Clay is still being produced by nature much more than what man is able to make use of in ceramics. We think the surface of the earth is permanent and unchanging. It is not so. This is only because we have the opportunity of observing it over a relatively limited period of time. Actually the earth has undergone continuous change and what is now vast areas continents was originally mountains or inlands covered by seas.
The familiar surface features of the earth that we know and see as mountains, plains, rivers, seas, deserts, lakes etc represent the cumulative effect of geological forces over millions of years. In remote geological time, the earth was a mass of molten material and the crust of the earth was a relatively thin, frozen layer covering a very hot interior. Rocks which are formed by the cooling of molten material are called igneous rocks.
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