Lastly, the Boulak Museum contains a whole series of stone weapons and implements, showing in their workmanship a progressive development similar to that we find in Europe. Many archæologists are of opinion that the worked flints found in the plains of Lower Egypt date from Neolithic times. Those alone are Paleolithic which have been found in a deposit hard enough for the hollowing out of tombs, which are certainly earlier than the eighteenth dynasty. We must add, however, that neither with the Palæolithic nor with the Neolithic relics have been found any bones of extinct animals. Some savants go yet further: they think that these worked stones are but chips split off by the heat of the sun.37 A phenomenon of this kind is mentioned by Desor and Escher de la Linth in the Sahara Desert; Fraas quotes a similar observation made by Livingstone in the heart of Africa, and one by Wetzstein, who, not far from Damascus; saw hard basalt rocks split under the influence of the early morning freshness. I have myself noticed similar phenomena in the Nile valley, but it must be added that the fragments of rock broken off by the combined influence of heat and humidity present very notable differences to those worked by the hand of man, and cannot really be mistaken for them. In Algeria have been preserved some most interesting relics of prehistoric times. If I am not mistaken, Worsaae was the first to note the worked stones in the French possessions in Africa. They have been picked up in great numbers, especially near the watercourses at which the ancient inhabitants of the country slaked their thirst, as do their descendants at the present day. The exploration of the Sahara daily yields unexpected discoveries; and already fifteen different stations formerly inhabited by man have been made out. In those remote days a large river flowed near Wargla, which was then an important centre, and a number of tools picked up bear witness to the former presence of an active and industrious population. At one place the flint implements, arrow-heads, knives, and scrapers are all of a very primitive type, and were found sorted into piles. This was evidently a _dépôt_, probably forming the reserve stock of the tribe. Wargla or perhaps Golea at one time appears to have been the extreme limit of the Stone age in Algeria, but quite recently traces of primitive man have been discovered amongst the Tuaregs. These relics are hatchets made of black rock, and arrow-heads not unlike those which the Arabs attribute to the Djinn; but as we approach the south we find the flints picked up more clumsily and unskilfully cut—a proof that they were the work of a more barbarous people with less practical skill. It is the megalithic monuments of Algeria, of which we shall speak more in detail presently, that are the most worthy of attention. As in India, we meet with them in thousands, and in certain parts of the continent they extend for considerable distances.