INSTITUTE OF SCIENCE, PHILADELPHIA. 203 



several distinct faunas, of which one was of true Miocene age, like the Vir- 

 ginia Miocene, while another might reasonably be regarded as genuine 

 Pliocene, and the stratigraphical equivalent in South Carolina of the Caloosa- 

 hatchie beds of Florida. This opinion was frankly stated in the introductory 

 remarks prefaced to Part I. of this paper (p. i), but the arguments by which it 

 was sustained were reserved for the geological summary with which this 

 memoir will be closed, in the hope that additional information of a positive 

 character might be received. 



In the review of the Post-Eocene Tertiaries of the United States, sub- 

 mitted for publication as Bulletin 84 of the U. S. Geological Survey in July, 

 1891,^ the present writer used the following language : 



" In South Carolina as in North Carolina paleontologists have been con- 

 fronted with a difficulty arising from the alleged co-existence in the same beds 

 of fossil mollusks elsewhere characteristic of different formations. In the fine 

 work on the Pliocene of South Carolina by Messrs. Tnomey and Holmes, 

 both Miocene and Pliocene species are included, with the result that, by some 

 authors, the whole fauna has been regarded as Miocene, and by others, in- 

 cluding the writers of the work in question, as Pliocene. Both conclusions 

 rest on the assumption that all the species referred to have been derived from 

 the matrix of a single horizon, although collected at a number of different 

 localities. This assumption appears insufficiently supported by the facts, 

 smce no critical stratigraphic investigation of the beds in question has ever 

 been made, and especially no researches directed to the solution of this par- 

 ticular series of discrepancies. It may, however, be assumed that no very 

 obvious stratigraphical differences, if any, exist, since otherwise it would seem 

 as if they must have compelled recognition before now. The shell marl from 

 which the fossils in question have been derived, in part, at least, exists as 

 patches of relatively small extent, occupying shallow depressions in older 

 deposits, which, as well as the marl and the superincumbent sands, are uncon- 

 solidated, loose, and liable to more or less shifting. The action of the torren- 

 tial rains which annually visit this region, the influences at work in subaerial 

 denudation, freshets and floods, as well as the earthquakes which occasionally 

 disturb the soil, offer means by no means inadequate to the confusion of thin, 

 superficial, incoherent strata of similar constitution already in contact with 

 one another — at least to an extent which would make it extremely difficult to 

 recognize any distinction of age or stratification on a casual examination. 

 There is, of course, no reason why, in this State, as elsewhere, some species 

 originating in the Miocene should not persist to the Pliocene, or even to the 

 present fauna, essentially unchanged ; as they are known to do in Florida, for 

 instance. If this were all, no question need be raised as to the synchronous 

 existence of species which have been collected from these beds. But this is . 

 not the real question ; on the contrary, it is entirely beside the point. What 

 we find in the supposed fauna of Messrs. Tuomey and Holmes is an aggrega- 

 tion of species of which some have (both north and south of this State) a defi- 

 nite stratigraphical position in certain Miocene beds where they have never 

 been found associated with certain others, as in the South Carolina deposits. 

 These others, again, are known to be associated in beds of Pliocene age 

 from which the aljove-mentioned Miocene types have never been collected. 

 Lastly, the known order of development deduced from the succession of 

 these forms — in regions where, as in Florida, the stratigraphical succession is 

 unquestioned, complete and distinct — is violated by their alleged contempo- 

 raneous existence in a locality so nearly adjacent. 



"Now, it seems to the writer that the supposition that the so-called 

 Pliocene of South Carolina represents a mechanical mixture of species of two 

 horizons, is more in harmony with what is known and with paleontological 

 experience than the view that these species, elsewhere diversely distinctive, 

 are, in this locality and for this occasion only, biosynchronous. At least it 

 would seem as if the onus probandi lies with those who would claim a normally 

 transitional character for these beds. 



' Now in press. 



