lost. This remarkable phenomenon is explained by the position of Aussa in the centre of a saline lacustrine depression several hundred feet below sea-level. While most of the other lagoons are highly saline, with thick incrustations of salt round their margins, Aussa remains fresh throughout the year, owing to the great body of water discharged into it by the Hawash.
Another lacustrine region extends from the Shoa heights south-west to the Samburu (Lake Rudolf) depression. In this chain of lovely upland lakes, some fresh, some brackish, some completely closed, others connected by short channels, the chief links in their order from north to south are:—Zwai, communicating southwards with Hara and Lamina, all in the Arusi Galla territory; then Abai with an outlet to a smaller tarn in the romantic Baroda and Gamo districts, skirted on the west sides by grassy slopes and wooded ranges from 6000 to nearly 9000 ft. high; lastly, in the Asille country, Lake Stefanie, the Chuwaha of the natives, completely closed and falling to a level of about 1800 ft. above the sea. To the same system obviously belongs the neighbouring Lake Rudolf (q.v.), which is larger than all the rest put together. This lake receives at its northern end the waters of the Omo, which rises in the Shoa highlands and is a perennial river with many affluents. In its course of some 370 m. it has a total fall of about 6000 ft. (from 7600 at its source to 1600 at lake-level), and is consequently a very rapid stream, being broken by the Kokobi and other falls, and navigable only for a short distance above its mouth. The chief rivers of Somaliland (q.v.), the Webi Shebeli and the Juba (q.v.), have their rise on the south-eastern slopes of the Abyssinian escarpment, and the greater part of their course is through territory belonging to Abyssinia. There are numerous hot springs in Abyssinia, and earthquakes, though of no great severity, are not uncommon.
(4) Geology.—The East African tableland is continued into Abyssinia. Since the visit of W. T. Blanford in 1870 the geology has received little attention from travellers. The following formations are represented:—
| Sedimentary and Metamorphic. | |
| Recent. | Coral, alluvium, sand. |
| Tertiary. | (?) Limestones Harrar. |
| Jurassic. | Antalo Limestones. |
| Triassic (?). | Adigrat Sandstones. |
| Archaean. | Gneisses, schists, slaty rocks. |
| Igneous. | |
| Recent. | Aden Volcanic Series. |
| Tertiary, Cretaceous (?). | Magdala group. |
| Jurassic. | Ashangi group. |
Archaean.—The metamorphic rocks compose the main mass of the tableland, and are exposed in every deep valley in Tigré and along the valley of the Blue Nile. Mica schists form the prevalent rocks. Hornblende schists also occur and a compact felspathic rock in the Suris defile. The foliae of the schists strike north and south.
Triassic (?).—In the region of Adigrat the metamorphic rocks are invariably overlain by white and brown sandstones, unfossiliferous, and attaining a maximum thickness of 1000 feet. They are overlain by the fossiliferous limestones of the Antalo group. Around Chelga and Adigrat coal-bearing beds occur, which Blanford suggests may be of the same age as the coal-bearing strata of India. The Adigrat Sandstone possibly represents some portion of the Karroo formation of South Africa.
Jurassic.—The fossiliferous limestones of Antalo are generally horizontal, but are in places much disturbed when interstratified with trap rocks. The fossils are all characteristic Oolite forms and include species of Hemicidaris, Pholadomya, Ceromya, Trigonia and Alaria.
Igneous Rocks.—Above a height of 8000 ft. the country consists of bedded traps belonging to two distinct and unconformable groups. The lower (Ashangi group) consists of basalts and dolerites often amygdaloidal. Their relation to the Antalo limestones is uncertain, but Blanford considers them to be not later in age than the Oolite. The upper (Magdala group) contains much trachytic rock of considerable thickness, lying perfectly horizontally, and giving rise to a series of terraced ridges characteristic of central Abyssinia. They are interbedded with unfossiliferous sandstones and shales. Of more recent date (probably Tertiary) are some igneous rocks, rich in alkalis, occurring in certain localities in southern Abyssinia. Of still more recent date are the basalts and ashes west of Massawa and around Annesley Bay and known as the Aden Volcanic Series. With regard to the older igneous rocks, the enormous amount they have suffered from denudation is a prominent feature. They have been worn into deep and narrow ravines, sometimes to a depth of 3000 to 4000 ft.
(5) Climate.—The climate of Abyssinia and its dependent territories varies greatly. Somaliland and the Danakil lowlands have a hot, dry climate producing semi-desert conditions; the country in the lower basin of the Sobat is hot, swampy and malarious. But over the greater part of Abyssinia as well as the Galla highlands the climate is very healthy and temperate. The country lies wholly within the tropics, but its nearness to the equator is counterbalanced by the elevation of the land. In the deep valleys of the Takazzé and Abai, and generally in places below 4000 ft., the conditions are tropical and fevers are prevalent. On the uplands, however, the air is cool and bracing in summer, and in winter very bleak. The mean range of temperature is between 60° and 80° F. On the higher mountains the climate is Alpine in character. The atmosphere on the plateaus is exceedingly clear, so that objects are easily recognizable at great distances. In addition to the variation in climate dependent on elevation, the year may be divided into three seasons. Winter, or the cold season, lasts from October to February, and is followed by a dry hot period, which about the middle of June gives place to the rainy season. The rain is heaviest in the Takazzé basin in July and August. In the more southern districts of Gojam and Wallega heavy rains continue till the middle of September, and occasionally October is a wet month. There are also spring and winter rains; indeed rain often falls in every month of the year. But the rainy season proper, caused by the south-west monsoon, lasts from June to mid-September, and commencing in the north moves southward. In the region of the Sobat sources the rains begin earlier and last longer. The rainfall varies from about 30 in. a year in Tigré and Amhara to over 40 in. in parts of Galla land. The rainy season is of great importance not only to Abyssinia but to the countries of the Nile valley, as the prosperity of the eastern Sudan and Egypt is largely dependent upon the rainfall. A season of light rain may be sufficient for the needs of Abyssinia, but there is little surplus water to find its way to the Nile; and a shortness of rain means a low Nile, as practically all the flood water of that river is derived from the Abyssinian tributaries (see Nile).
(6) Flora and Fauna.—As in a day’s journey the traveller may pass from tropical to almost Alpine conditions of climate, so great also is the range of the flora and fauna. In the valleys and lowlands the vegetation is dense, but the general appearance of the plateaus is of a comparatively bare country with trees and bushes thinly scattered over it. The glens and ravines on the hillside are often thickly wooded, and offer a delightful contrast to the open downs. These conditions are particularly characteristic of the northern regions; in the south the vegetation on the uplands is more luxuriant. Among the many varieties of trees and plants found are the date palm, mimosa, wild olive, giant sycamores, junipers and laurels, the myrrh and other gum trees (gnarled and stunted, these flourish most on the eastern foothills), a magnificent pine (the Natal yellow pine, which resists the attacks of the white ant), the fig, orange, lime, pomegranate, peach, apricot, banana and other fruit trees; the grape vine (rare), blackberry and raspberry; the cotton and indigo plants, and occasionally the sugar cane. There are in the south large forests of valuable timber trees; and the coffee plant is indigenous in the Kaffa country, whence it takes
