44 



GEOLOGY OF LA SALLE COUNTY. 



The g-lacier — moving- ice — seems to be the only 

 ag*ent adequate to the transportation of such enor- 

 mous masses, for that they have been carried long- 

 distances there is no doubt. There are no beds 

 of g-ranite nearer than central Wisconsin, none of 

 hornblendyte, iron-jasper and copper-bearing- rocks 

 nearer than northern Wisconsin and the upper 

 peninsula of Michig-an. There are distances of from 

 100 to 400 miles, some of it rather roug-h country 

 to be passed over, and the carriag'e of a block of 

 100 tons weig-ht over it would today be attended 

 with some difficulty. 



But if we suppose a g^reat g-lacier, or rather 

 mer de g-lace, to have covered that part of Canada 

 lying- west of Hudsons bay, extending- to the 

 Rocky mountains on the west and on the south to 

 lake Winnipeg- and the north shore of lake Supe- 

 rior, and having- a thickness of 2,500 to 3,000 feet 

 or more at the central part, we shall have an ade- 

 quate cause of the very strange phenomena con- 

 nected with the drift. 



A depth of ice of 2,500 feet may seem preposter- 

 ous, but we have masses of ice in the Alps as thick as 

 this, and probabh' much thicker, and the g-reat g-laciers 

 of Alaska front the sea with cliffs of ice more than 300 

 feet hig-h, and as the surface slopes upward as we 

 g-o inland they are probably at a distance from the 

 coast much thicker than on the sea face. Besides, 

 the conditions being- favorable, the formation of beds 

 of snow and ice 2,500 to 3,000 feet thick mig-ht occupy 

 a comparatively short time, and even much thicker de- 

 posits mig-ht be laid down. As the thickness increased 

 the pressure would become g-reater, and the ice about 

 the marg-in be pushed out, always moving- throug-h the 

 valleys, but able in time to surmount low^ hills, partly 



