Vol. 60.] EOCENE, ETC. SURROUNDING THE DARDANELLES. 207 



The river then apparently deserted its course for a more southerly 

 one, included in the present excavation of the Dardanelles below 

 Chanak, and conveyed the drainage both of the Dardanelles and 

 of the Ehodius valleys into the closed basin of the North iEgean. 

 The watershed dividing this new drainage from that which con- 

 tinued to follow the old course through the Sea of Marmora, must 

 have been to the south-west of Gallipoli, as no traces of the Ponto- 

 Caspian lake occur beyond this place, and its position was probably 

 determined by the subsidiary north-to-south fold of the Lower Ter- 

 tiary strata, which passes through Ibridji (see PI. XXII, fig. 2). 



The branch of this river-valley occupying the Upper Dar- 

 danelles would be of less width than the existing waterway, which 

 has an average breadth of about 2| miles, and therefore no traces 

 of it are now visible above Abydos. When its watershed was worn 

 down to the level (130 feet or less above the present sea) at 

 which the Sea of Marmora stood at that time, the valley would be 

 rapidly widened and deepened into the present section by the 

 outflow of the Ponto-Caspian. 



A violent outflow of this description would account for the 

 scooping-out of the remarkable cavity previously mentioned as 

 existing in the bed of the Bosphorus opposite Kandili (p. 263), in 

 which, going southward, the depth increases from 33 to 66 fathoms 

 in half a mile (see fig. 5, p. 262). This is immediately below the 

 Koumili-Hissar gorge, in which the sectional area of the present 

 channel is reduced to about 430,000 square feet, or three-quarters 

 of its normal waterway. The sectional areas of the northern end 

 of the channel abreast of Fil Burnu, and of the southern end, 

 between Old Seraglio Point and Leander's Tower, are each about 

 the same, that is, 560,000 square feet (28, sections). 



The high cliffs of soft material, which now bound the Dardanelles 

 and form so remarkable a feature (fig. 8, p. 266), would readily be 

 shaped by the carrying away of the material protecting their bases, 

 without the whole section between them being necessarily occupied 

 by water at any one time. 



Prof. Philippson concludes that the Xorth IEgean basins were not 

 occupied by the Mediterranean until Quaternary times ; that the 

 lowering of the collapsed regions is still going on ; and that, in 

 addition, a general subsidence of the iEgean land has taken place 

 since the beginning of the Quaternary Period (14, pp. 135, 139, 

 141). It is not possible, therefore, to ascertain what the water-level 

 in this district was when equilibrium took place between the Ponto- 

 Caspian and the Mediterranean, as all traces of this event have 

 been since submerged. So far as the Sea of Marmora is concerned, 

 the profile of the south-western entrance of the Bosphorus shows 

 that its level did not differ materially from the present one. 



There have been, as will now be shown, various considerable 

 oscillations of water-level since the opening of the Straits ; but, so 

 far as I am aware, there is no evidence to show that they have not 

 been quietly effected, in every case, by a gradual rise or fall of 

 the water. 



r 2 



