Igneous rock the partial melting of rocks within the mantle and crust. Extrusive igneous rocks cool and solidify quicker than intrusive igneous rocks. They are formed by the cooling of molten magma on the earth's surface. The magma, which is brought to the surface through fissures or volcanic eruptions, solidifies at a faster rate. Hence such rocks are smooth, crystalline and fine-grained. Basalt is a common extrusive igneous rock and forms lava flows, lava sheets and lava plateaus. Some kinds of basalt solidify to form long polygonal columns. The Giant's Causeway in Antrim, Northern Ireland is an example. The molten rock, with
Boring Lava Field quartzite-pebble xenoliths (rock fragments enveloped in a larger rock during the latter's development and solidification) can be observed among local cinder specimens, dating from Miocene to Pliocene Troutdale deposits. While the volcanic rock of Boring Lava was being emplaced over rock from the Troutdale formation, there was deformation that uplifted and dropped fault blocks to the southeast of Portland. Along the Washougal River, a large landslide occurred as a result of failure due to the Boring lava pushing down on rock from the Troutdale formation. Intrusions of Boring Lava formed outcrops at Highland Butte, La Butte, and potentially in the