in the graphic chapters of Herodotus, and the changes which the lapse of more than twenty centuries has since wrought in its configuration. The rivers of Europe would detain us long, not less perhaps by their historic interest than by the variety and attractiveness of their physical phenomena. One could scarce help lingering over the Rhine, with its source among Alpine glaciers, its lakes and gorges, its castles and antique towns; and when once the narrative entered the classic ground of Italy, it would perhaps become more antiquarian than geological. The ravine of Tivoli, for instance, would certainly lay claim to a whole chapter for itself, with its long-continued river action, its ancient travertin, its beautiful calcareous incrustations, and above all its exquisite scenery. [Footnote 53: "Fontium qui celat origines Nilus" a description not less true now than in the days of the Sabine bard.] "Domus Albuneæ resonantis, Et præceps Anio, ac Tiburni lucus, et uda Mobilibus pomaria rivis."[54] [Footnote 54: "Albuna's grey re-echoing home, And Anio, headlong in his foam, And grove of Tivoli, And orchards with their golden gleam, Whose boughs are dipping in the stream That hurries to the sea." Hor. _Carm._ L vii. 12.] And when could we exhaust all, that might be said about the rivers of our own land? "Of utmost Tweed, or Ouse, or gulfy Dun, Or Trent, who, like some Earth-born giant, spreads His thirty arms along the indented meads Or sullen Mole, that runneth underneath; Or Severn swift, guilty of maidens' death; Or rocky Avon, or of sedgy Lee; Or coaly Tyne, or ancient hallow'd Dee; Or Humber loud, that keeps the Scythian's name; Or Medway smooth, or royal-towered Thame." Passing to the new world, a vast field would spread out before us: the Mississippi, the Atchafalaya, the Ohio, the St. Lawrence, the Amazon, and many other rivers that in some cases rise high among the regions of perpetual snow, and after traversing large areas of country in the temperate zone, fall into the waters of tropical seas. By studying such examples of river-action and delta-formation as are presented by these gigantic streams, we should arrive at some conception of the conditions anciently at work in producing our present coal-fields. Nor would our researches assume aught like completion until after a scrutiny of all the larger and more important rivers of the globe. Such a work could be undertaken, perhaps, only by another Humboldt. Its successful accomplishment would certainly insure the highest renown to its author, and incalculable benefits to science.