CHAP. X.] 



CONTINUITY OF TET. CHALK. 



479 



And the following table, showing the number of 

 foraminifera common to the Atlantic mud and various 

 geological formations in England : — 



The morphology of the foraminifera has been 

 studied with great care, and the differences between 

 closely allied so-called species are so slight that it is 

 possible that in many cases they should only be 

 regarded as varieties ; but this careful criticism and 

 appreciation of minute differences renders it all the 

 more likely that the determinations are correct, and 

 that animal forms which are substantially identical 

 have persisted in the depths of the sea during a con- 

 siderable lapse of geological time. 



In the late deep-sea dredgings by M. de Pourtales 

 off the American coast, and by H.M. ships ' Light- 

 ning ' and ^Porcupine,' and Mr. Marshall Hall's yacht 

 ' Noma ' off the. west coast of Europe, no animal 

 forms have been discovered belonging to any of the 

 higher groups, so far as we are as yet aware, speci- 

 fically identical with chalk fossils ; and I do not think 

 that we have any right to expect that such will be 

 found. To a depth of 5,000 feet or so a large portion 

 of the North Atlantic is at present heated very con- 

 siderably above its normal temperature, while the 

 Arctic and Antarctic indraught depresses the bottom 



