XVI INTRODUCTION. 



the past history of life on the earth — of determining the 

 gradual stages by which our present animals and plants 

 have become what they are, and have assumed their present 

 geographical distribution. Thus was attained the " science 

 of ancient life," which was named Palaeontology by 

 H. D. de Blainville and Fischer von Waldheim in 1834. 



The Department of Geology in the British Museum 

 chiefly deals with fossils from the latter point of view, and 

 attempts to explain the main features in the life of the 

 Present by reference to that of the Past. 



Note to the Geological Time-scale. — The names in the three columns 

 to the left are applied only to periods of time. The names in the two 

 columns on the right are those of actual strata deposited during the time- 

 periods opposite which they are placed. These strata or rock-groups are 

 only a few out of the many that might have been mentioned, and it must 

 not be inferred that those in the European column are the precise 

 equivalents of those next them in the British column. It is just because 

 rock-formations in different parts of the world so rarely are equivalent 

 that a time-scale is needed to which each can be referred. The absolute 

 duration of the divisions on the time-scale is a matter of pure conjecture ■ 

 but their relative duration can be roughly estimated from the thickness 

 of the rocks. An attempt is made to represent this relative duration by 

 the diagram to the right, which is based on the thickness of the rocks in 

 N.W. Europe. 



