﻿Yol. 66.] THE ORDOVICIAN OF THE GLENSAUL DISTRICT. 



259 



Greenaim felsite, and overlying it, is a fine section, showing the 

 following succession, in descending order : — 



Thickness in feet, 

 (3) Calcareous gritty tuff, with some small patches of limestone 



breccia and one of graptolitic beds 180 



(2) Very coarse tuff or breccia, with impersistent bands of 



fine tuff 750 



(1) Tuff, coarse and fine, with two calcareous bands and one 



patch of graptolitic beds 150 



.All these rocks dip regularly in a north-westerly or north-north- 

 westerly direction. Band 1 consists of tuff, containing fragments 

 (chiefly of felsite) reaching the length of an inch or more. For 

 much of its outcrop it is ill-exposed, being often covered by peat ; 

 but at its western end, near the fault, it is finely seen. Here it 

 includes a band of limestone (97), 1 while a second band extending 

 westwards from the bed of a stream half a mile farther east under- 

 lies a graptolitic bed (148). 



The second of these bands is of limestone breccia exactly similar 

 in character to those present in the Tourmakeady district, — that 

 is, consisting of angular fragments of limestone and of felsite 

 embedded in a matrix of calcareous grit. There is no evidence of 

 crushing in connexion with this deposit. 



The first-mentioned deposit (97) is of quite a different character, 

 consisting of blocks or wisps of limestone mingled with crushed 

 and twisted masses of shale, the whole giving the clearest possible 

 evidence of strong disturbance. This deposit occurs along a marked 

 line of fault, and doubtless represents what was once a series 

 of beds of limestone and shale now converted into a mass of 

 fault-breccia. The limestone of these blocks is red, grey, or white, 

 and of crystalline or horny texture. From some of these, and 

 especially from those consisting of red crystalline limestone, we 

 obtained the following fossils : — 



Camerella cf. cuneatella, 



(very common). 

 Camerella sp. 

 Lingula sp. 

 Orthis obtusa, Pander. 

 Orthis parva, Pander. 

 Blectambonites sericea, Sow. 

 Porambonites sp. 

 Holopella sp. 



Dav. 



Trochonema aff. umbilicatum, Hall. 

 Subulites elongatus, Aug. 

 Bronteopsis sp. 

 Cheirurus sp. 

 Bathyurellus sp. 

 Elanusweaveri, Eeed. 

 Illcemis sp. 

 Bemopleurides sp. 

 Telephus hibernicus, Eeed. 



The section at the spot numbered 148 merits a further de- 

 scription, as it is the only important place where we found 

 graptolitic beds interbedded among the ashy and calcareous series 

 (Shangort and Tourmakeady Beds). 



The rocks are exposed in the bed of a streamlet which, flowing 

 northwards from the felsite forming the Greenaun ridge, enters 

 the Glensaul river south of Garranagerra. The main felsite mass 



1 These numerals in parentheses indicate the localities where specimens 

 were collected, and are shown on the map (PI. XX). 



