In the figure provided below, what type of igneous intrusion is the horizontal rock unit indicated by the arrow?
A)dike
B)sill
C)pluton
D)laccolith

Question

In the figure provided below, what type of igneous intrusion is the horizontal rock unit indicated by the arrow? 
A)dike 
B)sill 
C)pluton 
D)laccolith

Quizplus · Accepted Answer

The horizontal rock unit indicated by the arrow is a sill. This is because it is a tabular, sheet-like intrusion that has been injected between layers of pre-existing rock, parallel to the pre-existing layering or stratification. Sills differ from dikes in that dikes are discordant, crosscutting through the pre-existing rock, while sills are concordant. Plutons are large, irregular-shaped intrusive bodies, and laccoliths are a type of pluton that has a mushroom-like shape, bulging upward into the overlying rock. Neither of these terms are appropriate to describe the feature indicated by the arrow in the figure.

In the Figure Provided Below, What Type of Igneous Intrusion