Yol. 65.] THE ROCKS OF THE TOERJIAKEADY DISTRICT. Ill 



(4) In the upper part of Stream C, where to the west 

 of G-ortanalderg it follows a north-aud-south course. 

 — Here a small thickness of radiolarian cherts, black slates, and 

 fine grits is seen dipping north 25° west, and is overlain by a little 

 quartzose grit. The black slates have yielded Diplograptus (Ghjpto- 

 graptus) dentatus, Brongn.,and small brachiopods (Pholidops sp. and 

 Orbiculoidea '!). The cherts from this locality are very pure, 

 black, siliceous rocks, breaking with an excellent conchoidal 

 fracture. It is in them that we have found the best-preserved 

 radiolaria in the district, drawings, of some of these being reproduced 

 in fig. 4, p. 112. Unfortunately, the specimens are too imperfect to 

 allow of proper determination. Nearly all seem to consist of three 

 concentric spheres, and show a single radial spine : but Dr. Hinde 

 thinks it very probable that they were furnished with more spines 

 originally. In one specimen no radial spine is shown, and there 

 are several spokes connecting the different spheres. This specimen 

 Dr. Hinde feels inclined to refer to the genus Rhodosphcera, Haeckel, 

 while the form with three concentric spheres bears some resemblance 

 to Spongosphcera tritestacea, Rothpletz, 1 from the Silurian of Langen- 

 striegis, in Saxony. Sponge-spicules are present in this chert, 

 but; they are few in comparison with the abundant radiolaria, and 

 the rock is a genuine radiolarian chert (see PI. V, fig. 6). 



The grits and cherts show signs of much disturbance, and a little 

 higher up the stream the main mass of (?) Bala grits occurring to the 

 west is faulted against them, the line of crush being well seen in 

 the stream-banks. 



(5) Half a mile west of Drumcoggy Rectory. — Sepa- 

 rated from the area No. 3 by red felsite is a small patch of green 

 quartzose grits associated with cherts. The rocks at this spot have 

 the usual strike, and the only point requiring special comment is that 

 coarse grits are here seen underlying the cherts instead of overlying 

 them. 



(6) Half a mile north-west of Drumcoggy Rectory. — 

 Here occurs another small area of cherts, having a length of about 

 300 yards. The cherts are (as usual) red and black, are associated 

 with bands of grit, and though as a rule considerably disturbed, 

 retain the prevalent north-westerly dip. The felsite along the south- 

 western border shows crushing. 



(7) Near Gortbunacullin Farm Bridge. — Here in the 

 stream is a rather better section than usual of the cherty series, but 

 the cherts are not so thick or so well-marked as at some places. A 

 considerable thickness of grit is seen both overlying and underlying 

 them. A small patch of tuff, presumably belonging to the Arenig 

 Series, was noted on the eastern border of the felsite about 300 yards 

 north of the bridge. 



1 Zeitschr. Deutsch. Geol. Gesellsck. vol. xxxii (1880) p. 449. 



