The part labeled A is a sill and the part labeled B is a d(y)ke.
A sill is a mass of igneous rock that intruded horizontally and laterally through rock layers already existent - it's a horizontal intrusion.
A d(y)ke is also a mass of igneous rock, but this time that intruded vertically across rock layers, many times, through an already existing crack - it's a vertical intrusion.
