LIFE ON THE EARTH. 107 



Sandstone of Lochmaben in Dumfriesshire, with va- 

 rious undetermined Ichnites. 



Cetacea appear to be totally absent from any of 

 the deposits older than the Tertiary Strata, a cir- 

 cumstance more remarkable since the discovery of 

 terrestrial Mammalia in the Oolitic Strata of Pur- 

 beck and Stonesfield, and the Bone-bed of Wiirtem- 

 berg. The Crag of Suffolk (Pleiocene) is the oldest 

 tertiary deposit in our Islands containing Cetacea. 

 In no district of Europe do they reach downward 

 even to the earliest series of Tertiary Strata. Above 

 this D'Orbigny counts four genera in the Parisian, 

 seven in the Falunian, five in the sub-Apennine strata 

 fifteen, the maximum, in the modern seas. In a 

 general point of view, the Cetacea, Great Reptiles, 

 and Great Fishes, 



Csenozoic Cetacea, 



Mesozoic 

 Palaeozoic 



Great Reptiles, 



Placoid and Ganoid Fishes, 



may be regarded as successively the dominant races 

 of the Sea, the Cetacea taking up the functions 

 which had been exercised by the Enaliosaurians. 

 The earlier races of Cestraciont Fishes, with their 

 crushing teeth, may be thought very well suited 

 to such food as the shelly Mollusca, the strongly- 

 walled Encrinites, and the cuirassed Crustacea of 

 the early periods might furnish; and when their 



