The Formation of Limestone Deposits

A look at Limestone Deposits in the Lehigh Valley

Limestone

Developed and Produced by
The Delaware & Lehigh National Heritage Corridor

Written And Illustrated By
Lance Leonhardt

e-book Publishing software provided by Killer Interactive, LLC.
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Limestone is a dense, heavy, durable rock found in expansive layers in the valleys of Lehigh, Northampton and Bucks counties.

Limestone has been quarried in the area for more than 200 years and is the main ingredient in cement.

It's also a long-lasting building stone used in the construction of homes, court houses, canal locks and locktender's houses. Limestone burned in small kilns was pulverized and spread onto farm fields to create better soil for growing crops.

Because of its great abundance of limestone, the Lehigh Valley became the world's leading producer of cement during the late 1800s and well into the 1900s. Cement production in the Lehigh Valley continues today although at a much lower capacity.

Limestone Deposits

Limestone is a dense, heavy, durable rock found in expansive layers in the valleys of Lehigh, Northampton and Bucks counties.

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About 470 million years ago, Pennsylvania was located near the equator along the edge of a large land mass that would one day become the continent of North America. At that time, Pennsylvania was covered almost entirely by a warm, shallow tropical ocean where marine reef ecosystems flourished. The story of limestone, the rock from which cement is made, begins with the shells of sea creatures that lived in - and made - these ancient marine reefs.

The marine reefs growing in the shallow seas were home to many varieties of shell-making animals such as coral, snails, squid, and now-extinct trilobites. Many of these marine reef animals, as well as algae growing in the seas, used calcium and carbon dioxide dissolved in the seawater to make calcium carbonate, or limestone, which was the main substance in the reef animals’ hard, protective shells.

One of the major reef organisms was, and still is, coral. Coral are tiny animals that build a small cup-like shell of limestone in which to live. As thousands of individual coral animals join together over time, they form a single colony called a coral head. As the colonies grow, they add more limestone to the reefs and, in turn, build the reefs larger as time passes.

Formation of Limestone

About 470 million years ago, Pennsylvania was located near the equator along the edge of a large land mass that would one day become the continent of North America. At that time, Pennsylvania was covered almost entirely by a warm, shallow tropical ocean where marine reef ecosystems flourished. The story of limestone, the rock from which cement is made, begins with the shells of sea creatures that lived in - and made - these ancient marine reefs.

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Coral Head
Snails
Cephalopod
Trilobite
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Tentacles
Mouth
Stomach
Limestone Cup-Shell
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As reef organisms die, their limestone shells provide a foundation for new living organisms that continue the growth of the reef. As generation after generation of reef organisms live and die, the reef thickens and grows upward layer by layer.

The reefs thickened enormously during the millions of years that the shallow seas were present. The weight of a reef growing upon itself compressed and changed the deeper layers of dead shells into limestone rock, a gray-colored sedimentary rock.

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Since many reefs formed and were buried over a long period of time, the ages of the limestone rock in our area range from about 520 to 440 million years.

Marine Carbonate Reef

As reef organisms die, their limestone shells provide a foundation for new living organisms that continue the growth of the reef. As generation after generation of reef organisms live and die, the reef thickens and grows upward layer by layer.

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Continent
Continental Rock
Reef Shelf
(Living Coral Heads)
Limestone
(Older dead reef becomes limestone rock)
Bolder Slide
Bolder Slide
Submarine Fan
Shallow Seas
Reef Slope
Continent
Marine Limestone Reef
Shallow Seas
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The collision of continents that took place over millions of years led to the formation of several mountain chains in Pennsylvania, the last-formed chain being the Appalachian Mountains, around 280 million years ago.

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These long-term mountain building events jammed, folded, and crumpled the limestone rock formed from the old reefs into a belt of limestone that runs southwest to northeast through a portion of Pennsylvania called the Great Valley, which includes the Lehigh Valley.

Layers of Limestone Rock

The collision of continents that took place over millions of years led to the formation of several mountain chains in Pennsylvania, the last-formed chain being the Appalachian Mountains, around 280 million years ago.

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One particular band of ancient reefs in the middle of the Lehigh Valley, near the towns of Coplay, Northampton, Bath, and Nazareth, is made of very pure limestone rock. Its purity makes it especially good for producing cement, one of the most important building materials in the world.

This band of limestone is several hundred feet thick at some places and is located at, or near, the surface. Limestone quarries have been dug into this band of limestone since the late 1800s, to extract the limestone for cement making. Digging continues to this day.

Limestone blocks for building homes and other structures were cut from this limestone band and others in the area since the early 1700s.

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The shells of prehistoric sea creatures have become our homes, sidewalks, bridges, and roads.

Limestone Belt

One particular band of ancient reefs in the middle of the Lehigh Valley, near the towns of Coplay, Northampton, Bath, and Nazareth, is made of very pure limestone rock. Its purity makes it especially good for producing cement, one of the most important building materials in the world.

