I had the chance to sample the Alden Pyrite bed, within the Ledyard shale of the Ludlowville formation, this past May in a stream bank near the town of Alden, NY. The Alden Pyrite bed is so named because it is a layer of shale that has a high proportion of the fossils replaced by pyrite and often encased within nodules of the same mineral. Karl Wilson has a nice page of what he's found in the Alden pyrite beds at his website. Here is some of what I found:
A partial Mucrospirifer
This is a pelecypod that is partially surrounded by pyrite as well as having the shell replaced. It's likely a Nuculites triqueter or Nuculoidea corbuliformis.
A Gastropod which could be of the Bembexia genus.
This was the prize of the trip for me. A nice large Tornoceras uniangulare fossil. This is a nice comparison piece those that I've found at Arkona.
Another brachiopod that was relatively abundant was Ambocoelia umbonata
Another small Pelecypod
The day I was at the creek there was another gentleman who was actively mining the layer. He found two Spyroceras fossils, one of which had a large nodule of pyrite at one end. The Ludlowville formation is middle Devonian in age (Givetian stage).