1883.] NATURAL SCIENCES OP PHILADELPHIA. 199 



held, Prof. Heilprin maintained, by a very large body of geolo- 

 gists. But it can readily be shown by a logical deduction that at 

 least one of the conclusions arrived at (I) is, in almost certainty, 

 erroneous ; and that the second, based upon this one, derives no 

 confirmation from the supposed facts. If, as is contended, several 

 distinct faunas — i. e., faunas characteristic of distinct geological 

 epochs — may have existed contemporaneousl}^ then evidences of 

 inversion in the order of deposit ought to be common, or, at any 

 rate, they ought to be indicated somewhere, since it can scarcely 

 be conceived that animals everywhere would liaA'^e observed the 

 same order or direction in their migrations. Given the possible 

 equivalency in age, as claimed, of the Silurian fauna of North 

 America with the Devonian of the British Isles and the Carbon- 

 iferous of Africa, or any similar arrangement, why has it never 

 happened that when migration, necessitated by alterations in 

 the physical conditions of the environs, commenced, a fauna with 

 an earlier facies has been imposed upon a later one, as the Devonian 

 of Great Britain upon the Carboniferous of Africa, or the Amer- 

 ican Silurian upon the Devonian of Britain ? Or for that matter, 

 the American Silurian may have just as well been made to succeed 

 the African Carboniferous. Why has it just so happened that a 

 fauna characteristic of a given period has invariably succeeded 

 one which, when the two are in superposition, all over the world (as 

 far as we are aware), indicates precedence in creation or origina- 

 tion, and never one that can be shown to be of later birth? 

 Surely these peculiar circumstances cannot be accounted for on 

 the doctrine of a fortuitous migration. Nor can it be claimed 

 that, through the interaction of the evolutionary forces, a 

 migrating fauna with an early -life facies will in each case at the 

 point of its arrest have assumed the character of the latei'-day 

 fauna which belongs to that position. Therefore it appears inex- 

 plicable that a very great period of time could have intervened 

 between the deposition of the fauna of one great geological epoch 

 at one locality, and that of the same or similar fauna at another 

 locality distantly removed from the first. In other words, the 

 migrations, for such must undoubtedly have been the means of the 

 distant propagation of identical or very closely related life-forms 

 (unless we admit the seemingly untenable hypothesis that equiva- 

 lent life-forms may have been veiy largely developed from inde- 

 pendent and very dissimilar lines of ancestry), must have been 

 much more rapidly performed than has generally been admitted 

 by naturalists. {Sic Huxlej^ : "All competent authorities will 

 probably assent to the proposition that phj^sical geology does not 

 enable us in any way to reply to this question, Were the British 

 Cretaceous rocks deposited at the same time as those of India, 

 or are they a million of years younger or a million of years 

 older?") 



But what applies to the broader divisions of the geological 

 scale also applies to the minor divisions. Thus the subordinate 



