294 Proceedings of the Royal Society of Edinburgh. [Sess. 
quartz. A typical quartz-keratophyre forms the rock of a great sill at 
Craigmushat Quarry, Gourock (Renfrewshire). This contains numerous 
small, euhedral phenocrysts of felspar belonging to at least two groups. 
Some show multiple twinning in a zone surrounding an irregular core of 
untwinned felspar. From the extinction the external zone may be referred 
to albite-oligoclase (Ab 85 An 15 ). Other phenocrysts with a square cross- 
section are simply-twinned, and have a mottled appearance due to an 
intergrowth of albite, or to albitisation. There are also elongated laths 
which also show simple twinning. These are referred to orthoclase, 
probably a soda-bearing variety. The felspar phenocrysts are embedded 
in a groundmass consisting of large and small quartz areas rendered 
curiously ragged and irregular in outline owing to their indentation by 
the terminations of small felspar laths. The latter are euhedral, especially 
where partly or wholly enveloped by quartz. Their determination is 
difficult, for the crystals are very turbid, and the groundmass is full 
of diffused secondary chloritic material. They appear to be untwinned 
and to have straight extinction. Hence they probably belong to 
orthoclase. 
Mention should also be made of the large druses in this rock, which 
are lined with an assemblage of beautifully crystallised minerals, including 
quartz, calcite, fluor-spar, and others. In thin section small cavities lined 
with beautiful euhedral quartz crystals may be seen, the remainder of the 
space being filled with calcite. The only ferro-magnesian constituents in 
the rock are the diffused chloritic alteration products in the groundmass, 
and sporadic clusters of large irregular grains of titaniferous magnetite. 
There is also some apatite. The texture is very dense, as the minute 
constituents of the groundmass are closely felted together, and present an 
almost felsitic appearance. 
A quartz-keratophyre from the Burnho Burn, Campsie Fells, has been 
collected by Mr J. V. Harrison. This rock contains little clusters of 
sanidine phenocrysts in a dense, felsitic, quartzo-felspathic groundmass. 
Mr Harrison has also obtained a quartz-keratophyre from one of the 
numerous acid dykes of the Misty Law area. In this rock there are a few 
small phenocrysts of soda-orthoclase in a thoroughly felsitic groundmass 
in which much quartz is visible. The only ferro-magnesian constituents 
are a few small specks of magnetite, and pseudomorphs in magnetite 
after biotite. 
The felsites, which are very abundant as dykes in the Meikle Bin area 
of the Campsie Fells, the Misty Law area of the Renfrewshire hills, and 
on the eastern coast of Great Gumbrae island, are probably not very 
