36 A NATURALIST IN MEXICO. 



sumed all manner of fantastic shapes, and seemed like the 

 bodies of monstrous animals. From this passage others 

 branched off to right and left. Beyond the circular open- 

 ing we passed into a large vaulted chamber of stone, 

 with a high roof supported by enormous stalactitic pillars. 

 Farther on we climbed up a high, broken piece of rock, and 

 descended again by a low, narrow opening, through which 

 we were obliged to crawl, and which, from its closeness, 

 and the heat and labor of crawling through it, made us pant 

 with exhaustion. This brought us to a rugged, perpen- 

 dicular hole, three or four feet in diameter, with steps barely 

 large enough for a foothold, worn in the rock. The pass- 

 age here descended rapidly, and we were again obliged to 

 stoop to avoid knocking our heads against the roof of the 

 passage. It then enlarged into a rather spacious cavern, 

 which was filled with gigantic stalactitic columns. Here 

 our journey in this direction ended. Several passageways 

 led from this chamber, but they had not been explored, and 

 the guides would not attempt their exploration. What lay 

 beyond no one knew. Leaving this chamber we returned 

 to the circular well near the mouth of the cave, and explored 

 a long passage leading in a northerly direction. This was 

 found to descend rapidly for three or four hundred feet, and 

 then to end in a shelving point. The greatest depth of this 

 cave was 180 feet, and the longest passage explored by us 

 one eighth of a mile. The whole range of hills was com- 

 posed of transition, or mountain limestone, and was said 

 to contain many such caves as the one we had just visited. 

 Swallows {^Stelgidoptej'yx serripeniiis) were seen flying about 

 the outer chamber of the cave in great numbers, and seemed 

 to be constructing nests on the rugged face of the walls. 

 The view from the summit of the Sierra was very picturesque; 

 away to the south could be seen two parallel ranges of 

 mountains, the intervening spaces being well wooded. To 



