The similarity of conformation and nature of the rocks
on both sides of the continent; but there is a difference
in the structure of the subtending ridges, as may be understood
by the annexed ideal geological section.
==
[The ASCII edition cannot include the drawing of the cross-section,
but the comments are included in full. - A. L., 1997.]
IDEAL SECTION ACROSS SOUTH CENTRAL AFRICA,
INTENDED TO SHOW THE ELEVATED VALLEY FORM OF THAT PORTION OF THE CONTINENT.
- - - - - - - - - - - - - - - - - - -
WEST.
[Terrain] [Remarks]
Sea. CALCAREOUS TUFA.
TRAP. With modern shells, and similar to those now found
in the sea adjacent, with strongly magnetic iron ore.
MICA SCHIST. Dipping East.
SANDSTONE (like that of East Africa). The rocks
Pungo Andongo. of Pungo Andongo are a conglomerate of rounded shingle in
Rocks 4000 feet. a matrix of sandstone, and stand on horizontal sandstone,
on which fossil palms appear.
Fault.
RED SHALES CAPPED BY FERRUGINOUS CONGLOMERATE.
Soft red shale or "keele".
G| 5000 feet.
R| Water boils
E| at 202 Deg.
A| On top, ferruginous conglomerate; below that, red shale,
T| 4500 feet. with banks of gravel.
| Lake Dilolo.
C| TUFA AND TRAP. In Londa, the bottom of the valley
E| 2500 feet. is formed of ferruginous conglomerate on the surface;
N| Lake Ngami. hardened sandstone, with madrepore holes,
T| banks of gravel, and occasionally trap;
R| south of 12 Degrees, large patches of soft
A| TUFA. calcareous tufa, with pebbles of jasper,
L| agates, &c., lie on various horizontal traps,
| amygdaloids with analami and mesotype, which is
P| burst through by basaltic rocks forming hills,
L| and showing that the bottom of the valley
A| RADIATED ZEOLITE. consists of old silurian schists;
T| there are also various granitic rocks
E| cropping through the trap.
A|
U| BASALTIC ROCKS. Augitic porphyry and basalt,
.| with tufa over it.
Place of Great Cataract.
MICA SCHIST. White mica schist dipping west, and gneiss.
5000 feet. Kalomo.
Water boils GRANITE. With black mica.
at 202 Deg.
MICA SCHIST. White mica schist and white marble.
Hill tops TRAP. Hot fountain; conical hills of igneous rocks,
4000 feet. containing much mica.
Bottoms 3500 feet.
MICA SCHIST. Pink marble dolomite,
on hills of mica schist, of various colours, with trap,
schorl in gneiss, kyanite or disthene gneissose mica
in the schist.
1500 ft. COAL IN SANDSTONE. Specular and magnetic iron
on various igneous rocks; finely laminated porphyry;
granite; hot fountain.
Sandstone overlying coal; trap dykes;
syenitic porphyry dykes; black vesicular trap,
penetrating in thin veins the clay shale of the country,
converting it into porcellanite, and partially
crystallizing the coal. On this sandstone
lie fossil palms, and coniferous trees
converted into silica, as on a similar rock in Angola.
COMPACT SILICEOUS SCHIST.
IGNEOUS ROCKS. Trappean rocks, with hot fountain.
CALCAREOUS TUFA. Arkose, or granitic grit,
with modern shells covered by calcareous tufa.
Sea.
EAST.
The heights are given as an approximation obtained from observing
the boiling point of water, they are drawn on a scale of 1/10 of an inch
per 1000 feet in altitude. The section is necessarily exaggerated
in longitude, as it was traversed in different latitudes,
the western side being in 8d-12d, the eastern 15d-18d S.
==
We can see from this hill five distinct ranges, of which
Bolengo is the most westerly, and Komanga is the most easterly.
The second is named Sekonkamena, and the third Funze.
Very many conical hills appear among them, and they are generally
covered with trees. On their tops we have beautiful white quartz rocks,
and some have a capping of dolomite. On the west of the second range we have
great masses of kyanite or disthene, and on the flanks of the third and fourth
a great deal of specular iron ore which is magnetic, and containing
a very large percentage of the metal. The sides of these ranges
are generally very precipitous, and there are rivulets between
which are not perennial. Many of the hills have been raised by granite,
exactly like that of the Kalomo. Dikes of this granite may be seen
thrusting up immense masses of mica schist and quartz or sandstone schist,
and making the strata fold over them on each side, as clothes hung
upon a line. The uppermost stratum is always dolomite or bright white quartz.
Semalembue intended that we should go a little to the northeast,
and pass through the people called Babimpe, and we saw some of that people,
who invited us to come that way on account of its being smoother;
but, feeling anxious to get back to the Zambesi again,
we decided to cross the hills toward its confluence with the Kafue.
The distance, which in a straight line is but small, occupied three days.
The precipitous nature of the sides of this mass of hills
knocked up the oxen and forced us to slaughter two, one of which,
a very large one, and ornamented with upward of thirty pieces of its own skin
detached and hanging down, Sekeletu had wished us to take to the white people
as a specimen of his cattle. We saw many elephants among the hills,
and my men ran off and killed three. When we came to the top
of the outer range of the hills we had a glorious view.
At a short distance below us we saw the Kafue, wending away over
a forest-clad plain to the confluence, and on the other side of the Zambesi,
beyond that, lay a long range of dark hills. A line of fleecy clouds appeared
lying along the course of that river at their base. The plain below us,
at the left of the Kafue, had more large game on it than any where else
I had seen in Africa. Hundreds of buffaloes and zebras grazed
on the open spaces, and there stood lordly elephants feeding majestically,
nothing moving apparently but the proboscis.
