We found the arrow pointing to the path across the top of Mungrisdale Common. Makes a change from a cairn! There is very little rock visible on the rolling grassy marsh so it was interesting to look at these. They are called spotted slate. The long needle-like crystals are andalucite. The country rock in these parts is Skiddaw slate, formed when the two separate continents bearing England and Scotland collided. This is one form of metamorphism mainly to do with pressure. Later there was an igneous intrusion of magma underground that produced Skiddaw granite. The heat baked the Skiddaw slate in a ring around the magma called a metamorphic aureole. That allowed recrystallization and hence the spotted slate. This is contact metamorphism. The middle photograph seems to show iron in the layers. Could that account for the higher than expected magnetic field strength??
