Humboldt's expression) succeed each other in layers, (se suivent par couches;) and the traveller passes in review, in the course of two days, the whole scale of vegetation.
The parasitic plants of the Tropics are exchanged at a very early period for the evergreen oak, and the deadly atmosphere of Vĕrăcrūz, for the sweet, mild air of Jălāpă: a little farther, the oak gives place to the fir; the air becomes more piercing; the sun, though it scorches, has no longer the same deleterious effect upon the human frame; and nature assumes a new and peculiar aspect. With a cloudless sky, and a brilliantly pure atmosphere, there is a great want of moisture, and little luxuriancy of vegetation: vast plains follow each other in endless succession, each separated from the rest by a little ridge of hills, which intersect the country at regular intervals, and appear to have formed, at some distant period, the basins of an immense chain of lakes. Such, with some slight variations, is the character of the Table-land from Mexico to Chĭhūāhuă. Wherever there is water, there is fertility; but the rivers are few, and insignificant, in comparison with the majestic streams of the United States; and, in the intervals, the sun parches, in lieu of enriching the soil. High and barren plains occupy but too large a portion of the centre of the country, between Zăcătēcăs, Dŭrāngŏ and Săltīllŏ; nor does nature recover her wonted vigour, until the streams, which gradually filter from the Cordillera,
