Vol. 65.] ROCKS OF THE TOURMAKEADY DISTRICT. 107 



Kinahan & Symes, 1 and after them Mr. Kilroe, 2 detected the 

 presence of graptolites in this series, Mr. Kilroe finding in the 

 stream west of the Monastery, Tourmakeady, ' black shales with 

 Lower Llandeilo, or perhaps even Arenig graptolites.'* This ob- 

 servation, it will be seen, we have fully confirmed. 



The following are the principal exposures of these rocks : — 



(1) In the stream close to Tourmakeady Lodge. — In 

 the lower part of the stream south-east of the Lodge (outside the 

 area of our map) the coarse conglomerates are finely exposed, and 

 are apparently overlain by the fine grits, slates, and cherts. The 

 actual junction is not clearly seen, but there is no evidence that it 

 is a faulted one, and the beds close above the conglomerate have 

 the usual north-westerly dip. Slightly higher up the stream the 

 cherts show a certain amount of disturbance, and north-north-east 

 of the Lodge the series includes a few thin bands of tuff. A small 

 intrusion of felsite separates the Arenig Series from the (?)Bala 

 conglomerate which is seen at the bridge north of Tourmakeady 

 Lodge. A small patch of tuff occurs in a field about 300 yards 

 east-north-east of that house. 



No fossils have as yet been found in the slates, despite careful 

 search ; but microscopical examination of the cherts reveals the 

 presence of rounded bodies, some of which have an inner ring 

 concentric with the circumference, and these are strongly sugges- 

 tive of casts of radiolaria. Sponge-spicules are fairly common, and 

 Dr. Hinde suggests that a group of minute claw- shaped bodies is 

 made up of denticles from the radulae of some gasteropod. This 

 chert is derived rather from the silica of sponge-spicules than from 

 radiolaria. 



(2) In the Mount Partry neighbourhood. — This area 

 stretches for a mile in a north-easterly direction, from the road 

 leading westwards from the hotel. By far the best section occurs 

 in the bed of the Treanlaur stream (Stream C) ; it is, in descending 

 order, as follows : — 



[See also fig. 1, p. 108.] 



TJiickness in feet. 

 7. Coarse green grit, very quartzose and felspathic. 



6. Fine grits and cherts about 20 seen. 



5. Fine gritty tuffs 60 



4. Coarse tuff 50 



3. Fine gritty tuffs 60 



2. Fine grits, cherts, and slates, including a black band full 



of graptolites at about 20 feet above the base 50 



1. Coarse conglomerate, thickness seen very considerable: 



assuming the dip to be constant, it would be about 850 



This stream- section is the finest exposure of the Arenig rocks 

 in the district, and differs from that in the Tourmakeady stream 



1 Mem. Geol. Surv. Irel. Sheets 73, 74 (in part), 83 & 84 (1876) pp. 27 etseqq. 



2 Ann. Eep. Geol. Surv. U. K. for 1896 (1897) p. 49. 



