188 f^g Simons, (Sfcsajs, nttir Urfriefas. [ix. 



The great mass of the chalk is composed as we have 

 seen, of the skeletons of Globigerince, and other simple 

 organisms, imbedded in granular matter. Here and 

 there, however, this hardened mud of the ancient sea 

 reveals the remains of higher animals which have lived 

 and died, and left their hard parts in the mud, just as 

 the oysters die and leave their shells behind them, in the 

 mud of the present seas. 



There are, at the present day, certain groups of animals 

 which are never found in fresh waters, being unable to 

 live anywhere but in the sea. Such are the corals ; those 

 corallines which are called Polyzoa', those creatures 

 which fabricate the lamp-shells, and are called Brachio- 

 poda ; the pearly Nautilus, and all animals allied to 

 it ; and all the forms of sea-urchins and star-fishes. 



Not only are all these creatures confined to salt water 

 at the present day ; but, so far as our records of the past 

 go, the conditions of their existence have been the same : 

 hence, their occurrence in any deposit is as strong 

 evidence as can be obtained, that that deposit was 

 formed in the sea. Now the remains of animals of all 

 the kinds which have been enumerated, occur in the 

 chalk, in greater or less abundance ; while not one of 

 those forms of shell-fish which are characteristic of fresh 

 water has yet been observed in it. 



. When we consider that the remains of more than three 

 thousand distinct species of aquatic animals have been 

 discovered among the fossils of the chalk, that the great 

 majority of them are of such forms as are now met with 

 only in the sea, and that there is no reason to believe 

 that any one of them inhabited fresh water the collateral 

 evidence that the chalk represents an ancient sea-bottom 

 acquires as great force as the proof derived from the 

 nature of the chalk itself. I think you will now allow 

 that I did not overstate my case when I asserted that 



