i6o 



THE STORY OF THE EARTH. 



Fig. 3^ — The base of Gal- 

 erit.-s sub-rotundus, 

 showing the central po- 



sition of the mouth 

 from the Upper Chalk. 



recognised, the material is amorphous and a 

 product 6l decomposition of organisms. This 

 may be evidence that a large part of the sub- 

 stance of the chalk not only 

 consists of the remains of 

 animals which preserve their 

 forms, but that the remain- 

 der of it passed through the 

 bodies of animals which have 

 left little other record of then- 

 existence. 



The fishes are the chief 

 link between the Chalk and 

 the Upper Greensand, a la;\ 

 number of small sharks oi 

 the two deposits being iden- 

 tical. There is the greatest 

 contract between the beds in mineral character; 

 and in the principal types of fossils, because the 



Upper Greensand gives a record of conditions of 



the shore where sediment was accumulating; and 

 the chalk gives evidence of conditions in the open 

 almost beyond the limit to which, sediment 

 was earned, thus demonstrating how great the 

 difference in fossils may be with a slight interval 

 m time. The conditions compared are such, in 

 the two deposits, as may be found on the one 

 hand on the SOUth-weSt shores of Ireland at the 

 present day, and on the Other hand on the ocean 

 floor 400 Or 500 miles to the west m the Atlantic, 

 where an organic deposit is now accumulating 

 which Closely resembles the chalk. But the sharks 

 On the [rish COaSt are not limited to the shore, 

 and leave their remains m the open OCeafl as well ; 



iiv as happened in the ages of the Upper 



ind and chalk. Just as sea-urchins occur 



