Glossary
I hope these explanations help you in your understanding
and enjoyment of this subject!
Dolerite: An igneous (once molten) rock. It has a medium
grained texture meaning its constituent crystals can be seen with a hand
lens. It is quite dark often being slightly
green. Large expanses of dolerite are being
quarried for roadstone aggregate on Clee Hill.
Erratic: When glaciers travel they can pick up very large blocks of rock or other material which flow along with the glacier. However,
when the glacier is melting it can no longer support the large
material and boulders are dumped. These are known as erratics as they are
often in strange places and are made of rock types otherwise found
locally. A famous erratic stands outside the
Public Library in central Shrewsbury.
Genera (Genus):
Part of the scientific name given to organisms under the system
known as the 'Binomial Classification'. The same Genus name is given to a set
of species that share particular features.
Igneous: rock that was molten at some point in its
cycle. This could be lava or molten rock that never reached the
surface. Caer Caradoc is largely made from igneous rock (but it is NOT a
volcano; nor is the Wrekin!).
Limestone: A calcareous rock with a high proportion of the mineral
calcite (calcium
carbonate). It is formed either by precipitation of calcium carbonate from
the water; by the fossilization of a large number of fossils with calcareous
skeletons; or by a mixture of the two. Wenlock Edge has a good variety of
limestones.
Magma: Rock in its liquid,
or molten, state whilst it is underground. When it breaks through to and
flows over the
surface it is termed lava.
Marl: Rock made up of very
fine particles (clay and silt) mixed with a similar proportion of calcium
carbonate.
Sandstone: Rock made up of sand grains. There are different grades
depending on the size of the grains and their shape. Such grains may be
clearly visible with the naked eye (coarse) or with a hand lens (fine). The
Grinshill quarries have produced the best quality building stone in the County.
Sedimentary: Rocks
formed from sediment that settled over time either in water or on land and then
compressed and/or cemented to form rock by burial beneath further layers of sediment.
Sill: A body of igneous
rock that has been injected (whilst molten) along the bedding of other, usually
sedimentary, rocks (cf. a Dyke, which has
been injected across the bedding).
Tectonic:
Stresses, usually very large, related to earth movements caused by the constant 'drifting' of the
Earth's crust. The crust comprises continental and oceanic plates whose movement can result in
crumpling the ground (folding) and breaking it up (faulting). Injection of
molten rock can lead to Volcanic eruptions, the
heat and stress can cause Metamorphism, and active
fault movement can generate Earthquakes.
Tors: Crags of rock which
have often been weathered by the action of freeze-thaw resulting in
break-up and the production of debris as slopes of loose material below them. This is
well seen on the
Stiperstones Ridge and below the summit of Titterstone Clee.
