[3] 
Reports and Proceedings—G'eological Society of London. 239 
east these tongues amalgamate and form large masses, in which the 
foliation is less marked. Moreover, in this direction the large 
masses are often fringed with pegmatite, especially on their southern 
and eastern edges. Where the rock is a gneiss, it is composed of 
oligoclase, muscovite, biotite, and quartz, but contains no microcline. 
As the gneissose character becomes less marked, the oligoclase 
diminishes in amount, and microcline begins to appear, especially 
towards the margins of the masses. In the most south-easterly of 
these microcline is greatly in excess of oligoclase. 
The differences in structure and composition of these masses are 
believed by the Author to be due to the straining off of the crystals 
of earlier consolidation during intrusion under great pressure. The 
still liquid potash-bearing portion of the magma was squeezed out 
and forced into every plane of weakness in the surrounding rocks ; 
and that portion of it which contained the highest percentage of 
potash finally consolidated as pegmatite. 
Special attention is directed to the distribution of pegmatite. 
This rock is widely distributed in the Southern Highlands, and cuts 
across every known system of folding. It is consequently newer 
than any member of the metamorphic series. 
The surrounding metamorphic schists are next dealt with. These 
are remarkable for their highly crystalline condition, and also on 
account of the presence of many minerals known to occur in regions 
where thermometamorphism has taken place. The characters of the 
more important minerals are described in detail. The rocks of 
the metamorphic area become less and less crystalline as they are 
followed towards the Highland border. Three zones, characterized 
respectively by the minerals sillimanite, cyanite, and staurolite, have 
been roughly mapped. The more important rocks found in these 
zones are described in detail, and evidence is given to show that the 
boundaries between the zones do not in all cases coincide with the 
strike of the rocks. Thus, a thin bed of quartzite, which retains its 
character in consequence of the simplicity of its chemical composition, 
may be followed through all the zones; whereas the bed adjacent to 
it is in the outer zone a staurolite-schist, in the intermediate zone 
a cyanite-gneiss, and near the contact with the igneous rock a coarse 
sillimanite-gneiss. Hvidence is given to show that the original 
rocks formed a sedimentary series. 
The phenomena are compared with those of other areas where 
thermometamorphism has taken place ; and the conclusion is reached 
that the differences are of degree rather than of kind. The special 
features of the area in question are attributed to the depth at which 
the change was produced. 
The singular Fucoid-like impression, long known from the older 
Paleozoic Rocks of North America, under the name of Arthrophycus 
Harlani, has just been sent home from the Gold-Coast-Colony, West 
Africa, by Mr. Ferguson to Professor J. W. Judd, F.R.S., who has 
presented a specimen to the British Museum (Natural History), 
Cromwell Road, S.W. 
