150 FIELD GEOLOGY. 



like the tablets ; every fossil may then be fully ex- 

 amined and handled, while the labour and time ex- 

 pended in the process of gumming them down is 

 thereby avoided, and the additional advantage of space 

 is gained at the same time. The names may be written 

 on separate pieces of card-board, and either placed loose 

 in the tray or pinned on to its edge. 



Value of Palceontological Evidence. Having now 

 explained the method in which the fauna and flora of 

 a district should be collected and worked out, we are 

 in a position to estimate the full importance and use- 

 fulness of the information thus obtained, and the light 

 which is often thrown by this knowledge upon such 

 questions as the relative and comparative age of beds, 

 and the physical conditions under which they were 

 deposited. 



The insight afforded by Paleontology into these sub- 

 jects' was briefly pointed out at the commencement of 

 Chapter i, but may now be more fully explained. 



First, as regards the various conditions under which 

 rocks may have been formed, we find that our know- 

 ledge is chiefly derived from the evidence furnished by 

 the organic remains they contain. It is clear that the 

 terrestrial, fluviatile, lacustrine, estuarine, or marine 

 origin of the fossils may generally be ascertained by a 

 comparison with the habits of the living species belong- 

 ing to the same or nearly allied genera. 



But we may go farther than this, and even obtain 

 some idea of the probable climate of past periods ; when 

 we find in certain beds the bones of crocodiles, snakes, 

 and turtles, together with palm-fruits and remains of 

 other plants which now live only in tropical regions, 



