Plunkett — On the Ex})loration of the Knockninny Cave. 479 



face of Knockninny, which. I shall now adduce. Along the top of the 

 hill there are several large "swallow holes" corresponding in every 

 feature almost with those I have examined in the valleys surrounding 

 Cuilca, with this exception, that no water passes through them. I 

 went down into these holes, and after removing the rubbish and dehris 

 on the surface, I found in every one of them rounded sandstones of 

 various sizes mingled with limestones. I also saw similar stones here 

 and there in the ditches which form the fences on the hill, which were 

 gathered off the surrounding surface. Now the nearest sandstone 

 strata in the locality are in the mountain ridge rising in the south-west 

 side of the valley adjoining the hill, and the intervening valley is 400 

 feet lower than the top of Knockninny, where the "swallow holes" are. 

 All these phenomena to my mind clearly show that Knockninny gradu- 

 ally rose like a huge boss or outlier, as the surrounding and softer strata 

 were being worn away by denudation. I have examined its slopes, from 

 its east and west^shoulders to its base, and found beds of gravel at inter- 

 vals down the whole way, which I regard as the dehris left behind 

 when nature's sculpture was forming the hill. One of these beds 

 occurs 26 feet below the mouth of the cave, and is exactly the same as 

 is found in the bottom of the cave underneath the sandy clay, I ex- 

 amined an escarpment in the ridge opposite, intervening between Cuilca 

 and Knockninny. Through it the valley passes on its way from the 

 base of Cuilca to the lake ; in the centre of the valley Knockninny rises, 

 and I found at an elevation of about 700 feet above the valley, gritty 

 sandstone, the dehris of which I found in the rivulets which traversed 

 its surface, and it corresponded with what I found in the cave, mingled 

 with limestone gravel. All these facts point to extraordinary changes 

 of the surface of the country which surrounds Knockninny. 



Since the" water which formerly passed through the cave retreated 

 to a lower level, leaving the floor dry and covered with this deposit, 

 the adjoining strata have been removed to a depth of 330 feet below 

 the entrance of the cave. A question here suggests itself — did man 

 inhabit the cave immediately after it became dry, or not until the 

 surface of the country had assumed its present outlines? The evidence 

 found in the cave is in favour of the former hypothesis, as there was 

 not a single particle of cave earth associated with the flint implements 

 or human remains found in the lower stratum. And it is hardly pro- 

 bable that, during the long period which must have elapsed from the 

 time the cave became dry, and formed a refuge or dwelling for savage 

 tribes, till the time the valley assumed its present appearance, no cave 

 earth would be deposited. 



Suppose we assume that the cave was not occupied until the sur- 

 rounding surface of the country presented its present configuration, 

 then we are bound to believe that the cave earth must have accumu- 

 lated very slowly, so much so that an inch would not be formed while 

 330 feet of rocky strata were washed away. And if we take Croll 

 and Geikie's calculations as to the rate at which valleys are scooped 

 out (which is extremely slow), although they state that they have 



