while the parallels between Europe and America, or the ancient Palearctic and Nearctic Regions, have been discussed by GERVAIS, LEIDY, COPE, FILHOL, SCOTT, V. ZITTEL and SCHLOSSER. LYDEKKER has broadly covered the whole field in his Geographical History of Mammals.

It may seem remarkable that a nearctic palæontologist should enter the palæarctic field, as the herald of a conference and agreement upon common usage of terms, but I make no apology because the matter arose from necessity rather than choice; several years ago the discovery of some new types of rhinoceroses in this country directed my attention afresh to the study of the Tertiary fauna of Europe as parallel with that of America, in the succession of European and American types it appeared that there were most interesting similarities between rhinoceroses as widely separated as the present regions of Colorado and southern France, but upon attempting more than a general comparison I was confronted by a lack of definite time scale between the levels in which these animals occur. The available correlations by COPE, FILHOL, SCOTT, V. ZITTEL and others proved too indefinite at certain points. This difficulty became so obstructive that a more exact correlation of European and American horizons appeared to be an essential basis not only for the phylogeny of the rhinoceroses but for that of other types of mammals of Europe and North America. We need a unified old world system as a starting point for comparison. As a matter of fact there is even at the present moment no consensus of opinion or common usage among palæarctic palæontologists as to the larger divisions of the Tertiary.

The Trial Sheets:-As an initial step towards a more exact correlation I offer here a provisional classification of the Tertiary of Europe with critical discussion of the reasons for placing the larger division lines at certain points, also a comparison chiefly with the Eocene of America, both accomplished with as much aid from workers past and present as could be mustered. This classification probably contains many errors, some of them, perhaps, of a gross description. As I freely criticise and differ from some of my colleagues, I trust they will

freely criticise, correct and expand this preliminary parallel and the methods of attack here advocated. Realizing that an acceptable working basis could only be secured by coöperation I drew up in 1897 a Trial Sheet of the Typical and Homotaxial Tertiary Horizons of Europe' and circulated it abroad for criticism. This proved to be a rather faulty trial; extremely valuable corrections and additions were received, especially from my friends Professor GAUDRY, Professor v. ZITTEL, Professor DEPÉRET and Doctor SCHLOSSER, Madame PAVLOW, Doctor BOULE, and Mr. R. LYDEKKER. These criticisms were embodied in a Second Trial Sheet' which was issued about April 15, 1898. This sheet was used as a basis for further personal discussion with the above palæontologists, also with Professor LEPSIUS of Darmstadt, Doctor FORSYTH MAJOR of the British Museum and others. In course of a tour in foreign museums, I was greatly aided by many other critics, and made also numerous observations of my own which bear upon the Holarctic parallels. A 'Third Trial Sheet' is issued in connection with this address; it is probably more accurate than its predecessors but it is still lacking both in the desired exactness and fullness. The closer comparison of the post-Eocene divisions of the Tertiary fauna of Europe and North America must be deferred for a full report which is in preparation.

I. AVAILABLE EVIDENCES OF PARALLELISM Among the tests of approximate synchronism of deposition. in the Nearctic and Palæarctic regions are the following:

1. COMMON GENERA AND SPECIES: the presence of identical or closely allied genera and species. This time honored and obvious basis of comparison is now rendered most difficult by the diversity of usage in generic and specific definitions.

2. SIMILAR STAGES OF EVOLUTION: the similarity in the stage of development of allied phyla, as expressed in the pattern of the molar teeth, in the transformation of the premolar teeth, complication of the molar teeth, in the reduction of digits, etc. This test of synchronism is comparatively novel. For example, the remarkably definite transformation of the fourth

premolar of the Plagiaulacida or of the premolars of the Perissodactyla afford certain very exact data for correlation purposes.

3. SIMULTANEOUS INTRODUCTION OF NEW FORMS: the sudden appearances in both Nearctic and Palearctic regions of types which have no known ancestors in lower horizons and have apparently originated elsewhere, either in Africa or in South America. The value in chronology of these immigrations has not been fully recognized.

4. PREDOMINANCE OF CERTAIN TYPES: the predominance or spread of certain types as of the Perissodactyla in the Middle Eocene, or of the Artiodactyla in the Upper Eocene and Oligocene are in the nature of supplementary evidence.

