[Illustration: ARRIVAL OF THE EXPEDITION ON THE BANKS OF THE ZAMBESI.]
Perhaps the portions of Africa which are the most interesting on account of geological investigations which have been made, are the valley of the Nile in Egypt, and the Desert of Sahara. It is well known that the river Nile annually overflows its banks in Egypt, and the inundation remaining a considerable period, a thin layer of soil is each year added to that which existed there before. This Nile mud, as it is called by geologists, has been the subject of considerable scientific examination for many years. In his work upon the “Geological Evidences of the Antiquity of Man,” Sir Charles Lyell gives a full account of certain systematic borings in the Nile mud which were made between the years 1851 and 1854, under the superintendency of Mr. Leonard Horner, but who employed to practically conduct the examinations an intelligent, enterprising, and faithful Armenian officer of engineers, Hekekyan Bey, who had for many years pursued scientific studies in England, was in every way qualified for the task, and, unlike Europeans, was able to endure the climate during the hot months, when the waters of the Nile flow within their banks. Sir Charles Lyell states that the results of chief importance arising out of this inquiry were obtained from two sets of shafts and borings--sunk at intervals in lines crossing the great valley from east to west. One of these consisted of fifty-one pits and artesian perforations made where the valley is sixteen miles wide between the Arabian and the Libyan deserts, in the latitude of Heliopolis, about eight miles above the apex of the delta. The other line of pits and borings, twenty seven in number, was in the parallel of Memphis where the valley is five miles wide. Besides Hekekyan Bey, several engineers and some sixty workmen, inured to the climate, were employed for several years, during the dry season, in the furtherance of these interesting investigations.