Kilroe — Discovery of Carboniferous Outliers, Co. Donegal. 65 



age of the beds remained enveloped in a haze of obscurity, until 

 Mr. Wilkinson, one of the party, placed the end of his walking- 

 stick upon a very fine impression of Stigmaria. At the same instant, 

 Dr. Geikie, judging from the other evidence mentioned, had arrived 

 at the conviction that the beds were of Carboniferous age. We had 

 been traversing the beds north-westward, and had reached a point 

 at which their thickness seems greatest, the basal character of the 

 deposit here giving place to white fine-grained grit. I had 

 previously traversed the beds south-westward, though not through 

 this point, and had thus missed the decisive evidence as to their 

 age. With very little trouble we succeeded in finding several 

 impressions similar to that first met with ; and being satisfied that 

 the beds constitute a Carboniferous outlier on the summit of; the 

 central mass of Slieve League, we crossed " The One-man's-pass" to 

 the north-western limb, aud found the beds there exactly similar to 

 those crowning the central mass, though somewhat coarser. The 

 strata lie almost horizontally on flaggy quartzite, which dips at 50° ; 

 and on tracing the boundaries, the western outlier was found to 

 occupy an area of some twenty, and the eastern some sixty acres. 



The occurrence of Stigmaria would suggest that these beds, 

 though littoral, represent an elevated horizon in the Carboniferous 

 Formation — perhaps that of Millstone Grit. It may, however, be 

 questioned whether such evidence is determinative upon the point, 

 this fossil having been found at all horizons in the formation, and 

 even in Upper Old Red Sandstone. A very fine specimen of 

 this fossil was sent to the museum some thirty years ago by Sir 

 Richard Griffith, from the shore of M'Swyne's Bay, near Killybegs, 

 Co. Donegal ; and Dr. Haughton, in a Paper read in December, 

 1860, mentions Stigmaria as one of several plants sent him by Mr. 

 Harte, from Yellow Sandstone of Darney, near Dunkineely. Both 

 these specimens were from lower Carboniferous beds. 



It is suggestive, also, that Millstone Grit caps several of the 

 Leitrim and Cavan hills on the opposite shore of Donegal Bay. 

 Cuilcagh, forty-eight miles distant, is especially conspicuous from 

 Slieve League, the Millstone Grit there occurring at an elevation of 

 2180 feet above datum. But at Truskmore, near Benbulben, 

 twenty-two miles off, Upper Limestone reaches the 2000 feet 



1 See Explanation to accompany Sheet 44, Memoirs of the Geological Survey. 



