OBSERVATIONS ON TYPHLOMOLGE RATHBUNI. 75 



and Vaughan, p. 260), during which the part that now forms the 

 plain was thrown down and the northern part which now consti- 

 tutes the plateau was left behind. In consequence of this fault- 

 ing, any particular geologic stratum now lies deeper on the side 

 thrown down than on the plateau. 



It was apparently this faulting which has led to the formation 

 of many cracks in the rock layers. The caves near the escarp- 

 ments of the Edwards Plateau represent gigantic cracks. Be- 

 sides this factor there is still another cause leading to the forma- 

 tion of caves in this region. The entire area of the Edwards 

 Plateau constitutes a huge outcrop of the Cretaceous. In the 

 soft strata of the various cretaceous formations of the plateau, 

 numerous caves have been formed by the mechanical force of the 

 \vater combined with its dissolving action. By this process most 

 of the rivers of the Edwards Plateau have disappeared almost 

 entirely from the surface, and their former beds are dry. These 

 rivers have sunken beneath the surface where they flow in sub- 

 terranean channels. 



THE SAN MARCOS ARTESIAN WELL. 



When the Artesian Well of the U. S. Fish Hatchery in San 

 Marcos (Fig. i) was drilled in 1895, a number of water reser- 

 voirs were opened up by the drill. At present only the water is 

 used which rises from a depth of approximately 190 feet. Here 

 a cave filled with water was opened up ; in it the Typhlomolge 

 lived. The water in this cave must have been under a pressure 

 sufficiently high to carry it up 190 feet. The Typhlomolge, thus, 

 lived most abundantly in water under high pressure and without 

 any access to air except that present in the water. The water of 

 this cave belongs to the so-called " sweet water " horizon of the 

 Edwards limestone in which formation the cave is located. 



We measured the temperature of the water as it comes out of 

 the tube of the well as approximately 21.5 C. Among the fauna 

 of the cave from which the water of the San Marcos Well rises, 

 are particularly conspicuous two crustaceans, both unpigmented 

 and eyeless, an isopod, Cirolanides texensis and a decapod, Palce- 

 monetes antrorum. The latter species is of particular importance, 



