| About 300 to 500 million years ago, slates were layers of black mud on the bottom of shallow seas. As epochs passed, the mud hardened by the process of compaction and cementation.
At the same time the sea basins sank, allowing vast amount of new sediments to settle upon the hardening mud.
After some 2 to 400,000,000 years the slates-to-be were firm shales that lay beneath younger formations 5 to 6 miles thick.
As the Paleozoic Era came to an end, the continents were squeezed by rocks beneath the oceans. They pushed the hardened sea muds upwards, shoving and crumpling them into huge, high folds. |
