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If rocks are pushed into the deeper parts of the earth’s crust, or if they are sufficiently long in contact with molten magma, they may eventually come to be completely or partially melted. In such cases, the minerals with the lowest melting point become liquid first, but eventually the whole rock is converted into magma and the cycle thus begins anew. During the rise of the magma in the crust, various exchange reactions between it and the adjoining wall-rock may take place. For instance, the molten portion of a partially fused rock may be squeezed out and may re-crystallise later somewhere else; ‘rafts’ detached from the walls of the magma chamber may be incorporated in the magma; or the solution remaining after the crystallisation of a magma is almost complete may permeate into the surrounding rock and eventually crystallise to form veins some distance away from its parent mass.