Though sedimentary rocks occur in Mexico, they are not the predominant feature of the country.

Ridges of limestone hills lie on the slopes of the great volcanic mass toward the coast; and at a still lower level, just in the rise from the flat coast-region, there are strata of sandstone.

On our road from Vera Cruz we came upon sandstone immediately after leaving the sandy plains; and a few miles further on we reached the limestone, very much as it is represented in Burkart's profile of the country from Tampico upwards towards San Luis Potosi.

The mountain-plateaus, such as the plains of Mexico and Puebla, are hollows filled up and floored with horizontal strata of tertiary deposits, which again are covered by the constantly accumulating layers of alluvium.
Our heavy pull up the mountain-side has brought us into a new scene.
Every one knows how the snow lies in the valleys of the Alps, forming a plain which slopes gradually downward towards the outlet Imagine such a valley ten miles across, with just such a sloping plain, not of snow but of earth.

There has been no rain for months, and the surface of the ground is parched and cracked all over.