The course of the Brahmaputra through Assam is roughly from north-east to south-west, but at a place called Sadiya the main stream, there known as the Dihang, turns sharply to the north. At that point, too, it receives an important tributary on its left bank called the Dibang. During the winter of 1912-13 Captain F. M. Bailey, an officer of the Indian Political Service, was employed by the Government to survey the Dibang basin, while another party had gone through the Abor country to survey the Dihang. Early in 1913 Captain Bailey and Captain Morshead of the Royal Engineers collected what stores they could and started off from the village of Mipi on the upper waters of the Dibang. Their aim was to cross into the Dihang valley, and to follow the river upstream to the Tibetan plateau. Captain Bailey had been with the Lhasa expedition, and had had a long record of exploration in different parts of Tibet, so he had all the qualifications needed by the pioneer. But his party was imperfectly equipped, since it started more or less on the spur of the moment, and had no time to obtain proper stores from India. He trusted to the prestige won by the Abor expedition, and his experience of the ways of the Tibetans, to furnish him with coolies and local supplies. The reader's attention is now prayed for the map. The first business was to cross the high passes separating the Dibang from the Dihang. The weather proved abominable, and for part of the route only half rations could be issued. As they descended into the valley of the Dihang they found once more cultivation and villages, and they were able to supplement their stores by shooting game, especially pheasants, which teemed by the roadside. It was necessary to establish touch with the Abor Survey party lower down the river, and accordingly they had to halt for some days. At a place called Kapu they managed to take the altitude in the river bed, and found the height above sea level to be 2,610 feet--an important result, for they were able to take no other observation at water level below the main gorges. These foothills of the Himalaya were inhabited chiefly by savage tribes akin to the Abors, who were known generically as Lopas. But as the expedition advanced up the river they came to the country of the Pobas, who were under Tibetan influence. At Lagung, which is about the centre of the hairpin bend, the course of the river turned west. It might have been possible for them to have followed it some thirty miles farther, but they were pressed by a Poba official, with whom they made friends, to go north-east into the absolutely unknown country of Po-me, which would enable them to make a circuit and reach Gyala at the head of the gorges. Captain Bailey considered that it would be easier to explore the gorges by going downstream.