From the decomposed porphyry of the mountains carbonate of soda comes down in solution to the valleys.  Much of this is converted into natron by the organic matter in the soil, and forms a white crust on the earth.  More of the carbonate of soda, mixed in various proportions with common salt, drains continually out in the streams, or filters into the ground and crystallizes there.  This is why there is not a field to be seen, and the land is fit for nothing but pasture.  But when the rains come on in a few months, say our friends in the diligence, this dismal waste will be a luxuriant prairie, and the cattle will be here by thousands, for most of them are dispersed now in the lower regions of the tierra templada where grass and water are to be had.

My companion and I climb upon the top of the diligence to spy out the land.  The grand volcano of Orizaba had been hidden from us ever since that morning when we saw it from far out at sea, but now it rises on our left, its upper half covered with snow of dazzling whiteness,—­a regular cone, for from this side the crater cannot be seen.  It looks as though one could walk half a mile or so across the valley and then go straight up to the summit, but it is full thirty miles off.  The air is heated as by a furnace, and as we jolt along the road the clouds of dust are suffocating.  We go full gallop along such road as there is, banging into holes, and across the trenches left by last year’s watercourses, until we begin to think that it must end in a general smash.  We came to understand Mexican roads and Mexican drivers better, even before we got to the capital.

Before us and behind lay wide lakes, stretching from side to side of the valley; but the lake behind followed us as steadily as the one before us receded.  It was only the mirage that tantalizes travellers in these scorched valleys, all the long eight months of the rainless season.  It seemed beautiful at first, then monotonous; and long before the day was out we hated it with a most cordial and unaffected hatred.

Soon a new appearance attracted our attention.  First, clouds of dust, which gradually took a well-defined shape, and formed themselves into immense pillars, rapidly spinning round upon themselves, and travelling slowly about the plain.  At one place, where several smaller valleys opened upon us, these sand-pillars, some small, some large, were promenading about by dozens, looking much like the genie when the fisherman had just let him out of the bottle, and saw him with astonishment beginning to shape himself into a giant of monstrous size.  Indeed I doubt not that the story-teller was thinking of such sand-pillars when he wrote that wonderful description.  You may see them in the East by thousands.  As they moved along, they sucked up small stones, dust, and leaves; and our driver declared that they had been known to take the roofs off houses, and carry flocks of sheep into the air; “but these that you see now,” said he, “are no great matter.”  We estimated the size of the largest at about four hundred feet in height, and thirty in diameter; and this very pillar, walking by chance against a house, most decidedly got the worst of it, and had its lower limbs knocked all to pieces.