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Another is mentioned by Clavigero: “The Bridge of God; thus they call a vast mass of earth above the deep river Atoyaque, near the village of Moleaxac, about a hundred miles from Mexico, in the direction of Scirocco, over which carts and carriages pass without difficulty. It might be taken for a fragment of the adjacent mountain, torn from it, in times of old, by an earthquake.”—History of Mexico, L. 1, § 3.

This cave, or passage, is cut out of the live rock with such precision that the inequalities on one side correspond with the projections on the other side, as if that mountain had parted on purpose, with its turns and windings, to make a passage for the waters between the two lofty walls on both sides; they being so like each other, that if they were joined together they would cover each other without leaving any cavity between them.

“Marble is very frequently found on the banks of most of these rivers: slate rocks also are seen there, and I have often had occasion to observe the close affinity between these two kinds of rock. I had made the same remark in the Cordilleras. There slate and marble often touch one another, and I have seen some rocks which were slate at one end and marble at the other. Every new liquefaction of rock, analogous to slate, and cementing its layers, makes the whole rock harder and more compact; the rock is no longer slate, but becomes marble. Another rock, called schist, is also subject to this transformation. Sometimes the layers not only are cemented together, but one piece of rock joins, as if by chance, another; and if the whole is then exposed to the action of gravel and of flint stones, rolled by flowing water, it is, as it were, rounded off, becomes nearly cylindric, and assumes the appearance of the trunk of a tree; so that it is