Hi there, no, it's not your imagination. the very dark coloured marks are bushes and shrubs, and the marks on the light green areas are what we Brits call spoil heaps. These are made as the chimney shafts were dug out,and the spoil was tipped away over the sides of the tunnel. In fact, these spoil heaps often look like lava flows, if you see what I mean. I hope this info proves useful to you.
dark as it looks inside - this is only a short one
my son said thanks for the comments but you do know that life working on the railway isn't as glorified as it at first might seem you know. Those lads in the carridge works do a lot of hard work and a lot of the time it's mundaine d.i.y. and they're hardly ever thanked for all the hard work that they put into making those coaches look as beautiful as they do.
Great set, thanks for posting!
The water level wasn't all that low only about two or three feet, but low enough to get some good photos. Also, I could have walked 3/4 of the way across on the old trackbed. I didn't fancy that in case the power co. pumped water back into the resevior. You don't know how fast it would fill.
Disused by the Ffestiniog Railway, the power company paid for the re-routing of the track as compensation when they flooded the line to create Tanygrisiau resevoir.