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 tube or from pāhoehoe flows where the lava is moving under the surface. Lava usually leaves the point of eruption in channels. These channels tend to stay very hot as their surroundings cool. This means they slowly develop walls around them as the surrounding lava cools and/or as the channel melts its way deeper. These channels can get deep enough to crust over, forming an insulating tube that keeps the lava molten and serves as a conduit for the flowing lava. These types of lava tubes tend to be closer to the lava eruption point. Farther away from the eruption point,