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"Igneous rocks or lavas of various composition."-Whitney, 1902

Amygdaloid

"Igneous rocks or lavas of various composition."-Whitney, 1902

Basaltic Columns at Finagl's Cave in Scotland. It is formed entirely from hexagonally-jointed basalt.

Basaltic Columns

Basaltic Columns at Finagl's Cave in Scotland. It is formed entirely from hexagonally-jointed basalt.

Section of the Cantal district of France, showing the reconstruction of the old volcano with its succession of lava flows.

Cantal District of France

Section of the Cantal district of France, showing the reconstruction of the old volcano with its succession…

Cross-section of the Caucasus along the Grusinian military road. Dark beds are lava streams.

Caucasus

Cross-section of the Caucasus along the Grusinian military road. Dark beds are lava streams.

Fissures produced by the Charleston Earthquake of 1886.

Fissures

Fissures produced by the Charleston Earthquake of 1886.

Picture of a mountain erupting.

Mountain

Picture of a mountain erupting.

Vesuvius as seen from Naples with the lava streams of 1872 in dark.

Vesuvius

Vesuvius as seen from Naples with the lava streams of 1872 in dark.

An eruption of Mount Vesuvius.

Mount Vesuvius

An eruption of Mount Vesuvius.

An experimental illustration of the mode of formation of volcanic blister cones composed of viscid lavas.

Volcanic Blister Cone

An experimental illustration of the mode of formation of volcanic blister cones composed of viscid lavas.

The sides of volcanic cones are often rent during the eruption, and the fissures filled with lava, which hardens and forms rocky ribs called <em>dykes</em>. Sometimes the central cone becomes choked, and secondary or parasitic cones are formed.

Volcanic Dykes and Parasitic Cones

The sides of volcanic cones are often rent during the eruption, and the fissures filled with lava, which…

"Ideal section of a volcano." -Dryer, 1901

Volcano

"Ideal section of a volcano." -Dryer, 1901

"The internal structure of many cones has been laid bare by prolonged erosion after the volcano has become extinct." — Hinman, 1888

Section of a volcano

"The internal structure of many cones has been laid bare by prolonged erosion after the volcano has…