﻿258 ME. C. I. GAEDINEE AND PEOF. S. H. EETNOLDS ON [May ig>IO, 



Shangort Beds in the Tourmakeady district only in their relatively 

 more calcareous character. 



The lithological distinction which we found it convenient to 

 draw in the Tourmakeady district between the Shangort and the 

 Tourmakeady Beds scarcely holds in the Glensaul district, and we 

 consequently describe the two sets of deposits together. 



The succession of these rocks is as follows, in descending 

 order : — 



Thickness in feet. 

 (4) Variable grits and tuffs with graptolitic beds and many- 

 calcareous bands, principally of limestone breccia, and a 



thick series of coarse tuffs or breccias ? 



(3) Felsite of Greenaun and Tonaglanna 1100 



(2) Grits and tuffs 470 



(1) Coarse breccia of Lettereeneen 75 



The cross-faults which traverse the district divide it into three 

 portions. In the eastern (or Greenaun and Garranagerra) portion, 

 the most complete series of the grits and tuffs overlying the felsite 

 occurs ; but the associated calcareous bands are little developed, and 

 the series underlying the felsite is imperfectly seen. 



In the middle portion, tuffs which we consider to be the 

 equivalents of those overlying the felsite are well exposed, though 

 here part of the felsite and the tuffs underlying it are entirely 

 faulted out. It is in this portion of the area that the finest develop- 

 ment of the calcareous rocks occurs. 



In the western (or Tonaglanna and Lettereeneen) portion, nothing 

 is seen of the rocks overlying the felsite ; but there is a fine develop- 

 ment of the rocks lying between it and the Mount Partry Beds. 

 The following exposures of these beds have been studied by us. 



(1) The Garranagerra and Greenaun exposures. — The 

 rocks underlying the Greenaun felsite are seen in scattered ex- 

 posures all along the southern face of the hill. About a third of a 

 mile to the east of the summit, the succession is in descending 

 order : — 



Thickness in feet. 



(3) Coarse grit about 20 



(2) Gritty tuff 420 



Gap covered by peat 240 



(1) Very coarse tuff or breccia seen 40 



The gritty tuff is similar to the Shangort Beds prevalent in the 

 Tourmakeady district, and to those immediately to be described 

 which occur on the northern slopes of the Lettereeneen ridge, 

 where they underlie a thin band of coarse grits and overlie a 

 coarse breccia, both these rocks being exactly similar to those 

 occurring in the area under consideration. 



The very coarse tuff is only seen in one isolated exposure about 

 a third of a mile east-south-east of the summit of Greenaun, and is 

 composed of large fragments of felsite, some of them amygdaloidal. 

 No fossils were found in any of these beds. North-west of the 



