——eE 
Ss 3.3 
7 
; 
Geological Society of London. 327 
seems to represent the Tremadoce shale of Britain, and, like it, contains 
pisolitic iron-ore. Representatives also of the Arenig and Bala beds 
are found. A slight unconfermity marks the base of the Silurian. 
Three Graptolitic zones occur. The lowest, or Diplograptus zone, 
identical with the Birkhill shales, contains thirteen species of Grapto- 
lites; the next, or Priodon zone (four species), resembles the Brathay 
Flags; the upper, or Co/onus zone (five species), resembling the Upper 
Coldwell Beds of the Lake-district. Above these follow representa- 
tives of Wenlock, Ludlow, and probably of the Passage beds. The 
author, with the evidence of these, discussed the ‘‘ colonies’ theory of 
M. Barrande, pointing to the non-intermixture of species, notwith- 
standing the irregular repetition of the zones, the non-occurrence of 
these colony species in intermediate beds, and other reasons. The 
stratigraphy and paleontology of several of these colonies was discussed 
in detail, showing it to be more probable that their apparent inter- 
calation with later faunas is due to repetition by faulting. 
3. “On the Pre-Cambrian Rocks of the North-western and Central 
Highlands of Scotland.” By Henry Hicks, Esq., M.D., F.G-S. 
The author, after examination, considers the rocks of the following 
districts to be wholly or in part Pre-Cambrian :— 
(1) Glen Finnan, Loch Shiel to Caledonian Canal.—In the former 
district the rocks are gneiss, often massive. In Glen Firmilee is a 
series which the author regards as newer and Pebidian. At Farofern 
are quartz rocks which the author identifies with those beneath the 
limestone in Glen Laggan, near Loch Maree, and probably of Silurian 
age. At Bannavie is a granite which the author considers to be Pre- 
Cambrian. 
(2) Fort William and Glen Nevis.—In this district chloritic schists 
and gneiss occur, which the author regards as Pebidian. 
(3) Ballachulish, Glen Coe, and Black Mount.—Chloritic schists and 
quartzites occur here, followed near Loch Leven unconformably by 
Silurian rocks. On the east of the Ardsheal peninsula, there is 
granite, which the author believes to be Pre-Cambrian. Going east- 
wards from Ballachulish we have slates, probably of Silurian age. In 
Glencoe are granite-banded felsite, gneiss, breccia, resembling as a 
whole the rocks of the Welsh Arvonian group. Between the Black 
Mount and Loch Sullich are traces of a. great Pre-Cambrian axis, 
bringing up the gneissic series; this is traceable also towards Glen 
Spean and Loch Laggan to the N.E. 
(4) Lyndrum to Callander.—South and east of the former are gneisses 
and silvery mica-schists. Crystalline limestones and serpentines are 
associated near Loch Tay, resembling those in the Pebidian series of 
North Wales. 
The author states that the Silurian (and Cambrian) rocks flank the 
Pre-Cambrian in lines from N.E. to 8.W., and overlap Ben Ledi on 
the south side. Thus here, as elsewhere, subsequent denudation has 
removed enormous masses of the more recent rocks, only here and 
there leaving patches of these in folds along depressions in the old 
Pre-Cambrian floor. 
