Vol. 65.] THE ROCKS OF THE TOTJEMAKEADY DISTRICT. 115 



breccia. We are inclined to think that the rock which we have 

 just described, is a fault-breccia, for the followiug reasons : — 



(«) It occurs close to the line of fault separating the coarse Arenig grits 



clipping west 10° south from the Llandeilo tuffs on the east, which dip 



about north-westwards. 

 (b) The underlying fine grits show extensive rupture and displacement just 



where the breccia is seen, and resemble exactly the masses of grit and 



slate included in the breccia. 

 (0) The matrix of the breccia is quartzose and gritty, closely resembling the 



grits on the west. 



(9) The Shangort and Derrassa area. — We believe that 

 this area is separated by a fault from that just described. The 

 outcrop of the gritty and cherty series widens considerably in the 

 neighbourhood of Derrassa, where the rocks are seen striking up 

 against the green felsite-intrusion, and are almost bisected by a 

 southward-projecting tongue of red felsite. At the north-eastern 

 end of the outcrop in Stream H, the Carboniferous conglomerate is 

 seen resting directly upon the grits. 



A strip of chert, having a probable width of only some 30 or 

 40 yards, can be traced for nearly 500 yards along the south-eastern 

 border of the brown felsite-mass north-west of Shangort. 



(b) The Llandeilo Rocks. 



It may, perhaps, be desirable to state succinctly at the commence- 

 ment of our description of the Llandeilo rocks that although, for 

 the sake of convenience, we divide them into two groups, a gritty 

 and ashy series and a calcareous series, and apply the name of 

 Shangort Beds to the former, and of Tourmakeady Beds to 

 the latter, yet the two groups are intimately associated, and we 

 consider them to be of the same general geological age. 



(6 1 ) The main gritty and ashy series (Shangort Beds). 



In addition to the tuffs which we have already described when 

 dealing with the Arenig rocks, others are continually met with 

 throughout the whole district. West of the great red felsite-mass 

 they occupy an irregular strip extending from near Tourmakeady 

 Lodge to Shangort, and then, after a break in their continuity, they 

 are again seen in the neighbourhood of Derrindaffderg. While some 

 of these rocks are normal tuffs with little non-igneous matter, the 

 great majority contain a large proportion of gritty material. Every 

 gradation may be traced, from a pure grit through an ashy grit and 

 a gritty tuff, to a tuff almost entirely free from non-igneous matter. 

 They vary, too, greatly in coarseness, some being very fine tuffs, 

 others very coarse breccias, which may contain large or small blocks 

 of limestone. 



When unweathered, these gritty tuffs are very hard, and appear 

 to be almost, if not entirely, unfossiliferous. They readily weather, 



