200 
PROFESSOR T. J. JEHU AND DR ROBERT CAMPBELL ON 
lenticular form, and have sometimes been fractured. We conclude, therefore, that 
the altered sediments exhibit dynamic metamorphism superposed on an earlier con- 
tact metamorphism induced by the intrusion of the diabases which are now in the 
condition of hornblende schists. 
The sediments within the hornblende-schist area in the Corrie Burn region are 
in the form of intensely corrugated, fine-grained schists (Plate IV, fig. 6), partly of the 
nature of black phyllites, partly soft green schists, the original character of which is 
doubtful, but which may represent fine volcanic muds. The two types are sometimes 
interlaminated. 
X. Comparison of the Margie Grits with the Leny Grits. 
The Leny Grits immediately to the north of the Highland Border Rocks comprise 
a varied assemblage of sediments. Grits or greywackes, usually green in colour, less 
often red or dark grey, predominate. Locally, as in the belt which is well exposed 
in the Craigmore quarry, they became conglomeratic. They are accompanied by 
intercalations of blue- and purple-coloured slates. 
The grits are, on the whole, very uniform in composition. Quartz, felspars, and 
micas are as a rule the only minerals found as pebbles and larger grains, and the 
matrix consists usually of minute clastic grains of the same minerals, together with 
a finely crystalline aggregate of authigenous chlorite and colourless micas. The 
relative proportions of the constituent fragments show considerable variation. Most 
frequently quartz predominates : sometimes, however, felspar grains are quite as 
numerous as those of quartz. Most of the grits are richly charged with large clastic 
muscovites and biotites. The quartz, as in the Margie Grits, is mainly granitic. 
The larger grains and pebbles of felspar are for the most part microcline, perthite, 
or orthoclase ; plagioclase, ranging from albite to andesine, but mainly oligoclase, 
is dominant among the smaller grains. In the Craigmore conglomeratic grits red 
microcline is almost the only felspar present ; on the other hand, among the finer 
grits occur types in which there is little or no microcline. The heavy constituents 
are chiefly zircon, green and brown tourmaline, and iron ores. Composite rock 
fragments are of somewhat rare occurrence except in the Craigmore grits, which are 
abundantly charged with large and small subangular pieces of a green mudstone 
closely resembling the mudstones interbedded with the Margie Grits in the Corrie 
Burn. Among the rock fragments have ' been noted also microcline granite, micro- 
pegmatite, spilite, chert (more crystalline than that of the local Highland Border 
Rocks), jasper, and quartzite. Schistose rocks have not been observed. 
If we set aside the basement breccias, in which the constituents are for the most 
part of local origin, and consider the normal Margie Grits, we find that their most 
distinctive character (when compared with the Leny Grits) is the almost invariable 
occurrence of scattered fragments of black shale, which are absent from the latter 
series. The dominant constituents of the grits of both series, as already indicated, 
