INTRODUCTION 3 



all of the mineral matter in bone or shell and replace it with other minerals that the water 

 carries in solution. This is called replacement ; many Ohio fossils have been replaced by 

 pyrite and silica, a few with marcasite and other minerals. If the fossil is not replaced by 

 minerals, it may be encased in rocks and all the liquids and oils in its body may be squeezed 

 out; this process is called distillation. Many Ohio fossil fishes are preserved in this way. 

 When plants are preserved by squeezing they are called compressions. The groundwater 

 seeping through the rock may dissolve the shell or bone completely without replacing it with 

 other minerals. In that case, if the rock has hardened before the fossil is dissolved out, the 

 rock retains the imprint of the fossil, making a mold. Sometimes the mold is later filled with 

 mineral matter, producing a cast, which is a replica of the original fossil in different material. 



The tracks and trails made by animals on wet sand or mud are sometimes covered immed- 

 iately by new layers of mud or sand. If these sediments harden into rock, the tracks and trails 

 may be preserved. Tracks give us an idea of the size of the animal that made them, the 

 number of its toes, whether it had claws or not, and many other details. Several tracks made 

 by the same animal are called a trail; from it we can find out the length of the animal's stride, 

 whether it walked on two or four legs, and whether the body or tail dragged on the ground or 

 not. 



Burrows of worms and other animals without backbones may be filled with material 

 different from the muds or sands in which they have been dug. If these materials become rock, 

 the shape and size of the burrow can be studied and sometimes the animal that made it may be 

 found fossilized in its burrow. 



Coprolites are fossilized dung. The word is derived from two Greek words meaning 

 dung and stone. 



HOW FOSSILS ARE NAMED . At first, you may be satisfied to know that you have fossil 

 corals, clams, fish and ferns. You will soon collect fossils, however, for which there are 

 no common names and so you will want to learn what names scientists have given them. The 

 naming of fossils has been going on for a long time (before the seventeenth century and even 

 in antiquity) but the system in general use is one invented by Carl Linne', a Swedish naturalist 

 of the eighteenth century. His system is accepted because no one has thought of a better one 

 and because it can be used by people speaking all modern languages. It would be very nice 

 if we could have English names for our fossils; the trouble is that the same kinds of fossils are 

 found in France, Germany, Russia, and China, where they might be given French, German, 

 Russian, or Chinese names. Linne's system gives plants and animals, living or fossil, 

 names derived from Latin and Greek which are acceptable to all. 



Linne' divided nature into three kingdoms: animal, vegetable, and mineral. The animal 

 and vegetable kingdoms are divided into large groups, called phyla, each phylum into smaller 



groups called classes, each class into orders, each order 

 *0y) into families, each family into genera, each genus into species. 



Plants and animals, fossil or living, are usually referred to by 

 G^sY <^-v the name of the genus and species; the generic name is capital- 



\*TC^^_) ized, the specific name is not. Since each genus belongs in a 



J family and each family in a class, the system indicates the 



degree of relationship between species. 



The examples in Table I give an idea of the relationship be- 

 tween several kinds of animals. From it we can see that man 

 and the dog are more closely related than they are to the frog; they 

 belong in the same class and the frog belongs in another (fig. 2). 

 Similarly, the oyster and the scallop are closer to each other 

 than they are to the frog, man, and the dog. All five of them are 

 closer to each other than they are to the plants, which belong 

 in another kingdom. 



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