THE MESOZOIC AGES. 233 



only with a niggardly hand on their successors ! 

 Nature gives us no explanation of the mystery. 



" From scarped cliflf and quarried stone, 

 She cries — ' A thousand types are gone.' " 



But why or how one was taken and another left she 

 is silent, and I believe must continue to be so, because 

 the causes, whether efficient or final, are beyond her 

 sphere. If we wish for a full explanation, we must 

 leave Nature, and ascend to the higher domain of the 

 Spiritual. 



Note. — In the description of the chalk on page 227, it should 

 have been stated that it contains, in addition to the tests of 

 Foraminifera, great quantities of the minute oval or rounded 

 calcareous bodies named Coccoliths, and believed to be of 

 vegetable origin. There are also some reasons for believing 

 that much of the chalk was not deposited in water so deep as 

 that in which similar deposits are now usually found, though 

 it is no doubt strictly an oceauic formation. 



