32 ON A PIECE OF CHALK i 



chambered shells called ammonites and belemnites, 

 which are so characteristic of the period pre- 

 ceding the cretaceous, in like manner die with it. 

 But, amongst these fading remainders of a 

 previous state of things, are some very modern 

 forms of life, looking like Yankee pedlars among 

 a tribe of Bed Indians. Crocodiles of modern 

 type appear; bony fishes, many of them very 

 similar to existing species, almost supplant the 

 forms of fish which predominate in more ancient 

 seas; and many kinds of living shell-fish first 

 become known to us in the chalk. The vegetation 

 acquires a modern aspect. ' A few living animals 

 are not even distinguishable as species, from those 

 which existed at that remote epoch. The Glcli- 

 gerina of the present day, for example, is not 

 different specifically from that of the chalk ; and 

 the same may be said of many other Foraminifera. 

 I think it probable that critical and unprejudiced 

 f examination will show that more than one species 

 i of much higher animals have had a similar lon- 

 gevity; but the only example which I can at 

 present give confidently is the snake's-head lamp- 

 shell (Tercbratidina caput serpentis), which lives in 

 our English seas and abounded (as Tcrebratulina 

 striata of authors) in the chalk. 



The longest line of human ancestry must hide 

 its diminished head before the pedigree of this 

 insignificant shell-fish. We Englishmen are proud 

 to have an ancestor who was present at the 



