September 6. 1889.] 



SCIENCE. 



165 



the entombment of its remains has always oCcurfed under acci- 

 dental conditions. 



(4) The record of marine life is necessarily more complete than 

 that of any other, because the seas have furnished continuous and 

 more uniform conditions than either the land or fresh waters, and 

 because the preservation of its remains was a natural consequence 

 of the conditions under which that life existed. Therefore the 

 record of marine life was less modified by other than evolutional 

 changes of a cosmical character than that of the land and fresh 

 waters, and it is consequently more trustworthy as an index of the 

 progress of geological time. 



(5) Breaks or interruptions in the succession of marine forms of 

 life have been coincident with breaks of continuity, or with changes 

 in the characters of the sediments by which their remains were en- 

 tombed. These breaks in sedimentation, and in the succession of 

 living organisms, are used by all geologists as indicating the de- 

 limiting boundaries of geological epochs, periods, and ages respec- 

 tively, as well as of formations and systems. Their causes were 

 independent of the existence of life, and their occurrence was ac- 

 cidental with reference to it. 



It therefore follows that the recognizable time record in one 

 part of the world is necessarily different in its divisions from that 

 of any other part. For example, a period the close of which was 

 marked by such interruptions as have been mentioned in one part 

 of the world would be continued in other parts as long afterward 

 as the occurrence of similar breaks there should be postponed. 

 While such interruptions were occurring in one or more parts of 

 the world, life and sedimentation were continuous and unaffected 

 by them in others. This is plainly shown in the case of the Chico- 

 Tejon series in California, because no inter-delimiting boundary 

 occurs between its cretaceous and the tertiary portions, as has 

 already been explained ; while an evident hiatus exists between 

 the uppermost known cretaceous and the lowermost known tertjary 

 both in Europe and a large part of North America. 



(6) While there has been progressive development in the order 

 of succession of living organisms from lower forms in earlier, to 

 higher forms in later geological time, the rate of progress of that 

 development has not been uniform in all parts of the world for the 

 same kinds of life. For example, the plant life of North America 

 is now understood to have reached, in later mesozoic time, a higher 

 stage of development with relation to animal life than it had in 

 Europe ; and the difference in grade among the now living indige- 

 nous faunas of the different continents respectively, indicates that a 

 similar difference in the rate of development has also prevailed in 

 different divisions of the animal kingdom. 



(7) The various stages of progressive development of living or- 

 ganisms have been marked by the successive introduction and ex- 

 tinction of class, ordinal, family, and generic types ; and yet certain 

 of those types survived in some parts of the world during long 

 epochs after they had become extinct in other parts. This propo- 

 sition is supported by such facts as that of the survival into the 

 Laramie, Arapahoe, and Denver epochs, of dinosaurian faunas which 

 apparently show little if any indication of decadence or of ap- 

 proaching extinction ; and also by the survival of highly organized 

 representatives of mesozoic families and genera to the present time. 

 Therefore it is not to be expected that we should find exactly the 

 same association of fauna! and floral types, or evidence of more 

 than approximately the same grade of development of life in con- 

 temporaneous but widely separated formations. Therefore, also, 

 the custom which has been adopted by some paleontologists of 

 making the assumed absence of certain of those types a distin- 

 guishing element in the chronological diagnosis of formations is by 

 no means to be commended, even if it were possible for us to dis- 

 cover remains of all the forms of life which then and there existed. 



