Amphibolite Sills

Walking along, looking down at my feet, I see that the rocks have made an almost sudden change into Amphibolite.  Amphibolite is an mafic igneous rock that contains a large amount of meta-greywacke.

The rocks then tell us that hot magma must have been present deep within the earth to form here.  Boudinage (meaning sausage shaped) are meta-greywacke in this photo.

These boudins were formed by extension of a bed being stretched and defromed amidst less compitent surroundings.  The copitent bed begins to break up and results in the formation of sausage shaped boudins.  Here sigma 1 and sigma 3 are shown.

Migmatite.  Photo coutesy of Callan Bentley.

Here is a picture of migmatite along the Billy Goat Trail.  In the boudinage above, migmatite is a little hard to see.  But, in the cracks between the necks of the boudins there appears to be migmatite present.  This happens because magma was the fluid available to fill the empty space.