260 Proceedings of the Royal Irish Academy. 



it is impossible to say with certainty anything definite with regard to the 

 formation of the roof. So far as could be seen, however, it appeared to be 

 irregular, as if its height were due to falls of rock, the debris of such 

 fallen roof, especially in the lower parts, being subsequently carried away by 

 the rush of water. The floor of the upper portions of the chamber is almost 

 entirely covered with rock debris, while that of the lower portions consists of 

 smooth rock coated with a deposit of red clay some 2 inches thick. This area 

 is remarkable in another way. Although the rock is exceedingly smooth, its 

 surface is scored by a series of parallel groovings running from top to bottom, 

 each grooving being about 9 inches across and about 1 inch deep. These 

 grooves are difficult to account for, except on the supposition that great 

 volumes of water flowed down the inclined stratum. It was impossible to get 

 a general view of these grooves owing to the coating of clay, and to the fact 

 that the exploration of that portion of the chamber was attended with 

 difficulty and danger. 



The upper portions of both the eastern and western chambers of the Old 

 Cave rise at least 80 feet above the floor of the water-tunnel, by which they 

 are now entered; so that it is not unlikely there were formerly other entrances 

 which are now obscured by glacial drift. 



It is a fact worthy of note that these bedding-plane chambers occur at the 

 most southerly part of the caves, which are also at the lowest level. The 

 great deposits of red clay, which will be dealt with later, also occur in these 

 chambers, and nowhere else. 



Chambers of Type 1. — Old Cave; Eastern and Western Chambers. 

 New Cave : Gallery of Arches, two chambers to the south of the Four 

 Courts. 



The second type of passage seems to be formed as the resultant of the 

 bedding-planes and the secondary joints, and is to be found in the majority of 

 the passages which run east and west. These passages are on the average 

 about 5 feet in height, and exhibit cross-sections as in fig. 2. In certain 



Fig. 2. 



of these cases there is evidence that a considerable volume of water has 

 at some time flow^ed along the passage ; whilst in others it seems more 

 likely that the stream has pursued a course below the present floor, and that 



