CHAPTER IV. 



SIGNS OF PAST GLACIATTON. 



The facts from which we draw the inference that vast 

 areas of the earth's surface which are now free from gla- 

 ciers were, at a comparatively recent time, covered with 

 them, are fourfold, and are everywhere open to inspection. 

 These facts are : 1. Scratches upon the rocks. 2. Exten- 

 sive unstratified deposits of clay and sand intermingled 

 with scratched stones and loose fragments of rock. 3. 

 Transported boulders left in such positions and of such 

 size as to preclude the sufficiency of water-carriage to 

 account for them. 4. Extensive gravel terraces bordering 

 the valleys which emerge from the glaciated areas. We 

 will consider these in their order : 



1. The scratches upon the rocks. 



Almost anywhere in the region designated as having 

 been covered with ice during the Glacial period, the sur- 

 face of the rocks when freshly uncovered will be found to 

 be peculiarly marked by grooves and scratches more or 

 less fine, and such as could not be produced by the action 

 of water. But, when we consider the nature of a glacier, 

 these marks seem to be just what would be produced 

 by the pushing or dragging along of boulders, pebbles, 

 gravel, and particles of sand underneath a moving mass 

 of ice. 



Eunning water does indeed move gravel, pebbles, and 

 boulders along with the current, but these objects are not 

 held by it in a firm grasp, such as is required to make a 

 groove or scratch in the rock. If, also, there are inequali- 



