found to characterize the European formations is found in the Cretaceous series of the valley of the Upper Missouri river. Here we have a series of strata which has been held to represent the European Cretaceous series from the Gault to the Upper Chalk, inclusive. In the lower division of this American series there has long been known to exist a flora which, when it was first discovered, was referred by the best authority to the age of the Eocene Tertiary. Even so late as the past year, Mr. J. Starkie Gardner has expressed the opinion that these plants are more likely to be of Eocene age than earlier. Now the strata containing this assumed Tertiary flora are overlaid by a series, several thousand feet in thickness, which contains an abundance of marine types that correspond with those of the Cretaceous of Europe. Indeed, several of the species are regarded as identical; and the types embrace reptiles, fishes, and cœlenterata, as well as all the classes of mollusca. Then, resting upon this series, and its Atlantic border equivalent, we find the whole Tertiary series, at least up to the close of the Miocene. Furthermore, a considerable number of these American Tertiary forms are usually regarded as identical with European Tertiary species. It would thus seem that both the stratigraphical and concurrent paleontological evidence are decidedly against the Tertiary age of that flora, and in favor of its Cretaceous age, notwithstanding its homotaxial relationship to the Tertiary flora of Europe.

The commingling of types in one formation which, in Europe, respectively characterize two or more separate formations, is a matter of not uncommon occurrence in America and other parts of the world. These cases occur where the order of the formations seems to agree well with that of the accepted European standard; and they apparently merely show that the types referred to began their existence earlier, or continued it later, as the case may be, than they were known to have done in Europe. In the other cases the discrepancies are seen to occur as between marine faunas on the one hand, and land faunas and floras on the

other; and those discrepancies amount to an actual reversion of the usual order. In the cases which I shall now mention, however, the discrepancies consist in either the actual or relative earlier introduction, or later continuation, of certain types among both marine and continental faunas and land floras, than is required by the European standards. In these latter cases there is of course a confusion of homotaxial relationship, of the formations which contain the commingled types, with other formations; but there is not necessarily any reversion of the order of occurrence of the types, as there is in the cases already mentioned.

I ought not in this connection to omit mention of the so-called colonies of Barrande, in Bohemia, which, as he contended, bear a marine Silurian fauna, alternating with strata which bear a Primordial one. But as the truth of Barrande's position has been seriously questioned, I need not discuss it in these remarks.

Even after what we have seen of the history of the received opinions concerning the synchronism of formations, it is still a somewhat remarkable fact that, although the blending of the faunas of certain formations into each other by the commingling of types, which are regarded as characteristic of each respectively, has been so long known and so often demonstrated, that the idea of universal restriction of types to narrow time-horizons should be so persistently held. Indeed, the fact that such a commingling of types as I have referred to has been so well recognized that it has made its impress upon the terminology of geology. Thus the term Permo-Carboniferous has long been used in America to designate strata which partake of both Coal-Measure and Permian characteristics; and the same term has been applied by Dr. Toula to strata which bear a similar fauna on the island of Spitzbergen.

The terms Cretaceo-Jurassic and Cretaceo-Tertiary have been respectively applied to New Zealand strata for obvious reasons. The former term has also been applied to Chilian strata by Darwin; and the latter, (but erroneously, I think.) to the Lara

mie Group of our own country. Mr. Gardner would even extend the application of this latter term so as to embrace all that series of strata from the Dakota Cretaceous to the Laramie Group, inclusive. These terms, and the instances I have given of their application, are quite sufficient to show the existence of the facts to which I have called your attention. But the following instances of the early introduction and late continuance of certain important types are of especial interest in this connection.

From strata in Northwestern Punjab, India, which are by all geologists admitted to be of Carboniferous age, a remarkable collection of fossils was made which contained specimens of a species of Ammonites. Upon the announcement of this fact its truth was not only questioned by European paleontologists, but some went so far as to deny the possibility of the association of that genus with a Carboniferous fauna. Afterward the wellknown paleontologist Waagen visited the locality and himself collected there specimens of Ammonites, Ceratites, and Goniatites, all associated together in the same layers with characteristic Carboniferous forms.

