INTRODUCTION 1 7 



for example, Scolithus from the upper Cambrian sandstones of 

 the Appalachian region. Burrows are likewise formed in rocks 

 on exposed coasts by sea urchins, in rocks and wood by different 

 species of pelecypods (Lithodomus, Teredo, etc.), in soft earth 

 by mammals. All of these burrows are capable of preservation 

 as fossils under favorable conditions. 



Coprolites. — The contents of the intestine and the excre- 

 ment of many ancient animals, especially of fish and reptiles, 

 are often preserved and such fossils have received the name of 

 coprolites. These are usually nodular or contorted in appear- 

 ance and phosphatic in composition. They often contain such 

 indigestible remnants of the animal's food as portions of scales, 

 bones, teeth or shells. Recent deposits are known as guano and 

 are largely due to the excrement of sea birds and of such marine 

 mammals as seals. 



Restoration of fossils. — Since fossil organisms are built on 

 the same general plan as living ones, a reconstruction of their 

 appearance when living, like their identification and classifica- 

 tion, is a matter of comparison. The broader and deeper one's 

 knowledge of living species, the nearer the truth is apt to be 

 one's conclusions. The relation between the soft, unpreservable 

 portions of an animal, and the hard parts capable of preserva- 

 tion, is very close. The shell, for example, is such an intimate 

 part of the animal that an injury to it means a lessening of the 

 vitality of the entire organism, while the loss of it means death 

 (Fig. 4). It is, accordingly, incorrect to speak of the animal and 

 its shell as though the shell were a house which the animal could 

 leave at will. An invertebrate animal may thus be divided, for 

 convenience of description, into body (the soft parts) and shell ; 

 a vertebrate may be considered as flesh and skeleton. 



In the restoration of a fossil the better preserved the material, 



the truer to life will be the result. In very fine-grained shales 



and limestones impressions of the soft parts are often preserved 



to even minute details. Thus in making a restoration of the 



trilobite, Triarthrus, extinct since the end of the Paleozoic, the 

 c 



