course of the Namyau on the railway between Hsipaw and Lashio.
The physical characters of the Irrawaddy Valley vary considerably as we proceed from north to south. The whole of the country is low-lying, but isolated ridges and ranges of hills are nearly always visible in the landscape. Towards the north, the low hills are covered with dense jungle, but in the a dry zone,a extending from Shwebo to Thayetmyo, extensive sandy plains are found between the ridges, often recalling in the characters of their scenery and vegetation the desert regions of Western India. Further south, again, the broad plains of the delta support a luxuriant vegetation owing to their proximity to the sea coast. One of the highest elevations in this section of Burma is the hill of Popa, 4,981 feet, an extinct volcano of Pliocene age, situated in
the Myingyan district, but some of the peaks in Wuntho, further north, rise to over
The Irrawaddy rises in the little-known country to the north of British Burma, but far south of the sources of the Salween. The depression in which it flows seems to have originated in early Tertiary times, when a great north to south dislocation developed along the edge of what is now the Shan Plateau ; and as this difference in level became more accentuated the tributaries of the Irrawaddy, the Shweli and the Myitnge appear to have cut back into the former drainage area of the Salween, which, from the depth of its channel, in comparison with that of the upper Irrawaddy on one side, and of the Mekong on the other, appears to be the oldest of the three rivers. In fact, it is only this great depth
of its channel that has saved it from being captured by one or the other of its neighbours.
In its course below the aConfluencea of its two main branches, the Mali Kha and the Nmai Kha, near Myitkyina, the Irrawaddy resembles the larger rivers of India, though it has not yet reduced its valley, even near its delta, to the same level of erosion as the Ganges or Indus. The principal tributary is the Chindwin, draining the eastern flanks of the ranges dividing Upper Burma from Assam. The Sittang is an independent river, flowing due south along the foot of the Shan Plateau, whence it derives most of its water. It is separated from the Irrawaddy Valley by a low divide, known as the Pegu Yoma.
The Arakan Yoma, with its northern extension into the lofty parallel ranges divid-
ing Burma from Bengal and Assam, is almost a terra incognita to geologists. The principal feature of this tract is the extraordinary number of definite ranges rising successively in height from the sea coast on the west and decreasing equally gradually towards the Irrawaddy Valley. The rivers flow as a rule either due north or south, but they occasionally cut directly through the ranges in echelon, without any apparent cause. A case in point is the Kaladan, or Koladyne, which enters the sea at Akyab, the main stream of which is crossed at least three times in traversing the hills between Chittagong and the plains of Burma, at each crossing flowing either due north or south. The highest known point in these hills is Mount Victoria, in the Pakokku Chin Hills, 10,400 feet above the sea.
Lakes.aOn the Shan Plateau, in spite of
the numerous hollows without visible outlet referred to above, lakes are not common, the water sinking away through fissures in the limestone, the prevailing rock, though temporary ponds often form after heavy rain. One permanent lake, known as the In-le, occupies an extensive depression at Fort Stedman in the Southern Shan States, covering an area of about seventy square miles. It is probably due to the subsidence of the limestone caused by underground solution, the original fissures having become sealed up by the deposits of the numerous streams that feed the lake. In the Irrawaddy Valley the most important lake is the In-daw-gyi situated at the north end near Mogaung. This is a sheet of water about sixteen miles in length by six in breadth. The formation of its basin is probably due to recent differential movements of the surface, or perhaps to irregular accumulation of the Upper Tertiary sands and silts, among which the lake lies. Some small lakes in the Lower Chindwin district have been shown by Mr. R. D. Oldham to be due to volcanic action of a peculiar type, the depression in which they lie being craters caused in each case by a single eruption. (Rec. G.S.I., Vol. XXXIV., p. 137).
Hot and Mineral Springs. aHot springs are very numerous on the Shan Plateau and in Tenasserim, issuing along lines of faulting. The best known is that of Ta Pong, near Lashio, where the hot water rises along the line of a fissure extending for several hundred yards, and approaches boiling point in temperature. The water is remarkably pure, containing less than one-half per cent, of solid matter. The hottest spring in Tenasserim is at Pai, in Tavoy, the water having a temperature of 198A F. Other large springs occur on the Ataran River.
A considerable quantity of coarse salt is manufactured from the water of a salt spring at Bawgyo, near Hsipaw, in the Northern Shan States, and is mainly consumed by the tribes east of the Salween. The water of this well contains about 60 per cent, of chloride and 35 per cent, of sulphate of soda (Noetling, Rec. G.S.I., Vol. XXIV., p. 129 ; La Touche, Id., Vol. XXXV., p. 97).
Numerous salt springs occur in the Lower Irrawaddy valley in Pegu, and there was formerly a considerable manufacture of salt from them. Most of them are found along the base of the Arakan Yoma to the west of the river.
Mud Volcanoes.aThere are two groups of mud volcanoes in Burma, one at Minbu, on the west bank of the Irrawaddy, and the other in the islands of Ramri and Cheduba, between
NATIVES GOLD WASHING IN THE MOUNT PLACIER DEPOSIT, SHAN STATES.NATIVES GOLD WASHING IN THE MOUNT PLACIER DEPOSIT, SHAN STATES.