A couple of weeks ago, I found an 'old' CD with several photos of my eurypterid-collecting jaunts - it was dated 2003. One of the photos showed a quarry wall with a very distinctive layer of rock - beautifully brecciated. I believe it has gone unnoticed by fossil collectors and researchers and likely reflects the occurrence of an earthquake, over 410 million years ago, that shook up the lime muds and then lithified to form this interesting bed of rock.
I have posted an image of this quarry wall at:
http://eurypterids.net/EurypteridMonth18.html