Lakes of Andine character, and others, exist throughout Mexico, the remnants of much larger lake systems, which occupied the filled-up "troughs" of the mountains, before described. Some of these sheets of water are exceedingly beautiful in their disposition and environment. Foremost among them is Chapala, in the State of Jalisco, near the handsome city of Guadalajara; and equally picturesque those smaller sheets of water in Michoacan--Lakes Cuitzeo and Patzcuaro. The remarkable groups of lakes in the Valley of Mexico, around which the Aztec civilisation flourished, comprise six salt-water and one (that of Chalco) fresh-water lake. The two maps given in these pages, of the disposition of these lakes at the time of the Conquest[26] and at the present day, respectively, show how remarkably their waters have shrunk during the intervening centuries. Indeed, this may have followed a certain drying-up process which seems to have been going on throughout the whole Andine region of the Americas, and which is evidenced by retiring snow-caps in Peru, and the receding of Lake Titicaca. [Footnote 26: See page 76.] The climate and temperature of Mexico follow certain marked zones, depending upon elevation, as already indicated in the opening chapter. Both on the Atlantic and Pacific slopes these zones are encountered--the _tierra caliente_ up to 3,000 feet elevation above sea-level; the _tierra templada_ to 5,000 or 6,000; and the _tierra fria_ above that altitude. On the tropical lowlands the heat of the torrid zone is experienced, but is not necessarily oppressive, although the European or American traveller who prefers a less enervating climate hastens to exchange that region for the more bracing air of the uplands. The night breezes, however, compensate largely for the heat of the sun, and render bearable, and indeed agreeable, the Vera Cruz littoral and the Yucatan peninsula, by the lowered temperature they afford. The rains also, which have their season from June to November, do much to refresh the atmosphere. Indeed, the year is divided mainly by the matter of rainfall into a wet and dry period, the summer and winter of other countries being unknown; or, rather, one might say, that the daytime is the summer and the night-time the winter, so marked are the diurnal changes of temperature.