That Goniatites should be found in Carboniferous strata was to have been expected; but if the Ceratites and Ammonites had been found separately and unassociated with any other fossils, no European paleontologist would have hesitated to refer the one to the Triassic, and the other to the Cretaceous. In fact, Dr. Waagen has placed the Ammonite referred to under a generic group which is an especially characteristic one among Cretaceous faunas. This instance of the commingling of types which are characteristic of different periods is a remarkable one in all respects, and especially as showing the very early differentiation of even subgeneric forms, which are generally believed not to have existed until a much later period. Confirmatory of the fact of this introduction before the close of the Paleozoic age, of types which are especially characteristic of the Mesozoic, Professor Heilprin has announced the discovery of an Ammonitic form among a characteristic Carboniferous fauna from Texas.

The commingling in New Zealand strata of types which are usually found to characterize separate formations has already been referred to, but in this connection I also wish to mention the reported discovery in those islands of Belemnites, Belemnitella, and Plesiosaurus in strata which have usually been classed as Tertiary. There seems to be little reason to doubt that this is an instance of a natural transition from the Cretaceous to the Tertiary, so gradually accomplished that it cannot be said where the one ends and the other begins.

A similar survival of Mesozoic types into an epoch, the strata of which bear otherwise the fullest evidence of homotaxial relationship to the Eocene Tertiary, occurs in California. Here there is found a species of Ammonite associated with numerous genera which all paleontologists have agreed in regarding as characteristic of the Tertiary. The series of strata which contains this belated Ammonite is some ten thousand feet in thickness, the lower part of which is homotaxially related to the Cretaceous, and the upper part is similarly related to the Tertiary, with the exception just mentioned. Still, this series of strata has every appearance of having been produced by continuous sedimentation, and of presenting an intercommingling of Cretaceous and Tertiary types through the greater part, if not the whole, vertical range of the series.

In the cases which have just been mentioned, the continuation of ancient types among those of later origin, or of more modern characteristics, the comparison was made between the different members of one and the same fauna for the different portions of its existence; but in the case now to be considered, the comparison is to be made between continental faunas and floras. The case referred to is that of the Laramie Group. It will be remembered that in my address before this society last year I made some extended remarks upon this group, showing that it was deposited in a great inland sea of brackish and fresh waters. Comparison, therefore, is to be made between the aqueous fauna

of such a sea, and the land fauna and flora which existed upon its borders. I have upon several occasions called attention to the fact that brackish and fresh-water faunas have undergone far less differentiation during the lapse of geological epochs than marine faunas have. I cannot now contrast the aqueous fauna of the Laramie Group with any open-sea fauna, but, together with its contemporaneous flora and land molluscan fauna, it contrasts strangely with its contemporaneous land vertebrate fauna.

The aqueous fauna of the Laramie Group is mainly molluscan ; and while the brackish-water forms show their relationship to the preceding Cretaceous marine fauna, the fresh-water and land mollusca are largely of types that now exist. The flora is also of a very modern character; but the vertebrate land fauna is largely Dinosaurian. I need not tell a paleontologist that here is a most remarkable mixture of types. The extraordinary biological character of this group will be still more conspicuously seen when I mention that I have collected the characteristic mollusca of this group where they were associated with Dinosaurian remains; and in the same series of layers I have also obtained numerous species of plants, several of which have by competent authority been identified with European Miocene species, and two of them with species now living in the United States. That is, we have evidence that a large molluscan fauna, and a luxuriant dicotyledonous flora, both containing species that we can with difficulty, if at all, distinguish from living forms, existed contemporaneously with great Dinosaurian reptiles such as have always been regarded as peculiar to the Mesozoic age.

The instances which I have presented demonstrate that in different parts of the world there are many and material departures from the European paleontological standard; but in no case have we seen that departure to be so great when marine formations are compared with each other as they are when formations containing a marine fauna are compared with those containing a continental fauna or flora. I therefore quite agree with those