Glossary
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Palaeogeographic
Involving the reconstruction of the Earth's physical geography through the geological past, including the distribution of land and seas, the depths of the seas, geomorphology of the land and climatic belts.
Pelagic
Species living in the surface waters or middle depths of the sea.
Periglacial
The regions fringing an ice sheet.
Permeable
A rock is permeable if water can pass through it.
Permian
Geological period, covering 280 to 225 Million years, representing the last pert of the Palaeozoic era.
Petrography
The detailed description and systematic classification of rocks, based on mineral content and textural relations.
Photosynthetic activity
The process by which some organisms convert energy in sunlight to chemical forms of energy that can be used by biological systems.
Placer
A mineral deposit containing economic quantities of valuable minerals, formed by the processes of sedimentary accumulation. Placer deposits are loose and easily worked, and mining usually takes the form of dredging. Fossil placer deposits are more expensive to exploit.
Planning Policy Guidance (PPG)
Planning Policy Guidance notes set out the UK Government's national policies on different aspects of planning. They are being replaced by Planning Policy Statements.
Planning Policy Statements (PPS)
Planning Policy Statements set out the UK Government's national policies on different aspects of planning. They are gradually replacing the Planning Policy Guidance notes.
Pleistocene
Geological epoch preceding the Holocene, dating from approximately 10,000 - 1,800,000 years BP. This forms the lower division of the Quaternary era.
Plume
A zone of dispersion.
Porosity
A rock is said to be porous if it possesses cavities between the mineral grains making up the rock which can contain liquid.
Porphyry
An igneous rock, in which crystals constitute 25% or more of the volume.
Potential Special Area of Conservation (pSAC)
Conservation sites that have been advised to the UK Government as SACs but not yet submitted to the EU.
PPG
See Planning Policy Guidance.
PPS
See Planning Policy Statement.
Precautionary Principle
An internationally recognised approach to the management of risk where scientific knowledge is incomplete. Uncertainty should not be used as a reason for postponing cost-effective measures to prevent environmental degradation. Society should assume that potential risks are real and address them accordingly.
Prehistoric
A catch-all term for the pre-Roman periods.
pSAC
See Potential Special Areas of Conservation.