A GUIDE 



TO THE 



FOSSIL MAMMALS AND BIKDS. 



GALLEEIES Nos. 1, 2.— FOSSIL MAMMALIA. 



The ]\Iammalia, or warm-blooded quadrupeds which nourish 

 their young with milk, are so modern, geologically speaking, 

 that most of theii* fossil remains occur in comparatively 

 superficial deposits where they have not been much petriiied 

 or mineralised. A large proportion of the fossil hones of 

 this Class thus appear almost as fresh as those of newly- 

 prepared skeletons, being merely stained by the sand or mud 

 in which they have been buried. Some of the bones, from 

 the most recent deposits and Pleistocene formations, are 

 indeed changed only by the loss of their animal-matter, 

 wliich causes them to become brittle and powdery ; and 

 when the?e are disinterred it is necessary to harden them 

 Ity treatment with a solution of gelatine or glue, which often 

 produces a shiny surface. ]\Iost of the Ijones from the 

 sandstones, shales, and limestones of the earlier Tertiary 

 formations, have their animal-matter replaced by silica and 

 oxides of iron, which also fill their interstices and impart to 

 tliese specimens a natural hardness. 



The fossil ]\Iammalia are arranged in the Galleries not 

 ■ according to their geological age Init primarily in the natural 

 groups recognised by zoologists. The extinct representatives 

 of each Order are placed together, the various Sub-orders 

 and Families being usually arranged in a descending scale 

 from the higliest to the lowest. This arrangement within 

 the Order obviously corresponds more or less with the 

 geological succession of its various representatives ; for the 

 higher groups occur later in time, the lower groups earlier. 



