48 Proceedings of the Royal Irish Academy. 



a lower level, the amount varying locally even on the same level according to 

 the volume of water circulating in the passage. It also appears to me 

 probable that there would be a tendency for the postulated reduced level of 

 discharge to maintain itself for some considerable time at the level of the 

 next lower bedding plane in the limestone, and thus allow of considerable 

 solution at that level, causing undercutting and collapse of dividing walls, 

 which is a feature of the Castlepook cave, and a process which is indeed 

 taking place even now on a limited scale : vide " Threatening Gallery." 



Referring to the map of the cave (I'late VII), most of the points just 

 touched on will be apparent. The principal shelf is a conspicuous feature, 

 forming a narrow border to the deep clefts or chasms which were once filled 

 with sand and gravel (indicated by dots), all of which was removed by Mr. 

 Ussher. 



It was by -in h excavation thai the cave was opened up, the map showing 



the present extent of tl pollings which are accessible, hut by no means 



indicating the real extent of this cave, which is capable of considerably more 

 excavation and enlargement at the hands of future workers. 



The geological evidence as to the age of the cave is of an inconclusive 

 character, and may be summarized as follows: — There is a high degree of 

 probability that the whole of the region, including the highest summits in 

 the vicinity of Castlepook, was overridden by the great ice sheet of the 

 Glacial Epoch at the period of its maximum development. The resulting 

 boulder-clay, while consisting largely of local material, contains a very few 

 pebbles of a granite similar to that got east and south of Limerick, and most 

 probably derived from a source in Connemara. Some boulders of this rock 

 occur in the walls of the fields on the Blopes above the caves, and Mr. G. W. 

 Lamplugh as well as the writer got them in the stream beds in the vicinity. 



No f on gn erratic of any description was found amongst the hundreds of 

 stones taken from the cave by Mr. Ussher and examined by the writer. 

 Many boxes of specimens were also seen at the Museum, but all were of local 

 rocks only. This (confessedly negative) evidence would seem to indicate that 

 there was no post-glacial, late, or even perhaps inter-glacial circulation of 

 water in the cave so far as our evidence goes, otherwise erratics of granite 

 would be likely to occur in the deposits. Their apparent absence can be 

 readily accounted for on the supposition that the pre-glacial orifices were 

 sealed up under a covering of boulder-clay. Hence it would appear likely 

 that the cave was excavated by a pre-glacial drainage system — an inference 

 which is strongly supported by the largely pre-glacial facies of the fauna 

 associated with the cave deposits. 



ween this fauna and the fox-earth with remains of domestic animals 



