52 THE STORY OF THE EARTH. 



And beyond those shores of the chalk sea were 

 land surfaces of islands and continents on which 

 plants and animals survived from age to age. 



Lands have never ceased to exist from the 

 earliot ages. They have changed their forms. 

 Their height of elevation above the sea has been 

 altered ; they have been broken up into islands 

 and re-united with other islands newly formed. 

 The lands which exist at the present day are built 

 up almost entirely of water-formed rocks, which 

 have been spread out one upon another in the 



an, Every continent shows this history : a 

 ession of ancient sea-beds, with the dep< 



formed upon them, alternating occasionally with 



old land surfaces which make known epochs when 

 the sea-bed emerged from the ocean, and became 

 land as it is now. 



The shores, with their pebble beds and other 

 evidences of tidal movement of the waters, have 

 persisted from the earliest times, changing their 

 positions upon the globe, as the lands altered 

 their forms, never entirely passing away through 



the long epochs of geological time, although they 

 only occasionally come back again to the pi; 



in which shores had previously existed. 



The open ocean with its limestones has proba- 

 bly been equally persistent and as variable in form, 

 v little is known Ol limestones which may have 

 ted in the earliest geological ages. But from 

 their thickness and importance m the time named 



Devonian and Carboniferous, and in all subse- 



quent times, it is inferred that the open ocean has 



isted, though its depth has varied. There 



(an have been no breaks in geological time, 



though the tcs in the continuity of land 



Surfaces, in the continuity <>t' shore lines, and the 



