Amongst the innumerable country residences which nestle on the shores of the Bosphorus, those of Balta-Liman, Therapia, and Buyukdere are the best known, for they have been the scenes of historical events; but there is no spot throughout this marine valley which does not excite admiration. These marvels of nature will, before long, have added to them a marvel of human ingenuity. The width of the channel between the castles of Rumili and Anadoli is only 600 yards. It was here Mandroclus of Samos constructed the bridge of boats across which Darius marched his army of 700,000 men when he made war upon the Scythians, and on this identical spot it is proposed now to construct a railway bridge which will join the railways of Europe to those of Asia. A current runs through the Bosphorus, from the Black Sea to the Sea of Marmara, at a rate of from two to six miles an hour; and although several geographers conclude from this that the level {104} of the former is higher than that of the latter, this must by no means be looked upon as an established fact. We have already noticed the exchange between the waters of the Mediterranean and of the open Atlantic, which takes place through the Strait of Gibraltar. A similar exchange is going on here, and the outflowing surface current is compensated for by an inflowing under-current. The outlying houses and villas of Constantinople extend northwards along the Bosphorus as far as the two Genoese castles of Rumili-kavak and Anadoli-kavak. This extension coincides with the geological features of the ground, for no sooner have we turned our backs upon the houses than we find ourselves shut in between cliffs of dolerite and porphyry, which extend as far as the Black Sea, where they terminate in the precipices of the Cyaneæ, or Symplegades, the famous rocks which opened and shut, crushing the vessels that ventured to pass through the strait, until Minerva fixed them for ever. These volcanic rocks are barren, but the Devonian strata to the south of them are beautifully wooded. The Turks, unlike the Spaniards and other Southern nations, love and respect nature; plane-trees, cypresses, and pines still shade the shores of the Bosphorus; and the vast forest of Belgrade covers the hills to the east of Constantinople, from which the city draws its supply of water. Birds, too, are better protected than in many a Christian land. The plaintive cooing of doves is heard wherever we turn, flights of swallows and aquatic birds skim over the surface of the Bosphorus, and now and then we encounter a grave stork perched upon the top of a tree or of a minaret.