Something moves through the shallow tropical sea. As it comes closer through the warm water it can be identified, from its iridescent sheen, as an ammonite, Psiloceras planorbis. This is a cephalopod from the same family as squid and nautilus. This means that we are leaving the Triassic and entering the unknown future of the Jurassic, some two hundred million years ago.
The nearby land is moving slowly North from its present position about thirty degrees North of the equator. It will take the next two hundred million years to move to its present day location at fifty two degrees North – at about the same speed as our fingernails grow.
Life is good, the seas are warm, there is plenty of food so all the animals – especially the ammonites grow and evolve to take advantage of the good conditions. There are different types but all from the same family, all over the world. Their fossils can therefore be used as indicator species as their evolution is very fast – in geological terms.
Storm clouds gathered and it started raining. It continued raining. It then rained some more and it became heavier as a tropical storm was created from the energy contained in the warm sea. The storm moved inland and the deluge increased as the clouds cooled during their climb over the mountains. Riverlets formed and began rushing down the steep mountains and across the coastal plain where they combined to form mighty rivers. These rivers carried grass, mud, trees and peat into the sea where our ammonite was unable to filter nutrients out of the normally clear, now heavily polluted, water. It suffocated and fell down through the water column to rest on the fine mud being deposited on the sea floor. It was soon covered and started its slow change into a fossil.
The storms eased and the sea water slowly cleared. There were some surviving ammonites. These were the ones that had managed to keep breathing and feeding during the mud onslaught and went on to breed so producing slightly different animals that had inherited the mutations that allowed their parents to survive. These are called Psilocera Liasicus.
This sequence of storms and clearing seas continued for many millions of years and can be seen, for example, on the foreshore at Kilve in Somerset where there is an alternating sequence of hard pure limestones and organic black shales. Time passed, these shales were buried, heated and compressed to form kerogen from which oil can be extracted – with difficulty, as the oil companies found out when they tried it. One of them was led by Dr Forbes Leslie who sought to establish Shaline Ltd, a limited company with a capital of a million and a half pounds, chaired by the Duke of Atholl, in the 1920s. The original retort can still be seen as can the remains of the shed which was where the oil works was. By the end of the decade it was found that only about 50% extraction from the shales was possible – the rest of the oil was used to heat the retort. This meant that the shales were not commercially viable so the system was shut down and abandoned.
The hard limestones are pale yellow-brown on the surface and a pale blue on the inside. They are known as the Blue Lias and make excellent building stones. They can be seen in buildings across Somerset.
Fred Mudlock put down his fourteen pound sledge and wiped his forehead free of the sweat and dust. He had been using the traditional quarryman’s technique of driving iron wedges in behind a block of limestone to ease it away from the quarry face. This method is slower than the blasting that is used in aggregate quarries but these blocks would be used to make fully dressed building stones so the traditional method produced the best quality stone, even though it was hard work.
He was working at the Blue Lias face of Ashen Cross Quarry in Somerton, Somerset. The block he was freeing from its resting place today was to be sawn to size in the works using a diamond-tipped 5ft diameter saw and then used as facing stone ashlars for the new development just outside the village
Fred was buying one of these houses and so had specified Blue Lias stone for the window and door lintels – he would carve these himself and so have a real attachment to the house. How many people could say that they had wrenched some of the construction materials of their home from the living rock? He especially liked the ammonite fossil in the front door lintel that he had carefully carved around.
Fred had been living in this house with his family for twenty three years when he decided to downsize for his retirement and move to a two bed bungalow just down the road. Both children had got married and moved out so it was too big for just himself and his wife, Rosemary.
The eager young estate agent, in his new overlarge suit, arrived to survey the house, measure up and prepare the details ready to offer it to potential buyers.
‘How old is this house Mr Mudlock?’ he asked
‘A little over two hundred million years,’ said Fred.
© Richard Kefford Eorðdraca
My Kindle books are on Amazon – Here