two gigantic glacier-areas that drained the mountains 

 between Monte Rosa and the Sondrio. 



The sizes of the lakes and their depths were then shown to be, in 

 several cases, proportional to the magnitude of the glaciers that 

 ground out the basins in which they lie, and to the circumstances 

 whether the pressure of ice was broadly diffused, or vertical as in 

 narrow valleys. 



Finally, it was shown that rock-basins holding lakes are always ex- 

 ceedingly numerous in and characteristic of all countries that have 

 been extensively glaciated. Lakes are comparatively few in the south- 

 ern half of North America, but immediately south and north of the 

 great lakes and the St. Lawrence the whole country is moutonnee and 

 striated, and is also covered with a prodigious number of rock-basins 

 holding water. The same is the case in the north of Scotland, the 

 whole area of which has been moulded by ice ; and east of the Scandi- 

 navian chain, in another intensely glaciated region, the country is 

 covered by innumerable lakes. 



THE ORIGIN OF THE EXTERNAL FEATURES OF THE LAND. 



In a paper on the above subject presented to the British Associa- 

 tion, by Prof. Jukes, President of the Geological Section, the author 

 asked, in the first instance, how the variations of the surface called 

 mountains, hills, cliffs, glens, valleys, and plains, were formed. He 

 took, first, the formation of great plains, and showed that although 

 gome were formed as plains on horizontal beds, few even of these 

 retained the original surface of the position, but had more or less a de- 

 nuded surface. Many equally level plains were low and level because 

 mountainous masses of rock, often greatly disturbed and contorted, 

 had been removed from above the present surface. The central plain 

 of Ireland, and other plains in the British Islands, were formed in 

 this way. All mountains, except volcanoes or " hills of ejection," 

 were either "hills of circumdenudatiou," formed by the wearing 

 down and removal of the rocks formerly around them, or " hills of 

 uptilting." In the latter, the lowest rocks appeared in the central 

 parts of the chain, often reared into the highest peaks, and these 

 central beds dip on either hand under higher and higher groups, 

 which come in as we recede from the axis of the chain. The beds 

 have been raised by mechanical force acting from below ; but this, 

 however it had tilted or bent them, could not remove them, so that 

 the successive exposure of lower and lower beds as we approach the 

 axis of the chain must be owing to the external erosion of moving 



