166 LAY SERMONS, ESSAYS, AND REVIEWS. [ix. 



the death and decay of the soft parts of the sea-urchin and the 

 growth of the coralline to the full size which it has attained. If 

 the decay of the soft parts of the sea-urchin ; the attachment 

 growth to maturity, and decay of the Crania; and the sub 

 sequent attachment and growth of the coralline, took a year 

 (which is a low estimate enough), the accumulation of the inch 

 of chalk must have taken more than a year : and the deposit of 

 a thousand feet of chalk must, consequently, have taken more 

 than twelve thousand years. 



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

 ledge 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 circumstances 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 implements, 

 obviously worked into shape by human hands, under circum 

 stances which show conclusively that man is a very ancient 

 denizen of these regions. 



It has been proved that the old populations of Europe, whose 

 existence has been revealed to us in this way, consisted of 



