116 MR. GARDINER AND PROF. REYNOLDS ON THE [May 1909, 



however, into a crumbly brown rock resembling a soft sandstone, 

 and traces of fossils, generally in a very poor state of preservation, 

 can then nearly always be found in them. At certain localities 

 near Gortbunacullin a considerable series of fossils was obtained, 

 which clearly proved the deposit to be of Llandeilo age. 



For descriptive purposes the district may be subdivided as 

 follows : — 



(1) The area west of the Tourmakeady - Drnm- 

 coggy red felsite. — This area, which has a length of about 

 2 miles, is bounded on the west by the coarse (?) Bala conglomerate, 

 the boundary being traceable with fair regularity and continuity. 

 On the east it is bounded by the red felsite, and the boundary 

 is most irregular and sinuous. The ashy rocks are not well 

 exposed, and their principal interest lies in their association with 

 the peculiar patches of limestone-breccia which we describe in 

 the sequel. A series of small intrusions of felsite, andesitic rock, 

 and hornblende-lamprophyre pierce the tuffs. Between the Bohaun 

 road and Stream C are several exposures of tuffs, coarse and fine, 

 striking in the normal north-north-easterly direction, but they 

 do not merit a detailed description. The gritty tuffs which are so 

 prevalent farther north at Gortbunacullin are first met with in a 

 low bank by the Smithy bridge, where they have yielded the 

 following fossils in a very poor state of preservation : — Plectam- 

 bonites sericea, Sow., PI. quinquecostata, H'Coy, Ortliis elegantida, 

 Dalm., Scenidium sp., Cybele connemarica, sp. nov. 



Some 200 yards up the stream an Illcenus was found in cal- 

 careous grit. The Llandeilo grits lie east of the angle made by 

 Stream C, and are separated from the Bala grits and conglomerates on 

 the west by a narrow area of Arenig slates and cherts which show 

 much faulting, the stream for a time following the Arenig band. 

 Gritty tuffs are exposed at various points in the moorland north- 

 east of Gortanalderg, but no section of these rocks is met with until 

 one reaches the east-and-west road which joins the main road 

 south of Drumcoggy Kectory. Here is a fairly good section of 

 tuffs, variable in character, which at a point (293) 1 just south of 

 the road yielded the following fossils: — Plectambonites sericea, Sow., 

 PI. quinquecostata, M'Coy, Ortliis sp., Illcenus sp., Cyphaspis sp., 

 and Pliomera cf. barrandei, Billings. 



(2) Tbe area between Stream P and the southern 

 part of the green f elsite-intrusion. — This is an irregular 

 area, having a length of about a mile and a maximum width of 

 about half a mile. Its north-western boundary is not clearly defined, 

 but we believe that the Llandeilo tuffs are here faulted against the 

 Arenig grits, slates, and cherts. On the east the area is bounded 

 by the red felsite, the junction being very sinuous. Along the 



1 These numerals in parentheses throughout the paper indicate localities, 

 shown in the map (PI. IV), where fossils or rock-specimens were obtained. 



