Besides this, traces of more recent volcanic action abound, in the
shape of numerous extinct craters in the high plateaus, and immense
"pedrigals" or fields of lava not yet old enough for their surface to
have been disintegrated into soil. 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. There is hardly a tree to be
seen except clumps of wood on the mountain-sides miles off,--no
vegetation but tufts of coarse grass, among which herds of
disconsolate-looking cattle are roaming; the vaqueros, (herdsmen) are
cantering about after them on their lean horses, with their lazos
hanging in coils on their left arms, and now and then calling to order
some refractory beast who tries to get away from the herd, by sending
the loop over his horns or letting it fall before him as he runs, and
hitching it up with a jerk round his hind legs as he steps within it.