Ah, I see. A kind of 20 questions quiz!

I understand that they are from the same place as thuringians that we know as waterstones, but not the importance of the contrast of stone type. After all, thuringian waterstones are far removed from the ash/clay/chalk etc sedimentary deposits (which incidentally were laid down in the Ordovician period) that through a process of sedimtation-compaction-metamorphosis formed shales and schists and finally the waterstones we know and use.

That stones of a completely different nature are found within sedimentary layers and have a more adamantine nature is only natural - further metamorphosis has once again changed the nature of the layers that were once just a lot of loose uncompacted mud and grit.

Such fornations can be produced by shear forces or the proximity of great heat, as in Wales where we find a particularly long seam of harder rock amongst the softer slate. Here we find slatestone, lyn idwal, grecian oilstone and possibly the mythical cutlers greenstone.

Ordovician hones are by no means rare. The honing slates at Melynllyn and those from the caradoc beds were laid down in ordovician times. Ther are sandstone hones from York of the same period. Some are even older of course, hailing back to cambrian times.

To demystify the subject:

The Paleozoic age consisted of 7 eras, the 4 oldest being-
1 cambrian, 540-490 million years ago,
2 ordovician, 490-443
3 silurian, 443-417
4 devonian, 417-434

I have never seen the particular stone whose name I, along with my american friends, apparently cannot pronounce, but I did enjoy the quiz.

Regards,
Neil