Strange Lichen pattern on rocks!

I was walking in the woods with some Blacksmith friends when we saw this rock.  It was in a small wet spot on the trail with some flowing water.

I think there are two kinds of Lichen on the rock.  One is mottled brown, and the other makes the interesting white and black pattern!  I think the white and black must kill off or displace the other at it expands.  It is both startling and pretty to find in the woods.  At first I thought someone had made very intricate artwork on the rocks.