542 BIOLOGY OF THE SEAS OF THE U.S.S.R. 



naturally be linked with the change of sea-level. Similar mountain-forming 

 processes may probably be discovered also in the Central Caspian. 



Although the second explanation may have some truth in it, it is possible to 

 show, as has been done in a graphic form by Brujevitch, that the fluctuations 

 in the level of the Caspian Sea are in close accord with the quantity of water 

 supplied by the rivers. The mightiest water-artery feeding the Caspian Sea, 

 the Volga, brings into it on the average about 270-8 km 3 of water each year. 

 According to G. Bregman's calculations about 75-6 per cent of the whole 

 supply of fresh water is brought by the river Volga (the average annual in- 

 flow from rivers, measured over many years, has been 355 km 3 ). The con- 

 formity between the fluctuations of sea-level and those of the inflow of the 

 Volga waters is so close that the direct influence of the latter on the level of 

 the Sea has been established (Fig. 258). 



Zenkevitch considers that the greatest part of the shore of the Caspian Sea 



Fig. 257. One of the latitude contours of the Caspian Sea bottom in its southern part 

 (Solov'ev, Kulakova and Agapova). 



bears a definite imprint of the effect of a considerable lowering of its level, 

 characteristic of the whole Quaternary period. A huge lowland area was sub- 

 merged by the ancient Caspian in the north, and now its shores are moving 

 southwards along the completely flat surface of the ancient sea-bed. Only the 

 extensive delta of the Volga is under the influence of fluvial factors and is 

 growing as a result of alluvial accretion. All along the rest of the shore the 

 morphology is not clearly defined, and the water's edge may recede up to 

 20 km to the south, due to the effect of on-shore and off-shore winds. 



The western (Caucasian) shore consists of relatively solid Neogene car- 

 bonate rock. Nevertheless alluvium-bearing currents may be formed along 

 this coast. Alluvium deposited by them is supplied by large rivers (Samur, 

 Sulak, etc.) and by the washed out sea-bed, from which a mass of shell gravel 

 is cast up on to the beach. South of the Apsheron peninsula the coast is more 

 irregular with a number of headlands and a whole archipelago of islands, 

 mud-volcanic and others, lying to seaward. Farther south, within the area of 

 the delta of the river Kura, the stretch of friable alluvial shore begins and 

 extends to within the boundaries of Iran. 



The abundant shallows round the Apsheron peninsula have a peculiar 

 structure. Complex tectonic structures have been discovered on the bottom, 

 some of them oil-bearing, and marine petroleum works have been set up there. 



