from Vera Cruz we are enabled to observe
something of the orographical structure of the country and the agencies
that have been at work. The coastal plains are sedimentaries of
Tertiary formation. The _medanos_, or sand-dunes, of the coast, blown
into singular forms by the prevailing _norte_ from the Gulf, give
place, as we proceed inland, to the foothills of the Eastern Sierra.
Here the Cretaceous formation is shown--the hard crystalline
limestone--and this, from its durable nature, has furnished material
for the new breakwater at Vera Cruz. Again, as we proceed, the lower
rocks are sheeted with the lava of former eruptions of volcanoes, worn
away at times by the ravines, and showing the points of Cretaceous
rocks protruding; and volcanic dust from the same source drifts hither
and thither, and at times has been compressed by the elements into a
soft tufa. The great sheets of lava, as in certain places in the Valley
of Mexico, are of remarkable appearance on the face of the country, the
scorified aspect seemingly little changed since the moment when the
fiery sheet must have poured devastatingly down the countryside.

The rock-formation of Mexican landscape gives rise to exceedingly
picturesque and romantic scenery in places, and to diverse
configurations of striking beauty, among which we shall often draw rein
as we journey, or which will attract us continually to the
observation-point of our Pullman car as the train winds along. Upon the
Gulf of Mexico or the Pacific slopes the territory is grand and broken
in the extreme, and presents curious and beautiful examples of
rock-scenery. The natural monoliths of the _barrancas_ of the State of
Hidalgo are strange examples of scenic geology; monumental caprice of
Nature in megalithic structure, as shown by the remarkable basalt
columns of the profound Gorge of Itzala. Vari-coloured lichens cover
these basalt pillars, affording singular contrast of light and shade.
Through the gorge a torrential stream flows, and the floor of the
valley is covered with fragments of obsidian, or volcanic glass,
gleaming black and brilliant, which has been brought down by the waters
from the Cerro de Navajas. This obsidian, or Itzli, was the material
from which the Aztecs made their knives and weapons, and this was their
prehistoric quarry. The red lava deserts of Sonora are weird and
remarkable.

Mexico is divided hydrographically into three systems: the Atlantic, or
Gulf of Mexico waters