82 OUTLINES OF FIELD-GEOlJ 



Apart from the interest of fossils in relation to the 

 evolution of life, there are five important purposes to 

 which the geologist can apply them : ist, to throw light 

 upon revolutions in climate ; 2nd, to restore former con- 

 ditions of geography; 3rd, to detect former movements 

 in the crust of the earth ; 4th, to afford horizons whirh 

 serve to unravel geological structure ; and 5th, to fix t he- 

 relative geological date of rocks. 



i. Climate. Within certain limits, fossils may be 

 employed to show under what conditions of climate the 

 geological formations of bygone ages were accumu 

 We know, for example, that in the older Tertiary periods 

 in Europe the temperature must have been considerably 

 higher than it is now, for in strata of that age we find 

 among the fossil plants, forms of palm, custard -apple, 

 laurel, fig, and numerous conifers; together with remains 

 of turtles, crocodiles, sea-snakes, tapir-like pachyderms, 

 and many mollusca belonging to genera now living in 

 warmer seas than those of Western and North-Western 

 Europe. On the other hand, it can be shown that the 

 general climate of Central and Northern Europe at a 

 later time became quite arctic in character, for the 

 remains of the reindeer and the musk-ox occur in super- 

 ficial formations even far south in France ; lx>ncs of the 

 arctic lemming, mammoth, woolly rhinoceros, and other 

 northern mammalia, mark the cave-deposits and other 

 surface accumulations in the South of England; shells 

 now extinct in our littoral waters, but still living in those 

 of northern seas, abound in the clays which fringe the 

 coasts of the West of Scotland. 



It must be borne in mind, however, that the argument 



