704 GEOGKAPHICAL AND GEOLOGICAL BOTANY. 



eluding ^Sequoias, Taxodium distichum, Abies excelsa, Common Spruce, 

 Salisburias, Oaks, Planes, Poplars, Elms, Birch, Maples, Walnuts, Magno- 

 lias, Andromeda, Viburnum, Zamia, Vines, Ivies, Ferns, and many others, 

 more or less correctly referred to existing generic types, but, in any case, 

 affording evidence of a subtropical or warm temperate climate. It is 

 conceivable, then, that the plants of the Miocene epoch, so many of 

 which are of American types, started from Greenland and were dispersed 

 throughout Europe, Asia, and America. linger and Heer supposed that 

 the plants might have migrated from America to Europe by way of a now 

 sunken continent, the Atlantis of Plato, the position of which is marked 

 by the accumulations of Sargasso Weed. The presence of American 

 genera, Clethra &c. in Madeira, has already been alluded to with re- 

 ference to this view. Asa Gray and Oliver, however, consider that the 

 existing evidence is more favourable to a migration from America through 

 Asia to Europe ! 



Pleiocene Flora. The Dicotyledons predominate, and are most varied, 

 as in existing vegetation; the Monocotyledons are rare; and the Pal- 

 macese of the preceding epochs are wanting. The general analogy of the 

 flora is with those of the temperate and warmer regions of Europe, North 

 America, and Japan at the present day. According to the determinations 

 made by palaeontologists, many existing genera are represented, such as 

 Glyptostrobus, Taxodium, Salisburia, Cyperacese, Comptonia, Thymelacese, 

 Santalaceae, LauraceEe, Liqnidambar, Nyssa, Robinia, Gleditschia, Bauhinia, 

 Oassia, Acacia, Rhus, Juglans, Ceanothus, Cclastrm, Sapindus, Lirioden- 

 dron, Cappari*, Sideroxylon, Achras, Symphcos, Cornacere, Myrtaceae, 

 Pomaceae, Tiliaceas, Magnoliaceae, &c. This list includes especially 

 modern North-American genera, which existed at that time in Europe. 

 Quercus, Ace?', &c. appeared then as now. 



Pleistocene Deposits. The glacial drift and the diluvial deposits be- 

 longing to this group afford hardly any recognizable vegetable remains, 

 beyond fragments of fossil wood of Coniferae, met with occasionally in 

 connexion with the bones of extinct Mammalia and in a few Lignite 

 beds. 



The flora of the Glacial period still exists in Alpine districts. 



4. Floras of Early Formations of the present Geological Period. 



The formations referable to this group consist chiefly of freshwater 

 calcareous deposits (tufa), the older peat-bogs, and forests now buried or 

 submerged beneath the sea. 



The remains existing in calcareous tufa have not yet been well inves- 

 tigated, partly because the beds are not greatly developed in most 

 countries, and partly because they usually contain only casts of vege- 

 table structure, produced through incrustation. As far as we know, the 

 plants are similar to those of the existing floras of the regions, with a 

 lew exceptions. 



The old peat-bogs, especially of Northern Europe, often contain vast 

 quantities of recognizable vegetable remains, belonging to species no 

 longer growing in the same spots, but found further south, as remains of 

 Corylus, Pinus picea, &c. in the Shetland Islands, of Oaks, Maples, Limes, 

 Ash, &c. in Sweden, beyond the present limits of those plants. 



