250 FRAGMENTS OF SCIENCE. 



such as those of the Rhine and the Rhone, which 

 we might conveniently call valleys of the first order. 

 The mountains which flank these main valleys are 

 also cut by lateral valleys running into the main 

 ones, and which may be called valleys of the second 

 order. When these latter are examined, smaller 

 valleys are found running into them, which may be 

 called valleys of the third order. Smaller ravines and 

 depressions, again, join the latter, which may be called 

 valleys of the fourth order, and so on until we reach 

 streaks and cuttings so minute as not to merit the 

 name of valleys at all. At the bottom of every valley 

 we have a stream, diminishing in magnitude as the 

 order of the valley ascends, carving the earth and 

 carrying its materials to lower levels. We find that 

 the larger valleys have been filled for untold ages by 

 glaciers of enormous dimensions, always moving, grind- 

 ing down and tearing away the rocks over which they 

 passed. We have, moreover, on the plains at the feet 

 of the mountains, and in enormous quantities, the very 

 matter derived from the sculpture of the mountains 

 themselves. 



The plains of Italy and Switzerland are cumbered 

 by the debris of the Alps. The lower, wider, and 

 more level valleys are also filled to unknown depths 

 with the materials derived from the higher ones. In 

 the vast quantities of moraine-matter which cumber 

 many even of the higher valleys we have also sugges- 

 tions as to the magnitude of the erosion which has 

 taken place. This moraine-matter, moreover, can only 

 in small part have been derived from the falling of 

 rocks upon the ancient glacier ; it is in great part 

 derived from the grinding and the ploughing-out of 

 the glacier itself. This accounts for the magnitude of 

 many of the ancient moraines, which date from a 



