flows for 70 miles nearly due north to the south side of Lake Tsana
(Dembea). This great island-studded basin, which stands some
3000 feet below the normal level of the plateau, has somewhat the
aspect of a flooded crater, being of nearly circular form, with a
diameter of about 40 miles, an area of over 1200 square miles, and
a depth in some parts of 250 feet. Tsana has been identified with
the Coloe Palus of the ancients, which, although placed some
12° too far south by Ptolemy, was described as a chief reservoir of the Egyptian Nile and the source of the Astopus, which
was certainly the Blue Nile. At the south-east corner the rim of
the crater is, as it were, breached by a deep crevasse through which
the Abai escapes, and here develops a great semicircular bend
like that of the Takazze, but in the reverse direction—east, south,
and north-west—down to the plains of Sennar. In this section of
its course its swirling waters rush over a long series of cataracts
and rapids, descending from a height of 6000 feet at the outlet to
about 1400 feet at Fazokl, where it crosses the Abyssinian frontier,
and flows with a sluggish current through the plains of Sennar to its
confluence with the White Nile at Khartum, 1300 feet above sea level. At Fazokl, where it becomes the Bahr-el-Azreq (Blue Nile),
it is joined on its left bank by the auriferous Tumat, and higher
tip by the Yabus, both intermittent affluents from the South
Ethiopian uplands. In Sennar it receives on its right bank two
important tributaries from the Abyssinian heights, the Cinder, a
very long and apparently perennial stream, and the Rahad,
waterless in the dry season, copious and richly charged with sediment during the rains from June to September. At this period
the discharge of the Blue Nile rises from 6000 to 220,000 cubic feet
per second, thus greatly exceeding that of the White Nile itself,
which is only about 175,000 cubic feet during the floods above the
confluence. The economic importance of the Blue Nile as the
great fertiliser of Egypt is elsewhere discussed. (Nile; Egypt.) On
the east side of the Abyssinian plateau the chief fluvial basin is
that of the Hawash (Awash, Awasi), which rises on the landward
side of the coast range, and, like the other large Ethiopian rivers,
describes a great semicircular bend on its seaward course between
the Shoa uplands and Gallaland. After emerging on the Afar
(Danakil) lowlands through a broad breach in the eastern escarpments of the plateau, it is joined on its left bank by its chief
affluent, the Germama (Kasam), and then trends round to the
north-east in the direction of Tajura Bay. Here the Hawash is
a copious stream nearly 200 feet wide and 4 feet deep, even in
the dry season, and during the floods rising 50 or 60 feet above
low-water mark, thus inundating the plains for many miles along
both its banks. Yet it fails at any time to reach the coast, and
after a winding course of about 500 miles runs out in the Lake
Ausa basin, some 60 or 70 miles from the head of Tajura Bay.
This remarkable phenomenon is explained by the position of
Ausa in the centre of a saline lacustrine depression, which stands at
present several hundred feet below sea-level. Recent surveys give
174 metres for the Assal lakelet near the bay, and several of the
other surrounding badds (basins) may even be lower, although the
Hawash itself still flows at an elevation of 620 metres below its
junction with the river Addifuha, where it begins to descend
through a chain of badds down to Ausa. While most of the other
lagoons are highly saline, with thick incrustations of salt round
their margins, Ausa remains fresh throughout the year, owing to
the great body of water discharged by the Hawash into this closed
basin. Formerly the whole of the Afar and neighbouring Adal
(Somali) and Dawari (Galla) territories formed part of the Red
Sea, which flooded the now dry rift-valley right up to the
foot of the coast range. Another lacustrine region, not however
of marine, but perhaps of igneous origin, extends from the
Shoa heights southwards to the Samburu 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 ZwTai, 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 side by grassy slopes
and wooded ranges from 6000 to nearly 9000 feet high ; lastly, in
the Asilli country Count Teleki’s Lake Stefanie, the Chuwaha
of the natives, completely closed and falling to a level of 3700 feet
above the sea. To the same system obviously belongs the neighbouring Lake Rudolf (Gallopa or Buzz), which is larger than all
the rest put together, and terminates southwards with an active
volcano, thus betraying the igneous origin of these basins and
bringing them into line with Gregory’s “Great Rift Valley.”
With the determination of the lower course of the Omo, one of the
few remaining problems in African geography has been solved.
