538 



Captain Spratt on the Undercurrent [June 15, 



water flows for a great part of the year as a skimming surface movement 

 around and across the Sea of Marmora and through the Dardanelles, and 

 at no greater depth than from 20 to 40 fathoms, viz. that of the harrier 

 ridges between the Black Sea and iEgean, there occurs for several days in 

 the year a strong reverse current into the Black Sea from the iEgean. This 

 reverse current is frequent during the autumn and winter months, when 

 the Black Sea rivers are at their lowest, so that the Black Sea level is then 

 frequently overbalanced by the pressure of westerly gales in the Mediter- 

 ranean or iEgean. 



Therefore it is this recurring return current into the Black Sea that 

 maintains, as I found to be the curious or interesting fact, the iEgean or 

 Mediterranean density in the deeps of the Sea of Marmora in all depths 

 below about 40 fathoms, and therefore that restores also the lost salinity 

 of the Black Sea through the flow of diluted water so prevalent as a sur- 

 face-current from it. 



This return-current occurs sometimes for two or three days at a time, 

 and occasionally at a rate even greater than the general outflowing current 

 of 2 and 3 knots. The same occurs at the Kertch Straits. 



Therefore, instead of the Black Sea being washed fresh, unless there 

 was an undercurrent to restore it, as Dr. Carpenter argues, its normal 

 density is restored by the surface return-current, as also that of the Sea of 

 Azof. 



But I am induced to believe, as I have elsewhere stated*, that the Black 

 Sea has not become a diluted or brackish sea from a previously salt sea, but, 

 on the contrary, from a freshwater lake has become a brackish one. 



This I infer to be the fact from the latest deposits existing around the 

 shores of the Black Sea, Sea of Marmora, and Dardanelles being of fresh- 

 water origin, a large Dreissena and a freshwater Cockle in them being 

 mistaken previously for a Mussel and Cardium until I discovered the 

 error. 



Having thus shown these physical conditions as facts in connexion 

 with the Black Sea, and that the undercurrent theory is a fallacy where it 

 was expected and insisted upon as being a predicted necessity, as a con- 

 stant counterbalance to the surface-outflow, from the great difference in 

 the densities between the Black Sea and iEgean, viz. 13° and 29°, as shown 

 by a common hydrometer, I shall now refer to the Baltic Sea and German 

 Ocean, where even a greater difference in the saline density exists ; and 

 I shall be able to show also that precisely the same conditions of outflow 

 and inflow exist there, and that it is surface-currents only which restore 

 the lost salinity, and that no undercurrent is necessary there to prevent the 

 saltness of the Baltic from being washed out ; that, in fact, no undercurrent 

 system does exist as a means of restoring the equilibrium and maintain- 

 ing the normal conditions of that sea. This I shall show from Dr. 

 Forchhammer's observations ; but he has evidently mistaken the right 



* Crete, vol. ii. p. 349. 



