[56] There is no need to multiply examples, for every reader must have seen how rocks have been vaulted, and lands tunnelled, by underground rivers. At one part of her course, for example, the Guadiana flows underground for twenty miles, forming a vast bridge above which 100,000 sheep can pasture. [57] When the glacial theory of their formation was young and argumentative it encountered at first a sneering opposition from Sir Roderick Murchison, the famous geologist, who in 1864 wrote as follows to Sir William Denison: “In my anniversary address to the Geological Society you would see the pains I have taken to moderate the icemen, who would excavate all the rock-basins by glaciers eating their way into solid rocks.” But he failed to “moderate the icemen”; and Sir Roderick himself, a few years before his death, gave what is called “a tardy acquiescence” to their evidence. He became a frigid iceman. As Dr. Robert Munro has said, evidence which may be clear and convincing to one trained mind may not have the same effect on another--a fact which should at least warn us to be tolerant in matters of opinion. [58] Dates in Egyptian history are obscure, but these give the period approximately. [59] “Encyclopædia Britannica,” 11th edition, article “Arpino.” [60] M. Degrand, in his “Ponts en Maçonnerie,” draws attention to the fact that arches of this elementary sort have been discovered in Mexico where they represent a dead civilization to which no date can be assigned. Degrand draws his information from two books; “Histoire du Royaume de Quito,” par Don Juan de Velasco, Paris, 1840, and “Monuments anciens du Mexique,” par de Waldeck et Brasseur de Bourbourg, Paris, 1866. At Palanqué, in a building supposed to be a temple of the sun, a large bay that opens into the sanctuary has an elliptic arch formed with courses of dressed stone that project one beyond the other: “_un arc surbaissé formé d’assises de pierres de taille posées avec une forte saillie les unes par rapport aux autres._” [61] “Encyclopædia Britannica,” article “Mycenae”; see also Sir William Smith, “Dictionary of Greek and Roman Geography”; and note what M. Degrand says in his “Ponts en Maçonnerie.” [62] See E. Degrand, Vol. II, p. 124; and see also the “Traité d’Architecture,” by Léonce Reynaud. [Illustration: SMYRNA: ROMAN BRIDGE AND AQUEDUCT--THE POINTED ARCHES ARE EASTERN RESTORATIONS] CHAPTER THE THIRD A FEW WORDS ON THE ROMAN GENIUS I