I now understand my mistake - it's the Up platform surface in the photo, not the track bed! Sorry for the red herring. Looks typical weather for Portmadoc in the two goods trains passing photo. Now here is something about the gunpowder trains from Penrhyn. I was told back when Cooks was still in business that gunpowder vans had a white diamond on the van side, but I have never had this substantiated. Any ideas from an explosive expert?