Chapter 4: Up From the Inferno: Magma and Igneous Rocks
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(4.1) What a Geologist Sees: Antarctic Sill
This dark sill, exposed on a cliff in Antarctica, is basalt; the white rock is sandstone. A geologist’s sketch shows the cliff face as viewed face on.
(4.2) What a Geologist Imagines: Volcanic Neck at Shiprock
At this ancient volcano at Shiprock, New Mexico, ash and lava flows have eroded away, leaving a “volcanic neck”. Large dikes radiated outward from the center, like spokes of a wheel. The softer rocks that once surrounded the dikes have eroded away, leaving a wall-like remnant of the dike exposed. Shiprock was once in the interior of a volcano or below a volcano.
(4.3) What a Geologist Sees: Pluton at Torres del Paines
Torres del Paines is a spectacular group of mountains in southern Chile. The light rock is a granite pluton, and the dark rock is the remains of the country rock into which the pluton intruded. A screen of country rock (in the lower half) hides the front of the pluton. A geologist’s sketch labels the two major rock units.
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