Ch. XV.] THEORY OF A MIOCENE ATLANTIS. 275 



are common to Miocene Europe and to the living flora of America, 

 and that this is more especially true of those closely-allied or homo- 

 logous species which are known by their fruits as well as their leaves, 

 the force of his argument will be fully appreciated by all who believe 

 that each species has had a single birthplace, or has been formed in 

 one limited geographical area from which it may have migrated to 

 distant parts ; for Heer supposes the homologous living species to be 

 the hereditary descendants of their closely-allied Miocene progenitors. 

 But when the reasoning is founded on plants which have only a 

 generic connection, as in a great part of Heer's work, and everywhere 

 throughout the essay of Professor Oliver, its force depends on the 

 previous assumption that, not only the individuals of a species, but 

 also the different species of a genus, have radiated from certain geo- 

 graphical areas which constituted the original starting-points of such 

 genera. This is not the place to enter into a question so difficult and 

 unsettled as that of the origin of species, but whether we adopt or re- 

 ject the doctrine of transmutation, it is necessary to bear in mind, 

 when we compare the recent and fossil flora and endeavor to ascertain 

 whether the miocene plants came to Europe by a western or eastern 

 route, that a single identical or very closely-allied species is of more 

 value than a great many genera represented by species not closely 

 allied. Thus, for example, Heer considers the walnut-tree of QEningen 

 called Juglans bilinica to be homologous with the living American 

 hickory, Juglans nigra, and that another Upper Miocene walnut of 

 Europe, Juglans vetusta, is homologous with our common walnut, 

 J. regia, which was first brought into Europe from Persia. "When, 

 therefore, the Swiss Professor founds on the one an argument in favor 

 of a migration across an Atlantic continent for the Miocene walnuts 

 of Switzerland, and Professor Oliver founds on the other an Asiatic 

 route for the same, their reasoning is logical and its cogency is great 

 in proportion to the identity or very near affinity of the fossil and 

 recent plants which are compared. But several other Tertiary wal- 

 nuts of Switzerland have a comparatively remote bearing on the ques- 

 tion of a Miocene Atlantis, because Juglans, as a genus, flourished in 

 Europe in the Eocene, and even, according to Goppert, in the antece- 

 dent Cretaceous period. Some, therefore, of the Miocene species of 

 Juglans may have come from indigenous European Eocene, or even 

 Cretaceous ancestors ; and the same remark applies to a great number 

 of the genera of other orders and classes which are common to the 

 Miocene flora of Europe and to older tertiary rocks. Thus eight out 

 of 232 fossil species of Monte Bolca, a locality where the rocks belong 

 to the ISTummulitic or Middle Eocene period, pass up into the Miocene 

 formations, according to Massalongo and Heer.* 



The Proteacese also abounded in the Eocene strata of England, France, 



O 7 7 



and Italy, and in the cretaceous rocks at Aix-la-Chapelle. To these 

 * Recherches, &c, Heer and Gaudin, p. 79. 



