the nature of the strata that form our coal-measures, sandstones alternating with shales, these again with coals and fire-clays, together also with the terrestrial origin of the coal-seams, and the occasional presence of true marine organisms, make it evident that, to obtain any modern analogue to such a condition of things, we must examine those localities where large bodies of fresh water, carrying sediment and vegetation from the land, mingle with the sea. Let us then look for a little at the operations now in progress at the mouths of the larger rivers, and mark how far they elucidate the structure and history of a coal-field. "Egypt is the gift of the Nile." Such was the conclusion arrived at by one of the most diligent observers of ancient Greece--the venerable Herodotus.[67] He sailed up the river marking all the leading features in its scenery, and noting the more apparent evidences of ancient physical changes. His remarks on these subjects form one of the earliest specimens of scientific reasoning that have come down to us, and are remarkable for their correctness and the truly inductive mode of thought which they evince. Modern travellers have amply confirmed the opinions of the father of history, and we now know that but for its central river, Egypt would be a vast dreary expanse of arid sand like the neighbouring deserts of Lybia. The Nile, by annually inundating the country, deposits over it a stratum of rich loam, and thus not only waters the land, but continually renews the soil. The sediment in this way brought down has gradually encroached upon the waters of the Mediterranean, being heaped up at the river mouth into shifting sand-banks, islets, and great tracts of low, swampy ground, slightly raised above the sea-level. Through this series of silting deposits, the river sends a number of branches, often winding in labyrinthine convolutions, and ever changing their course, by wearing away the silt at one place, and throwing it down at another. The area traversed by the mouths of the Nile was called by the Greeks the Delta, from its similarity in form to the Greek letter, and the name has since been given to all such fluviatile deposits, whether they have this general form or not. [Footnote 67: _Euterpe_, 5.--His words are very emphatic. "To one of ordinary intelligence, who has not heard of it before, but sees it, Egypt is manifestly land acquired by the inhabitants, and a gift from the river--δωρον τον ποταμον." The 10th and 12th chapters of the same book deserve especial study for the admirable inductive style in which the historian compares the phenomena observable in Egypt with what were well known as the results of river action in other lands. The passages might be quoted word for word in the most rigid scientific argument of any modern geologist.]