DAE WIN AND HIS CRITICS. 65 



abundance, are only known to us by a few 

 fragments of bone ; and how many more must 

 have utterly perished, especially among species 

 of small size, without leaving even a vestige 

 of their existence behind, although they may 

 have numbered hundreds of thousands of in- 

 dividuals ! When we consider the upheavals, 

 depressions, denudations, floods, earthquakes, 

 and volcanic eruptions which have acted on 

 and metamorphosed the crust of the earth 

 for countless ages, and then remember how 

 small a portion of its surface has yet been 

 geologically examined, we cease to wonder at 

 the deficiency of connecting links, whether 

 between individual species, or entire Classes, 

 and have rather cause to be surprised that, 

 under such unfavourable circumstances, we 

 should already know even as much as we 

 do of the past life of the earth. 



Yir " Some facts of geographical distribu- 

 tion supplement other difficulties." 



Geographical distribution will be discussed in 

 a subsequent chapter, and need not be dealt 

 with in this place. 



