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Dike
 Dike/Dike swarm – Dikes occur when igneous rocks break through the surrounding rock. They are usually associated with volcanic activity on a large scale, for example, the splitting of continents. The dike swarms of northern England, Northern Ireland and Scotland possibly occurred during a phase of the widening of the Atlantic Ocean.
Dike
A wall-like sheet of igneous rock that cuts across other rocks. (See also: Contact metamorphism and Intrusive rock, intrusion.)
Dike swarm
A collection of hundreds or thousands of parallel dikes.
Diorite
An igneous rock that forms underground. It has properties between gabbro and granite; it has the same composition as the lava called andesite. Diorite is the typical rock of dikes and sills. It is a medium- to coarse-grained igneous rock that contains about two-thirds feldspar and one-third dark-coloured minerals.
Dolomite
A carbonate mineral made from calcium and magnesium. This mineral is similar to calcite; but because it contains magnesium as well as calcium, it is more resistant to weathering. It is
Scotland
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Dike
Dike
opaque, dull white and is slightly harder than calcite. It is found in sedimentary rocks.
E
Eluviation
The washing of clays from the topsoil to the subsoil in slightly acid soils. The result is to make the subsoil heavy and difficult for farmers to work. It is commonly found in acid brown soils. (See also: Alfisol and Illuviation.)
Epoch
A part of a period of geological time. In this time a rock series can be laid down.
Erode, erosion
The twin processes of breaking down a rock (called weathering) and then removing the debris (called transporting). In some
Northern Ireland
places both processes happen together. For example, in a river
a stone being carried by the river may crash into the bank and chip a stone in the bank. This chipping is weathering. The fast-flowing water will then carry this chip away. This is transport. In a soil, however,
the two parts of the process may be separated by hundreds of years. Rainwater reacts with rock at the base of the soil – weathering. But the soil only moves much later. The word soil erosion refers to the washing away of the soil when it is left unprotected, for example, on farmland. This is really accelerated transport, for the weathering part of the erosion process happened long before. (See also: Chemical weathering; Gulleying; Weathering.)
England