TRANSACTIONS OF SECTION E. 577 
2. The Newly Discovered Cave of Atoyac (Mexico) : A Contribution to_the 
Study of Cave-development. By M. M. Autores, L.es-Sc., L.G.S, 
Introduction.—When we follow the railway line from Vera Cruz to the City 
of Mexico we cross, first, a line of dunes behind which extends a swampy plain of 
Pleistocene sands. Ata slightly higher level stands another plain of Pliocene age, 
built chiefly by the mud streams coming down from the neighbouring volcanic 
cones, After Passo del Macho we meet for the first time a longitudinal ridge of 
limestone, which is a spur of the Western Sierra Madre. This limestone contains 
a number of hippurites and rudiste, establishing its Middle Cretaceous age. The 
railway runs over this limestone from the 80th kilometre across Orizaba as far 
as the 180th kilometre near the station of Esperanza, after which the country is 
completely covered by volcanic ejecta. 
Upon this calcareous bed, sink-holes swallowing up rivers are of very frequent 
occurrence. The Spanish name for a funnel-shaped depression of this kind is 
sumidero, and one of the railway stations has been called by this name. These 
sumideros correspond to an extensive system of subterranean channels; the deepest 
are still used by underground streams, whereas the higher ones are mostly dry, 
and have reached a state of old age, characterised by the deposition of sinter and 
the formation of stalactites tending to obstruct them again. The cave of Atoyac 
is an instance of this class. 
Location —The mouth of the cave is located amidst steep slopes 900 metres east 
of the station at Atoyac, about 70 metres below the railway, and 26 metres above the 
present level of the river flowing at the bottom of the gorge. The opening was 
discovered during the summer of 1906 by Seiior Sanchez when hunting big game 
among these precipices. During the following autumn the writer had an oppor- 
tunity of visiting it with Professor C. de la Torre (Havana University), and of 
making a rapid survey of it. The entrance is partially closed by the fall of débris. 
The strike of the cretaceous limestone at this point is north to south, the dip is 
about 75 degrees east, and the jointing is approximately perpendicular to the strike. 
A glance at the plan of the cave shows that the succession of channels and 
chambers is not random, but presents a rectangular arrangement. The main 
passages run in a north to south direction, according to the strike ; they may be 
called subsequent. They are connected by smaller transverse corridors corre- 
sponding to the joint planes and obsequent to the direction of the strata. 
The features of the interior were briefly described and accounted for. A trans- 
verse corridor is partially closed by a high ridge which has been probably formed 
by the blocks of limestone falling from the roof, damming back the water and 
slowly covered by the sinter deposited by the cascade. Near the top of the cave 
is a series of narrow tortuous passages, recalling to the mind the worm of a still. 
They are superposed one above another, and suggest the progressive tunnelling down 
of the waters. All these narrow tunnels run to the bottom of a vertical shaft, 
which the writer was not able to explore; but a constant current of fresh air 
(temperature 20° Centigrade) gives evidence of a direct communication with the 
surface of the soil. It corresponds in all probability to a chimney by which the 
surface waters were formerly engulfed. 
Conclusion.—A careful analysis of the succession of chambers composing the 
cave of Atoyac proves that the work of excavation of the limestone by the waters 
has been controlled, down to its most minute details, by the planes of bedding and 
by the system of joints and of fractures. Subterranean waters always take 
ee of these natural planes of division in dissolving or in eroding calcareous 
rocks. 
Up to the great dam, pottery has been found, and there is evidence of the 
utilisation of this cave by the Indians some five centuries ago. The situation is 
so favourable that it nas probably been used as a rock shelter at a much earlier 
period. The author thinks that if the actual sinter floors were carefully removed, 
and methodical investigations conducted, they would lead to valuable additions 
to our knowledge of American pre-history. The proximity of a railway station 
would greatly facilitate this research. 
1907. PP 
