290 THE TRANSFORMATIONS OF THE ANIMAL WORLD 



the generality of these oscillations of the foreshore, 

 accompanied by the formation of superposed 

 heteropic deposits, paleontologists are so rarely 

 able to follow in one spot the regular evolution of 

 marine faunas of littoral habitat through the 

 successive stages of the same country. In the 

 upper Tertiary lands of Belgium, Van den Broeck 

 has shown that the malacological fauna of the 

 black upper Miocene sands of Antwerp has no 

 roots in the subjacent Oligocene clay, the more so 

 that there is a gap in the upper Oligocene at this 

 point. These ancestors and these affinities of the 

 Black Crag fauna must be sought for farther East 

 in the early Miocene deposits of North Germany, 

 whence the sea reached, by overflooding in the 

 second half of the Miocene period, the till then re- 

 claimed Belgian plains. This Belgian Miocene 

 fauna, progressing with slight modifications con- 

 tinuously from East to West, causes the blossoming, 

 in the Suffolk of England, of a Pliocene fauna, less 

 southern in character, which forms its natural 

 descendant. Finally, cold currents from North 

 America have caused the gradual refrigeration of 

 the Anglo-Belgian basin and finally introduced 

 into these regions northern forms, an indication 

 of a new flooding of the deposits from West to East, 

 in an inverse direction to the former one. The 

 influence of currents is here combined with the 

 displacements of foreshores to bring about the 

 migration of fauna, and of their essential modifica- 

 tions throughout Neogene times. 



Fontannes has made analogous observations on 

 the Neogenous faunas of the basin of the Rhone. 



