Pench — Climatic Features in the Land Surface. 167 



tion of the eroded material in higher levels around this center. 

 The same can be said of eolian action. Wind can blow sand 

 and dust from lower levels to higher ones, and if its action 

 were long continued, it could lower the surface of vast tracts 

 of land and raise the surface of others ; the lowered surfaces 

 could lie below the raised ones. 



In order to understand more thoroughly the difference of 

 river action on the one hand and of glacial and wind action on 

 the other, let us consider their probable final results. In the 

 course of time the rivers will totally degrade the continents to 

 vast peneplains and will extend them seaward by the accumu- 

 lation of river plains ; then they will have no action. A polar 

 ice-cap will attack its floor if the slope of its surface is greater 

 than the reversed slopes of its floor, and around this eroded 

 area accumulation will go on. The difference of height be- 

 tween the central eroded area and the peripheral belt of deposi- 

 tion will be theoretically the larger the greater the thickness of 

 the ice-cap, and it is theoretically possible that a very thick 

 and moving polar ice-cap could finally excavate a deep basin in 

 the polar region which would be surrounded by a high morainic 

 belt. These processes would not only be accomplished on the 

 land, but the ice-cap could also act on those parts of the sea- 

 bottom which are not deep enough to make the ice float ; and 

 the morainic belt could therefore be accumulated as well on 

 the land as on the bottom of the sea. But where the bottom 

 of the sea becomes too deep, the ice-cap would break into pieces 

 which would float away as icebergs and distribute the morainic 

 material over vast areas of the sea-bottom. Let us assume that 

 wind action operates unhindered by vegetation and the action 

 of running water. Then the constant trade-winds w r ould con- 

 tinually carry with them sand and dust which were accumulated 

 in an equatorial belt, where the trade winds cease, and this 

 action would be continued as long as the area eroded by the 

 wind were not invaded by the sea. It could be eroded be- 

 neath sea-level as long as there were coast regions protecting 

 it as natural levees against the waters of the ocean. Wind 

 action does not necessarily stop at sea-level ; the depressed 

 areas of the land clearly show us that it is continued farther 

 down. If, however, those natural levees are destroyed, vast 

 regions denuded by wind action below the sea-level would 

 suddenly be inundated and converted into seas. The material 

 transported by the wind would be deposited not only on the 

 land, but also in the neighboring seas, and an increase of the 

 equatorial land area would be the consequence of continued 

 wind action. Thus, by mere eolian activity, the distribution 

 of water and land could be altered. 



The effects of polar ice-caps and continual wind action would 



