68 LIFE ON THE EARTH. 



slaty cleavage as to render the search for fossils 

 ineffectual by any of these circumstances. The ma- 

 terials are fine-grained or arenaceous, with or with- 

 out mica, in laminae and beds quite distinct and of 

 various thickness, by no means unlikely to retain 

 impressions of a delicate nature, such as those left 

 by Graptolites, or Mollusks, or Annulose crawlers. 

 Indeed, one or two such traces are supposed to have 

 been recognized, so that the almost total absence of 

 the traces of life in this enormous series is best 

 understood by the supposition that in these parts of 

 the sea little or no life existed. But the same re- 

 mark of the excessive rarity of life in the lower de- 

 posits is made in North America, in Norway, and in 

 Bohemia, countries well searched for this very pur- 

 pose, so that all our observations lead to the conviction 

 that the lowest of all the strata are quite deficient of 

 organic remains. The absence is general it appears 

 due to a general cause. Is it not probable that during 

 these very early periods the ocean and its sediments 

 were nearly devoid of plants and animals, and in 

 the earliest time of all which is represented by sedi- 

 ments, quite deprived of such ? 



2. The variety of life in the sea continually aug- 

 ments from the lower Cambrian rocks upwards, in 

 such a way as to leave no doubt of the richer fauna 

 of the Llandeilo series being a part of the same 



