No doubt the latter treatment answers very well! [Illustration: OLD MEXICAN BRIDGE NEAR TEZCUCO.] There is an old Mexican bridge near Tezcuco which seems to be the original _Puente de las Bergantinas_, the bridge where Cortes had the brigantines launched on the lake of Tezcuco.

This bridge has a span of about twenty feet, and is curious as showing how nearly the Mexicans had arrived at the idea of the arch.

It is made in the form of a roof resting on two buttresses, and composed of slabs of stone with the edges upwards, with mortar in the interstices; the slabs being sufficiently irregular in shape to admit of their holding together, like the stones of a real arch.

One may now and then see in Europe the roofs of small stone hovels made in the same way; but twenty feet is an immense span for such a construction.

I have seen such buildings in North Italy, in places where the limestone is so stratified as to furnish rough slabs, three or four inches thick, with very little labour in quarrying them out.