Igneous Intrusions form when magma cools and solidifies before it reaches the surface.
pluton - igneous rock that hardens underground
sill - igneous intrusion the forms between rock layers
dike - igneous intrusion that cuts across rock layers
laccolith - a mushroom shaped igneous intrusion
batholith - largest of all plutons - unknown size - makes up the core of mountains
stock - small batholith less than 100 square kilometers
neck - the remnants of the hardened lava in the throat of a volcano after erosion

dike&sill.jpg