Yol. 65.] JtOCKS OF THE TOURMAKEADY DISTRICT. 109 



The cherts are exposed, not only in the stream but in a field-drain 

 south of Mount Partry, and in the road north-north-west of 

 St. Mary's Monastery. 



The coarse tuff, although only some 50 feet thick in the stream, 

 broadens out on both sides, and forms the hill of Mount Partry 

 and that to the north-west of the Monastery. The bed passes, in 

 places, into a coarse breccia, with large angular blocks of felsite 

 lying in a matrix of an ashy typo. This deposit at each locality is 

 suggestive of a vent ; but, as it appears to be regularly interbedded 

 among finer tuffs, we hesitate to claim it as such. 



The upper band of fine grits and cherts (Band 6) is seen again 

 close to the point where the Mount Partry road branches off, about 

 a third of a mile to the north-west of the hotel ; while the coarse 

 grits (Band 7) are well exposed in a road-cutting close by, where 

 they contain small blocks of felsite and chert. The latter rocks 

 are also exposed to the north of the wide strip of coarse ashes east 

 of the Treanlaur stream. Along the whole of its north-western 

 boundary this coarse grit appears to be in contact with felsite, 

 though the junction, even in the Treanlaur stream, is never actually 

 seen. 



(3) In the district between Gortanalderg and Drum- 

 coggy Bectory. — The coarse conglomerate occurs in stream D 

 about half a mile south of Drumcoggy Bectory, but no cherts or 

 slates are seen there. Another patch of the conglomerate is seen 

 near the eastern end of the east-and-west road, which crosses the 

 area described in this paper a short distance south of the Bectory. 

 The coarse conglomerate is not met with to the north of this point. 



Commencing about half a mile east-north-east of Gortanalderg is 

 a large exposure of the Arenig rocks, forming a roughly triangular 

 area and having a length from south-west to north-east of about 

 400 yards. The rocks, though considerably disturbed, retain in the 

 main the prevalent north-westerly dip, and appear to be entirely 

 surrounded by felsite, which is faulted against the cherty series on 

 the north-east and south-east sides, and is seen resting upon them 

 along part of the western border. 



The lowest beds seen are black slates and cherts, and then, after 

 a gap, comes a considerable exposure of black and red cherts 

 interbedded with coarse quartzose and felspathic grits. All these 

 beds are contorted, and recall most vividly the Arenig cherts of the 

 Ballantrae district. 



When the series is followed in the direction of dip, that is, north- 

 westwards, exposures of black chert and fine grit are found to 

 alternate, the whole series being subsequently overlain by coarse 

 quartzose grits closely resembling those of the Mount Partry and 

 St. Mary's Monastery region. 



The northern end of the triangle is occupied by a somewhat 

 variable series of grits and tuffs. 



