532 J. Parkinson—Foliated and non-Loliated Rocks, 
I believe, more accurately, the latter is intrusive. In places this is 
almost a granite, and is characterized by porphyritic crystals of 
orthoclase, half an inch or so in length, often retaining their 
rectangular outlines. Now and again these rocks are cut by a second 
gneiss, also containing biotite, though not in great quantity, and 
distinguished from the first by containing no phenocrysts and by 
being on the whole of finer texture. Distinct in certain localities, no 
hard and fast line probably exists in reality between the two. 
A differentiation obvious in one place had not apparently taken place 
in another. 
Associated with these rocks, and clearly later in date than they, are 
masses and veins of a coarse pegmatite (the crystals of pink orthoclase 
may be a couple of inches in length), and here and there aplite veins 
still later in date cut through the whole. 
_ To avoid misconception it should be stated that, in this locality, 
the biotite-hornblende-schist above mentioned exists only as fragments, 
and not in well-defined exposures free from acid intrusions. The 
evidence rests on lenticular bands and inclusions with torn and frayed- 
' out edges passing more or less rapidly into the surrounding gneiss. 
In such a series it is useless to expect constant lithological types, 
and the country between Netim and Ibum,,a distance of 24 miles, 
provides examples to show that every gradation exists between the 
rocks above mentioned. The principal points are born out by the 
excellent exposures of rock on the Calabar River and on an important 
tributary joining the main stream where it is crossed by the Ibum 
Path, a few miles south of that village. Near the path a biotite- 
granite is the predominant rock, but higher up the main stream 
irregular fragments of a fine micaceous gneiss or schist are contained 
in a gneiss of more acid composition. The biotite in the former rock 
forms minute flakes, and the quartz and felspar cannot be differentiated 
by the naked eye. Later than either is a coarse quartz-orthoclase- 
plagioclase rock, some of the quartz grains being nearly a quarter of 
an inch in length. This is a pegmatite. 
Examination of thin sections shows that in the micaceous gneiss or 
schist reddish-brown flakes of biotite are the only coloured constituent, 
with the exception of a few grains of an iron oxide and some small 
garnets. The felspars are represented by microcline, orthoclase, and 
an acid plagioclase, quartz is rather less abundant than the felspars, 
and exhibits crush shadows. The structure of the rock is granulitie, 
and quarts de corrosion occurs here and there. The more acid gneiss 
consists almost entirely of quartz and of felspars of the same varieties 
as in the first instance. Lobed growths of quarts vermiculé in felspar 
are common. ‘The rock differs but little from a granite. 
Passing to the tributary stream above mentioned we find the 
irregular relation of basic to acid components giving place to a regular - 
banded structure, occasionally well developed over a comparatively 
large surface of rock. Relation to the more irregular type is shown 
by the ends of a band tailing out into elongated wisps or streaks. 
The rapid loss of foliation, by which the gneisses pass into granites, 
may be studied between the Calabar River and Ibum. The former 
rock contains angular inclusions, i.e. more basic patches, obliquely 
