riiAr. IX. IN ANY SINGLE FORMATION. ogj 



roiM(\scntIiig formations, elsewhere thousands of feet in thick- 

 ness, and which must have required an enormous period for 

 (heir accumuhition ; yet no one ignorant of this fact woukl have 

 snspecled the vast lapse of time represented by the thinner for- 

 mation. Many cases could be f]fiven of the lower beds of a 

 formation havin*^ been upraised, denuded, submcrj^ed, and then 

 i('-covercd by the upper beds of the same formation — facts, 

 shcnving what wide, yet easily-overlooked, intervals have oc- 

 curred 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 

 (luring the process of deposition, which would never even have 

 been suspected, had not the trees chanced to have been pre- 

 served : tluis Sir C Lyell and Dr. Dawson found carboniferous 

 beds 1,400 feet tliick in Nova Scotia, with ancient root-bearing 

 strata, one above the other, at no less than sixty-eight diiferent 

 levels. Hence, when the same species occur at the bottom, 

 middle, and top of a formation, the probability is that they have 

 not lived on the same spot during the whole period of depo- 

 sition, but have disappeared and reapj)eared, perhaps many 

 times, during the same geological period. So that, if such spe- 

 cies were to undergo a consid(n-al)le amount of modification 

 during any one geological period, a section would not include 

 all the fin(^ intermediate gradations which must on our theory 

 have existed between them, but aljrupt, though perhaps slight, 

 changes of form. 



It is all-important to remember that natin-alists 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 dilference between 

 any two forms, they rank both as species, uidess tliey are en- 

 abled to coimect them together by the closest intermediate 

 gradations. And this from the reasons just assigned we can 

 seldom hope to effect in any one geological section. Supposing 

 B and C to b(; two sjiecies, and a third. A, to l)e found in an 

 older and underlying bed; even if A were strietly intermediate 

 l)(!tween B and C, it would simply be ranked as a tliird and 

 distinct sjiecies, unl(\ss at the sam«; time it could be most 

 closely coimected with either one or l)oth forms 1)>' intermediate 

 varieties. Nor should it be forgotten, as before explaitied, that 

 A might ])(; the actual ]irogenitor of B and C, and yet might 

 not necessarily be strictly intermediate between them in all re- 

 opccts. So that we might obtain the parcnt>specics and its 



