52 



PHYSIOGRAPHY 



another, reach valleys where there are permanent streams. These 

 may be small, when they are called creeks or brooks; or large, when 

 they are called rivers. Streams which flow but part of the time, as 

 after a rain-storm, during wet weather, or only a part of the year, 

 are temporary or intermittent streams. All streams flow in depres- 

 sions. The small depressions which carry off rain-water from 



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Fig. 41. Gullies on slope above a valley flat. 



slopes just after a shower are gullies (Fig. 41). Ravines are larger 

 depressions of the same sort, and valleys are larger still. 



Just as the tiny streamlets unite with one another to form creeks 

 and these join to make rivers, so the gullies in which the smallest 

 temporary streams flow, often unite to form wider and deeper gullies 

 (Fig. 41). These, in turn, join one another to make ravines, and 

 ravines lead to valleys. Valleys, like streams, usually end at the 

 ocean or a lake; but in some cases, especially in arid regions, they 

 end on dry land (Fig. 42). Large streams generally flow in large 

 valleys, and small streams in small valleys, but to this general rule 

 there are some exceptions. 



