250 FRAGMENTS OF SCIENCE. 



think, thus: We have, in the first place, great valleys, 

 such as those of the Ehine and the Shone, 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 cut- 

 tings 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 di- 

 mensions, always moving, grinding 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 



