36 SIE J. W. DAWSON ON FOSSIL "WOODS FROM 



in diseutaugliug the nomenclature of the plants and fixing their geological age, is of the 

 greatest value, and shows how liable the palteobotanist is to fall into error in determining 

 species from imperfect specimens. Our American species, no doubt, require some revision 

 in this respect. 



I have, also, while writing out the above notes for publication, received the paper of 

 same author on the Eocene beds of Ardtun, in Mull, and am fully confirmed thereby in the 

 opinion derived from the papers of the Duke of Argyll, and the late Prof E. Forbes,' that 

 the Mull beds very closely correspond in age with the Laramie. The Filicites Hebridica, of 

 Forbes, is our Onodea sensibilis. The species of Ginkgo, Taxus, Sequoia and Glyptostrobus cor- 

 respond, and we have now probably found a Podocarpus, as noted above. The Platanites 

 Hebridica is very near to our great Platanus nobil.is. Cori/lus Macquarrii, is common to both 

 formations ; as well as Populus arctica, and P. Richardsoni while many of the other exogens 

 are generically the same, and very closely allied. These Ardtun beds are regarded by 

 Mr. Gardener as Lower Eocene, or a little older than the Gelindeu series of Saporta, and 

 nearly of the same age with the so-called Miocene of Atanekerdluk, in Greenland. Dr. G. 

 M. Dawson and the writer have, ever since 18*75, maintained the Lower Eocene age of our 

 Laramie, and of the Fort Union group of the Northwestern United States, and the 

 identity of their flora with that of Mackenzie Eiver and the upper beds of Greenland, and 

 it is very satisfactory to find that Mr. Gardener has independently arrived at similar con- 

 clusions with respect to the Eocene of Great Britain. 



An important geological consequence arising from this is, that the period of warm 

 climate, which enabled a temperate flora to exist in Greenland, was that of the later Cre- 

 taceous and early Eocene, rather than, as usually stated, the Miocene. It is also a question 

 admitting of discussion whether the Eocene species of latitudes so different as those of 

 Greenland, Mackenzie Eiver, N. "W. Canada and the Western States, were strictly contem- 

 poraneous, or successive within a long geological period in which climatal changes were 

 gradually proceeding. The latter statement must apply at least to the beginning and close 

 of the period ; but the plants themselves have something to say in favour of contempora- 

 neity. The flora of the Laramie is not a tropical but a temperate flora, showing no doubt 

 that a much more equable climate prevailed in the more northern parts of America than at 

 present. But this equability of climate implies the possibility of a great geographical 

 range on the part of plants. Thus, it is quite possible, and indeed highly probable that, 

 in the Laramie age, a somewhat uniform flora extended from the Arctic seas through the 

 great central plateau of America, far to the south, and in like manner along the western 

 coast of Europe. It is also to be observed that, as Gardener points out, there are some differ- 

 ences indicating a diversity of climate between Greenland and England, and even between 

 Scotland and Ireland and the South of England, and we have similar differences, though 

 not strongly marked, between the Laramie of Northern Canada and that of the United 

 States. When all our beds of this age, from the Arctic sea to the 49th parallel, have been 

 ransacked for plants, and when the palœobotanists of the United States shall have suc- 

 ceeded in completely unravelling the confusion which now exists between their Laramie 

 and the Middle Tertiary, the geologist of the future will be able to restore with much 

 certainty the distribution of the vast forests which, in the early Eocene, covered the now 



' Journal of the Geol. See, London, vol. vii. 



