168 Penck — Climatic Features in the Land Surface. 



consist in the movement of material from higher latitudes into 

 lower ones, and the areas of erosion and deposition would show 

 a zonal arrangement, whilst running water transports from 

 higher regions to lower ones, and the corresponding areas of 

 its action are controlled by the existing distribution of water 

 and land. Glaciers and winds accomplish an important trans- 

 portation of material from lower to higher positions. What 

 we see in river action consists only of a downward transporta- 

 tion, and it generally ceases at sea-level ; it can only be exer- 

 cised below it in countries which extend for other reasons 

 below this level, as for example, in the border regions north 

 of the Caspian sea ; whilst glaciers and winds could make vast 

 depressions of the land beneath the sea-level. 



These differences between visible river action on the one 

 hand and glacial action on the other seem to be at first sight 

 very strange, but a closer inspection shows that when speaking 

 of river action we generally have in mind the processes which 

 go on above the level of the river. We generally do not think 

 of the processes performed in the river bed itself, for they are 

 hidden under the water. But the study of river beds reveals 

 that here much material is carried upwards and that the depth 

 of the rivers is not at all limited by the sea-level. All river 

 beds which reach the sea lie below the level of the sea near 

 their mouths, and their bottoms extend the deeper and the 

 farther below the sea-level the greater their volume. On the 

 other hand, if we speak of glacial or wind action we have 

 always in mind the processes going on in the beds of these 

 moving fluids. These beds are of far larger extent than those 

 of rivers, and therefore the action performed in them is far 

 more conspicuous. The action of rivers in their beds gives 

 origin to all those subserial processes which widen the vertical 

 trench of a river into a valley and produce slopes towards the 

 river. These subserial processes are the more important for 

 the development of the earth's surface-features ; they per- 

 form what we usually call river action, but they are not con- 

 trolled by the movement of water, and belong to that class of 

 phenomena which are dependent on the action of gravity. 



The actual surface features of the land differ from those 

 which are produced by continuous river, glacial and wind 

 action. The land is not leveled down to a peneplain, no 

 mountainous moraines are formed around vast depressions, 

 and there is no equatorial belt of wind deposition between 

 regions where deflation produced lowlands. We meet with 

 elevations which are still in the state of being degraded and 

 which are not made by glacial or eolian accumulation. The 

 existence of those elevations reveals the existence of forces 

 which counteract the atmospheric agencies, and which have 



