172 E VOL U TION A ND DOGMA . 



species of this character had their habitat in the 

 district, and in its vicinity, the only tangible evidences 

 which we yet possess that they ever existed, are the 

 tracks and foot-prints which they left in the shales 

 and sandstones of Connecticut and New Jersey. 



In other cases, again, all that has so far been 

 discovered of what, in their time, were manifestly 

 important species, is a single tooth, or a single bone, 

 or even only a small fragment of bone. That future 

 research will disclose remains of these species, in 

 larger quantities or in greater numbers, there is 

 reason to believe, but however rich the finds may 

 be, it will always be true that the fossils which have 

 been preserved are but an insignificant portion of 

 those which were actually formed, and that the re- 

 mains of organisms which were fossilized were but an 

 infinitesimal part of those which were completely 

 destroyed before fossilization was possible. 



Darwin's observations on sessile cirripeds corrob- 

 orate in the most striking manner what has been 

 stated in the preceding paragraphs, and show how 

 a large group of animals, represented by an extraor- 

 dinary number of individuals all over the world, in 

 every latitude and " inhabiting various zones of 

 depths from the upper tidal limit to fifty fathoms," 

 may fail to leave even a trace of their existence during 

 long geological periods. " Not long ago, paleontolo- 

 gists maintained that the whole class of birds came 

 suddenly into existence during the Eocene Period ; 

 but now we know, on the authority of Prof. Owen, 

 that a bird certainly lived during the Upper Green- 

 sand ; and still more recently that strange bird, the 



