16 NATURAL SELECTION i 



earth to the population at the present time. Again, at each 

 epoch, the whole earth was, no doubt, as now, more or less the 

 theatre of life, and as the successive generations of each species 

 died, their exuviae and preservable parts would be deposited 

 over every portion of the then existing seas and oceans, which 

 we have reason for supposing to have been more, rather than 

 less, extensive than at present. In order then to understand 

 our possible knowledge of the early world and its inhabitants, 

 we must compare, not the area of the whole field of our geo- 

 logical researches with the earth's surface, but the area of the 

 examined portion of each formation separately with the whole 

 earth. For example, during the Silurian period all the earth 

 was Silurian, and animals were living and dying and deposit- 

 ing their remains more or less over the whole area of the 

 globe, and they were probably (the species at least) nearly as 

 varied in different latitudes and longitudes as at present. 

 What proportion do the Silurian districts bear to the whole 

 surface of the globe, land and sea (for far more extensive 

 Silurian districts probably exist beneath the ocean than above 

 it), and what portion of the known Silurian districts has been 

 actually examined for fossils? Would the area of rock 

 actually laid open to the eye be the thousandth or the ten- 

 thousandth part of the earth's surface? Ask the same 

 question with regard to the Oolite or the Chalk, or even to 

 particular beds of these when they differ considerably in their 

 fossils, and you may then get some notion of how small a 

 portion of the whole we know. 



But yet more important is the probability, nay, almost the 

 certainty, that whole formations containing the records of 

 vast geological periods are entirely buried beneath the ocean, 

 and for ever beyond our reach. Most of the gaps in the 

 geological series may thus be filled up, and vast numbers of 

 unknown and unimaginable animals, which might help to 

 elucidate the affinities of the numerous isolated groups which 

 are a perpetual puzzle to the zoologist, may there be buried, 

 till future revolutions may raise them in their turn above the 

 waters, to afford materials for the study of whatever race of 

 intelligent beings may then have succeeded us. These con- 

 siderations must lead us to the conclusion that our knowledge 

 of the whole series of the former inhabitants of the earth is 



