7 4 Proceedings of the Royal Irish Academy/. 



the series, and on the lithologieal characters of their component rocks, in 

 determining the position which must he assigned to them in the geological 

 record. As, therefore, the identity of the series is still more or less a matter 

 of conjecture, they have been named in the recent Survey memoir after 

 localities in which they occur, and the same nomenclature is adopted in the 

 present paper. The sequence of the series, in descending order, with their 

 probable stratigraphical positions, is given in the following table : — 



5. Cappnagower Series (Carboniferous). 



■i. Mauni Series (? Upper Old Eed Sandstone). 



3. Harbour Series (? Lower Old Eed Sandstone). 



2. Knockmore Series (? Upper Silurian). 



1. Bally toohy Series (7 Lower Silurian). 



Igneous Bocks. 

 Serpentine. 

 Epidiorite. 

 Lamprophyre. 

 Basic minor intrusions. 



Ballytoohy Series. — This series occupies the northern triangular promontory, 

 and consists of sandstones, and black and dark-grey shales, often highly 

 indurated, and in parts cleaved. The beds strike east and west, and are 

 folded into an irregular syncline. If we except the doubtful zone of crushed 

 rocks occurring in the townlands of Strake, Kill, and Glen, these are the 

 oldest rocks in the island. Although they have yielded no fossils, they may be 

 safely referred to the Lower Silurian system, and are indeed lithologically 

 similar to rocks of known Llandilo age occurring in other parts of Ireland. 



Knockmore Series. — The next group of rocks in ascending order has been 

 called the Knockmore Series. Outcropping over more than half the area of the 

 island, these beds enter into the formation not only of Croaghmore (Knock- 

 more), but also of Knocknaveen and most of the ground to the south of these 

 mountains. A great variety of rocks, a few of which are crushed and cleaved, 

 is included in this group. Several types of coarse-grained and fine-grained 

 sandstones, grey, pink, and green-coloured, as well as fine-grained con- 

 glomerates, calcareous mud-stones, and flaggy slates, are encountered on the 

 hill of Knocknaveen ; all of these dip southwards at high angles, from 70° to 

 the vertical. Croaghmore itself is formed of interbedded grey and greenish- 

 grey flaggy sandstones, red and purple shale and shaly sandstone, red sandstone, 

 and greenish-grey pebbly grit. Here the beds dip south-easterly from 

 5° to 45°, but change at Strake hamlet to north at 85°. South of the crushed 



