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Ordovician

The Ordovician 510-439 million years

After the life explosion witnessed in the Cambrian, Shropshire was set to experience explosions of a volcanic nature again. Through the Ordovician, Shropshire was split in two very different regions. The separation of the county into these two comes about because of a fault line. Not the Church Stretton fault (which had played an important role in the story until now) but the lesser-known Pontesford-Linley fault. This fault was the very boundary between land and sea. In the early Ordovician everything east of the Pontesford - Linley fault was land, everything to the west was sea.

The Ordovician was a time of enormous change. The Iapetus Ocean was closing, bringing Scotland and North England closer to the South of the country. Huge volcanic fields were born, creating the thick layers of lava and ash that are found around the Lake District and North Wales.

Shropshire was not spared this violence. The area to the west of the Pontesford–Linley fault is peppered with volcanic rocks. We can find evidence of ash, lava and large volcanic bombs, molten lumps of lava thrown out of a volcano that cool in the air before they hit the ground. The slow sea sediments that were building up here were punctuated by these volcanic eruptions and movements along the Pontesford-Linley fault, leaving interleaving layers of sea mud and volcanic ash. Shattered lava that may have been formed inside a volcano could be evidence of a volcanic cone in Shropshire!

On the other side of the fault, things were quieter. Land was being steadily eroded through much of the early Ordovician. Sea levels rose slowly and the land became flooded. Imagine standing on Caer Caradoc and looking down as the sea which filled the Church Stretton valley and lapped around the base of the hills. This area to the east of Caer Caradoc as studied by Murchison gives this time of the Ordovician its name – the Caradocian.

Not only was Southern Britain heading towards a collision with North America and Scotland, we were also about to crash into what would become Scandinavia. This was a relatively gentle event, folding the rocks around Shelve and the Pontesford-Linley fault and injecting molten rock into the crust.

At the end of the Ordovician sea levels dropped once more. This was due to an unusually strong ice age that gripped the planet for a million years. The ice could have stretched as far from the South Pole as 50º south of the equator. If the same thing happened today at the North Pole, the whole of Britain would be covered in ice.

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