Vol. 60.] EOCENE, ETC. SURROUNDING THE DARDANELLES. 263 



between Boumili Hissar and Kandili, where the general water- 

 parting between the present drainage to the Black Sea and that to 

 the Sea of Marmora crosses the channel (23). At Beikos Ostrea 

 edvlis, of which a specimen is now in the British Museum (Natural 

 History), has been found in grey clay, about SO feet below the 

 present water-level, and therefore the Devonian rock-bottom of the 

 lateral valley, which joins the Bosphorus at this place, must be 

 lower still. The Buyuk-Dere valley is also partly filled up with 

 brick-earth ; and if these and other lateral valleys were cleared of 

 their post-Tertiary accumulations, the Bosphorus channel would 

 take the shape of an ordinary river-valley, with numerous small 

 affluents. 



The slope of the longitudinal section along the deepest part of 

 the channel, with the exception of a remarkable hole of (iQ fathoms 

 abreast of Kandili, to which I shall refer later, is fairly uniform, 

 the depths increasing from 20 fathoms at the south-western end, 

 between Old Seraglio Point and Leander's Tower, to 3G fathoms at 

 the north-eastern entrance, abreast of Fil Burnu, in a distance of 

 14 sea -miles (see fig. 5, p. 262). 



The existence, already mentioned (p. 244), of strata apparently 

 older than Miocene at Old Seraglio Point, and the occurrence of 

 soundings with rocky bottom outside this point, make it probable 

 that a hard rock-barrier crosses the channel here to the Devonian 

 rocks at Scutari. This bar gives the shallowest water in the whole 

 distance, 167 sea-miles, between the Mediterranean and the Black 

 Sea ; it thus fixed a lower limit to the water-level of the Sea of 

 Marmora before the Dardanelles were cut, and now determines the 

 level at which the Black Sea would again become a closed basin. 



At the time of the completion of the cutting of the 

 Bosphorus valley, the water in the Ponto-Caspian 

 lake described by Prof. Andrussov must evidently 

 have stood at a level nearly 200 feet lower than at 

 present. 



I do not believe that any trustworthy evidence is available, or 

 likely to be obtained, to show whether the formation of the deep 

 depression (660 fathoms) of the Sea of Marmora preceded or followed 

 the cutting of the Bosphorus valley ; but the numerous earthquakes, 

 some of the isoseismals of which are evidently in connection with the 

 faults bordering this collapsed area (27, p. 151), render it probable 

 that the falling-iu of the Marmora sea-bed is still in progress. In 

 either case, however, the result of the recession of the Sarmatic 

 sea would be to leave one or more lakes draining north-eastward 

 through the Bosphorus river, and the water in these would be 

 freshened and lowered as the Bosphorus valley gradually attained 

 its present general profile at some time during the Pliocene Period. 



Then the level of the Ponto-Caspian lake commenced again to 

 rise, so that, in correspondence with this, the Sea of Marmora 

 gradually extended its limits westward to Gallipoli, and the 

 brackish-water bed of Caspian shells, that now forms the con- 

 glomerate upon which the town is built, was deposited. The rise of 

 water gradually reached the height indicated by the beach at Hora, 



