166 LIFE ON THE EARTH. 



ment of the present period. No Coal-fields, to last 

 even a single century, are now growing at the mouths 

 of our rivers ; no metallic veins are spreading 

 through the rocks that we can explore ; no great 

 catastrophe breaks down the barriers of seas, or 

 opens picturesque glens through the ridges of the 

 mountains. Yet the forces whose accumulated effects 

 seem to us so mighty are still alive, and still give 

 proof of their power to make further change in the 

 condition of the globe. 



If we trace back the physical history of the parts 

 of the earth best known to us, we shall be surprised 

 at the permanence of many of the great features 

 of the land and sea ; where these have changed we 

 can often clearly see the mode and almost the 

 mechanism of change, and not unfrequently discover 

 somewhat of the effect of these variations on the 

 distribution of ancient life, its mutation and dis- 

 continuity. 



The German Ocean is what remains of a wider 

 Tertiary Sea, which spread over a large part of the 

 country north of the Carpathians, extending east- 

 ward across the plains of Southern Russia, and north 

 of the Caucasus, but probably closed to the west- 

 ward. The Mediterranean of the Tertiary ages 

 stretched northward up the Adriatic gulf, to in- 

 clude the basin of the Po ; eastward and southward 



