188 EARTH FEATURES AND THEIR MEANING 



Although to-day so largely a barren waste, we know that the Karst 

 upon the Adriatic was in remote antiquity a heavily forested re- 

 gion and that it supplied the myriads of wooden piles upon which 

 the city of Venice is supported. The vessels which brought to 

 this port upon the Adriatic its ancient prosperity were built from 

 wood brought from this tract of modern desert. In the days of 

 Venetian grandeur the fertile terra rossa formed a veneer upon 

 the rock surface of the Karst and so retained the surface waters 

 for the support of the luxuriant forest cover. After deforestation 

 this veneer of rich soil was washed by the rains into the dolines 

 or into the few stream courses of the region, thus leaving a barren 

 tract which it will be all but impossible to reclaim (plate 6 A). 



Upon the steeper slopes 

 over the purer limestones, 

 the rain water runs away, 

 guided by the joints within 

 the rock. There is thus 

 etched out a more or less 

 complete network of nar- 

 row channels (Fig. 190, 

 p. 181), between which the 

 remnants rise in sharp 

 blades to produce a struc- 



FIG. 198. -Sharp Karren of the Ifenplatte in ture often simulated Upon 

 Allgau (after Eckert). ,, e t 



the fissured surface of a 



glacier that has been melted in the sun's rays (Fig. 401). These 

 almost impassable areas of karst country are described as Schratten 

 or Karrenf elder (Fig. 198). 



The ponore and the polje. To-day large areas of the Karst 

 are devoid of surface streams, nearly all the surface water finding 

 its way down the crevices of the limestone into caverns, and there 

 flowing in subterranean courses. The foot traveler in the Karst 

 country is sometimes suddenly arrested to find a precipice yawn- 

 ing at his feet, and looking down a well-like opening to the depth 

 of a hundred feet or more, he may see at the bottom a large river 

 which emerges from beneath the one wall to disappear beneath 

 the other. These well-like shafts are in the Austrian Karst known 

 as Ponores, while to the southward in Greece they are called 

 Katavothren. 



