Section 2: List of Special Terms

BPE: Before the Present Era. It is very difficult to date geological events. They took place over many millions of years, and there were no humans to record the events. Dates, as we use them today, don’t apply at all. Paleontologists use this phrase, Before the Present Era or BPE, to represent the passage of time. Some writers use “mya” (millions of years ago) or “ybp” (years before present) instead of BPE.

Core sample: a cylindrical slice of the earth’s layers made by a special drill that cuts into the strata below the surface. Core samples can be studied to learn more about geologic history. The typical core sample is between 20 and 200 feet in length. In North Dakota, cores have been collected and stored since 1918. In the early 1950s, the information from core samples helped to develop the oil industry. Some of these core samples were extraordinary. In 1954, the Mobil Oil Producing Company took a core sample of 4,375 feet from the Solomon Bird Bear oil well. Core samples are stored in at the Wilson M. Laird Core and Sample Library at the University of North Dakota. People interested in studying the core samples can visit the library or borrow the samples. Learn more about the Wilson M. Laird Core and Sample Library at

Coteau: (co TOE) A French word meaning little hills. The Missouri Coteau lies east of the Missouri River and west of the James River. It is an area where glaciers gouged out small lakes and ponds that do not drain into creeks or rivers.

Dinosaurs. Dinosaurs were a type of reptile. Their legs were placed squarely under their bodies. Some dinosaurs walked upright on two legs; others walked in a stiff-legged gait on four legs. They lived in the Mesozoic Era. Most dinosaurs became extinct about 65 million years ago. Many scientists believe that birds are the modern descendants of dinosaurs.

Erratics:  (er RAT iks) Rocks left by glaciers on the North Dakota prairies. Many of these are too big and heavy to have been washed away by water or blown away by wind. They are called erratics because they do not naturally occur in North Dakota. Erratic rocks were transported to North Dakota by glaciers.

Esker: (ESS ker) A ridge that marks the path of a stream that flowed through tunnels created under a glacier or through cracks in a glacier. These streams carried gravel, sand, and soil which were deposited along the stream bed. Wherever the gravel and sand were deposited by the stream, the surface is today marked by a long, winding ridge. These ridges can be as much as 100 feet high and a few hundred feet wide. If the top of the esker is flat, the stream flowed along the ground below the glacier. If the top of the esker is uneven, it is likely that the stream flowed on or through the glacier. Eskers generally contain a mix of gravel, boulders, and sand. The mixture means that the deposits have little economic value as gravel resources. Eskers, of course, are located only in the parts of North Dakota that were glaciated. The largest is the Dahlen Esker which is four miles long, 400 feet wide, and 80 feet high. It is located west of Fordville.

Extinction:  (ex TINK shun) The complete eradication, or disappearance, of a species of animal or plant. Extinction can occur in a particular place. For instance, horses became extinct in North America after the Last Ice Age, but continued to thrive and evolve in Europe, Asia, and Africa.

Formation:  A layer of rock that is distinct from other layers. When geologists look at a cliff or river bank, they see layers of different colors or textures. Each layer is a formation. Formations are usually consistent over a large area. Each formation represents the long period of time in which it was created. A Formation is named for a permanent nearby feature which may be a town or a creek or a hill. The Sentinel Butte formation is named after a prominent butte in Golden Valley County, but the formation is actually found over a large portion of southwestern North Dakota. Sometimes, several formations form a group. The Fort Union Group includes the Sentinel Butte, Ludlow, Cannonball, and Bullion Creek formations.

Geologist: (gee OL a jist) A person who studies earth and its rocks and minerals. Some geologists specialize in surface geology; others specialize in the geology of the layers of sediment below the earth’s surface.

Glacier: (GLAY sher) A sheet of ice usually formed from compacted snow that moves slowly carving the land underneath it as it goes. Glaciers pick up rocks, soil, and other materials as they move and leave those materials behind when they begin to melt.

Glacial till: Sediment remaining after a glacier retreated. The sediment was trapped in the ice, but dropped to the surface of the land as the glacier melted. The size of glacial till varies from tiny clay particles to boulders.

Iridium: (eer RID ee um) A rare mineral on Earth that is found in greater abundance on asteroids and meteors. This mineral is found in the ashy layer that is associated with the K-T boundary. This layer was deposited about 65 million years ago, at about the same time that dinosaurs became extinct. Many paleontologists and geologists believe that a large asteroid hit Earth (on the east coast of Mexico) and created an explosion of such intense heat that most life forms on Earth soon died. The dust raised by the explosion and the fires that followed fell back to the surface and formed a layer of ash containing iridium.

Lake Agassiz:  (AG a see) The group of meltwater lakes left behind by melting glaciers during the Ice Age. These lakes trapped sediment which eroded and filled the formerly narrow valley of the ancient Red River leaving the valley quite flat. Today’s Red River Valley is about 60 miles wide as a result of these meltwater lakes.

Lignite: (LIGG nite) A type of coal found in North Dakota. It is high in moisture, and low in heat production compared to bituminous or anthracite coals. Lignite produces about 8,300 BTUs per pound. (A BTU, or British Thermal Unit is a means of measuring the energy in coal. One BTU is the energy required to heat one pint of water one degree.)  By comparison, bituminous coal produces10,000 to 15,000 BTUs.  Anthracite coal produces13,000 to 15,000 BTUs. Lignite coal was used for many years in Northern Pacific Railroad engines. For many years, lignite heated most North Dakota state buildings as well as private homes.

Mammals. Mammals are animals that give birth to live young that depend on their mothers for nourishment (milk) until they are old enough to feed themselves from their surroundings.

Moraine: (mor RAIN) A hill of gravel or rock left by a melting glacier. Sully’s Hill National Wildlife Refuge is located on a series of wooded moraines on the south side of Devils Lake.

Paleontologist. (PAY lee on TOL o jist) A person who studies fossilized plants and animals that lived in ancient times.

Sediment: (SEDD ih ment) The material, either mineral or organic, that is deposited by wind, water, or ice.

Sedimentary rock: One of the three categories of rocks. Sedimentary rocks have been compressed from loose sediment that accumulated in layers over the course of geologic time. The other two categories of rocks are igneous and metamorphic.

Strata. (STRAT ah) Layers. The singular is stratum. This term is used frequently in reference to the layers of sediment deposited over millions of years below the earth’s surface.

Stratigraphy. (stra TIG raf ee) A graphic image of the layers of rock and sediments that lie beneath the surface. Stratigraphies vary from place to place depending on the types of events that deposited the sediments and events that might have cut through the layers. A person who studies geological layers is called a stratigrapher.