20 AN INTRODUCTION TO THE STUDY OF FOSSILS 



coloration of its adult forbears. The young Malayan tapir is 

 longitudinally banded, the adult loses these bands ; the young 

 wild swine are longitudinally banded, the adult are not; the 

 young lion is spotted, the adult is of uniform coloration. 



Color of fossils. — Recent organic calcium carbonate, 

 such as occurs in shells and corals, is white, except for the occa- 

 sional presence of a pigment or epidermis ; Tertiary shells are 

 darker, while those from the Paleozoic are, as a rule, darkest. 

 Likewise, whereas many recent shells are lined with mother-of- 

 pearl, very little is found in pre-Mesozoic shells. These changes 

 are due to one or more of several causes. The chalky aragbnite 

 becomes changed to the darker calcite. As the pores and inter- 

 stices become filled with some foreign substance light is excluded 

 and a darker color results. If the inclosing sediment is dark in 

 color, the fossil will be stained by it more and more deeply 

 according to the length of time inclosed. A secondary replace- 

 ment by calcium carbonate may likewise be accompanied by 

 foreign impurities, such as carbon or iron, and thus produce a 

 darker color. Hence the older the fossil, the greater is the prob- 

 ability, as a rule, of the shell being dark. This generalization 

 holds true too for vertebrate and arthropod remains, though 

 here the increasing dark color is mostly due to carbonization. 



The process of fossilization likewise rapidly destroys the epi- 

 dermis and the pigment present on many shells. Very little 

 pigment remains in pre-Cretaceous shells. Where shells are 

 light colored and originally had color bands, such are apt to be 

 preserved in fossils as dark bands. 



Fossil objects due to inorganic agencies. — Many objects 

 due to inorganic agencies are often called fossils. It is in 

 accordance with general usage, however, to reserve this name for 

 those objects having some relation to an organism, but the word 

 fossil may be conveniently used as an adjective before objects 

 due to inorganic agencies, such as ripple marks, to show that 

 they have been preserved in the earth's strata. On the mar- 

 ginal flats of an ocean may be formed and preserved marks of 



