Page:Philosophical Transactions - Volume 145.djvu/123

Rh may have been brought down at irregular intervals, and by unequal increments, they afford no data by which we can estimate the rate of increase of the detritus brought down by the same river, previously to the foundation of the sea-port town; nor can we discover whether the formation of the land, composed of travelled materials on which the town was built, and which stretches far inland from it, was the operation of a brief period of time or of one continued through a long series of ages.

Egypt affords the earliest authentic evidence of the existence of the human race, recorded in works of art; in its monuments we find the dawn of the historical period and of civilization; and that land alone, of all parts of the world as yet known to us, offers an instance of a great geological change that has been in progress throughout the whole of the historical period, down to the present day; and which, we have very reasonable grounds for believing, had been going on with the same uniformity for ages prior to that period when our reckoning of historical time begins. I refer to the annual inundation of the Nile, and the sediment that falls from its waters on the surface of the land it overflows.

The question of the raising of the valley of Upper Egypt and the formation of the Delta by the deposit from the Nile, has been a subject of controversy from the days of to our own time: there is scarcely a writer on Egypt who does not allude to it. , who visited Egypt about 455 years before our era, says that "the soil of Egypt is a black earth, cracked and friable, as if it had been formed by the mud brought down by the Nile from Ethiopia, and which has been accumulated by its overflowings. The greater part of the land is a present from the Nile, as the priests informed me, and it is the conclusion to which I have myself arrived. it seemed to me, in truth, that the whole extent of country lying between the mountains above Memphis was formerly an arm of-the sea." Thus far his conclusions are in the main correct; but he goes farther, conceiving that Lower Egypt was wholly formed within historical time; for he says, "in proportion as the land extended from Upper Egypt by the deposits of the Nile, a part of the inhabitants migrated into Lower Egypt." This latter theory of, which an examination of the geological features of the country has shown to be erroneous, was even recently adopted by the acute and learned , as we learn from the lectures he delivered at Bonn, a very short time before his death.

The theory of, supported by and , was combated in a learned disquisition, in the Memoirs of the Academy of Inscriptions and Belles Lettres, by , bearing the date of 1742 , and this memoir was replied to fifty years afterwards by the eminent geologist. The latter author observes, that the question of the effects of the inundations of the Nile on the formation of the Delta had been treated of by the