This immunity may be attributed, in my opinion, to the innumerable and extensive caves with which the whole country is entirely honeycombed; and the large number of immense natural wells, called Senotes, that are to be found everywhere. These caves and senotes afford an outlet for the escape of the gases generated in the superficial strata of the earth.

It is very difficult without the help of the books of the learned priests of Mayab to know positively why they gave that name to the country known to-day as Yucatan. This percolating through the pores of the stone is afterward found filtered clear and cool in the senotes and caves. Mayab, in the Maya language, means a tammy, a sieve.

These and many other things are told in connection with the caves and senotes; and we find them mentioned in the writings of the chroniclers and historians from the time of the Spanish conquest. No lakes exist on the surface, at least within the territories occupied by the white men.

A mile or so from Uxmal is another aguada; but judging from the great number of artificial reservoirs, built on the terraces and in the courts of all the monuments, it would seem as if the people there depended more on the clouds for their provision of water than on the wells and senotes.

These senotes are immense circular holes, the diameter of which varies from 50 to 500 feet, with perpendicular walls from 50 to 150 feet deep. These holes might be supposed to have served as ducts for the subterranean gases at the time of the upheaval of the country. Now they generally contain water.

In some, the current is easily noticeable; many are completely dry; whilst others contain thermal mineral water, emitting at times strong sulphurous odor and vapor. Many strange stories are told by the aborigines concerning the properties possessed by the water in certain senotes, and the strange phenomena that takes place in others.