Its upper course had long been identitied with the Fintire, which
rises on the northern slope of the Bore heights about 150 miles
south-west of Addis-Abbaba, and, after flowdng 38 miles north,
bends round east and south to the Zighero district, where it takes
the name of Omo. It was then supposed either to trend east to
the Juba or west to the Sobat until Bottego, on his last disastrous
expedition (1896), found that
it discharged into the closed basin
of Lake Rudolf. Its low7er reaches have since been visited by
Cavendish, Donaldson Smith, Austin, Wellby, Leontieff, Bulatovich, and others ; and the Niamiam, as it is here called, is now
known to be a noble perennial waterway, which is joined along its
middle course by the Gojeb, Jibie, Gumi, Kabish, and many other
affluents on both its banks, and for some miles above its mouth at
the north end of the lake flows in a deep channel varying with the
seasons from 50 to.500 feet in width. Throughout its entire
length of over 370 miles it has a total fall of about 6000 feet (from
7600 at its source to 1600 at lake-level), and is consequently a very
rapid stream, being broken by the Kokoby and other falls, and
navigable only for a short distance above its mouth. The Baraka,
Shebeyli, Juba, and Sobat, belonging only for short stretches of their
upper courses to the Ethiopian region, will be more .conveniently
described in their principal drainage areas. (Nile; Somaliland.)
The vertical disposition of the climatic zones, which is more or less common to all highland regions, and of which Mexico offers a typical example, is somewhat modified on the Ethiopian uplands by the irregular distribution of the rainfall, Climate; the varying aspect of the land, and other local con- flora; ditions. Nevertheless, striking analogies have been fauna. observed between the superimposed Mexican and Abyssinian zones, so that it is possible to construct a comparative table of the more salient features, and even of the respective terminologies of each, as under :—
| Climatic Zones. | Mean Range of Altitudes. |
Mean Range of Temperatures. |
Characteristic Flora. | |||
| 1. (Hot) |
Mex. | Tierra Caliente. | 0 to 4,000 ft. | 77°-82° F. | Banana, sugar, cocoa-nut, coffee. | |
| Abys. | Kwalla | 0 to 5,000 ft. | 70°-100° F. | Banana, cotton, date, coffee. | ||
| 2. (Temp.) |
Mex. | Tierra Templada | 4000 to 6,000 ft. | 62°-70° F. | Maize, wheat, tobacco, beans. | |
| Abys. | Voïna-dega | 5000 to 8,000 ft. | 60°-80° F. | Wheat, bamboo, terebinth, pulse, citron. | ||
| 3. (Cold) |
Mex. | Tierra Fria | 6000 to 9,000 ft. | 58°-64° F. | Jucca, pine, cedar. | |
| Abys. | Dega | 9000 to 14,000 ft. | 45°-60° F. | Pine, barley, oats, scrub. | ||
The correspondence is even closer than appears from this table, because the Mexican scheme excludes Alpine heights, which are included in the Abyssinian dega. Allowance has also to 0be made for the much lower latitude of the Ethiopian region (4 -16° N.) compared with that of Mexico (16°-32° N.), while the mean altitude of the two plateaux is about the same (7000 feet). Besides the above-mentioned plants, many other tropical forms— indigo, tamarinds, ebony, gummiferous acacias, baobabs—flourish in the Kwalla bottom-lands. Nearly all the European cereals, grasses, and shell fruits are indigenous in the Voina-dega, where are also met the orange, peach, apricot, and other fruit trees, besides the vine, zegba (Podocarpus), dhurra, tief, kolkwal {Euphorbia abissinica), juniper, and several species of sycamores, some of which grow to a gigantic size in the sheltered gorges of the intermittent mountain torrents. But in the dega, which includes all the more elevated plains, ambas, and upland valleys, little thrives except the hardier cereals, scrubby plants, and rich grasses affording excellent fodder for cattle, goats, and the long-haired native sheep. The South Ethiopian region between the Hawash and White Nile basins has also its three zones, which, as determined by M. Michel of the Bonchamps Mission {La Geographic, July 1900), are :—1. The wide treeless tableland between 6500 and 8500 feet high, covered in places with limestone strata, deeply scored here and there by the running waters. 2. The uplands between the sources of the Hawash and Omo rivers, stretching west to the valley of the Didessa, affluent of the Sobat. Here the ranges, which fall little below 10,000 feet, and are separated by deep valleys, are clothed with low forest, and lower down with scrub which has been partly cleared for cultivation. 3. A low, hilly region from 5000 to 5500 feet high, with scarcely any intervening level ground, but superabundantly watered by streams flowing to the Sobat, and yielding large quantities of coffee and honey. The hitherto almost unknown region stretching still farther south towards Lakes Rudolf and Stefanie proves to be much more elevated, and also more productive, than had been supposed. Alpine heights—one (Guge) nearly 14,000 feet—are spoken of by Bottego, Donaldson Smith, and other explorers near the lakes, and the waterparting between the Omo and Sobat basins, to which Bulatovich has given the name of the Tsar Nicholas Range, is surmounted in its northern section by several peaks over 10,000
