Cote—On the Geology of Slieve Gullion, in the County of Londonderry. 245 
the mineral veins, or may be a feature of the actual walls of those veins. ‘The 
hematite found upon the mountain contains, indeed, abundant drusy cavities lined 
with quartz. Dr. G. J. Hinde, F.R.S., reports as unfavourably concerning these 
cherts as he did concerning the siliceous rock of Beaghbeg. Certain ‘“ clear spots 
with curved outlines” in the chert of Letteran have to him ‘the appearance of 
being organic”; but ‘they are certainly not radiolaria even if they are organic.” 
Dr. Hinde, moreover, in the same letter, states that he recognises no likeness 
between these spots and any organisms, siliceous or calcareous, known to him. 
The schistose series to the north at present remains included in the ‘‘ Dalradian” 
of Sir A. Geikie.* It is thus by no means absolutely removed from the Ordovician : 
nor, on the other hand, is much encouragement held out that it will be proved to be 
later than the Archean era. Sir A. Geikief places the tuffs of Beaghbeg at the base 
of the local Dalradian series, and regards the gneiss below as comparable to the 
Lewisian, that is, as genuinely Archzean. It is perfectly possible, then, that the 
basic series of Sleve Gallion, which must stand or fall with that of Beaghbeg area, 
may be entirely Archean, as Mr. Nolan was prepared to believe in 1884. It is 
stated} that the ‘chloritic schists” overlie the pyroxenic series, and these schists 
are regarded in the same memoir as Ordovician. Thus Mr. Nolan connected 
the basic rocks with the supposed Archzean core, while Sir A. Geikie connected 
them, as almost everyone else seems to have done, with the ‘chloritic schists” 
themselves. It is safest to accept the happy mean offered us by the latter author, 
and to say that Slieve Gallion is formed of an eruptive ‘ Dalradian” series, pene- 
trated by a granite in Middle Devonian times. 
[ Note added May 10th, 1897.—Since this Paper was in the press, Sir A. Geikie 
has again treated of the Tyrone area in his ‘‘ Ancient Volcanoes of Great Britain,” 
vol. i., pp. 239-241, He now compares the volcanic series more closely with that 
of the southern margin of the Scottish Highlands, and places it as probably of 
Arenig age. The associated cherts ‘‘bear the closest resemblance to those of 
Arenig age in Scotland. But no recognizable Radiolaria have yet been detected 
in them.” The gabbros are described as occasionally including portions of the 
‘“‘slagey diabases.” The Slieve Gallion area is not referred to; but the above 
remarks may clearly be extended to it, and will support those who would place 
the ‘‘ Dalradian ” chloritic schists also in the Ordovician system. | 
* Anniversary Address, Quart. Journ. Geol. Soc. Lond., vol. xlvii. (1891\, Proceedings, p. 75. 
+ Ibid., p. 77. 
+ Mem. sheet 26, p. 14. 
TRANS. ROY. DUBL. SOC., N.S. VOL. VI., PART IX. 20 
