Stars like the sun may end up alone but they are born in stellar nurseries, with a thousand — or a hundred thousand — siblings. Over time, the family disbands, victims of gravitational nudges and other tidings after 4.5 billion years of life in the cosmos.

Types of Mountains

Mountains make up a large proportion of the earth's surface. Based on their mode of formation, four main types of mountains can be distinguished.

1.     Fold mountains. These mountains are by far the most widespread and also the most important. They are caused by large-scale earth's movements, when stresses may be due to the increased load of the underlying rocks, flow movements in the mantle, magnetic intrusions into the crust, or the expansion or contraction of some part of the earth. When such stresses are initiated, the rocks are subjected to compressive forces that produce wrinkling or folding along the lines of weakness. Folding effectively shortens the earth's crust, creating from the original level surface a series of waves. The upfolded waves are called anticlines and the troughs or downfolds are synclines.

Earth Movements and the Major Landforms

The face of the earth is constantly being reshaped by the agents of denudation - running water, rain, frost, sun, wind, glaciers and waves, so that our present landforms are very varied and diverse. But these agents only modify the pattern of mountains, plateaux and pains which have been modelled by movements of the earth's crust.

Since the dawn of geological time, no less than nine orogenic or mountain building movements have taken place, folding and fracturing the earth's crust. Some of them occurred in Pre-Cambrian times 600-3500 million years ago. The three more recent orogenics are the Caledonian, Hercynian and

Uses of Rocks

Rocks are very important economically. The thin surface layer of the earth, formed by the break-down of the rocks in various ways and by various processes, is known as soil. The geographer is, among other things, interested in the soil as the medium in which plants grow, hence the scene of production of most of man's food and most of his raw materials.
Man's vital water supply is connected with the nature of the rocks. Part of our drinking water is got by sinking wells to tap the sub-surface water which is filtered naturally during its passage through the rocks. The amount of surface run-off in the form of rivers and springs affects the siting of

The Influence of Rock Types on Landscapes

The appearance and characteristic features of landforms are greatly influenced by the underlying rock type. Softer rocks like clay and shale are worn down much faster than harder rocks like granite.
The ancient rocks which dominate a great part of West Africa have been so greatly worn down by erosion that they now appear as peneplains. Granite domes for inselbergs have been formed where the old rocks resist erosion: and in some cases, such resistant high rocks produce high relief, such as the Jos Plateau of Nigeria, the Akwapim-Togo-Atacora ridges and the Birrimian uplands of Ghana, and the interior plateaux and mountains of Sierra Leone, Shales, schists and sandstones, being less resistant, form the much lower, rounded hills. Recent river sediments form flat plains.