Deposits, Limestone Creek. 11 



the eastern bank of the creek the marble beds are capped by 

 blue unaltered limestones containing fossils (molluscs). 



In ascending the steep and rugged ranges to the east, the 

 porphyries become more compact and silicious, having a 

 greyish or reddish felsitic base, with small translucent 

 quartz-crystals, patches of pink-coloured felspar and 

 fragments of other rocks, the whole forming a breccia-like 

 mass, as seen in specimen No. 6. On the summit of Mount 

 Cobboras, and on the rocky-crested ridges near it, the rock 

 masses weather into vertical layers with a northerly strike. 

 Descending the eastern slopes of Mount Cobboras, the por- 

 phyries previously described give place to salmon-coloured 

 quartz-porphyries, almost granitic in structure and weather 

 in rounded masses. 



EXAMINATION OF CAYES. 



Cave No. 1. — Pendekgast's Cave. 



The first examined is that perforating a marble deposit 

 near the Limestone Hut (an out-station of Mr. James 

 Pendergast, of Mount Leinster). For reference this may 

 be called Pendergast's Cave. In examining the ground plan 

 of this cave (Diagram S), it will be seen that it traverses gener- 

 ally the line of strike of the strata. This is the case with 

 most of the caves examined, and would appear to indicate 

 their origin to be by percolation of water from the adjoining 

 creeks. Wit at I mean by this is that the present water 

 channel of the Limestone Creek, although in some cases at a 

 lower level than the orifices forming the entrances to the 

 caves, originally stood at a much higher level, and washed 

 the bases of the limestone bluffs ; then, percolating along the 

 lines of strike, gradually eroded a channel to a lower level; 

 and, owing to the calcareous mass being traversed by joints 

 and lines of shrinkage, the water charged with carbonic acid 

 gradually decomposed the hard crystalline masses, and by 

 the further mechanical action of silt and small stones eroded 

 a larger passage. The action of rain water from above, 

 acting similarly by its carbonic acid, derived from the decom- 

 posing vegetable matter covering the calcareous deposits, 

 would probably form many of the curiously-shaped holes 

 and crevices seen on the surface.* 



* Vide Boyd Dawkins' Cave Hunting, p. 53- 



