Oldest Fossiliferous Deposits. 343 



slates, itt Scotland ; but he might naturally conclude that all 

 pre-existing fossiliferous formations must be very insignificant, 

 since no pebbles containing organic remains have yet been de- 

 tected in the conglomerates of the old red sandstone. Great 

 would be the surprise of such a theorist, when he learnt that 

 in other parts of Europe, and still more remarkably in North 

 America, a great succession of antecedent sets of strata had 

 been discovered, capable, according to some of the ablest palae- 

 ontologists, of constituting no less than three independent 

 groups, which are each of them as important as the " old red" 

 or Devonian system, and as distinguishable from each other by 

 their organic remains. Yet it would be consistent with methods 

 of generalizing not uncommon on such subjects, if he still took 

 for granted, that, in the lowest of these " Transition" or Silurian 

 rocks, he had at length arrived at the much-wished-for termi- 

 nation of the fossiliferous series, and that Nature had begun 

 her work precisely at the point where his retrospect happened 

 to terminate. 



It may be useful to inquii-e, whence arises this strong ten- 

 dency to believe that the present limits of human knowledge 

 in geological science exactly embraces that period of past time 

 in which organic beings have flourished on the earth. If it 

 be a very common delusion, there must be some cause for its 

 popularity. Its source is, I believe, twofold ; first, it is almost 

 unavoidable that we should underrate the magnitude of the 

 subterranean changes now in progress at great depths in the 

 earth.' s crust ; and, secondly., that we should equally exaggerate 

 the amount of those which took place far below the surface at 

 former eras, especially those most remote from our times. 



In regard to the first of these sources of error, we have of 

 late years grown familiar with the proofs of great subsidence 

 and upheaval of land in modern times, without sufficiently re- 

 flecting on the enormous alterations in the condition, and pro- 

 bably the structure, of the subjacent parts of the earth's crust 

 which are implied by these movements. The connection of 

 such rising and sinking of the solid parts of the globe with 

 volcanic action, can be demonstrated in many places, and 

 fairly inferred in others, where the action of subterranean heat, 

 owing to its gi-eat depth, is latent. I have endeavoured else- 



