Chap. IX. GEOLOGICAL EECOED. 307 



If, moreover, they had been the progenitors of these 

 orders, they would almost certainly have been long ago 

 supplanted and exterminated by their numerous and 

 improved descendants. 



Consequently, if my theory be true, it is indisputable 

 that before the lowest Silurian stratum was deposited, 

 long periods elapsed, as long as, or probably far longer 

 than, the whole interval from the Silurian age to the 

 present day ; and that during these vast, yet quite un- 

 known, periods of time, the world swarmed with living 

 creatures. 



To the question why we do not find records of these 

 vast primordial periods, I can give no satisfactory 

 answer. Several of the most eminent geologists, with 

 Sir R. Murchison at their head, are convinced that we 

 see in the organic remains of the lowest Silurian stratum 

 the dawn of life on this planet. Other highly com- 

 petent judges, as Lyell and the late E. Forbes, dispute 

 this conclusion. We should not forget that only a small 

 portion of the world is known with accuracy. M. Bar- 

 rande has lately added another and lower stage to the 

 Silurian system, abounding with new and peculiar 

 species. Traces of life have been detected in the Long- 

 mynd beds beneath Barrande's so-called primordial 

 zone. The presence of phosphatic nodules and bitu- 

 minous matter in some of the lowest azoic rocks, pro- 

 bably indicates the former existence of life at these 

 periods. But the difficulty of understanding the ab- 

 sence of vast piles of fossiliferous strata, which on my 

 theory no doubt were somewhere accumulated before 

 the Silurian epoch, is very great. If these most ancient 

 beds had been wholly worn away by denudation, or 

 obliterated by metamorphic action, we ought to find 

 only small remnants of the formations next succeeding 

 them in age, and these ought to be very generally in 



