The wall on the north of the plain is scarcely less impenetrable, though Nature has cloven it almost through by the defile known as the Gurgi Boghaz, or Georgian gates, down which flows the infant stream of the Euphrates and is carried the road from Olti. But the portion of the Russian possessions from which it leads are mountainous and poor in supplies, and the narrows are blocked on the Turkish side by modern fortifications. In a geographical and geological sense this northern barrier corresponds to that on the south of the depression. A plateau-like character is not one of its least pronounced features--a feature which is presented with startling fidelity in the outline on the north of the plain of Pasin, where the heights are called Kargabazar (Fig. 163, p. 193). West of the Gurgi Boghaz they are broken into peaks, of which the most symmetrical is the beautiful cone of Sheikhjik--a constant source of admiration to an inhabitant of Erzerum. It consists of a mass of trachyte which has welled up from the middle of a crater. [177] As these heights extend westwards they have been less subjected to eruptive disturbances; and the fine landmarks of the Akhbaba Dagh, the Jejen Dagh and the Kop Dagh are composed of non-volcanic rocks. But these eminences serve to accentuate the prevailing flatness of the outline, which remains the outline of a block of tableland. Of little comparative width, this mass declines upon the north to the valley of the Chorokh. Erzerum, it will have been seen, is almost as difficult to get round as it should be impossible to take by direct assault from the east. If only Turkey were a naval power, able to cope with her adversary by sea, it would be a long time before this bulwark of her Asiatic empire could be broken down by a Russian attack. Herein lies the value to Turkey of help from a first-rate naval Power and the hopelessness of her position should it not be forthcoming. With her fleet in undisputed possession of the Black Sea, Russia might laugh at the irresistible defences of Erzerum. It would only be necessary to hold the garrison by an advance on the side of Pasin; and the real attack, if it were ever made, would come from the west, the vulnerable side, delivered by a column which should have been landed at the port of Trebizond, and which there would be nothing to prevent marching to Erzerum along the chaussée. Sevastopol and Odessa rather than Kars and Erivan are the storm centres from which will be let loose the forces that will sweep the Ottoman Empire out of Asia, when we shall be confronted with a brand-new set of barriers, precluding for the second time in history the entrance of commerce and enlightenment into these magnificent territories. In taking leave of this part of the subject, I must not omit to mention the route which a Russian army might be expected to follow in its progress westwards after the fall of Erzerum. As far as Erzinjan the course of the Euphrates would in general be followed,