Shell Union Oil Corporation

“ Many valuable minerals are found in veins running through rock. Veins can be formed when: (a) mineral-laden ground water seeps into cracks, evaporates, and leaves mineral grains that build up into a vein; (b) hot water from deep within the earth fills cracks, then cools and deposits much of the material in solution as minerals in a vein—sometimes including metals such as gold and silver; (c) molten gaseous material squeezes into cracks near the earth's surface, then slowly hardens into a vein. ”

“ A rock may be made almost entirely of one mineral or of more than one mineral. Rocks containing different combinations of the same minerals are different. Even two things made of the same single mineral can be quite different. Carbon may turn up as a lump of coal or a diamond. ”

“ The older the rock, the simpler the plant and animal life it contains. Thus fossils can give a clue to the age of the rock strata.
Fossils can teach history. They tell us about plants and animals that are now extinct—the dinosaur, for example. They can also tell of ancient climates. Coral found in rocks in Greenland suggests it must have once been warm. Remains of fir and spruce trees have been found in the tropics.
How are fossils formed? Teeth, bone and wood don't last long in their original state. However, buried materials decompose, leaving a film of carbon as a fossil. ”

“ Although shells take on many different shapes, they are much alike inside. Each has a foot, a breathing siphon, a tiny brain and heart, and a fleshy mantle which secretes lime for shell-building. Most true mollusks have eyes, but a few are blind. ”

“ Chambered nautilus is brother to the octopus, but he wears his castle permanently—and on the outside.
THE SHELL AS AN ARCHITECT. . .HOW DOES HE DO IT? Picture a vast undersea factory with billions of shells in constant production. Each is made slowly and entirely of lime which the little animal inside extracts from its food, almost from the first day of its life. Each shell builder flawlessly follows the shape and design of the species to which it belongs. ”

“ Matchboxes or pillboxes are excellent for small specimens. For display purposes, glass-covered cases are best to prevent handling of the shells. A shell's beauty is often deceptive. Many unattractive and drab shells are worth hundreds of dollars while the most colorful are frequently valued at a dollar or less. The rarity of a species determines its value. A truly valuable shell may come from deep, inaccessible waters or remote lands—or it may be one of an extinct species. ”

“ Tiny shells buried in sand can be netted in your sieve. Clinging ones must be chiseled off rocks. Frail, delicate clingers should be gently nudged loose with tweezers. Submerged sandbars are good spots to find several kinds of univalves and bivalves, but the latter will dig themselves quickly out of sight—as far down as several feet. When you see one going underground, don't dig directly over it—you might break its shell. ”

“ But whether you concentrate on an area close to home or travel across whole continents, you'll find that the pleasure and knowledge you gain from your collection are matched by the fun and adventure of the search. ”

“ Some of the best mineral specimens collected in New York City came from skyscraper and subway excavations. Help a New England farmer clear his field and you'll have more rocks than you know what to do with.
As for reference books, many states publish guides to mineral deposits. Mineralogical magazines list mineral localities.
Tips For The Field
Don't try to collect too much at once. Work early in the day or late in the afternoon. A hot sun on bare rock can make you sizzle—especially if you're loaded with equipment and samples. ”

“ Each tube secretes a tiny amount of lime which instantly adheres to the shell. The animal builds his shell to the proper size and thickness and determines its ridges and whorls. Some kinds of shells take two to five years to reach maturity. Others keep growing all their lives. Color tubes are spaced like holes on a player piano roll allowing pigments to tint the shell at the right spots in the growing design. ”

“ Most shells of interest to the collector are found in the sea— but not all. Living forest mollusks have been found 18,000 feet high in the Himalayas. And in this country a great variety of mollusks live in rivers, ponds, and even hot springs. Several species are peculiar to the Nile River. Also, species of mollusks live on land—for example the common garden snail.
Wherever you go, be it the South Seas, a mountain lake, or the shoals off the Gulf Coast, you'll find shells to collect and opportunities to expand your hobby. ”

“ Igneous rocks are formed at high temperatures or from molten materials. They come from deep beneath the earth. They can be intrusive or extrusive—depending on where they cooled off.
Sedimentary rocks are formed by the action of wind, water, or organisms. They usually are laid down on the bottom of rivers, lakes and seas. Most of the earth's surface is covered by these rocks. Oil is found in sedimentary formations. ”

“ All these sea animals come from eggs, all different according to species, but all laid in measureless abundance—sometimes released into the open sea, sometimes protected in homemade nests, sometimes encased in capsules strung like beads. Hatched, most baby mollusks swim freely for a while, their tiny, transparent bodies almost invisible to the naked eye. ”

“ In some areas, such as parks and marine sanctuaries, collection of shells and other marine organisms may be restricted or prohibited.
STARTING A COLLECTION. . .HERE'S HOW Knowing WHERE to look for shells you probably wonder WHEN is the best time. The answer is ANYTIME. Mollusks know no season. Some species appear suddenly for several days and then vanish; others can be found almost anytime. Most mollusks appear at night, but others work only in the daytime and go out of sight after dark. ”

“ Every day, hundreds of millions of them enter the earth's atmosphere. Most of them, however, are burned up by the heat from air friction and never reach the ground. Meteors large enough to reach the earth are called meteorites. Most minerals found in meteorites are the same as those we have on earth. But, there are some rare minerals known only in meteorites. Two of them are cohenite and schreibersite.
MAIN KINDS OF ROCKS Rocks are the building blocks of the earth's crust. They may be massive, as in granite ledges, or tiny. Soil, gravel, sand and clay are rocks. ”

“ These little animals are the natural food for many of the larger undersea creatures, so one of their greatest talents is hiding. Approaching danger, whether from octopus, fish or man, arouses caution in a small mollusk and it becomes as inconspicuous as it can. ”

“ Rocks containing asbestos are especially handsome and varied.
3. ROCK-FORMING MINERALS. These are the building materials of the earth. They make mountains and valleys. They furnish the ingredients of soil and the salt of the sea. They are largely silicates—that is, they contain silicon and oxygen. (Silicon is a nonmetallic element, always found in combination with something else. It is second only to oxygen as the chief elementary constituent of the earth's crust.) ”

“ The outside is rougher, sometimes with graceful ribs or concentric ridges or combinations of both. Univalves are conical and spiraling, with a series of whorls coming down like widening steps from the tiny nucleus on top. ”

“ Along any rocky shore, limpets grow as wide as two inches but remain hard to find. Their turtleback shells, covered with moss, look just like rocks, and they stick so tightly to the big stones that—even when they are seen—they can scarcely be pried loose. ”

“ They come from deep below the surface of the earth. If they cool off while below the surface, they form intrusive rocks, which may later be revealed by erosion. When magmas reach the surface red hot, they form extrusive rocks, such as volcanic rocks. ”