48 
TRANSACTIONS OF THE TEXAS ACADEMY OF SCIENCE. 
openings, or overflow valves, as it were, of underground rivers, flowing 
from south to north. In further evidence of this it should he stated that 
there are at intervals of a half mile, or a few hundred yards, several 
other cenotes stretching southward in a line from this first cenote of 
Xcolak. Crocodiles have been seen in the cenotes, so I was informed, 
and persons have been drowned while bathing in them, and. their bodies 
never recovered. Dr. Gaumer informs me that two species of fish Inhabit 
all of them— the only fresh water fish known in Yucatan — a pout and a 
sunfish. The writer caught both of these species with hook and line in 
Xcolak. 
An aguada is a water-hole that has a bottom, and is formed by water 
collecting during the rainy season in a natural depression of the ground. 
These are often of large size, holding sufficient water to last throughout 
the dry season. They are therefore entirely different in character from 
the cenotes. 
Such are the characteristics of the natural surface waters of Yucatan — - 
the water-holes where the wild animals of the country formerly drank, 
and do yet to this day. Many cattle water at them also, as shown by 
their tracks at Xcolak; and as witnessed by the countless thousands of 
ticks, both great and small, that swarm over the dead leaves and 
branches, and even on the heated surfaces of the bare ledges of rock that 
lie near the edge of the water, in places where cattle can get down the 
banks. Despite its appearance this water will quench the thirst, if given 
time and taken in sufficient quantity, and seems to leave no bad effects. 
At least the writer took copious draughts of it, warm and greenish as it 
was, during a whole day. Afterward, about 4 o’clock in the afternoon, 
impelled by the arid heat of the day, the dust, and the ticks, throwing 
all precautions to the winds, he stood on a clean bare platform of yellow 
rock in the shade on the north edge of Xcolak, where the depth was 
sheer and unknown, and dove many times into the greenish waters, and v 
swam in them; emerging therefrom with a delicious feeling of invigora- 
tion, both of body and mind. Such is Yucatan in the dry season. 
Since the above was written the peculiar features of Yucatan have 
been well described by Mr. Frank M. Chapman, of the American Mu- 
seum of Natural History, in a paper on birds observed at Chichen Itza 
(Bull. Am. Mus. X. H., vol. VIII, art. XVIII); and by Dr. C. F. Mills- 
paugh, of the Field Columbian Museum, in a work on the flora of Yuca- 
tan (Publications Nos. 4 and 15, Field Col. Mus., being Botan. series, 
Yol. I, Nos. 1 and 3). These, with some important observations given by 
Dr. Gaumer in a paper by Boucard on the birds of Yucatan (Proc. Zool. 
Soc. Lond., 1883, pp. 434-462), furnish a very clear idea of the meteoro- 
logic and geologic conditions prevailing in Yucatan, and the consequent 
quite anomalous biogeographic peculiarities which they, entail. 
