THE CITY ROCKS! Explore the Hidden World of Building Stone

A DIFFERENT SORT OF SEA LION

Introduction > Prologue > Building Stone

	Two impressive stone lions have flanked the main entrance to the New York Public Library at Fifth Avenue and 42nd Street since the building was dedicated in 1911. They have been called Patience and Fortitude, and also Lord Lenox and Lady Astor, in memory of the private Lenox and Astor libraries that merged to become the New York Public Library. They are famous landmarks and the library's official symbol. The library puts wreaths around their necks at Christmas.The American sculptor Edward Clark Potter carved the lions of pink Tennessee marble. Click here for a picture and more information. In the building stone industry, any high-quality, hard limestone may be called marble, even if it hasn't metamorphosed to marble. Tennessee's commercial marbles are actually limestones of this type--massive, crystalline, and dense. They occur in beds and lenses within the Holston Formation in the Valley and Ridge physiographic province of eastern Tennessee, a narrow band of folded rocks that date from the Ordovician period (500-440 million years ago).These rocks started out as sediments in shallow seas, over a continental shelf. They come in a variety of colors, from off-white to dark red. The dark red variety is called cedar marble. Tennessee cedar marble makes up the facade of the National Air and Space museum in Washington, DC. Tennessee consists of regions of rocks that become progressively younger from east to west. Each physiographic province in Tennessee is made up of rocks of a certain age. Click here to see a geological map of Tennessee. The Valley and Ridge province, which is mainly Ordovician in age, is near the eastern end of the state. In the middle of the Ordovician period, the first coral reefs appeared. Reefs existed earlier, during the Cambrian, but they were built by sponges and other organisms. The corals joined pre-existing groups of invertebrates, including trilobites, bivalve mollusks (similar to clams and oysters), snails, and cephalopods (mollusks related to today's nautilus, cuttlefish, octopus, and squid). Brachiopods were also abundant and diverse. Brachiopods have bivalve shells, but are not mollusks. The two halves of their shells are not symmetrical. They persist today, but are rare. Most died out during a mass extinction at the end of the Permian period (230 million years ago), when the shallow seas that had covered much of the continents began to retreat. The first fishes had just begun to appear in the Ordovician, but would not dominate the seas until the Silurian and Devonian periods. In Tennessee, and in much of eastern North America, calcium carbonate sediment accumulated in the warm, shallow continental seas and eventually compacted into limestone. Then, around 300 million years ago, the continents began to converge into the supercontinent Pangaea. The force of the long, slow collision between Africa and North America--think of sumo wrestling in extreme slow motion--buckled most of eastern North America into a long, folded ridge, the Appalachians. The Ordovician limestones in eastern Tennessee were pushed into long, narrow, northeast-southwest folds. Tennessee marble quarrying began in 1838, with a quarry near Rogersville in Hawkins County. Most of the quarries are in the Knoxville area. Tennessee marble is still being quarried and is used for statues, buildings, grave markers, and crushed stone. It is also part of the Lincoln Memorial, Grand Central Station in New York, and the Tennessee State Capitol, among many other buildings and monuments.

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