ORIGIN OP EIVBE TEEEACBS. 69 



have been formed; and while most of the terraces are due to the carving 

 and partial erosion of alluvium previously laid down, yet a residue remains 

 where narrow terraces may have been deposited in substantially their 

 present shapes, either at the sides of an ordinary river of great size or along 

 the margins of a mass of ice filling the central parts of the valley. The 

 question will be more fully discussed later (see Chapter VI). 



