ON A PIECE OF CHALK 79 



The foundation of all this calculation is, of course, a 

 knowledge of the length of time the Crania and the coralline 

 needed to attain their full size; and, on this head, precise 

 knowledge is at present wanting. But there are circum- 

 stances which tend to show, that nothing like an inch of 

 chalk has accumulated during the life of a Crania; and, 

 on any probable estimate of the length of that life, the 

 chalk period must have had a much longer duration than 

 that thus roughly assigned to it. 



Thus, not only is it certain that the chalk is the mud of 

 an ancient sea-bottom; but it is no less certain, that the 

 chalk sea existed during an extremely long period, though 

 we may not be prepared to give a precise estimate of the 

 length of that period in years. The relative duration is 

 clear, though the absolute duration may not be definable. 

 The attempt to affix any precise date to the period at which 

 the chalk sea began, or ended, its existence, is baffled by 

 difficulties of the same kind. But the relative age of the 

 cretaceous epoch may be determined with as great ease and 

 certainty as the long duration of that epoch. 



You will have heard of the interesting discoveries recently 

 made, in various parts of Western Europe, of flint imple- 

 ments, obviously worked into shape by human hands, 

 under circumstances which show conclusively that man is 

 a very ancient denizen of these regions. It has been proved 

 that the whole populations of Europe, whose existence has 

 been revealed to us in this way, consisted of savages, such 

 as the Esquimaux are now; that, in the country which is 

 now France, they hunted the reindeer, and were familiar 

 with the ways of the mammoth and the bison. The physi- 

 cal geography of France was in those days different from 

 what it is now — the river Somme, for instance, having cut 

 its bed a hundred feet deeper between that time and this; 



