A quarry is an open pit from which rock is removed for use in road building, construction, and concrete work, and for agricultural lime, stone slabs, and the manufacture of cement.
The Geological Surveys of most states will supply a list of producing quarries in their areas. Large-scale topographic maps show such excavations, both working and abandoned quarries, but such maps are often old. Local construction and paving companies can supply information, as they depend on nearby quarries for material. Most quarries have a tall crusher plant, surrounded by piles of rock, which is usually easy to find.
A typical quarry may be several square blocks in area and have a working face from thirty to well over one-hundred feet high. Its depth is dependent on the thickness of the usable layer of stone. The limestone which is quarried is usually in thick layers and not very fossiliferous.
The rock may look the same from the top to the bottom of the quarry, but often two or three important formations are included in one quarry wall. One formation only two feet thick may carry numerous fine fossils, while the rest of the rock is barren. With patience, these layers can be recognized in the quarry wall, and then in the broken rock on the quarry floor after blasting.
Generally, collecting from the freshly blasted rock is not very profitable unless the quarry is in dolomite rather than limestone and most of the fossils are casts and molds, which must be broken from fresh, un-
weathered material. Molds will break in half, and both halves should be saved to make fossil casts with plaster, rubber, or plastic at home.
The mold itself will usually reproduce the outer shape of the fossil. But it may contain an internal cast, a steinkern, which can properly be identified only if it has been found in the cavity of the external mold. It will often bear little resemblance to the outer appearance shown in the books. This is especially true of brachiopods. The relationship of a steinkern and its parent mold should be made clear in labeling.
Some types of fossils will not stand weathering, so whenever they are found in limestone, it must be in fresh material. These include carbonized films of Crustacea or worms, or such delicate specimens as crinoid crowns.
Some fossils pop loose from freshly broken rock and can be collected by breaking up the rock with a sledgehammer. The Mississippian crinoid calyxes found in Iowa, Illinois, and Missouri are collected this way. Some brachiopods also break out cleanly.
The best collecting in the quarry is from weathered material. Five years of weathering on what once appeared to be an unfossiliferous block of limestone can magically produce a coating of fossils. Furthermore, softening of the limestone makes removal of these fossils much easier. If the limestone weathers even longer, the fossils may drop out and can be collected on the ground. Too much weathering will obliterate fossils, but new ones are constantly exposed.
Weathered limestone can be found in several spots. Occasionally, elephant-sized boulders of solid rock are blasted out. These are too large for the crusher and not worth blasting to a usable size, so they are bulldozed into an unused area of the quarry floor. There they weather away, waiting for a fossil collector. Older areas of the quarry will have a certain amount of debris on the floor, including pieces that have scaled from the quarry wall. Collecting along a wall is always a risky business; a fossil from above may collect you on the way down. (See Chapter 7 for more about safety precautions on collecting trips.)
At times new roads are built into the pit, requiring fill, and artificial hills are built on one side of crushers so that the trucks can dump directly into them. These roads and hills are made of the native stone, and years of weathering may create fine collecting along their side slopes.
To quarry the merchantable rock the quarry operator must remove
overlying dirt and debris. He may also have to remove some layers of shale or impure weathered limestone; some quarries have mountains of this waste material. It may be the most fossiliferous, and it weathers the most rapidly.
Gray, muddy-appearing piles are shales, and yellowish or dark-gray rocky piles are limestones. All are worth examining for fossils. Good examples of such dumps are found at Waldron, Indiana, and Pegram, Tennessee. In both quarries, a thick limestone lies under the thin but highly fossiliferous Waldron shale of Silurian age. The shale that is scraped off and rejected is the real treasure trove. The barren limestone is worthless—except commercially.
Another place to look is below the bottom of the quarry. Water constantly seeps into any excavation and unless pumped out would flood the quarry. It does not take many months or years to turn a quarry into a good place to hunt ducks or catch fish but not to get road material. To keep the quarry dry enough to work, a deep pool or sump is needed. This is dug in a low spot in the quarry floor, usually a soft shale or unmerchantable limestone underlying the quarry's productive strata. What is unprofitable for the quarryman may be very rewarding for the fossil collector who carefully examines the dumps around the edge of the sump pit.
But the piles of crushed rock that are the quarry's stock in trade hold little of value for the collector. Fossils of any size have been disfigured by the crusher's jaws until only microfossils are left.
If at all possible, when collecting from dumps in quarries, first examine the working face to determine what layer produced the fossils you are collecting. This may be important in trying to date and identify the fossils later. The quarry operator is rarely able to tell what formations or even what age rock is being quarried. But some State Geological Surveys and universities have yearly field trips. If you can obtain a field trip guidebook that includes the quarry, there may be a picture or drawing of the quarry face with the formations listed. Characteristic fossils from these layers are listed by name or even illustrated in field trip guides. Annually the Bulletin of the American Association of Petroleum Geologists list guidebooks of this kind published during the year.
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