Geology (O-Level subject content)
The Geology (O-Level subject content) domain covers the whole Cameroon GCE O-Level Geology syllabus: Earth structure and plate tectonics; minerals and the three rock families; weathering, erosion, transport and deposition; folds, faults and geological maps; fossils and relative dating; and Cameroon's mineral and energy resources. The paper rewards precise definitions, labelled sketches and ordered geological reasoning rather than remembered slogans.
Core rules: minerals, rocks and the rock cycle
- A mineral is a naturally occurring, inorganic solid with a definite chemical composition and an ordered atomic structure. A rock is an aggregate of minerals, glass or organic matter.
- Igneous texture records cooling rate: extrusive rocks are fine-grained, intrusive rocks coarse-grained; mafic rocks are dark and silica-poor, felsic rocks light and silica-rich.
- Sedimentary rocks are clastic, chemical or organic; bedding, fossils, rounding and sorting record transport and deposition. Metamorphic rocks show foliation or recrystallisation controlled by parent rock, temperature and pressure.
- The rock cycle links melting, crystallisation, weathering and erosion, deposition and lithification, and metamorphism.
Structures, maps and time
Strike and dip describe inclined beds; anticlines and synclines are folds, while normal, reverse and strike-slip faults record tension, compression and shear. Relative dating uses superposition, original horizontality, cross-cutting relationships, inclusions and faunal succession. Plate boundaries are divergent, convergent or transform; the Cameroon Volcanic Line is an intraplate volcanic chain, not a plate margin.
Worked example
Sandstone A is cut by a vertical igneous dyke B. Dyke B is truncated by an erosion surface overlain by conglomerate C. A fault D displaces conglomerate C. Order the events oldest to youngest. Reasoning: B cuts A, so B is younger than A. The erosion surface truncates B before C is deposited, so C is younger than B. D displaces C, so D is younger than C. Order: A → B → C → D; the erosion surface is an unconformity.
Traps that cost marks
Do not call a rock a mineral. Do not say "cooled slowly" without linking slow cooling to large crystals. Do not label a fold as a fault. Do not give an age order without naming the principle. Do not place Mount Cameroon on a constructive plate boundary; it lies on the Cameroon Volcanic Line. Lake Nyos was a CO2 release, not a lava eruption.