Cote & CunnincHAM—On Certain Rocks styled ‘‘Felstones.” 815 
the same faults cut the Carboniferous sandstone, and may even be 
of Cainozoic Age. The Carboniferous beds overlie both the first 
and second series of dykes, without being penetrated by 
them. 
The third series of dykes includes the intrusive basalts and 
dolerites that follow so persistent a north-west and south-east 
trend throughout ourislands. These are now generally admitted 
to belong to the Cainozoic epoch of activity. Associated with 
them are one or two veins of rhyolite-pitchstone, the characters 
of which are thoroughly in harmony with those of undoubted 
products of our Cainozoic voleanoes.t The dolerite dykes of this 
series cut through the felstones, and are clearly of later date. 
It has been recognised in recent years that the “ felstone” 
series of the north-west of Ireland contains rocks of somewhat 
dissimilar character. In 1888, Messrs. Mitchell and Kilroe? 
described several masses in the area of Barnesmore as mica-trap, 
porphyrite with hornblende, syenite with quartz, &c. <A general 
northerly direction is noted for the dykes of this series which 
lie to the east and south-east of Lough Hask. Dr. J.8. Hyland,’ 
in 1890, gave an admirable description of some of the dykes east 
of Lough Swilly, classing them, for the first time, with the 
lamprophyres of Rosenbusch, and placing them in the camptonite 
division. In 1891 the same author* described two other lampro- 
phyres from the county of Donegal, regarding them as amphibole- 
vogesites, or as basic allies of the compact syenites rather than of 
the compact diorites. He pointed out at the same time that the 
felstones and felstone-porphyries of the area presented a wide 
range of structure and constitution; some are even “allied to 
micro-granites.”’ 
Messrs. M‘Henry and Watts’ mention a number of occur- 
rences of lamprophyre in northern Ireland, including a vogesite 
1Mem. Sheets 3, 5, 9, &c., p. 147. Aliso W. J. Sollas, ‘“‘On Pitchstone and 
Andesite from Tertiary Dykes in Donegal,”’ Scien. Proc. Roy. Dublin Soc., vol. viii. 
(1893), p. 87; and Sir A. Geikie, ‘‘ Ancient Volcanoes of Great Britain,’’ vol. il. 
(1897), p. 118. 
2 Mem. Sheet 24, pp. 32 and 33. 
3 Mem. Sheets 1, 2, 5, 6, and 11, p. 44. 
4Mem. Sheets 3, 4, 5, 9, &c., pp. 141-143. 
5 « Guide to Coll. of Rocks and Fossils,’’ Geol. Sury. Ireland (1895), pp. 71—75. 
