[39] Regarding the sunken reef encountered by the fleet after leaving Koreatis, Sir Alexander Burnes says: “Near the mouth of the river we passed a rock stretching across the stream, which is particularly mentioned by Nearchus, who calls it _a dangerous rock_, and is the more remarkable since there is not even a stone below Tatta in any other part of the Indus.” The rock, he adds, is at a distance of six miles up the Pitti. “It is vain,” says Captain Wood in the narrative of his _Journey to the Source of the Oxus_, “in the delta of such a river (as the Indus), to identify existing localities with descriptions handed down to us by the historians of Alexander the Great ... (but) Burnes has, I think, shown that the mouth by which the Grecian fleet left the Indus was the modern +Piti+. The ‘dangerous rock’ of Nearchus completely identifies the spot, and as it is still in existence, without any other within a circle of many miles, we can wish for no stronger evidence.” With regard to the canal dug through this rock, Burnes remarks: “The Greek admiral only availed himself of the experience of the people, for it is yet customary among the natives of Sind to dig shallow canals, and leave the tides or river to deepen them; and a distance of five stadia, or half a mile, would call for not great labour. It is not to be supposed that sandbanks will continue unaltered for centuries, but I may observe that there was a large bank contiguous to the island, between it and which a passage like that of Nearchus might have been dug with the greatest advantage.” The same author thus describes the mouth of the Piti:—“Beginning from the westward we have the Pitti mouth, an embouchure of the Buggaur, that falls into what may be called the Bay of Karachi. It has no bar, but a large sandbank, together with an island outside prevent a direct passage into it from the sea, and narrow the channel to about half a mile at its mouth.” [40] All inquirers have agreed in identifying the Kolaka of Ptolemy, and the sandy island of Krokola where Nearchus tarried with his fleet, for one day, with a small island in the bay of Karâchi. Krôkala is further described as lying off the mainland of the Arabii. It was 150 stadia, or 17¼ miles, from the western mouth of the Indus,—which agrees exactly with the relative positions of Karâchi and the mouth of the Ghâra river, if, as we may fairly assume, the present coast-line has advanced five or six miles during the twenty-one centuries that have elapsed since the death of Alexander. The identification is continued by the fact that the district in which Karâchi is situated is called +Karkalla+ to this day. Cunningham _Geog. of An. India_, I. p. 306.