TRANSACTIONS OF SECTION C, 571 
west. The valley of the Cross is not included in this paper, except between 
Itaka, a village about half a day’s journey below the international frontier and 
the Government station of Obubura Hill. 
After briefly describing the monotonous belt of mangrove swamps which 
fringes the coast and the dense creeper-entangled bush which uniformly covers the 
higher ground of the interior, an attempt is made to classify and to give some 
account of the various types of crystalline rocks. These form the backbone of 
the country, and are bordered on their southern and northern sides by sediments of 
varying character, which from fragmentary fossils are very probably of Cretaceous 
age. ‘The crystallines are, however, from many points of view the more important 
group. 
The entire series presents a certain uniformity in whatever part of the district 
it is observed, and consists of mica schists, with which are associated some 
hornblende schists; a group of fine-grained biotite gneisses and garnetiferous 
granulites; intrusive granitoid gneisses; garnetiferous and tourmaliniferous 
pegmatites; granites and aplites. Owing to the exceedingly dense vegetation 
and the multifarious calls on the time of the traveller in such a country, the 
order of succession of these rocks must for the present remain uncertain, but it is 
believed that the order given represents the true sequence in time. The granites 
vary from rocks so poor in ferro-magnesian minerals as to be practically aplites, 
to otbers rich in biotite with large porphyritic crystals of orthoclase, Doubtless 
these rocks are of different ages. 
The latest igneous rocks are dykes of olivine basalt, which occur, though not 
commonly, in the crystalline series; while the same or a similar rock forms 
abundant sills in the sedimentary beds of the Cross River and its important 
tributary the Aweyong. A study of the pebbles collected from various river-beds 
shows the presence of andesites and porphyries. From the Calabar River, above 
Uwet, comes an interesting series of rocks, altered by the intrusion of a granite. 
Specimens contain an orthochlorite, allied to pennine, and ill-formed garnet and 
andalusite ; but mica schists are most abundant, and recall similar rocks to the 
north and east. 
The sediments, which are believed to be approximately of the same age 
whether found to the north or to the south of the Oban Hills, exhibit slightly 
different petrographical characters in the two localities. 
Everywhere the basement bed is an arkose, derived directly from the degrada- 
tion of the crystalline rocks, rarely conglomeratic, occasionally false-bedded. 
On the Cross River these sandstones are succeeded by shales, and, more rarely, 
by impure limestones. 
On the Aweyong River, for some distance above and below Ogomogon, a 
variability and rapid alternation of the strata are noticeable ; while on the southern 
side of the Oban Hills this variability in petrographical composition is very 
ih ; thin beds of limestone are found, and the dip, as in the north, is always 
small. ° 
_ Some incoherent sandstones found at Calabar, Adiabo, and elsewhere are 
intermediate in age between these sediments and the river alluvium. 
6. On Boulders from the Cambridge District, collected by the Sedgwick 
Club. By R. H. Rasrary, B.A. 
During the past two years several hundred boulders have been collected, 
chiefly from the region lying south and west of Cambridge. Among these rhomb- 
porphyries are fairly common, and other well-known rocks are recognisable. 
An examination of about fifty slices has led to the identification of several 
distinct rock types. Many are clearly referable to the soda-bearing series of 
South Norway, characterised hy egirine, arfvedsonite, and other peculiar ferro- 
magnesian minerals, Among these may be mentioned Nordmarkite and the 
corresponding soda-granite; also a nepheline syenite, near to laurdalite, and the 
above-mentioned rhomb-porphyries. 
