303 ABSENCE OF iNTERMEDiATE VARIETIES 



Many cases could be given of the lower beds of a formation 

 having been upraised, denuded, submerged, and then re-cov- 

 ered by the upper beds of the same formation — facts, show- 

 ing what wide, yet easily overlooked, intervals have occurred 

 in its accumulation. In other cases we have the plainest 

 evidence in great fossilized trees, still standing upright as 

 they grew, of many long intervals of time and changes of 

 level during the process of deposition, which would not have 

 been suspected, had not the trees been preserved : thus Sir C. 

 Lyell and Dr. Dawson found carboniferous beds 1,400 feet 

 thick in Nova Scotia, with ancient root-bearing strata, one 

 above the other, at no less than eighty-six different levels. 

 Hence, when the same species occurs at the bottom, middle, 

 and top of a formation, the probability is that it has not 

 lived on the same spot during the whole period of deposition, 

 but has disappeared and reappeared, perhaps many times, 

 during the same geological period. Consequently if it were 

 to undergo a considerable amount of modification during the 

 deposition of any one geological formation, a section would 

 not include all the fine intermediate gradations which must, 

 on our theory, have existed, but abrupt, though perhaps 

 slight, changes of form. 



It is all-important to remember that naturalists have no 

 golden rule by which to distinguish species and varieties ; 

 they grant some little variability to each species, but when 

 they meet with a somewhat greater amount of difference be- 

 tween any two forms, they rank both as species, unless they 

 are enabled to connect them together by the closest inter- 

 mediate gradations; and this, from the reasons just assigned, 

 we can seldom hope to effect in any one geological section. 

 Supposing B and C to be two species, and a third, A, to be 

 found in an older and underlying bed ; even if A were 

 strictly intermediate between B and C, it would simply be 

 ranked as a third and distinct species, unless at the same 

 time it could be closely connected by intermediate varieties 

 with either one or both forms. Nor should it be forgotten, 

 as before explained, that A might be the actual progenitor 

 of B and C, and yet would not necessarily be strictly inter- 

 mediate between them in all respects. So that we might 

 obtain the parent-species and its several modified descend- 

 ants from the lower and upper beds of the same formation, 

 and unless we obtained numerous transitional gradations, we 

 should not recognize their blood-relationship, and should 

 consequently rank them as distinct species. 



