PRECIPITATION AND VEGETATION 35 



oust it from the land it has reclaimed. But in many inland 

 regions over the world we find great sterile tracts of sand, because 

 there there is not the rain which is the essential preliminary 

 condition for vegetation that is, no constant gentle rainfall 

 throughout the growing season. In many such regions, if water 

 can be supplied by irrigation, the process of reclamation is easy 

 of this the geography book will furnish many examples. 



Our previous observations have, however, shown us that it is 

 a continuous supply of water through the growing season which 

 is necessary for plant-life occasional torrential showers will do 

 no good. In some such way we might lead on from the general 

 subject of deserts to the very interesting conditions which pre- 

 vail in the " Badlands " of parts of the United States. Here the 

 rainfall is too small to permit the formation of a continuous cover- 

 ing of vegetation, but nevertheless there is a not inconsiderable 

 precipitation which comes mostly in heavy falls of short duration. 

 The result of these falls on a surface deprived of any protective 

 covering of vegetation is that the land is carved into extraordinary 

 forms, like those shown in the illustration. The case is interest- 

 ing in that it shows that erosion by rain may be actually greater 

 in a region of limited rainfall than in one of considerable fall, 

 because the conditions in the former do not permit of a continuous 

 covering of protective vegetation. 



On a much smaller scale the same phenomenon is illustrated 

 by the increased rapidity of erosion produced in a country by 

 the destruction of the forests and the draining of marshes. There 

 is little doubt, for instance, that formerly much of England and 

 parts of the lowlands of Scotland were covered by marshes. 

 The effect of these marshes was to hold up the water as 

 may be well seen on an excursion to a moor, where the effect 

 of the moss Sphagnum should be especially pointed out. The 

 holding up of the water meant a slower and more equable flow- 

 ing of the streams. The disappearance of the marshes means 

 that the water reaches the sea more quickly, and it has therefore 

 greater carrying power. This is well seen in the case of the 

 Forth, for instance, which appears to be becoming yearly muddier, 

 that is, has had its power of erosion and transportation increased 

 by the draining of the country through which it flows. 



