Geology

The geology of the AMA consists of Precambrian Dahomeyan schists, granodiorites, granites gneiss and amphibolites to late Precambrian Togo series comprising mainly quartzite, phillites, phylitones and quartz breccias.

Other formations found are the palaeozoic accraian sediments - sandstone, shales and interbedded sandstone-shale with gypsum lenses.

The coastline of Accra comprises a series of resistant rock outcrops and platforms and sandy beaches near the mouth of the lagoons.

The coastline is exposed and because of the close and the Korle (Central Accra).

Soils

The soils in the metropolitan area can be divided into four main groups: drift materials resulting from deposits by wind blown erosion; alluvial and marine motted clays of comparatively recent origin derived from underlying shales; residual clays and gravels derived from weathered quartzites, gneiss and schist rocks, and lateritic sandy clay soils derived from weathered Accraian sandstone bedrock formations.

In many low lying poorly drained areas, pockets of alluvial ‘black cotton’ soils are found. These soils have a heavy organic content, expand, and contract readily causing major problems with foundations and footings.

In some areas, lateritic soils are strongly acidic and when saturated are prone to attack concrete foundations causing honeycombing.

Near the foothills are the large areas of alluvial laterite gravels and sands. Many of these deposits are being exploited in an uncontrolled manner for constructional purposes.