page_title: Country rock (geology)
hierarchical_section_title: Country rock (geology)
caption_attribution_description: English: Country Rock Intruded. A USGS map, from an article, about part of the US states of Virginia and West Virginia. On the article, can't find an explicit date (?!). Though as far as I can tell, the actual location is fictional. Notes, Figure 16. Eruption sequence of an Eocene diatreme following the hydrovolcanic model. A, Eruption commences when an intrusion reaches shallow depths and encounters a rich source of ground water; B, the breccia pipe propagates downward, creating a cone of depression of the water table, while a tuff ring forms around the central crater and the walls of the pipe collapse downward; C, material collapses into the pipe, allowing rocks from higher in the stratigraphic sequence to fall to lower levels, while forming some crude layering. Debris flows away from the crater walls to form volcaniclastic layering.
context_page_description: In geology, country rock is the rock native to an area, in contrast to any intrusion of viscous geologic material, commonly magma, or perhaps rock salt or unconsolidated sediments.
  Magma is typically less dense than the rock it intrudes, widening and filling existing cracks, sometimes melting the already-existing country rock.
  The term "country rock" is similar to, and in many cases interchangeable with, the terms basement and wall rocks.
  Country rock can denote the widespread lithology of a region in relation to the rock which is being discussed or observed.
context_section_description: In geology, country rock is the rock native to an area, in contrast to any intrusion of viscous geologic material, commonly magma, or perhaps rock salt (in salt domes) or unconsolidated sediments.
  Magma is typically less dense than the rock it intrudes, widening and filling existing cracks, sometimes melting the already-existing country rock. 
  The term "country rock" is similar to, and in many cases interchangeable with, the terms basement and wall rocks.
  Country rock can denote the widespread lithology of a region in relation to the rock which is being discussed or observed.
caption: All of "Devonian and younger", "Silurian", and "Ordovician" are country rock. The igneous intrusion leads to a volcanic eruption.
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