200 REPORTS ON INVESTIGATIONS AND PROJECTS. 



the more or less hilly or mountainous character of the original Pera 

 surface, which makes it difficult to distinguish elevations due to later 

 upwarping, and the lack of a good geologic map renders details of 

 physiographic inference uncertain. Nevertheless, effects of warping 

 were clearly observed in the relations of the Pera surface to the prin- 

 cipal heights and depressions. Neumeyer showed that the ^gean 

 is a region of recent subsidence. We regard this as a general lower- 

 ing of the whole surface, following upon the local sinking and rising 

 of downwarps and upwarps respectively. 



Istria arid Croatia. — The northern Adriatic is like the ^gean in 

 being a recently sunken land. The occurrence of fresh- water deposits 

 of Quaternary age on very small islets and of species peculiar to the 

 mainland is evidence of this well-established fact ; and, as in the 

 ^gean, the subsidence appears to have aSected an extensive area. 

 The region is also one of very pronounced warping of an unusual type. 

 In the peninsula of Istria there is a peneplain, recognized before 

 my visit by Dr. Norbert Krebs, of Triest, which is very clearly devel- 

 oped on the softer Tertiary rocks and to some extent on the Eocene 

 limestones. The summit of Monte Maggiore, above Abbazia, is a 

 mouadnock, and other isolated heights and mountain groups of the 

 mainland of Croatia hold a similar relation to the maturely eroded sur- 

 face of the peneplain of Istria. The ancient topography had reached 

 the same stage of erosion as that of western Asia Minor, when it 

 became warped. 



The evidence of warping is found in the position and attitude of 

 the old topographic surface. Its position, considered with reference 

 to the sea, is very variable. At Pola and along the coast from Fiume 

 to Zeuggand further southward, it rises from the Adriatic. In Monte 

 Maggiore it attains an altitude of a thousand meters, and it lies at 

 similar altitudes in the mountains of the eastern coast. These differ- 

 ences are such that the activit}' of erosion has been greatly acceler- 

 ated, and the surface is being destroyed in consequence of the change 

 from the low level at which it developed. There is nothing in these 

 facts which distinguishes the particular phase of warping from that 

 of many other districts in Europe and elsewhere. But when we trace 

 the surface as we might a stratum, in studying a region of folded 

 structure, we find that it exhibits downwarps and upwarps which are 

 long and narrow aud which have relations to one another similar to 

 those of parallel syuclines and anticlines. This is most conspicuous 

 along the Croatian coast and in the islands and canals of the Gulf of 

 Quanero. Beneath the canals the surface is submerged ; they are 

 long, narrow downv»^arps. In the islands the surface is slightly arched ; 



