The Geology of Baxter State Park and Mt. Katahdin

Glossary of geologic terms

Arête - A sharp, rugged crest of a mountain range or mountain spur formed by weathering and mass wasting between two or more cirques.

Bedrock - Solid rock or ledge which underlies loose gravel, soil, etc.

Biotite - Black mica.

Brachiopod - A phylum of marine, two-shelled animals. Also called lampshells.

Bryozoa - A phylum of coral-like animals also called moss-animals.

Cirque - A steep, deep valley head caused by glacier erosion.

Columnar joint - Joints in volcanic rocks which break the rock into five or six-sided columns.

Continental glacier - Glacier which is not confined to a valley. Also called an ice sheet or ice cap.

Conglomerate - A sedimentary rock composed of rock and mineral fragments the size of pebbles or larger.

Delta - A deposit of sediments at the mouth of a river.

Drift - A general term used to describe any type of glacial deposit.

Era - The largest division of geologic time. The names refer to the stage of development of life which characterize the eras.

Erratic - A glacially transported rock which is different from the bedrock on which it lies.

Esker - A long ridge of gravel and other stratified drift which formed in a tunnel at the base of a melting glacier.

Extrusive rock - Igneous rock which cools at the surface of the earth, also called volcanic rock.

Fault - A break or rupture in bedrock along which there has been differential movement.

Feldspar - A mineral composed of soda, lime, or potash and alumina and silica. The most abundant mineral constituent of granite.

Fossil - Any indication of prehistoric life which has some recognizable form.

Glacier - A mass of ice and snow, on land, which is now moving or has recently moved.

Hornblende - A dark colored mineral of complex composition which occurs in many granites.

Igneous rock - Rock formed from molten material called magma. Either intrusive (formed below earth's surface) or extrusive, such as volcanic, in origin.

Intrusive rock - Igneous rock which cools beneath the crust of the earth. Granite is the most common intrusive igneous rock.

Joint - A crack or fracture in a rock.

Kame - A small mound of stratified drift.

Kame terrace - A terrace deposit or stratified drift formed at the margin of a melting glacier.

Kettlehole - A depression in stratified drift formed as the result of the melting of a buried ice block.

Lava - Magma which has reached the earth's surface. Volcanoes are made of lava.

Magma - The molten or partially molten material, originating within the earth, from which igneous rocks are formed.

Mineral - Any naturally occurring inorganic element or compound.

Outcrop - Bedrock exposed at the surface of the earth.

Patterned ground - Rings, stripes, and other patterns formed in loose surficial deposits by frost.

Period - Subdivision of an era.

Pothole - A smooth-sided deep hole in bedrock formed by the abrasion of pebbles and boulders caught in eddies in streams.

Quartz - A mineral composed of silicon and oxygen. Characteristic of such igneous rocks as granite and such sedimentary rocks as sandstone.

Radioactive mineral - Any mineral which contains some radioactive element such as uranium or thorium.

Rhyolite - An extrusive igneous rock having the same chemical composition as granite.

Ripple mark - Small ridges formed in sandy or muddy bottoms of streams, lakes and oceans by currents and waves.

Roche moutonnée - A smoothed, rounded bedrock outcrop formed by glacial erosion. Several of these features occurring together bear a fancied resemblance to a flock of sheep, hence the name, "sheeprock."

Rock stream - A crude stream of rocks which moves as a slow-moving landslide.

Sandstone - Sedimentary rock composed of rock and mineral fragments the size of sand grains.

Sedimentary rock - Rock formed from the accumulation of sand, mud or gravel.

Shale - Sedimentary rock formed from mud.

Stratified - Refers to layering in sedimentary rocks and certain kinds of glacial deposits.

Striation - A scratch on bedrock formed by debris lodged in base of overriding glacier.

Till - Glacial sediment composed of rock fragments of all possible sizes. Popularly called hardpan.

Tuff - Rock formed from volcanic ash.

Unstratified - Without layering. Refers particularly to such glacial deposits as till.

Valley glacier - Glacier confined to a valley. Also called a mountain glacier or an ice stream.

Volcanic ash - Small cinders and dust-sized particles produced by the explosive eruption of certain volcanoes. This material may be carried in the air for long distances from the volcano which formed it. The settling of this material results in beds of volcanic ash.

Introduction Bedrock Glacial geology Geologic features Acknowledgments Glossary References Plates

Last updated on January 11, 2008

Contents

The Geology of Baxter State Park and Mt. Katahdin

Glossary of geologic terms