460 THE JOURNAL OF GEOLOGY. 



overwhelmed by the effort to grasp its immeasurable antiquity ; 

 by the thought that while it has passed through all the chances 

 and changes of geological history, the structure which fitted it 

 for life on the earliest palaeozoic bottom is still adapted for a 

 life on the sands of the modern sea floor ? 



The everlasting hills are the type of venerable antiquity ; but 

 lingula has seen the continents grow up, and has maintained its 

 integrity unmoved by the convulsions which have given the crust 

 of the earth its present form. 



As measured by the time-standards of the zoologist lingula 

 itself is modern, for its life-history still holds locked up in its 

 embryology the record, repeated in the development of each 

 individual, of a structure and a habit of life which were lost in 

 the unknown past at the time of the lower Cambrian, and it tells 

 us vaguely but unmistakably of life at the surface of the primi- 

 tive ocean, at a time when it was represented by minute and 

 simple floating ancestors. 



Broadly stated, the history of each great line has been like 

 that of the echinoderms and brachiopods. The oldest pteropod 

 or lamellibranch or echinoderm or crustacean or vertebrate 

 which we know from fossils exhibits its own type of structure 

 with perfect distinctness, and later influences have done no more 

 than to expand and diversify the type, while anatomy fails to 

 guide us back to the point where these various lines met each 

 other in a common source, although it forces us to believe that 

 the common source once had an individual existence. Embry- 

 ology teaches that each line once had its own representative at 

 the surface of the ocean, and that the early stages in its evolu- 

 tion have passed away and left no record in the rocks. 



If we try to call before the mind a picture of the land surface 

 of the earth we see a vast expanse of verdure, stretching from 

 high up in the mountains over hills, valleys, and plains, and 

 through forests and meadows down to the sea, with only an 

 occasional lake or broad river to break its uniformity. 



Our picture of the ocean is an empty waste, stretching on 

 and on with no break in the monotony except now and then a 



