This next period, that known to geologists as the post-glacial or early modern, was characterised by an entire change of physical conditions. The continents of the northern hemisphere were higher and wider than now. The details of this we have already considered, and have seen that at this time the Mediterranean was divided into two basins, and a broad fringe of low land, now submerged, lay around its eastern end. This was the age of those early palæolithic or palæocosmic men whose remains are found in the caverns and gravels of Europe and Asia. What was the condition of Egypt at this time? The Nile must have been flowing in its valley; but there was probably a waterfall or cataract at Silsilis in Upper Egypt, and rapids lower down, and the alluvial plain was much less extensive than now and forest-clad, while the river seems to have been unable to reach the Mediterranean and to have turned abruptly eastward, discharging into a lake where the Isthmus of Suez now is, and probably running thence into the Red Sea, so that at this time the waters of the Nile approached very near to those of the Jordan, a fact which accounts for that similarity of their modern fauna which has been remarked by so many naturalists. I have myself collected in the deposits of this old lake, near Ismailia, fresh-water shells of kinds now living in the Upper Nile. If at this time men visited the Nile valley, they must have been only a few bold hunters in search of game, and having their permanent homes on the Mediterranean plains now submerged.