TRANSACTIONS OF SECTION C. 467 
distinguished, on mineralogical and textural grounds, as the Glasgow, Galston, 
and Cathcart types. 
3. Picrite-7’eschenite.—An ultra-basic differentiation facies of teschenite. 
Two types are distinguished, the Inchcolm and the Lugar, the latter being 
characterised by granular augite and abundant hornblende. 
4. Lugarite.—A leucocratic rock analogous to ijolite, containing about 50 per 
cent. of analcite and nepheline with titanaugite, barkevicite, and labradorite. 
5. Monchiquite-—A lamprophyric type usually occurring as a contact-facies, 
but occasionally as an independent mass. One occurrence contains huge pheno- 
crysts of hornblende and biotite. 
B. Rocks with conspicuous Nepheline. 
1. Theralite.—Two types are distinguished : one, the Bellow type, occurring 
in the picrite-teschenite sill of Lugar, is characterised by melanocratic habit, 
abundance of olivine, and poikilitic fabric; the other, the Barshaw type, is also 
melanocratic, but the chief coloured minerals are titanaugite and barkevicite. 
2. Hssexite.—Two types are recognised : the Carskeoch and the Crawfordjohn, 
the latter characterised by porphyritic augite and rather abundant nepheline. 
3. Kylite.—An olivine-rich, melanocratic end-facies of the essexite or thera- 
lite families, occurring as a homogeneous set of sills and bosses in the Kyle 
district of Ayrshire. 
C. Rocks without conspicuous Analcite or Nepheline. 
These rocks show their relations to the alkaline series by the abundance of 
purple augite and occasional nepheline, analcite, or soda-orthoclase. They are 
designated alkali-dolerites and essexite-dolerites, and some of them closely 
resemble the crinanites of Argyllshire. 
D. The Latrusive Rocks of the Mauchline Basin. 
The lavas comprise femic olivine-basalts (Hillhouse and Dalmeny types), 
analeite-basanites, analcite-nepheline-basanites, nepheline basalts, monchiquite- 
lavas, and limburgite. 
Of the above types, teschenite is by far the most abundant amongst the 
intrusive, and olivine-basalt in the extrusive rocks. The available evidence goes 
to show that the earliest rocks to be intruded were the teschenites, and that 
they were followed, in the order named, by picrite-teschenite, kylite and 
essexite, analcite-syenite, and essexite-dolerite. The Mauchline lavas were 
probably the effusive equivalents of the kylites and essexites. 
4. The Volcanic Rocks around the Ord Hill of Rhynie, Aberdeenshire. 
By Wiutam Mackin, M.A., M.D. 
These rocks occupy an area of two-thirds of a mile in length by a quarter of a 
mile in breadth, of which Ord Hill marks the centre, about half a mile west of 
the village of Muir of Rhynie, West Aberdeenshire. The group embraces at 
least three independent lava flows, with associated tuffs and interbedded and 
overlying sedimentary rocks, and lies on an eroded, eastward-sloping surface of 
the diorites and gabbros of West Aberdeenshire—rocks which have been con- 
sidered to represent an early and basic modification of the younger Grampian 
granite—and are cut off on the east by the boundary fault of the Old Red 
Sandstone outlier of Rhynie and Kildrummy. A small outlier limited to two 
or three square yards of surface, and representing a single lava flow, lies on the 
edge of the serpentine mass of Cnoc Cailliche about a mile south from the 
extreme southern end of the main area. The volcanic members of the group 
consist of grey to greenish coloured rhyolites, showing in places fine vesiculation 
and beautiful fluidal banding. ‘The usual minerals of such rocks—quartz, 
orthoclase, muscovite, biotite with at times an occasional augite, are present in 
an amorphous base. Flow-brecciation is a frequent feature and evidence of the 
effect of pressure is not entirely absent. The tuffs consist of fragments of 
rhyolite rocks—occasionally up to 2 inches in diameter—often rounded and en- 
circled with glassy coronas exhibiting fluidal banding. Broken crystals of quartz 
HH 2 
