222 OUR COMMON BRITISH FOSSILS. 



CHAPTER IX. 



FOSSIL LAMP-SHELLS (BRACHIOPODA). 



Reference has already been made to this class of 

 fossils as being by far the most numerous in the 

 Primary rocks. The limestones are not unfrequently 

 wholly composed of their ancient shells. They are 

 also very abundant in the Secondary strata, although 

 less numerous than in those preceding them ; whilst in 

 the Tertiary marine deposits they are much scarcer, 

 and in the Recent or present period comparatively 

 rare. Thus the Geological Record presents us with 

 the interesting spectacle of the rise, growth, decline, 

 and fall of one very large class of marine animals. 



Notwithstanding this inability on the part of the 

 Brachiopoda to compete successfully in the struggle 

 for existence with the more highly organized mollusca, 

 it is very singular how persistently certain genera 

 have maintained their distinctive features through 

 periods of time as vast as that which has extended 

 from the Silurian epoch to the present day, like the 

 Lingula genus, for instance, has done. One can 



