368 



FIRST YEAR SCIENCE 



cier, as well as upon the bowlders themselves. Scratches 

 of this kind are called glacial scratches or strice. They 

 are found abundantly in places that have been glaciated. 

 The rubbing of the rocks upon each other wears them 



away and grinds them 

 into fine powder called 

 glacial flour, which gives 

 a milky color to the 

 streams flowing from 

 glaciers. 



If a glacier extends 

 over a region where the 

 surface has been weath- 

 ered into soil, this fine 

 material may be shoved 

 along under the ice for 

 great distances. When 

 a glacier melts, all the 

 material which it has 

 moved along under it, 

 as well as that which it 

 has carried on its sur- 

 face or frozen into it, is deposited, forming what is called 

 ground moraine. This is the formation which constitutes 

 the soil of many of our northern states. 



The melting of glacial ice, whether by the sun's heat on 

 top, by friction on the bottom or from whatever cause, 

 produces streams which flow in the ice-cut channels under 

 the glacier and emerge in front, laden with rock, glacial 

 flour, and silt. Where the amount of material these 

 streams carry is great, it is usually deposited in an al- 

 luvial plain near the end of the glacier. 



The length of a glacier does not always remain the 

 same, but increases and decreases slowly in conformity 



THE FIKSCH GLACIER. 

 Notice the medial moraine. 



