Question

An igneous intrusion whose boundaries lie parallel to the layering in the surrounding country rock is considered to be:

Answer 1

...a concordant intrusion. In geology, "concordant" means the same as "sill" -- or, an intrusion that has gotten in between older layers of rock (or even beds of volcanic lava). An intrusion with boundaries parallel to layering in surrounding rocks suggests this, meaning it is considered to be a concordant intrusion.