DEEP-SEA LIFE. 443 



We might enlarge the list by taking from other waters species of 



Conus. Planaxis. Emarginula. Modiola. 



Pleurotoma. ColumbeUa. Chiton. Area. 



Mitra. Pisania. Butta. Chama. 



Murex. Pinna. Mactra, &c. 



which indicate in most cases low-water conditions. If, then, these 

 genera occur in association in an ancient deposit, we are required to 

 believe, if we affirm shallow-water conditions for the stratum, that 

 the changes in level of the ancient sea-bed went on so slowly that the 

 life gradually accommodated itself to change, finding the conditions 

 of existence easier by following the coast-line than by remaining fixed 

 on the sea-bed. This migration of life is implied in the recognition 

 of an ancient sea margin or shallow ocean by characteristic fossils. 



Marine Deposits of the Open Ocean. The deep waters of the 

 ocean, formerly thought to be barren, were proved by the researches of 

 Dr. Carpenter, Dr. Gwyn Jeffreys, Sir Wyville Thompson, 1 and Pro- 

 fessor Sars, to be rich in life, though Dr. Wallich, in his account of 

 the voyage of the Bulldog, was the first to make known the occur- 

 rence of deep-water foraminifera, shells, and echinoderms in the 

 northern seas. Dr. Carpenter observes that the abundance and variety 

 of animal life on a bottom on which the temperature is at least 2 F. 

 below the freezing point of fresh water, is a fact which has all the 

 interest of surprise ; and it is scarcely less remarkable that the forms 

 of molluscs, echinoderms, and sponges, which seem to be characteristic 

 inhabitants of this cold area, should attain a very considerable size. 

 The deep-sea exploration has yielded many genera previously supposed 

 to be extinct, and many types allied to extinct genera of the secondary 

 strata. Thus a crinoid from a depth of 2435 fathoms belongs to the 

 extinct apiocrinite type, and is associated with an urchin allied to 

 the flexible Echinothuria of the chalk. The vitreous sponges, like 

 Holtenia, recall fossil sponges of the Upper Greensand and Chalk ; 

 while the foraminifera and polycystinae present a similar interest. Of 

 the foraminifera, Globigerina and Orbulina live on the surface of the 

 ocean, and like the pteropods only reach the deeper waters after death, 

 when they are mixed with heavier-shelled forms which live on the 

 ocean floor. 



Extinction of Species. Species are most easily exterminated by 

 the struggle for existence. They drop away one by one, first by 

 diminution in numbers, then by limitation of the inhabited area, till 

 they cease to be met with in geological time. This process is similar 

 to that which has been recorded in human history, by which so many 

 birds have disappeared from the earth. Not to mention the moas, 

 still found with the feathers attached and with moa eggs buried in 

 Maori graves, there are the well-authenticated instances of the dodo 

 of Mauritius, and the solitaire of Keunion ; and Professor Alfred 

 Newton 2 records, among other extinct Mascarene birds, in addition 



1 "Depths of the Sea ;" and "Voyage of the Challenger in the Atlantic." 



2 Encyc. Brit., article " Birds." 



