There is good reason to credit the Egyptian traditions that the first colonists crossed over from Southern Arabia by the Red Sea from that land of Pun to which the Egyptians attributed their theology, and settled in the neighbourhood of Abydos, and that they made their way thence to the northward, at a time when the delta was yet a mere swamp,[69] and when they had slowly to extend their cultivation in Lower Egypt by dikes and canals. If we ask when the first immigrants arrived, we are met by the most extravagantly varied estimates, derived mainly from attempts to deduce a chronology from the dynastic lists of Egyptian kings. That these are very uncertain, and in part duplicated, is now generally understood, but still there is a tendency to ask for a time far exceeding that for which we have any good warrant in authentic history elsewhere. Herodotus estimated the time necessary for the deposition of the mud of the delta at 20,000 years; but if we assume that this deposit has been formed since the land approximately attained to its present level, allowing for some subsidence in the delta in consequence of the weight of sediment, and estimating the average rate of deposition at one fifteenth of an inch per annum, which is as low an amount as can probably be assumed, we shall have numbers ranging from 5,300 to about 7,000 years for the lapse of time since the delta was a bay of the Mediterranean. [69] _Herodotus_, Book II. chap. 15. It is true that the recent borings in the delta, under the officers of the British Engineers, have shown a great depth in some places without reaching the original bottom of the old bay. Some geologists have accordingly inferred from this a much greater age for the deposit than that above stated,[70] and in this they are in one respect justified; but they have to bear in mind that only the upper part of the material belongs to the modern period. A vast thickness is due to the pleistocene and pliocene ages, when the Nile was cutting out its valley and depositing the excavated material in the sea at its mouth. A careful examination of the borings proves by their composition that this is actually the case.[71] Geologists who have been guided by these facts in their estimates of time have been taunted as affirming that a great diluvial catastrophe occurred while quiet government and civilised life were going on in Egypt. The evidence for this early date of Egyptian colonisation of the Nile valley is, as everyone knows, doubtful, and it might be retorted that archæologists represent the Egyptian government as dating from a period when the Nile valley was an inland district, and when the centres of human population must have been, principally at least, on lands now submerged. [70] Judd, _Report to Royal Society_, 1885. [71] _Modern Science in Bible Lands_, where evidence of similar dates in other countries is stated.