It is to be greatly regretted that no comprehensive geological surveys of Africa have ever been made; because there are certain questions, eventually to be settled by geology, whose determination, it appears to be agreed, will be finally resolved by investigations in this continent. In a volume of this nature, designed for the general reader, those facts and reasonings only need be referred to which may be supposed to have the most interest. Reference has already been made to Sir Roderick Murchison’s exposition of the trough-shaped form of South Africa in his discourse before the Royal Geographical Society in 1852--an exposition which was so remarkably substantiated by Dr. Livingstone in his journey across the continent from Loanda to Kilimane. Though in its geographical configuration Africa is not greatly unlike South America, in its geological structure it much more resembles the northern continent of the western hemisphere. The Appalachian range of mountains extending through nearly the whole of the eastern portion of North America, parallel with the coast, and the Rocky Mountains and Sierra Nevadas in the west, bear a notable resemblance to those ranges of mountains in Africa, which, rising first in the northern portions of Senegambia, pursue a south-easterly, then a southerly course to near the southern limit of the continent, when they sharply bend toward the northeast, and with many lofty peaks, some of which reach the region of eternal snow, pass through Mozambique, Zanguebar, and end not until after they have passed through Abyssinia and Nubia, and penetrated the limits of Egypt. In Tripoli, Tunis, Algeria, and Morocco, is the Atlas range, between which and the beginning of the other the distance is hardly so great as that between the southern limits of the Appalachian range and the mountains of Mexico. The course of each of the great rivers of these continents is also across the degrees of latitude instead of generally parallel with the equator, as is the case with the great river of South America. There is a similarity also between North America and Africa in an extensive system of inland lakes of fresh water and vast extent. [Illustration: ARAB CHIEF OF CENTRAL AFRICA.]