The Malvern Hills are formed of some of the most ancient rocks in England, mostly
igneous and
metamorphic rocks from the late
Precambrian, known as the
Uriconian, which are around 680 million years old. The
Malvern Line or Malvern Lineament is the name applied to a north–south aligned
lineament which runs through the Malvern Hills and extends southwards towards
Bristol and northwards past
Kidderminster. It consists of a series of
faults and
folds which have the effect of bringing old Malvernian rocks to the surface. Being largely hard
igneous rocks, they have resisted
erosion better than those of the surrounding countryside and result in a striking line of hills of which the Malvern Hills are the most impressive. This line is considered to mark the edge of two
terranes – two once separate fragments of the Earth's crust now joined as one – the
Wrekin terrane to the west and the Charnwood terrane to the east. The main face of Gullet Quarry shows a cross-section through the Precambrian rock and exhibits many rock types including
diorite,
granite,
gneiss,
schist,
pegmatite and
dolerite. The evidence of the complex history of earth movements which formed the Hills can be seen by multiple joints, fractures, faults and shears, which make identifying changes in rock types difficult. Mineral deposits such as
haematite,
calcite and
epidote can be seen within these features. There is a tiny, man-made cave near the ridge of the hills called Clutter's Cave (or Giant's Cave or Hermit's Cave or Waum's Cave, after Walm's Well which is located on the boundary of News Wood below). The cave has been excavated into
pillow lavas. Some of the rounded 'pillow' shapes are still visible around the entrance to the cave.
Malvern water , Great Malvern, a popular café for walkers on the hills. The building on the right houses the spout from which the water surges into a basin. The quality of Malvern water is attributable to its source. The rocks of the Malvern Hills are amongst the oldest and hardest found in England; the geology is responsible for the quality of Malvern's spring water. The hills consist of
Precambrian igneous and
metamorphic rock, the oldest of which are about 670 million years old. The rocks are characterised by low porosity and high secondary permeability via fissures. Malvern water is rainwater and snow meltwater that percolates through fissures created by the pressures of
tectonic movements about 300 million years ago when advancing sedimentary layers of
Silurian shale and
limestone were pushed into and under older Precambrian rock. When the fissures are saturated, a
water table forms and the water emerges as springs around the fault lines between the strata. Depending on rainfall, the flow can vary from as little as per minute to over per minute. The water permeates through the rock which, because of its hardness, leaves little or no mineral traces in the water, while at the same time the very fine cracks act as a filter for other impurities. Rainfall on the Malvern Hills is thought to be sufficient to account for all the water that runs out of the springs, reflected for example in some spring flows six to eight weeks after heavy rainfall, and in reduced flows after a dry period. ==Ecology==