Country rock (geology) in geology when the term "country rock" is used include: When describing a pluton or dike, the igneous rock can be described as intruding the surrounding "country rock", the rock into which the pluton has intruded. When country rock is intruded by dyke, it is called "discordant intrusion," while intrusion by a sill indicates a "sub-parallel" or "concordant intrusion". Most intrusions into country rock are via magma. Usually, country rock is intruded by an igneous body of rock which formed when magma forced upward through fractures, or melted through overlying rock. Magma then cooled into solid rock, different from the
Lava New lava flows will cover the surrounding land, isolating the kīpuka so that it appears as a (usually) forested island in a barren lava flow. Lava domes are formed by the extrusion of viscous felsic magma. They can form prominent rounded protuberances, such as at Valles Caldera. As a volcano extrudes silicic lava, it can form an "inflation dome", gradually building up a large, pillow-like structure which cracks, fissures, and may release cooled chunks of rock and rubble. The top and side margins of an inflating lava dome tend to be covered in fragments of rock, breccia and ash. Examples