place runs between the lake of Tĕzcūcŏ and the range of hills which form the Eastern boundary of the valley: that to the Capital passes near the Southern extremity of the lake, and joins the great La Puebla road about four leagues from the gates of the town. We returned to Mexico by this route after an absence of six days, during which time we had made the tour of the whole valley, with the exception of the portion lying between Chalco and Săn Aŭgŭstīn de las Cūēvăs, which I visited subsequently on my way to and from Cuĕrnăvācă and Cūāūtlă.
As the season was advancing, and the heat increasing daily in the Tierra Caliente, I resolved not to defer my expedition to that place, and commenced my journey within a very few days after returning from Chăpĭngŏ. The distance from Mexico to Cuĕrnăvācă does not exceed twenty leagues, (fifty miles,) but it is difficult to perform it in a single day on account of the passage of the mountains to the South of the valley, both the ascent and descent being exceedingly rocky and precipitous; I therefore left the Capital on the evening of the 25th of February, and slept at the village of San Agustin de las Cuevas, about four leagues off, where I was again indebted for lodgings to the hospitality of the Marquis of Vibanco. San Agustin was formerly the favourite residence of the nobility and great merchants of the Capital, whose houses and gardens formed, by degrees, a village, the appearance of which, in 1803, Humboldt describes as singularly
