DESERTS AND DYING SEAS have left their mark in the east of the county. Massive erosion reduced the newly formed Pennine mountains to hills 250 million years ago. Desert sand dunes covered Leeds. As the land began to sink, the shallow Zechstein Sea flowed in from the north.
In a warm shallow sea reefs built up not far from the shoreline near the eastern margins of the county. Pale Magnesian Limestone for York Minster was quarried from the limestone ridge that was left.
The narrow limestone ridge has some of the richest wildflower meadows in the county.
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