240 



of brown quartz, nine inches in diameter, within the distance of a 

 small field of the mica slate. In every formation of rocks there are some 

 groups of beds, which differ in lithological character from others. To 

 the east of Cross Slieve, about half a mile inland, there is a band of 

 thin brown flaggy beds, and in these pebbles are extremely scarce, in 

 some beds none at all. The strike of the rock here is nearly parallel to 

 the shore, and so is this band, which may be about a furlong in thick- 

 ness. Pebbles of brown quartz prevail in the thick beds along the 

 shore, which is probably the fact that suggested the idea to Mr. Bryce 

 and Mr. MacAdam, that this shore-band is New Eed Sandstone ; but 

 if pebbles be large and numerous near the shore, so they are towards 

 the western margin, on the opposite side of the district, as I have just 

 stated. 



An east and west section through this district, in the widest part, 

 measures 454 perches through the townlands of Carnasheeran and Magh- 

 eryroy ; the dip near the shore is 40° south-east ; towards the western 

 margin it is 30° in the same direction ; say it averages 35° ; with these 

 data the thickness of the rock on land is obtained, which is 43,000 

 feet ; besides this, the beds on the east dive into the sea, and there 

 the additional thickness is unknown ; it may be as much more. 



The Cakbonifekotjs System. 



In Ireland the Carboniferous rocks may be divided into three sub- 

 divisions : — 



1. Old Eed Sandsone. 



2. Mountain Limestone, or Carboniferous Limestone. 



3. The Coal series. 



The Old Red Sandstone. 



There is but little Old Eed Sandstone in the county of Antrim- 

 only a thin band lying on mica slate about a mile south-east of Carey 

 Mill. Here the two systems are unconformable, as they are everywhere 

 else that I know. 



I have given elsewhere,* in a tabular form, the junctions of the older 

 rocks with Old Eed Sandstone, together with the dips and directions of 

 both, at seventy-eight localities, in twenty-seven of the counties of Ire- 

 land ; and shown that in this number not one case occurred of Old Eed 

 Sandstone being conformable with the underlying rock. In the same 

 paper I gave the average thickness of the Old Eed, taken from sixteen 

 of the clearest sections I know, as 840 feet : four of the best gave an 

 average of 1018 feet: in short, about 1000 feet may be considered as 

 the average thickness of the Old Eed Sandstone in Ireland. 



In that paper I further endeavoured to show that, after the great 

 disturbing forces, which rolled the earliest stratified rocks into un- 

 dulations, followed by a powerful denuding agency, that broke up 



* "Journal of the Geological Society of Dublin," vol. vii., p. 115. 



