CHAP. X.] CONTINUITY OF THE CHALK. 479 
And the following table, showing the number of 
foraminifera common to the Atlantic mud and various 
eeological formations in England :-— 
Common to the following Formations. 
Total ss —— SSS ase. val 
ee Rhetic 
| eat ae tong | London ene Upper Lower and Per- | Carbo- | 
sulniites |) CRIs clay. Chalk. | Jurassic. | Jurassic. Upper mian. | niferous. | 
Trias. | 
| 
m0) 53°) 28 4 19 7 7 7 ey i 
The morphology of the foraminifera has been 
studied with great care, and the differences between 
closely allied so-called species are so shght 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 
‘Norna’ 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. Toa 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 
