47 million years ago what county was once a lake?

Germany

Explanation:

Due to the finding of numerous amounts of fossils and sediment layers in what was once a mine in the southeastern part of Germany, it is now thought that the Messel mine (near Frankfurt) was once part of a giant series of lakes aout 47 million years ago.

The area was mined for coal, which is a rock formed formed from organic material exposed to intense geological compression. The area must have been a regional depression because it was the destination of muddy sediments that were deposited there.