﻿Vol. 66.] THE ORDOVICIAN OP THE GLENSAUL DISTEICT. 263 



but sometimes becoming coarse. Farther west a less continuous 

 fourth band of limestone breccia may be traced. 



Throughout this part of the area the prevalent rocks are coarse 

 breccias, probably corresponding to Band 3 in the Greenaun and 

 Garranagerra area, although the fragments weather differently, 

 tending to stand out from the matrix rather than to weather more 

 rapidly than it. Farther north, in the neighbourhood of the road 

 and river, come highly calcareous gritty tuffs passing at times 

 into nearly pure grey limestones. The tuffs correspond exactly to 

 those forming Band 3 in the Greenaun and Garranagerra region. 

 The following fossils were found here in the limestone bands : — 

 Orthis testudinaria, Dalm., and Streptis affinis, Reed ; in the more 

 easterly band at 353, and a little farther north-east, Galymene sp., 

 Pliomera sp., Orthis testudinaria, Dalm., and a Meristellid; in 

 the more westerly band at 361 we found Nileus armadillo, Dalm., 

 Cheirurus (?) sp., Orthis sp., Plectambonites sericea, Sow. ; and in 

 the bed of the stream at 354, along the same line of strike a 

 few yards to the north-east, Ulamus sp., Lingula brevis(?), and 

 Siphonotreta (?) sp. 



Throughout this central area neither the tuffs, whether fine or 

 coarse, nor the limestone breccias show any trace of bedding, and 

 in consequence their dip and their thickness are not ascertainable. 

 The limestone-breccia bands, however, give the strike, and the 

 limestone exposed in the Glensaul river-banks has the prevalent 

 north-north-westerly dip of the great majority of the rocks of the 

 district. 



It is definitely stated in the Geological Survey Memoir that the 

 limestone bands are bent into anticlinal curves * ; and, if this be so, 

 the four limestone-breccia bands shown in the map might be all 

 merely repetitions of one or two bands, but of this we are unable to 

 obtain any evidence. 



The breccia is almost entirely made up of angular fragments of 

 white and grey limestone, but fragments of felsite and of bright 

 red chert also occur. 



(3) The Tonaglanna and Lettereeneen exposures. — No 

 Shangort or Tourmakeady Beds are seen in this area overlying the 

 felsite. Underlying it is a fine section, showing the following 

 bands in descending order : — 



Thickness in feet. 



(4) Coarse grit 20 



(3) Gritty tuff, with cherty bands towards the base 520 



(2) Coarse breccia 75 



(1) Fine banded tuff 55 



By far the most conspicuous band is the coarse breccia which 

 forms the summit of the ridge stretching north-eastwards from the 



1 Explan. of Sheets 73, 74 (in part), 83, & 84, Mem. Geol. Surv. Ireland, 

 1876, p. 67. 



