Page:Africa by Élisée Reclus, Volume 1.djvu/180

 reddish clay. Red is the normal colour of the Abyssinian rocks, the very veins

of quartz being often of a pink hue, caused by the oxide of iron. According to; Heuglin, at least one of the craters, from which were formerly ejected the Hamasen lavas, has been perfectly preserved. Rising midway between Keren and Adua to a height of about 400 feet, it is stated to present the appearance of a crater but recently extinct, although Rohlfs, following the same route, failed to discover it. To the south, on the eastern edge of the plateau, rise the isolated cones of other volcanoes. Some of the Tigré crests are veritable mountains, not merely in absolute altitude, but also in their elevation relative to the surrounding plains. Thus east of Adua, the cleft cone of Semayata attains a height of 10,306 feet, or over 3,000 feet above the town occupying a depression of the plateau at its base. 7 Eastwards, near the outer ledge of the uplands, are other lofty hills, one of which, Aleqwa, rises to a height of 11,250 feet. To the west, between the Mareb and Takkazeh, the plateau gradually falls, the relative heights of the mountains diminishing in proportion.

The loftiest headland of northern Abyssinia is separated from Tigré in the north and east by the semicircular gorge of the Takkazeh, while the affluents of this great river encircle the plateau on the south-west, thus isolating the Simen (Samen, Semen, Semien, or Semieneh), that is the "northern" or "cold region." The mean height of its escarpments exceeds 10,000 feet, whilst the surrounding valleys of the Balagas to the south and of the Takkazeh to the north, are respectively 5,000 and 6,000 feet lower. Hence the 80 Miles. waters flowing from the snowy Simen uplands have a very rapid course, in many places broken by cascades. One of these cataracts Heuglin describes as fading some 1,500 feet into a chasm which appears to have been a crater partly destroyed by erosion. Like most of the other fragments of the Abyssinian plateau properly socalled, the Simen uplands consist entirely of voleanic, basaltic, trachytic, phonolithic,