T. BELT ON THE STEPPES OF SOUTHERN RUSSIA. 845 



sand and silt, the sand often false-bedded. In some of the higher 

 beds of sand there were groups of the shells of Unio pictorum, var. 

 elongatula, with the two valves united, lying, as the mollusk had 

 lived, with the smaller end,of the valves pointing upwards. I saw as 

 many as twenty individuals in some groups, all lying in the same 

 position, and with even the ligament still preserved. Entire shells of 

 a species ofAnodon occurred in the same position, but singly in more 

 silty beds ; they were so tender and brittle that they fell to pieces 

 when I attempted to extract them. Shells of Paludina, Bithinia, 

 and Cyclas were very abundant, especially in the false-bedded sands ; 

 but they looked as if they had been drifted, and the valves of the 

 Cyclas were never united. The beds upwards became more silty. 

 In following the formation along the cliff, it was found to be very 

 variable, and often contained no shells. Whenever the sands were 

 false-bedded the drifted shells of Cyclas and Paludina appeared 

 again. At the point where the section fig. 2 was taken, the beds 

 graduated upwards into the diluvial clay, and in the upper part con- 

 tained shells of Planorbis complanatus. In the more sandy layers 

 I found a few fragments of Aclacna edentula and drifted valves of 

 Dreissena polymorpha. Dr. Jeffreys has found amongst the shells a 

 single fragment of Cardium edule ; and fragments of Buccinum and 

 other shells from the underlying Sarmatic beds are not uncommon. 

 I also obtained a few small pieces of bone *. 



The molluscan fauna of the fluviatile beds, although separated 

 from the present time by the whole period of the deposition of the 

 thick and wide-spread diluvium, shows a remarkable resemblance 

 to that of the present Sea of Azof. On the beach, thrown up by 

 the waves, I found shells of Aclacna edentula, Dreissena polymorpha, 

 Unio pictorum, var. elongatula, and others, the same as those of the 

 prediluvial sands. The principal difference in the fauna is, that the 

 shells of Aclacna and Dreissena are much more abundant on the 

 present beach, and have their valves united, indicating, probably, that 

 the water is now more saline. 



Diluvium. — Above the fluviatile beds lie thick deposits of clay 

 and sand, which generally present three divisions, although the 

 middle one is sometimes absent. The lowest of these is a stiff dark 

 brown or bluish brown unstratifled clay, often calcareous. In some 

 parts it becomes a little sandy at the base, and graduates into the 

 stratified beds below. At the point where the section fig. 2 was 

 taken, I found shells of Liih ocj lyphus, Bithinia, Fairbanlda,Valvata, 

 Planorbis, Succinea, and Helix in the lower part, where it began to 

 be obscurely stratified, and Planorbis complanatus, also, in the first 

 six feet of the unstratifled clay. The lower clay is succeeded up- 

 wards by irregular beds of sand, and these, again, by a thick deposit 

 of yellowish-brown unstratified clay. In some places the upper 

 clay contains numerous calcareous concretions ; in others it is more 

 arenaceous, and is then used for brick-making. This bed at the top 

 graduates into the black earth, or " Tchornozem," which is merely a 



* For a complete list of the shell?, by Dr. Jeffreys, see the end of this paper. 