(8) Correlation of lake and inland sea deposits with those of 

 open-sea origin, even within the same continental area, is necessa- 

 rily a matter of uncertainty. This uncertainty is due to the great 

 difference in the character of the faunas of those waters respect- 

 ively, to the fact that constituent members of faunas of inland wa- 

 ters were not so diversely differentiated in the course of geological 

 time as were those of marine waters ; and also the inevitable want 

 of geographical continuity of the two classes of deposits with each 

 other, even in cases of actual contemporaneity. The only really 



trustworthy paleontological means of determining the equivalency 

 or contemporaneity of deposits in such cases as these is the specific 

 identification of such remains of land animals and plants as may 

 have found entombment in then existing contiguous inland waters, 

 on the one hand, and marine waters on the other. For reasons 

 mentioned in proposition 6, the mere similarity of types, even of 

 the more highly organized animals and plants, which may be dis- 

 covered in different districts cannot be relied upon as indicating 

 contemporaneity. Geographical continuity of strata being always 

 wanting in such cases, the only aid to be expected from stratig- 

 raphy in determining equivalency of the formations must come 

 through the discovery of the overlying or underlying position of the 

 inland deposits with reference to marine deposits of known geolog- 

 ical age. 



It will be seen that these propositions involve serious question- 

 ings of the validity of certain methods and practices common among 

 many of those geologists who devote themselves mainly or exclu- 

 sively to paleontology. Such questionings afford scope for elabo- 

 rate and varied discussions, but I shall close my present remarks 

 with only a brief reference to the general subject of a proper rec- 

 ognition of a universal scheme of geological classification, which 

 must of course have a biological basis. 



The greater part of my own geological studies having been 

 prosecuted from a biological standpoint, I am naturally not disposed 

 to underestimate the value of paleontology as a branch of geolog- 

 ical investigation, nor to encourage, even by incidental utterance, 

 those who do. But I am sure no greater harm can be done to pa- 

 leontological science than either to encourage, or to fail to oppose, 

 the erroneous views which some of its votaries are shown by their 

 own publications to entertain. For example, it is apparent to 

 every one who is at all familiar with paleontological literature that 

 many authors assume to designate with precision the geological 

 age of any and all fossils submitted to them, as well as the taxono- 

 mic position of the strata from which they were obtained, without 

 reference to stratigraphy, or to any related geological fact. 



Those paleontologists who make this unwarranted application 

 of their science to systematic geology, all use the scheme of classi- 

 fication that has been established for Europe, and use it as if it 

 were of infallible application to all other parts of the world, and 

 also as if it were already absolutely perfected for that continent. 

 While I have no inclination to question the general accuracy of the 

 European scheme of classification for that continent, I do not hesi- 

 tate to express the opinion that it is not of infallible application to 

 other parts of the world, except as to its larger divisions, and that 

 even in this respect it will need modification. That is, I hold that 

 investigations of the formations which are found upon any given 

 continent or great division of the earth's surface ought to be prose- 

 cuted, first, with relation to one another, and second, with reference 

 to their ultimate, not immediate, correlation with those of other 

 continents or divisions. 



It is true that the general consensus of geological thought and 

 opinion has long been in favor of adopting the European scheme 

 of classification in all, or nearly all, its details as applicable to all 

 other parts of the world, and every considerate naturalist will treat 

 such opinion with deference. But prevalence of opinion is by no 

 means proof of its accuracy. None of the older naturalists present 

 need be reminded of the great revolution in opinion that took place 

 a little more than twenty years ago ; and the older geologists will 

 remember that the degree of displacement, the amount of consoli- 

 dation, the crystallization and the lithological composition, of 

 strata, were once accepted by all geologists as indices of the geo- 

 logical age of the formations which they composed. Remember- 

 ing these incidents in the history of natural science, it does not 

 seem unreasonable that present opinions should be frequently ques- 

 tioned, even those which are generally accepted. 



I do not wish to be understood as condemning the scheme of 

 classification now in use. nor even as recommending the present 

 substitution of it by any other ; but I insist that for universal appli- 

 cation, it is plainly imperfect. A scheme of classification, as a 

 working rule, is not only a convenience but a constant necessity ; 

 so constant, indeed, that I have not been able to present these re- 

 marks without its aid. But while the one which has been estab- 

 lished for Europe ought by no means to be discarded, it ought to 



