Looks like lichens of some sort. Is that an ash tree? I see a lot of the bluish looking lichen stuff on the white ash I cut around here.
Lichens. If it is just one side, or thicker on one side, that side is north. Good to remember when finding your way in the woods.
I popped my raft in Manistee MI National Forrest and had to walk out of the woods. That's how I found the way out. Took three hours but I found a road and a Ranger. Best thing I ever learned from a book or was it a movie.
There are at least two different types of lichen on that tree, the yellow one and the grey one that is all over the tree wherever the yellow one isn't. There are a lot of different lichens and it seems like certain types of lichen prefer certain types of trees. Other lichens grow on dirt or on rock. Lichens don't get any nutrients from the tree or do any damage, they just use the tree for something to grow on.
http://www.lichen.com/bigpix/Fcaperata.html This may be what you found. Great website on lichens. http://www.lichen.com/bigpix/Fsoredica.html This also looks like it.