Page:Africa by Élisée Reclus, Volume 1.djvu/179

 The crest of this mountain is a chaotic mass of rocks of all sizes, which might be supposed due to volcanic eruptions, but which are indebted for their present form to slow meteoric action. These rocks, lying obliquely on each other, form the arched roofs of numerous caves, which have been artificially worked into dwellings and in many places connected by galleries. One has even been hewn into a monastery and a church, which is annually visited by thousands of pilgrims from every part of Abyssinia. South of Keren stands the Isad Amba, or "White Fortress," another rock famous in the religious annals of Abyssinia. This

mountain rises almost vertically about 4,000 feet above the Barka Valley, its sharp peak scarcely affording sufficient space for the site of the convent walls.

In Abyssinia proper, commencing at the Hamasen plateau, the base of the uplands is at once broader and more elevated than in the Bogo (Bilen) country, its mean height exceeding 7,460 feet. Like most of the Ethiopian mountain masses, Humasen is covered with trachytic or basaltic lavas, which are themselves overlaid by a reddish or yellowish earth. There can be little doubt that this ochrous soil covering the Abyssinia plateaux consists of decomposed lava, like the vast laterite masses stretching over the Dekkan and most of southern India.

In various localities basaltic columns are found partially changed to masses of