Project Gutenberg's Let's collect rocks & shells, by Shell Oil Company

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Title: Let's collect rocks & shells

Author: Shell Oil Company

Release Date: December, 2003 [Etext #4768]
[Yes, we are more than one year ahead of schedule]
[This file was first posted on March 15, 2002]

Edition: 10

Language: English

*** START OF THE PROJECT GUTENBERG ETEXT LET'S COLLECT ROCKS & SHELLS ***

This etext was produced by Justin ([email protected]).

CONTENTS

COLLECTING SEASHELLS SEASHELLS. . .WHAT ARE THEY? THE SHELL AS AN ARCHITECT LET'S MEET SOME SHELLS WHERE TO LOOK STARTING A COLLECTION. . .HERE'S HOW COLLECTING ROCKS ROCKS ARE MADE OF MINERALS MAIN KINDS OF ROCKS COLLECTING GEMS FOR THE LUCKY FEW

INTRODUCTION

Millions of people throughout the world have found many hours of pleasure, adventure and education by collecting either rocks or shells.

This booklet won't tell you everything there is to know about rocks and shells. That would require many large volumes. We only want to arouse your curiosity about two delightful pastimes that are so broad and varied that they can lead to a career or a satisfying hobby.

Shell Oil Company's interest in the subjects comes from its history and the nature of its business. The name—chosen by a company that was founded years before anyone thought of drilling for oil—comes from the seashells this company brought from the Orient for use in mother-of-pearl items such as buttons and knife handles.

Now its world-famous emblem (the Pecten) is recognized by millions of people in every walk of life. It's on service stations, trucks, buildings, oil derricks and chemical plants. Even the company's industrial lubricants are named for shells because shells have the same scientific names everywhere in the world.

For an oil company, rocks have a special interest. Crude oil is found not in underground lakes or pools but in the tiny spaces between grains of sand or in the pores of rocks. Only certain types of rock formations are favorable to the accumulation of oil. Thus, oilmen need to know everything they can about the right kind of rocks.

Shell has scientists who work with rocks all day and laboratories filled with rock, mineral and crystal specimens. We are always learning new things about them.

The pages that follow provide basic information about two subjects that can be richly rewarding whether you follow them for profit, as Shell does, or for pleasure, as millions of people around the world do.

SEASHELLS. . .WHAT ARE THEY?

First, a seashell is one of the 100,000 species of backboneless animals belonging to the zoological group known as the Mollusca. Mollusks include not only the familiar clams, scallops and snails, but also the squids, octopus and Chambered Nautilus. Other "shells" found in the ocean include those of crabs, lobsters, barnacles and sea urchins.

True molluscan shells come in two main varieties: BIVALVES and UNIVALVES. Bivalves have two valves, fitting together along a toothed hinge on one side, and kept closed by means of ADDUCTOR MUSCLES. Univalves have only one shell, usually coiled, but sometimes shaped like a cap or miniature volcano. Some marine univalves can seal themselves inside with an operculum, which covers the open end of the shell like a trap door. 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. Many have teeth, called RADULAE.

Like any other animal, the mollusk generally moves about. It pushes along on the ocean floor on its foot, or it might swim a little. It lays millions of eggs and hatches countless baby mollusks. It lives its life in its shell, lugging it around, snuggling into it when alarmed, burrowing into mud, fastening itself to a rock and creating ingenious camouflage. It builds its calcareous house with a great instinctive talent for color and sculpture. . .and the closer it lives to the tropical zones, the more beautifully spectacular is its art.

The two parts of a bivalve shell are like thin saucers, concave inside, convex outside. The inside is smooth, polished. 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. Univalves may have spines on their shoulders. The opening, called the aperture, has a delicate right-hand rim called the lip and a heavy, left-hand edge called the columella.

[figure captions]

BIVALVE'S anatomy: a) foot, b) adductor muscles, c) gills, d) hinge, e) adductor muscles, f) siphon, g) stomach, h) mantle. Oysters, clams, mussels all have them.

UNIVALVE'S anatomy: As before, a) foot, b) siphon, c) mantle, but also d) operculum. Univalves include whelks, winkles, conchs.

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.

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. Then they start building a heavier shell and sink to the bottom.

Each shell's mantle contains a network of microscopic tubes. 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