334 PALEONTOLOGY. 



of dry chalk. Bones and teeth in this state quickly absorb a 

 solution of gelatine, and thus their original tenacity may be 

 restored* Petrified fossils need no such treatment ; they are 

 usually harder and more durable than the original bone itself. 



The interpretation of such fossil remains requires a com- 

 parison of them with the corresponding parts of animals now 

 living, or of previously determined extinct species. In the case 

 of the vertebrate animals, such comparison is limited to the 

 osseous and dental systems. The interpretation of a vertebrate 

 fossil, therefore, presupposes a knowledge of the various modi- 

 fications of the skeleton and teeth of the existing vertebrate 

 animals ; and the more extensive and precise such knowledge 

 may be, the more successful will be the efforts, and the more 

 exact the conclusions, of the interpreter. 



The determination of the remains of quadrupeds is beset, 

 Cuvier remarks, with more difficulties than that of other 

 organic fossils. Shells are usually found entire, and with all 

 the characters by which they may be compared with their 

 analogues in the museums, or with figures in the illustrated 

 books, of naturalists. Fishes frequently present their skeleton 

 or their scaly covering more or less entire, from which may 

 be gathered the general form of their body, and frequently 

 both the generic and specific characters which are derived 

 from such internal or external hard parts. But the entire 

 skeleton of a fossil quadruped is rarely found, and when it 

 occurs, it gives little or no information as to the hair, the fur, 

 or the colour of the species. Portions of the skeleton with the 

 bones dislocated, or scattered pell-mell — detached bones and 

 teeth, or their fragrnents merely — such are the conditions in 

 which the petrified remains of the mammalian class most com- 

 monly present themselves in the strata in which they occur. 



* The writer's experience of this effect led him to suggest the application of 

 a similar process to the long-huried ivory ornaments from the ruins of Nineveh 

 in the British Museum ; it proved successful . 



