Plunkett — On the Exploration of the Knochiiinni/ Care. 477 



This stratum (I have already stated) is composed of gravel with a 

 coating of yellow sandy clay, both of which, it is quite clear, were 

 carried in and deposited by water. On a careful examination of this 

 material, I was rather surprised to find that a large proportion of this 

 old silt and gravel was foreign, not only to the formation which the cave 

 penetrated, but even to the hill. Here in a cave near the top of this 

 isolated hill, I find the debris of a gritty sandstone, not found in the 

 locality except in a mountain ridge on the other side of the valley 

 nearly a mile distant, the cave having an elevation of 330 feet above 

 the valley bounding it on the one side, and 349 feet above Lough 

 Erne, which bounded it on the other. From whence did it come ? 

 This was the question I had to answer. In order to solve this difficult 

 problem, I commenced to investigate the physical phenomena connected 

 with the geology of the district, with which I was slightly familiar 

 before, but now felt that a closer inspection was necessary and impor- 

 tant, as I had found imbedded in this lower stratum containing the 

 foreign matter, the two wrought flints and portions of a human skull 

 described above. 



I shall describe the outlines of the country west of Knock- 

 ninny, and give a detailed account of facts I discovered, which clearly 

 show the extraordinary amount of denudation which has taken 

 place in this locality. 



Knockninny skirts a group of mountain ridges which lie on its 

 south-west side, and cover an area of about 15 square miles. This 

 area is represented on Jukes' map as a patch of coal-measures. The 

 slopes of one of these mountain-ridges rise from the other side of the 

 valley adjoining Knockninny, and terminate at an altitude of 1100 feet 

 above the sea level. The valley intervening between the base of this 

 mountain and Knockninny is about three-quarters of a mile broad. 

 Cuilca mountain raises its lofty crest further west, and at a distance of 

 5 miles from Knockninny, and is the highest of the group, and has an 

 altitude of 2188 feet above the sea. Standing on its summit you may 

 see a group of hills, to which I have referred above. The ridges or 

 hills (for they are of various shapes) lying next Cuilca approach 

 nearest to it in altitude ; and the hills forming the borders of the group 

 have a much lower altitude, especially those on the north-east side, 

 which pass from Cuilca with a gradation down to the valley of Lough 

 Erne. 



Cuilca is a ridge about 2^ mileslong, and is entirely composed of sand- 

 stone ; but in the slopes below its base the carboniferous limestone crops 

 out and is continuous round through the valleys and the base of the 

 mountains immediately surrounding. The hills also which form the 

 outskirts of this area (already referred to) with a similar altitude to the 

 valleys around Cuilca, are entirely composed of limestone, with the 

 exception of a thin patch of sandstone along their tops, Cuilca being 

 the backbone of the district divides the drainage system of the country, 

 and from its base there radiates in various directions a series of valleys 

 with a considerable incline for several miles, which broaden from one to 



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