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  • Glossary

    Glossary

    • Calcium carbonate: A chemical compound (formula CaCO3) occurring in rocks such as limestone, and the main component in coral skeletons and the shells of other marine organisms.

    • Coral: Small, marine animals (phylum Cnidaria) with tentacles around a central mouth opening, often producing large colonies or coral heads of individuals (called polyps) joined together by their skeletons made of calcium carbonate.

    • Coral reefs: Underwater marine habitats made by corals, algae, and shell-making animals that typically support large varieties of organisms in warm, shallow, clear, and sunny oceanic waters.

    • Ecosystem: A living, biological unit produced by the interaction of a community of different species present in a given area, with the physical environment (air, water, rock, light) through exchanges of matter and energy.

    • Limestone rock: A sedimentary rock made chiefly of calcium carbonate and often resulting from the compression and aging of the skeletal fragments of marine organisms such as coral and algae.

    • Marine reef ecosystem: A community of sea creatures interacting with their ocean environment by living in and around mound-like structures built up near the surface over time by calcium carbonate-producing corals and algae.

    • Trilobite: Small, extinct, marine arthropods having jointed-legs and an oval-shaped outer skeleton (exoskeleton) divided into three length-wise lobes with many horizontal segments. Among the most successful of all early animals, Trilobites were mostly bottom-dwelling predators, scavengers, and filter-feeders that lived in the oceans from about 520 million years ago to their extinction 250 million years ago.

    • Sedimentary rock: A layered rock resulting from the settling and packing of solid particles (such as sand and mud) that have been weathered, transported and deposited at the earth’s surface and within bodies of water by wind, water, or ice.

    • Great Valley: A chain of valley lowlands associated with the Appalachian Mountains that stretch about 1200 miles south to north in eastern North America. In southeastern Pennsylvania, the Great Valley Section consists of a very broad lowland that lies south of Blue Mountain/Kittatinny Ridge and includes the Lehigh Valley.

    • Cement: A gray powder manufactured from limestone rock that when mixed with water, sand, and gravel will “set” or harden into a rock-like building material (concrete).

  • CC

    Lesson Text

  • Standards

    Pennsylvania Academic Standards

    7.1. Geography

    7.1.4.B.
    Describe and locate places and regions s defined by physical and human features.

    Geography Glossary

    Place – an area with distinctive human and physical characteristics; these characteristics give it meaning and character and distinguish it from other areas.

    Region – an area with one or more common characteristics or features that gives it a measure of consistency and makes it different from surrounding areas.

    3.2. Physical Sciences: Chemistry and Physics

    3.2.4.A4.
    Recognize that combining two or more substances may make new materials with different properties.

    3.3. Earth and Space Sciences

    3.3.4.A1.
    Describe basic landforms.

    Recognize that the surface of the earth changes due to slow processes and rapid processes.

    3.3.4.A2.
    Identify basic properties and uses of Earth’s materials including rocks, soils, water and gases of the atmosphere.

    3.3.5.A2.
    Describe the usefulness of Earth’s physical resources as raw materials for the human made world.

    3.3.4.A3.
    Recognize that fossils provide evidence about the plants and animals that lived long ago and the nature of the environment at that time.

    3.3.4.A4.
    Recognize Earth’s different water resources, including both fresh and saltwater.

    3.3.4.A6.
    CONSTANCY/CHANGE – Identify simple changes in the earth system as air, water, soil and rock interact.

    Earth and Space Sciences Glossary

    Atmosphere – the gaseous mass or envelope surrounding a celestial body, especially the one surrounding the Earth, and retained by the celestial body’s gravitational field.

    System – a set of interacting or interdependent entities, real or abstract, forming an integrated whole. An open system usually interacts with some entities in their environment. A closed system is isolated from its environment.

    4.3. Environment and Ecology

    4.3.4.A.
    Identify ways humans depend on natural resources for survival.

    Identify resources used to provide humans with energy, food, employment, housing and water.

    4.3.4.B.
    Identify the geographic origins of various natural resources.

    Environment and Ecology Glossary

    Natural resources – any materials produced by nature that can be used to produce goods or provide services.

  • My Map

    • Magnetite & Hematite ore Deposits
    • Limonite ore Deposits
    • Anthracite Coal Deposits
    • Slate Deposits
    • Surface Carbonate Rock Deposits
      (Limestone and/or Dolomite)
    • Limestone mined for cement
      (manufacture & cement plants)
    • Geography
    • Water
    • Counties
    • Cities
    Magnetite & Hematite ore Deposits
    Limonite ore Deposits
    Anthracite Coal Deposits
    Slate Deposits
    Surface Carbonate Rock Deposits
    (Limestone and/or Dolomite)
    Limestone mined for cement
    (manufacture & cement plants)
    Geography
    Water
    Counties
    County Names
    City Names

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