5. CONVERGENCE AND DIVERGENCE OF PALEARCTIC AND NEARCTIC FAUNE: far closer than in any known Tertiary or Quaternary stage, were the relations existing in the Holarctic region during the Upper Jurassic period. The resemblances among these minute mammals, as found in the Purbeck of England and the Como beds of Wyoming are most astonishing, for of thirteen genera, six have their English counterparts, and the family characters are very close as regards the remainder. (See OSBORN, '88, pp. 186-7.) It would be rash to say whether or not continuous close geographical connections existed from the Jurassic throughout the Cretaceous, but in the next Nearctic and Palearctic parallels which we can draw, namely in the Basal Eocene between the Torrejon of New Mexico and the Cernaysien of France, the resemblances are again very close. During the Upper Eocene the faunal parallels became decidedly less close, in fact the correlation can only be established by relatively few forms. In the lower Oligocene the faunal relations. suddenly became again much closer between the old and new worlds and they remained close throughout the later Tertiary until the middle of the Pleistocene period.

II. CLASSIFICATION OF THE EUROPEAN TERTIARY Invertebrate palæontologists have naturally taken the leadership in the classification of the old world Tertiary, their vertebrate confrères having followed, adapted and modified the system.

Without question the final classification will be by a synthesis of evidence derived from invertebrate and vertebrate remains, from the comparison of marine, fresh water and terrestrial forms of life with each other and with earth movements. In numerous instances the exclusive use of one class of evidence has led to serious errors.

The great faunal Periods or Systèmes, Eocene, Miocene, Pliocene, and Pleistocene we owe to LYELL. The Oligocene was proposed by BEYRICH ('54, pp. 640-666), chiefly on geological grounds, and although confirmed by the Berlin Geological Congress some doubts are entertained as to its ultimate utility and survival.

D'ORBIGNY, divided the Eocene into the lower (I) Suessonien, in which we find fossil mammals deposited chiefly north of Paris around the Suessonien gulf, and the upper (II) Parisien in which the deposits are chiefly around Paris and in the Helvetien canal of the south of France and Switzerland.

The stages and substages of the palæarctic Tertiary employed in the Third Trial Sheet, are chiefly the proposals of MAYER-EYMAR ('89), D'ORBIGNY, DUMÉRIL, SUESS, and LAPPARENT ('85)-all invertebrate palæontologists. The history or authorship and synonymy of the Étages, Montien, Thanétien, Suessonien, etc., may be found in the two palæogeographical essays by MAYER-EYMAR ('89, p. 26), and CANU ('95, pp. 53-56), in which a reclassification of the entire Tertiary is advocated upon the hypothesis of the relation between the perihelions of the globe and the sedimentary substages, as shown in the Tableau 1, of CANU ('95, pp. 12-13). For the purposes of the mammalian palæontologist however, the Lyellian system is more convenient.

Valuable tables of European faunal parallels are given by V. ZITTEL ('93). The fullest lists of European mammals in different horizons are those collected by SCHLOSSER ('87-'90) and DEPÉRET ('85-'95) in his memoirs on the Miocene and Pliocene. A mine of wealth for an investigation of this kind is SCHLOSSER'S Literaturbericht ('83-'97); the writer has referred to it constantly and can hardly express his indebtedness.

TROUESSART'S ('97) Catalogus would have been far more valuable if localities had been cited as well as the geological divisions.

The first step is to ascertain how far the Periods or Systèmes can be paralleled in America and Europe and similar permanent limits placed between them. The second is to establish, as convenient divisions of each, Upper, Middle, Lower, or Lower and Basal. It is not too much to hope that the synchronism of these periods in the entire Holarctic region during the Tertiary can be established with considerable exactness. The Stages and Substages present much greater difficulty and may prove impossible owing to the absolute independence of the earth movements which caused them in the old and new worlds. It is perfectly evident that the overlapping of these deposition stages would be the rule and that exact synchronism would be largely coincidence and therefore highly improbable. All that we can reasonably hope to establish in the near future is an approximate parallelism of the Stages; ultimately the lines of overlap may be determined.

III. COMPARISON OF THE EOCENE IN EUROPE AND

AMERICA

1. The Puerco without a Faunal Parallel

The base of the American Eocene is the Puerco, which has been observed by COPE and WORTMAN to immediately overlie the upper Cretaceous in northern New Mexico.

Contrary to the prevailing opinion and usage there is in Europe no known fossil mammal deposit parallel to the basal Eocene or Puerco of America. The Puerco fauna proper is

older than the oldest in Europe.

We may therefore provisionally conclude that the fresh water Puerco deposits were approximately of the same age as the earliest marine and brackish limestones of the Suessonien Sea, namely, the Montien (Calcaire grossier de Mons, Belgium), or marls, Heersien, (Marnes de Heers), Maudunien (Marnes de Meudon), all resting unconformably on the Cretaceous.