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SCIENCE. 



[Vol. XIV. No. 344 



marine paleontological record is broken at the base of the Laramie 

 formation. Still, thie opinion that we have a continuous record 

 there from cretaceous into tertiary time is strongly supported by 

 paleontological and stratigraphical evidence. But we come now 

 to consider the mesozoic of the Pacific coast region, where we shall 

 find proof of unbroken continuity of marine deposits from the up- 

 per cretaceous to the tertiary. Time will not permit me now to 

 discuss the mesozoic of western British America, which Dr. G. M. 

 Dawson, Mr. Whiteaves, and other Canadian geologists have done 

 such excellent work upon, and I must therefore confine myself 

 mainly to the California section. 



The rocks of this portion of the Pacific coast region have been 

 so greatly displaced since their deposition that their study is more 

 difficult than that of the rocks of the interior region. Still, our 

 knowledge of the upper part of the Pacific coast mesozoic is quite 

 satisfactory. The oldest mesozoic strata of the California section 

 which I shall specially refer to on this occasion were, by the Cali- 

 fornia geologists, assigned to the lower cretaceous, under the name 

 of the Shasta group. But these strata do not probably represent 

 the very earliest part of the cretaceous period. 



The exact relation of the Shasta group to the cretaceous forma- 

 tions above it has not yet been made clear ; but Mr. Diller's inves- 

 tigations in northern California seem to indicate that the hiatus 

 between them is not so marked as has been supposed. The geolo- 

 gists of the California Survey did not recognize any formation as 

 belonging between the Shasta and Chico groups, but Dr. G. F. 

 Becker has reported upon a series of strata m Mendocino county 

 which he believes to be later than the Shasta, and earlier than the 

 Chico. Upon examining the fossils which he collected from those 

 strata, some of the species of which have also been found at Todos 

 Santos Bay in Lower California, I concurred in his opinion, and 

 suggested for those strata and their equivalents the name of Wal- 

 lala group. Still, actual contact of this group with any other cre- 

 taceous strata has not yet been discovered, and its actual taxonomic 

 position is not known. 



From the base of the Chico'group upward, the series of Califor- 

 nia strata which has been referred to the cretaceous is so well 

 known that little if any difference of opinion exists as to essential 

 facts concerning it, although a wide difference of opinion has arisen 

 as to their significance and importance. This series, aggregating 

 more than ten thousand feet m thickness, was divided into two 

 groups by the California geologists; namely, the Chico below and 

 the Tejon above, although they recognized the fact that there is no 

 distinct break, either paleontological or stratigraphical, between 

 them. 



A considerable number of fossil invertebrates, among which are 

 a species of baculites and several ammonitic forms, constitute such 

 a decided mesozoic feature of the fauna of the lower portion of this 

 Chico-T6jon series that the California geologists naturally and prop- 

 erly referred it to the cretaceous, The upper, or T^jon, portion 

 contains a fauna that is so obviously cenozoic in character that 

 several geologists, especially Heilprin and Conrad, have strenuously 

 contended that it is of eocene age. A large proportion of these 

 Tejon species are found to be so common in the Chico portion that 

 if they were not there commingled with the cretaceous forms just 

 referred to, the tertiary age of those lower strata would hardly be 

 questioned. In short, there is in this stratigraphically unbroken 

 Chico-Tejon series of California, a gradual transition of faunal char- 

 acteristics from the cretaceous to the tertiary. 



This transition was recognized by Mr. Gabb, and yet he referred 

 the whole series to the cretaceous. His view was that, a portion 

 of the series being assigned to the cretaceous, the remainder of it 

 must follow, because the series can only be arbitrarily divided ; and 

 other geologists still entertain a similar opinion. By whatever 

 name or names this great series of strata may be known, it is plain 

 that it represents a continuous portion of geological time, extending 

 from the later mesozoic to the earlier cenozoic age inclusive. There- 

 fore the mesozoic series of strata in this portion of the Pacific coast 

 region has really no definable upper limit. 



