TRANSACTIONS OF SECTION C. 465 
8. Report on the Preparation of a List of Characteristic Fossils. 
See Reports, p. 135. 
MONDAY, SEPTEMBER 9. 
The following Papers were read :— 
1. The Sequence of Volcanic Rocks in Scotland in relation to the 
Atlantic-Pacific Classification of Suess. By Joun 8. Fuerv, 
M.A., D.Sc. 
The recognition of two great families of igneous rocks, the Atlantic and the 
Pacific, and their relation to certain types of earth-movement, which we owe to 
Harker, constitutes one of the greatest advances in rational petrology. 
In Scotland we may take the Carboniferous volcanic rocks as typically 
Atlantic, while the volcanic rocks of Lower Old Red Sandstone age are charac- 
teristic of the Pacific group. We may add to the Atlantic two other series, the 
Permian or late-Carboniferous volcanic rocks of Ayrshire and East Fife, and 
the nepheline-basalts (presumably Tertiary) of Caithness, with their associated 
camptonites and monchiquites. 
The Tertiary volcanic rocks of the Hebrides are Ailantic and are 
associated with movements of Atlantic types. There is much reason in ascrib- 
ing also to this period the north-west dykes, so abundant in Scotland, which 
contain not a few nepheline-bearing rocks, 
The remaining volcanic rocks of Scotland are of distinct type. They com- 
prise the Tayvallich lavas (perhaps pre-Cambrian), the Upper Cambrian volcanic 
rocks of the Highland border, and the silurian (and ordovician) lavas of the 
Southern Uplands. Pillow-lavas with Keratophyres, &c., characterise this group. 
They are not connected with movements either of Atlantic or of Pacific kind, 
and may be placed in a special family. 
2. The Older Granite in Lower Dee-side. By G. Barrow. 
A brief description was given of the mode of occurrence and composition of 
one of the older Granite intrusions in Lower Dee-side. In place of forming 
large coherent masses it tends rather to minute subdivision, permeating the 
crystalline gneisses over large areas. Excellent examples of lit-par-lit intrusion 
may be seen on the north side of the Dee, about, and west of, Banchory. The 
granitic material in these cases forms minute sills, varying from an inch to 
several feet thick, and almost rigidly parallel to the foliation of the associated 
gneiss into which it has been intruded. The ground here is comparatively 
flat, and the-method of feeding the sills cannot be clearly made out. But on 
the opposite or south side of the river the ground is much steeper, and in the 
hill-faces dyke-like intrusions can be seen, from which the sills proceed. They 
commence a little below the crest of the dyke, where they are smallest and 
shortest; they are seen to become steadily thicker and longer as we descend 
further below the crest of the dyke. In the interior of the latter the granite 
is usually grey, and contains more biotite than muscovite; oligoclase is also 
usually abundant; the oligoclase and biotite steadily diminish in amount as the 
rock is traced towards the taper end of the sills. At this point there is little 
oligoclase, and often no biotite; muscovite is fairly common, often in large 
crystals, and the bulk of the felspar is of alkaline composition. It appears 
that the fissures in which the dykes occur were filled with igneous material, and 
that under great pressure the walls were burst open and the still liquid 
material forced out, and thus separated from that which had already segregated 
out. The phenomenon may be described as magmatic differentiation intensified 
by dynamic action. Further, the material (pegmatite) which occurs on the 
extreme ends of the sills is often far coarser than that met with in the centre 
1912. HH 
