Part I. § 2.]_ _ ARCHABAN. 643 
son, of the Geological Survey of Ireland, have shown that in Donegal 
there exists a massive granitic gneiss which they identify with the funda- 
mental gneiss of the north-west of Scotland, and which they find to be 
covered unconformably by the quartzites, limestones, and other crystalline 
rocks, that were shown by Harkness to be continuations of the similar 
‘series of Lower Silurian masses in the Scottish Highlands. The charac- 
teristic red Cambrian sandstone of the later region, however, has not been 
detected in Ireland. 
In England and Wales certain isolated tracts of crystalline rocks have 
been recently referred by Dr. Hicks,? Professor Bonney,’ and others to a 
pre-Cambrian age. Beneath the fossiliferous Cambrian strata of St. 
- David’s certain crystalline masses appear in which, according to Dr. 
Hicks, there is a lower group (Dimetian) consisting of quartzose and 
granitoid rocks, including coarse gneiss, bands of impure limestone or 
dolomite, schists, and dolerites; a middle group (Arvonian) composed 
essentially of contemporaneous voleanic rocks, rhyolitic felsites, volcanic 
breccias and halleflintas or felsitic tuffs, forming, with the foregoing 






= = 
Fic, 318.—PucKERED LAMINEZ BETWEEN PARALLEL BANDS OF GNEISss, 
Loco TORRIDON. 
group, a total nearly 15,000 feet thick; and an upper group (Pebidian) 
made up of slaty and comparatively little altered rocks, and fully 3000 
feet thick. In North Wales and Anglesea other areas of crystalline rock 
have been assigned to a similar geological position. Professor Bonney 
has described some of the masses as true lavas having so perfect a 
rhyolitic structure that they might almost be classed with recent 
rhyolites, and as beg of contemporaneous origin with the rocks 
among which they lie, for fragments derived from them are abundant in 
the strata overlying them up to the base of the Cambrian series. On 
the other hand, Professor Ramsay believes that the so-called ‘“ Pre- 
Cambrian” areas are only highly metamorphosed portions of the 
Cambrian rocks with associated igneous intrusions.* Again, in the 
1 Geol. Mag. 1881, p. 506. Kinahan, Op. cit. p. 427. Hull, Trans. Roy. Dublin Soc. 
i, (2nd. ser.), 1882, p. 243. 
2 Quart. Journ. Geol. Soc. xxxiii. pp. 229; xxxiv. p. 285, 295. Geol. Mag. 1879, 
. 433. 
i. Quart. Journ. Geol. Soc. xxxiy. p. 144; xxxv. pp. 305, 309, 321. Hughes, Op. cit. 
XXxiv. p. 137; xxxv. p. 682; xxxvi. p. 237. 
* Mem. Geol. Survey, vol. iii., “Geology of North Wales.” Dr. Callaway (Q. J. Geol. 
Soc. xxxvii. p. 210) has described the gneissic and slaty rocks of Anglesea akan) 
9) ait. Za 
_ 
