Adam Sharpe, senior archaeologist, Cornwall County Council, on mining and the natural environment

Mining and the natural environment have always been inextricably linked. Geological and geomorphological processes which took many millions of years to develop determined the resources available for mining and the sites where they awaited discovery and exploitation. Long ago, miners learnt the tell-tale signs of mineralisation - the characteristic greens of secondary copper minerals, the reds of iron-bearing rocks, the hard resistant whiteness of quartz stringers and reefs, the local softening and erosion of other altered rocks that signalled the presence of valuable ores. Elsewhere they began to realise that common plants were stunted or absent where such minerals occurred, or that some species - indicator plants - alone thrived where certain minerals lay not far beneath the surface. They dowsed, tasted the water, learned the smells of pyrite and mundic - developed a sense of geology that was instinctual long before it was written down or scientifically analysed - picking up subtle hints from their natural environment - clues that unerringly guided them to what it was they sought.

In turn, their activities changed the environment. Rocks whose weathering products were far more acidic or toxic to plant life than those experienced in the landscape - softened and tamed by long exposure to wind, water and bacteria - were brought from deep beneath the earth in vast quantities, broken into fragments, crushed to fine sands, burnt so that they turned to toxic gases, discarded as waste and spread across its surface or spilled into its watercourses. Across its landscape, environments were created which had not existed in Cornwall or West Devon for tens of millions of years. The few plants which could live there are very specialised - pioneer species which can gain a tenuous foothold in such dangerous habitats and after many decades create the conditions where other, less tolerant species could, perhaps, build on the shallow, poor soils they had painstakingly created. A slight change in their habitat - the disturbance of the surface of a waste dump, the spreading of a mere inch of nutrient-rich topsoil, the removal of a mineral-rich input to a stream - can undo the work of centuries and destroy such habitats for ever.

These are special places - rare not only in Cornwall, but worldwide. Some are so free-draining that they resemble miniature deserts, others are so utterly saturated with acidic water that only the most primitive species can survive, many are rich in freely-available toxic minerals whose closest comparisons are lava flows. The plants and animals that survive - and in many cases thrive here - are often unusual and find these conditions nowhere else in a landscape which agriculture has slowly modified over thousands of years - these are wild, primitive and important places in our landscape - but also vulnerable places - for their inhabitants are often small and undramatic, their value often unrecognised until they have gone. These are the homes of rare mosses and lichens, of stunted variants of common plants, of bare sands and clays, exposed rocks and the insects, beetles and other animals which are found here and which can survive nowhere else. Many generations of such plants and animals must have lived out their lives in islanded areas like these, utterly isolated from contact with other such colonies, that subtle changes brought about through specialisation and inbreeding may have occurred. Other species rely on chains of sites like these, spread throughout the landscape, moving from one oasis to another in what is to them a sterile and inhospitable desert of farmland and townscape. Remove enough of these sites, and they are trapped.

The contents of the spoil heaps, hacked as they have been from deep below the ground, are also extremely important resources for the geologist and mineralogist. These are types of rocks and minerals which simply do not occur at the surface, where millions of years of exposure to air and water chemistry, coupled with the effects of some of the smallest, yet most abundant life forms on the planet have changed them into the stable, familiar materials which make up most of our environment. They provide rare and valuable glimpses into the formation of our planet and the way it has developed. Seventy one globally-rare species of minerals were recorded in Cornwall up until 1992 from such sources - twelve had never been recorded anywhere in the world before that date, and it is certain that many more await discovery. The words "waste" and "spoil" are often so wrongly applied to such sites - these are treasure houses which may prove to be as important for the knowledge of the natural world which they provide us as the copper and tin from which they were once separated and discarded.

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Alec Gwynn of West Cornwall Geology Tours 07887 556245 www.cornwallgeology.co.uk on the geology of the St Just Area from Gurnard’s Head to Cot Valley

Although dominated by the Lands End granite complex, this unique area offers an interesting array of features associated with the emplacement of the granites into the surrounding ‘country rocks’.

Gurnard’s Head offers perhaps the best example and exposures of metamorphosed basics(greenstone-hornfels) and metasediments (altered Mylor slates), and Spillitic Pillow lavas offer further interest.

Porthmeor cove exhibits two small granite bodies(plutons) which are the only well exposed and complete examples of this feature in the whole of South West England, and numerous associated features can also be seen.

The classic mining site at Botallack, just east of St Just, illustrates the contact metamorphism of basic volcanic rocks and sediments by the Land’s End granite; the later complex development of mineral assemblages has produced the source for the Tin, Copper & Uranium mining previously so important to this area.

The exposure around Cape Cornwall is excellent, particularly in the coves to the north and south of the cape. Many features can be seen in the low cliffs of Priest's Cove and on the foreshore, depending on the tide. Porth Ledden is also an excellent locality, but is occasionally inundated with seaweed, blanketing the foreshore exposures and making footings treacherous. Care should also be exercised on the steep slopes of the cape itself, though good exposures of the metasediments can be seen from the safety of the paths skirting its base. With effort, entrance can be made into the mine workings in the cliffs, but this is not recommended to anyone without experience of Cornish mine workings and the proper equipment - they are dangerous; if in doubt, stay out.

A visit to the St Just area would not be complete without a visit to the Beach at Cot valley (Porth Nanven). This location is an important & excellent example of quaternary geopmorphology and exhibits a Raised Boulder beach, overlain by a considerable thickness of ‘Head’ deposits. This deposit demonstrates changes of sea-level during more recent (Quaternary) times.