308 



SCIENCE. 



[N. S. Vol. XXII. No. 558. 



abrupt mutations in order to account for them. 

 We are familiar with multitudes of cases 

 where genera, orders or even classes seem to 

 appear suddenly, but, as far as known to the 

 writer, not a single instance where any con- 

 siderable number of the minute morphological 

 variations called for by the -Darwinian theory 

 in leading up to the new types, can be satis- 

 factorily traced. It would appear, if the Dar- 

 winian theory were correct, that at least a 

 few of the radical replacements by altered 

 forms of life might be traceable by actual 

 fossil remains in the underlying rocks. 



The subject was very strikingly brought to 

 my attention some time ago in studying the 

 extensive family Pleurotomidse of the gastro- 

 pod Mollusca, — an important group, contain- 

 ing many genera and a vast array of species, 

 which seems to corae abruptly into being at the 

 beginning of the Tertiary period. Some spe- 

 cies supposed to belong to the family have been 

 described from the upper horizons of the Cre- 

 taceous, but these are not sufficiently numerous 

 or transitional in nature to affect the general 

 truth of the above statement. Some of the 

 better defined genera, such as Gemmula, ap- 

 pear abruptly in the earliest Eocene, in forms 

 fully as well developed as those now living, 

 and, in fact, some early Eocene species so 

 closely resemble living shells that it is scarcely 

 possible to distinguish them. There is not a 

 particle of generic change, even in the com- 

 plex embryo, from the time of their sudden 

 appearance at the opening of the Eocene to 

 the present time. Many genera, however, en- 

 dure only until the end of the Eocene-Oligo- 

 cene period, when there occurs again a rather 

 universal and abrupt change of generic types. 



At Vicksburg, Miss., appears a formation 

 generally assigned to the Lower Oligocene, 

 which may be resolved into two principal ho- 

 rizons, the lower of which is composed of fine 

 light gray fossiliferous sand, with but little 

 admixture of clay and alternating in thin 

 strata with subequal thicknesses of more or 

 less friable limestone, the upper consisting of 

 an equally fossiliferous ferruginous red marl. 

 In some places these two horizons are sepa- 

 rated by a bed of blackish-gray compact clay, 

 full of fossils which so closely resemble those 



of the upper marl that there can be but little 

 question of its properly forming part of the 

 upper horizon. These two horizons were prob- 

 ably separated by a time interval not very 

 great, geologically speaking, possibly not raore 

 than a few thousand years — a relatively short 

 time in the life history of most species, — 

 during which the lower beds may have ap- 

 peared above the ocean and have been subject 

 to denudation until they were again submerged 

 to receive the upper marls, the local conditions 

 having changed somewhat in the interval, as 

 shown by the different constitution of the 

 beds as related above. In regard to the Mol- 

 lusca of the two horizons, I find after a rather 

 thorough exploration of both, extending over 

 several years, that there is unexpectedly little 

 in common between them. Probably not more 

 than 40 per cent, of the species of either 

 horizon are common to the two, and, in several 

 instances, even these are at least varietally 

 modified. There are, of course, a number of 

 species of the lower beds represented by evi- 

 dent descendants in the upper marls, but 

 what it is desired to lay particular stress upon 

 in this connection, there are many widely di- 

 vergent or wholly unrelated types appearing in 

 the latter that are not even suggested in the 

 former. Perhaps the exploration is not as 

 yet sufficiently extended, but this is at least 

 the present status of knowledge, with an 

 equally thorough investigation of the two hori- 

 zons as they are now exposed in the bluff at 

 Vicksburg. 



The mutation theory is evidently the best 

 that has been advanced to account for these 

 known facts. It should be especially accept- 

 able to the theologians, also, as they maintain 

 the spiritual and undying nature of man. 

 If we conceive that man originated abruptly 

 by some unaccountable molecular change in 

 the ovum producing the original twins, Adam 

 and Eve, there can be no doubt of the time 

 when man became thus immortal, whereas 

 there would be necessarily much uncertainty 

 as to the time when this occurred among 

 the successive infinitesimal increments of 

 brain development necessitated by the Dar- 

 winian theory. 



Born thus in the womb of the lower ani- 



