466 TRANSACTIONS OF SECTION C. 
of the dyke; the distribution of coarse and fine material being thus the reverse 
of that usually met with in small intrusions. 
This separation of the more acid and less acid material occurs in connection 
with every dyke and sill over the entire Dee-side area between Banchory and 
Aberdeen; the pegmatitic material forming a fringing margin, the breadth of 
which varies considerably. The largest of the sill-like masses occurs at Aber- 
deen, and part of the city is built on it; its great fringe of pegmatite veins is 
well displayed on the banks of the Dee near the railway bridge. 
The separation of the material rich in oligoclase and biotite from that richer 
in alkali-felspar and muscovite is not confined to each separate intrusion; it 
holds good for the intrusion as a whole. Well to the south of the Dee, 
especially nearer the coast, nearly the whole of the intrusions are more alkaline 
than those nearer the Dee; the pegmatite remains of much the same composition, 
but there is a considerable amount of schorl present in the southern area that is 
distinctly rare in the northern. 
There is considerable variation in the amount of foliation shown by these 
intrusions. In the moderate-sized or larger ones the centre is usually un- 
foliated, or but slightly so; toward the margins the foliation is more marked. 
The pegmatite fringe is rarely foliated if it occurs as veins or dykes; but it 
usually is more or less foliated if in thin sills. The foliation over most of the 
area is protoplastic ; post-consolidation crushing is rare. Indeed, it is only well 
seen in one case, where the granite has reached the present surface far south 
of the main series of intrusions, and within a lower temperature zone. This 
intrusion is cut open by a branch of the Cowie Water, close to the Stonehaven 
Road from Banchory. 
3. Lhe Alkaline Igneous Rocks of Ayrshire. By G. W. Tyrrunn. 
Recent work by Scottish petrologists has disclosed the fact that one of the 
greatest developments of rocks characterised by primary analcite as yet dis- 
covered is contained in the Midland Valley of Scotland. Geographically these 
rocks are localised in two main regions : one in Ayrshire, the other in the districts 
surrounding the Firth of Forth. There are also one or two subsidiary districts, 
as, for example, the neighbourhood of Glasgow. Geologically the analcite rocks, 
both intrusive and extrusive, are Carboniferous in age, and have a time-range 
extending from the Carboniferous Limestone to the very latest Carboniferous 
date in Scotland, possibly including also the early Permian. 
The Ayrshire region is practically bounded by the confines of that county. 
The intrusions of the analcite-suite penetrate the stratigraphical series from the 
Calciferous Sandstone to the lavas overlying the Upper Red Barren Measures 
of the Mauchline district. They occur in the form of stratiform sills, lenti- 
cular intrusive masses, volcanic plugs, and as a series of lava-flows. No masses 
of true plutonic habit are known. In this igneous episode, therefore, there are 
representatives of the volcanic phase and the phase of minor intrusions, but not 
the plutonic phase. It may be assumed that the latter, if developed at all, is 
still deeply buried, and has not yet been exposed by erosion. 
The petrological characters of the suite are very distinctive. In general the 
magmas were poor in silica and rich in alkalies, and in the latter soda is always 
in excess of potash. The rocks were so saturated with magmatic water that the 
characteristic mineral of the suite is analcite, which occurs in almost every 
member, sometimes abundantly, and with such relations to the other constitu- 
ents as to establish its undoubted primary character. ‘The characteristic femic 
mineral is a purple titanaugite. Olivine is also abundant, and some of the rocks 
contain soda-amphiboles (barkevicite and arfvedsonite). Nepheline and soda- 
orthoclase occur in subordinate amounts, and aegirine is found in the more acid 
rocks. 
The rocks have been classified as follows :— 
A. Rocks with conspicuous Analcite. 
1. Analcite Syenite.—In which alkali-felspar is dominant with abundant 
fresh interstitial analcite. 
2. Leschenite.—In which lime-soda felspar is dominant. Three types are 
