GEOLOGY OF BURMA.
By T. H. DE La Touche, Acting Director of Geological Survey of India.
ROM both a physical and stratigraphical point of view, Burma may be divided into three sections, contrasting strongly with each other in aspect and climatic characters. These are, proceeding from east to west: (i) The Shan Plateau, bounded on the west for a great part of its length by a continuous north and south scarp overlooking the valley of the Irrawaddy, and extending southwards, though in so dissected a condition as no longer to deserve the designation of aplateau,a into the province of Tenasserim ; (2) the valley of the Irrawaddy itself, including that of its tributary the Chindwin, and also that of the Sittangaa tract of low-lying country, not so absolutely flat as the Indo-Gangetic plains of India, but diversified by numerous ranges of low undulating hills, interspersed with level sandy or alluvial plains ; and (3) the hilly tract between the Irrawaddy and the Bay of Bengal, known in its southern portion as the Arakan Yoma (or range), and further north by the names of the different races of aboriginal tribes dwelling in the fastnesses of these almost impenetrable jungles athe Lushais, Chins, and c.
The Shan Plateau forms an elevated tract of country extending eastwards from the Irrawaddy Valley to that of the Mekong. The average elevation above the sea-level may be about 3,000 feet, but the surface is by no means even, and some parts of it rise to elevations of 8,000 feet ; the highest point is Loi Ling, 8,842 feet. Towards the south the plateau becomes much broken up and narrowed, until in Tenasserim it is reduced to a narrow strip of parallel jungle-covered ridges, which really represent only the western edge of the plateau to the north and divide the waters of the Bay of Bengal from the plains of Siam.
Rivers.aThe Shan Plateau is traversed from north to south by the deep trench of the Salween River, which rises far to the north in the highlands of Eastern Tibet, and takes an almost straight course to the sea at Moulmien, on the Gulf of Martaban. A peculiar feature of the course of this river through the plateau, is the fact that it receives no large tributaries, almost the whole of the drainage, even within a few miles of the river, finding its way either
into the Mekong on the east or the Irrawaddy on the west. The other principal rivers of the plateau are the Shweli and the Myitnge (pronounced Min-gay) or Nam Tu, the former rising close to the Salween in Southern Yunnan and falling into the Irrawaddy below Bhamo, while the latter drains the whole of the Northern Shan States, and for over 100 miles of the lower part of its course flows through a profound
canon, quite impassable for boats of any kind, with, in many places, absolutely vertical walls of limestone on either hand between 2,000 and 3,000 feet high. The well-known Gokteik viaduct carries the railway across a canon of this description on one of the main tributaries of the Nam Tu. A considerable amount of the drainage of the Shan Plateau is subterranean, the water sinking into deep depressions in the surface of all sizes, from a punch bowls a only a
few yards in diameter to enclosed valleys
10 miles or more across, and reappearing as springs in the deep canon-like gorges (Gen. H. Collet, J.A.S.B., Vol. LVII., Pt. iia p. 384). A peculiar result of this form of drainage is the growth in many of the streams of bars of calcareous tufa or travertine often several feet in height, and having the appearance of artificially built weirs. A fine series of these may be seen along the
HANDWORKED BAMBOO GOLD DREDGE ON THE MANGWENG RIVER, MOUNT PLACIER DEPOSIT, SHAN STATES.HANDWORKED BAMBOO GOLD DREDGE ON THE MANGWENG RIVER, MOUNT PLACIER DEPOSIT, SHAN STATES.