Gravel Pits

In northern parts of the United States, gravel and sand pits operate in concentrations of glacial sands and pebbles such as kames, eskers, or well-sorted moraines. Elsewhere, and in some parts of the north as well, gravel pits usually lie in old riverbeds or near rivers. Many gravel pits operate in the Mississippi River. Gravel and sand pits are marked on topographic maps, or they can be found in telephone books under the listing "Sand and Gravel."

Usually, the gravel in the piles is sorted as to size, and it is clean, so that fossils are easy to see. The fossils in one gravel pile may have originated from anywhere within a thousand-square-mile area and may be of half-a-dozen geologic periods, with many of the key features for identification worn away. However, a few pretty corals, usually silicified, can be found along with crinoid stems and pebbles that show cross sections of brachiopods, clams, and crinoids. Gravel pits from the Dakotas down to Texas and west to the coast produce an occasional worn piece of petrified wood.

Gravel pits anywhere in the United States, however, may turn up bones, teeth, and tusks of Ice-Age animals. These fossils are much better preserved than the waterworn pebbles of invertebrates and wood because the giant mammoths and mastodons were indigenous, and their bones settled to the bottom of a river or lake with little movement and suffered little damage or abrasion. A pit may operate for years without dredging up a single bone and then for a period of weeks run into masses of bones. The best place to look for these bones is in the office of the gravel pit; the bones and teeth arouse the curiosity of operators and wind up as doorstops.

Abandoned Gravel Pits
John Harris of the Field Museum pours thinned shellac over a crumbling mastodon leg bone. Large, porous bones such as this will disintegrate when they dry out.
Collecting in a gravel bed west of Fort Pierre, South Dakota. (Photo South Dakota Department of Highways)

The giant gold dredges in Alaska screen enormous quantities of gravel and sand for alluvial gold. Several were forced to abandon one area because of frequent breakdowns when mammoth bones and tusks clogged the machinery.

The bones, which are usually of one of the elephantlike animals, crumble when dried out after being wet for thousands of years. Museums soak the bones in penetrating liquid plastics or shellac, and this should be done by the amateur collector as well.

Tusks found in the continental United States are usually rotted and friable. When removed from the wall of a gravel pit they crumble. Alaskan and Canadian specimens have been preserved by long freezing. The specimens are of sufficiently high quality to have provided a flourishing trade in fossil ivory for many years. The Eskimos used fossil ivory for carving and for awls and fishhooks.

Gravel pits from Iowa westward into the mountain states and south into Texas produce numbers of fossil Pleistocene horse and buffalo teeth. These teeth are several inches long and usually dark brown or black. Mammoth teeth have a platelike structure and may break into slabs that are hard to recognize as parts of a tooth. They are generally white, yellowish, or brownish, and look like ivory. An entire tooth, which can weigh ten pounds or more, is a collector's prize. Mastodon teeth, which

Bison Teeth

Gravel pits in the West and Southwest are sources of teeth of Pleistocene vertebrates. This bison tooth came from Nebraska.

are even rarer, are readily recognizable as grinding teeth. From time to time bones and teeth of other animals from tiny rodents to giant beavers are found in gravel piles.

0 0

Post a comment