by Edgar Wagner
Our story starts about 300 million years ago in a warm, shallow sea just south of the equator. To the north, the sea bed plunged away into deeper water, and on the edge of the slope were reefs like those in the Pacific Ocean today. The shallow sea teemed with creatures which, when they died, added their shells to the mud on the sea floor. Over millions of years the sea floor sank, allowing the sediment to accumulate to a thickness of nearly 2 kilometres! Squeezed under the enormous weight, the lower layers were compressed to become limestone.
A large river was carrying huge quantities of sediment into the ocean from mountains far to the north. A great delta built outwards, filling in the deeper ocean, first with fine mud, then with sand and gravel, eventually burying the limestone. The fine mud became shale, and the coarser sediment became sandstone.
Sea levels fell, leaving shallow pools and meandering channels. The swamps were covered by primitive vegetation, but no birds sang, for the only creatures that flew were insects. No flowers brightened the landscape, for the flowering plants would not appear for another one hundred and sixty million years. From time to time the land was flooded, the forests died, and the dead vegetation was buried under yet more sediment to become coal.
Millions of years passed. The land became a desert. Deep, deep down, water rich in minerals was accumulating. Much of it may have been seawater that was trapped in the sediments. It began to rise through the folded and fissured limestones, in places dissolving more limestone to make the cavities bigger, but in others depositing minerals on the cavity walls. The fissure walls became coated with minerals such as fluorspar, lead, barytes and calcite, with small amounts of others such as ores of zinc and copper.
Over a very long period, the Earth's continents move. The area we are concerned with moved very slowly until it lay far to the north of the Equator. Enormous forces buckled the whole sandwich of limestone, shale, sandstone and coal into an irregular dome.
About 50 million years ago, the area began to be uplifted again, and erosion stripped hundreds of metres of sediment away. Rivers carried it to the sea to form sediments that will harden into new rocks that will one day become the hills and valleys of a new land. Because of the domed shape, the limestone appeared in the centre, with the shale and sandstone on top of it round the edges.
The Ice Age came, and torrents from the melting glaciers deepened the valleys, carving out the spectacular limestone gorges of what we now call the Peak District. Water draining from the high sandstone moors found its way underground on reaching the limestone, and slowly began to form the caves for which the area is famous.
At last Man came. One of his settlements lay on the north eastern edge of the limestone, where the sea bed of long ago had plunged away into deeper water. To the north lay a steep escarpment formed of the remaining cover of shale and sandstone. The Saxons called it "Aiune". Today we call it Eyam.
The processes that shaped the landscape continue today. The steep escarpment that towers over Eyam is the edge of what remains of the shale and sandstone, and it is still being broken up by the roots of plants, summer heat and winter frost, rain, and wind. It is carried away in heavy rain to the Derwent, and then to the sea.
All the local rocks formed during what geologists call the Carboniferous Period, and the limestone is called the Carboniferous Limestone. Along the line of Church Street the limestone disappears northwards beneath the next formation, the Edale Shale, which occupies the gentle slope up to the foot of Eyam Edge. The steeper hillside is formed of the much harder Eyam Edge Sandstone, and as we pass up onto Eyam Moor we reach the even coarser, harder Kinderscout Grit.
The great mineral veins which formed in the limestone generally run roughly from east to west, but smaller fractures, mostly running from south west to north east in this area, were also "mineralised". The area is dotted with old mine shafts, even in the village. Most are safely covered, but beware of straying from footpaths, for many open holes lie on the wooded slopes of the deep valleys.