Problems of S.W. Highlands of Scotland. 121 
Ben Ledi Grits can be most easily explained by their unconformable 
deposition on the southern edge of the Dalradian rocks. 
There has been assumed a transition from the Ben Ledi Grits to the 
intensely altered gneissic grits belonging to the Loch Lomond series, 
but the evidence for this passage is not convincing. The southernmost 
part of these comparatively unaltered rocks include cherts and shales 
which are marked on the Survey Maps as ‘Silurian(?)’.!. The exact 
age of these beds is doubtful. They may be Upper Dalradian and 
correspond to the great unconformity at the base of the Schiehallion 
Quartzites, or, as is more probable, they may be post-Dalradian in age. 
The relations of the Dalradian Schists is suggested as follows:— 
Algonkian . . . Torridon Sandstone. 
Honbic Dalradian. 
; Caledonian . . . Moine Gneiss and associated schists, 
Lewisian . ». » Fundamental Gneiss. 
The classification suggested in the address adopts Nicol’s succession 
in part, as it accepts the Aberfoil and Ben Ledi Series as younger 
than the Loch Lomond Gneiss against which they rest; and it is 
consistent with the less altered condition of the southern rocks and the 
steady diminution in the metamorphism of the rest of the series going 
northward, as for example, from the Loch Lomond Gneiss to the Loch 
Awe Grits, and from the garnetiferous mica schists of the Loch Tay 
Series to the black schists and unfoliated quartzites near Blair Atholl. 
The evidence in some points of this succession is still incomplete, 
especially as regards some of the rocks nearest Glasgow. The special 
problems on which further research would be most useful were 
therefore mentioned, in the hope that the members of the Glasgow 
Geological Society would investigate them. 
The subject is of interest from its bearing upon the early geological 
history and geography of North-Western Europe. The structure of 
Western Europe has been dominated by the formation of three great 
mountain systems, each due to pressure usually from the south, and 
each haying its younger rocks exposed mainly on the northern flanks of 
the chain. The youngest is the Alpine System, formed mainly in Upper 
Cainozoic times, and including the Pyrenees, Alps, Carpathians, ete. 
A somewhat similar mountain system, of which fragments remain in 
Southern Ireland, Devonshire, Brittany and Germany had been formed 
in Upper Paleozoic times; from its analogy with the Altai Mountains 
of Asia, Suess has called its mountains the European Altaids. Still 
earlier, in later Archean times, there was formed the first of these 
European mountain systems, of which fragments occur in Northern 
Treland, the Grampians, and Scandinavia. There are many interesting 
analogies between these old Grampians and the later Altaids and Alps. 
The old mountain system to which the Grampians belonged probably 
extended far westward into the North Atlantic and to its influence 
may be attributed the desert climate of Scotland during the deposition 
of the Torridon Sandstone. 
1 By kind permission of Dr. Horne it was announced during the address that 
Dr. Hinde has recently identified Radiolaria in the cherts of this series. 
