Book Review by Steve Matthews of Bookends.
Geology in the Lake District National Park by Phil Davies. Otley’s Steps. £10
Geology is nothing if not dramatic. For the person who can read the rocks, the Lake District tells “an epic story of ancient seas, violent volcanoes, colliding continents and a relatively recent ice age”. In looking at the Lakes we are looking at an area that was formed a mere 420 to 480 million years ago. The Earth has been around for 4.5 billion years. Those four to five hundred million years are a mere slice of geological time.
It began with sand, silt and clay being deposited in the sea bed off the ancient continent of Avalonia. Over twenty million years these sediments came to form a layer that was five thousand metres thick. This layer, compressed into sandstones, siltstones and mudstones, after much slumping and folding became the rocks that underlie Skiddaw and the surrounding mountains.
450 million years ago as the continent of Avalonia moved towards Laurentia, the great tectonic pressures of the slow collision caused the volcanic activity that produced the Borrowdale and Eycott Volcandic Groups of rock that characterise the more rugged mountains of the central Lakes.
The softer landscape of the southern Lakes was formed as more sediments were laid down and the distinctive limestones and siltstones of the Windermere Supergroup were formed.
The shaping of these materials took place 400 million years ago in the great mountain building process known as the Acadian Orogeny. The rocks were twisted and folded. It is only through the careful work of geologists over the last two hundred years that the intricate complexity of this folding which constitutes the rich and varied landscape of the Lakes has been slowly unravelled.
Today we are left with the eroded remains of those mighty movements of continents. They have been shaped and sculpted by the action of ice and water and wind over many millennia.
All this dramatic action can be seen clearly on the ground. Phil Davies directs us to thirty locations around the Lakes that illustrate the processes at work.
One “geosite” is the little church at Buttermere. The church is built of Ennerdale microgranite. The same pinkish granitic rock can be seen in the flanks of Red Pike and in the bed of Sour Milk Ghyll. Immediately outside the door of the Parish Room is a rock that shows the intense folding of the Buttermere Formation. “The Buttermere Formation is interpreted to be an ‘olistostrome’, that is the remains of a massive, submarine gravity slide or slump that disrupted the mudstone, siltstone and sandstone materials after they had been deposited.”
At Causey Pike “the thrust plane is exposed just below the summit of the fell” on the eastern side. It is part of a fault structure that runs for 35 kilometres from Ennerdale Bridge to Troutbeck. “Thermally metamorphosed Kirkstile strata have been thrust over sheared and fractured Buttermere formation.” It sounds complicated, but these dramatic movements can be clearly seen by the instructed eye. Phil Davies’s clear photographs show the formations, his captions explain what to look for and he provides maps to indicate the exact locations.
The wonderful landscape of the Lakes is there for all to read. This enthusiastic, well illustrated, detailed book by Phil Davies, should prove a very useful primer for any one who wants to learn to read the rocks.