It is true that by our present methods it is inconvenient to 

 classify a series of strata like this, but the recognition of its true 

 character is of far more importance than mere convenience of classi- 

 fication. Indeed this case constitutes one of the most instructive 



discoveries that has been made in the whole range of historical 

 geology ; and it should be understood as demonstrating that abrupt 

 transitions from one epoch, period, or age to another have always 

 been due to local or regional changes in physical conditions ; or, in 

 other words, to accidental circumstances. 



Concerning the relation of the other members of the California 

 section of the mesozoic to the Chico-T^jon series, or to each other, 

 and the relation of the lowest of those formations to the Jurassic, 

 our knowledge, as before mentioned, is imperfect. 



The satisfactory correlation of a part of the cretaceous forma- 

 tions of the interior region with those of the Atlantic coast region 

 has already been mentioned ; but we have never been able to satis- 

 factorily correlate any of the cretaceous formations of the Pacific 

 coast region which have been mentioned, with any of those of the 

 interior and Atlantic coast regions, even in cases of presumable 

 contemporaneity. If such correlations are ever made, we must ex- 

 pect them through the labors of the Canadian geologists in the 

 North-west. The whole fauna of each of the Pacific coast forma- 

 tions referred to seems to be different from that of any of the more 

 eastern formations, the few cases in which specific identity has 

 been recognized being of doubtful character. This inability to cor- 

 relate formations in different and not far distant parts of our own 

 continent, which were presumably contemporaneous in their origin, 

 may well cause us to doubt the correlation of at least a part of the 

 American formations with those of other parts of the world which 

 various authors have confidently assumed. 



It has already been shown that the lower limit of the North 

 American mesozoic must coincide with the lowermost triassic 

 strata in any given section, whether those strata are regarded as 

 representing the earlier or the later trias ; and that no strata hith- 

 erto recognized as Permian can be reasonably referred to the mes- 

 ozoic. That is, the lower limit is defined by a great break in the 

 geological record of this continent, constituting an hiatus, which 

 began before the full completion of paleozoic time and continued 

 until after the beginning of mesozoic time. 



But we are quite unable to designate clearly the upper limit of 

 the mesozoic in at least a large portion of this continent. It is 

 true that in the Atlantic coast region the upper limit of the mes- 

 ozoic is clearly marked where the marine eocene rests upon the 

 uppermost of the cretaceous strata there, but that delimitation is 

 produced by an hiatus. In portions of both the interior and Pacific 

 coast regions, however, it is quite impossible to clearly designate 

 the delimitating boundary between the mesozoic and cenozoic, 

 because in at least a part of both regions no break in either the 

 stratigraphical or paleontological record occurred until after cen- 

 ozoic time was fully established. 



In connection with the foregoing brief summary of the charac- 

 teristics of the North American mesozoic, certain views have been 

 expressed which I entertain in common with some, but not all, 

 other geologists concerning the correlation of formations and the 

 inter-relation of presumably contemporaneous fossil faunas and 

 floras. The following propositions are offered as the basis of 

 those views. A part of them, however, will not be questioned 

 by any geologist, but these are given with the others for the sake 

 of relevancy. 



(i) In accordance with the principles of modern biology, we 

 must conclude that, although it has not been demonstrated by 

 actual discovery, there has been a continuous genetic succession of 

 living organisms upon the earth ever since life began ; that is, 

 while numerous breaks in that succession have occurred, they have 

 never been of universal, but only of local or regional extent, and 

 they have been due to similarly restricted physical changes. 



(2) The record of that succession of living organisms has been 

 accomplished and preserved by the natural entombment of their 

 fossilizable remains in aqueous sedimentary deposits. Subsequent 

 physical changes have destroyed or rendered inaccessible a large 

 part of the record, and all we know of that succession is derived 

 from such of those remains as we have been fortunate enough to 

 discover. 



(3) The record of the succession of terrestrial life has been far 

 less complete, and has suffered greater interruptions, than that of 

 aqueous Hfe, because the record of the former has been made un- 

 der conditions which were irrelevant or inimical to that life, and 



