Tlie Karstlands of Westei^n Yugoslavia. 399 



With the contimied uplift of this region, the main streams 

 endeavoured to kee]) pace by cutting for themselves deep gorges 

 in the limestones. Thus the river Una, after following the strike of 

 the Triassic limestones as far north as Bihats, abruptly swings east, 

 cutting steep-sided gorges in the Cretaceous, Jurassic, and Triassic 

 limestones, before eventually draining into the Save. Similarly, 

 the river Narenta in its course from the Jablonitsa mountains to the 

 Mostar plain cuts through a series of impressive defiles, mainly 

 in Triassic dolomites, whose abrupt slopes in places attain a height 

 of over 2,000 feet above the level of the valley ; while the river 

 Zrmanja, in cutting its way across the strike of the Mesozoic lime- 

 stones around Obrovazzo, forms a vertical-walled canyon, over 

 600 feet deep. 



The majority of the streams seem, however, to have been unable 

 to keep pace with the continued uplift, and consequently the whole of 

 the Illyrian karstlands are studded with a series of inland drainage 

 basins aligned in the direction of the Dinaric folds. The pre- 

 dominating effect of this structure on the development of the 

 drainage is admirably illustrated along the Dalmatian littoral in 

 the neighbourhood of Zaravecchia (see Fig. 2), where the Cretaceous 

 and Tertiary limestones show the Dinaric trend, and the close 

 correspondence between the synclinal hollows and the alluvial 

 flats is very remarkable. While many of these closed basins occur 

 between two minor anticlinal axes, the outlines of others have been 

 determined in the main by longitudinal fractures. The latter type 

 is a very distinctive land form throughout Western Yugoslavia, 

 where it is universally termed a polje. 



Probably the largest enclosed basin is that of Gospits, in Westerix 

 Croatia, situate between the Velebit and Kapela ranges, where no 

 less than seven streams of considerable size (severally known as the 

 Lika) drain towards the centre of the basin, and for many months 

 of the year convert much of it into a seasonal lake or marsh. Much 

 of this inland basin is floored with Lower Pliocene freshwater lime- 

 stones and marls with thick beds of lignite. 



Underground Drainage Systems. 



Another consequence of the later Tertiary uplift has been that 

 erosive action in the soluble limestones and dolomites has tended to 

 work in a vertical direction, and many streams following the major 

 joints in the limestone have cut intricate subterranean channels 

 along their course. Thus the river Ljubljanitsa of Western Slovenia, 

 where it rises near St. Peter, 50 miles west of Ljubljana, is first 

 known as the river Poik. After flowing at the surface for 

 some distance over Lower Tertiary limestones, breccias, and shales, 

 it subsequently passes underground through the famous Adelsberg 

 caves, and eventually reappears at the surface as the river Unz at 

 Planina, where its volume is considerably augmented by the under- 

 ground drainage of the Zirknitz inland depression. The Adelsberg. 



