312 GEOLOGICAL SURVEY OF THE TEEEITOEIES. 



ize our Tertiary, even to the same latitude of 48°. South, in tlie Mis- 

 sissippi Tertiary, the palms appear with more trojiical forms, or with 

 the pinnately divided fronds of Galamopsis. Other genera represented 

 in warmer regions — Lygodium, Ficus, Latirus, &c. — have no species in the 

 arctic flora, and of our nineteen Tertiary species of oaks three only are 

 indicated in the Greenland flora, Quercus Drymeja, Q. Laharpi, Q. Lyellii, 

 all common to the whole extent of the Tertiary formations. One species 

 of Magnolia, described in the Arctic Flora, appears like an exception to 

 the general rule of geographical distribution of plants, according to 

 climate, as in the Tertiary strata of Mississippi five well characterized 

 species of this genus have been discovered, while there is but one as yet 

 from the northwestern Tertiary. This is probably the result of the 

 peculiar distribution observed at our time for species of magnolias. They 

 live generally gTouped in small areas, often at great distances from each 

 other, and without apparent regard to climatic circumstances. Though 

 I have traveled nearly over the whole extent of the coal-basin of Penn- 

 sylvania, I never met magnolias but on Silvery liock Creek, in the 

 upper part of Butler County, where there is in the bottom of the creek 

 a group of one dozen or more of large trees of this species. The same 

 kind of grouping of these fine trees is remarked in Kentucky and Ten- 

 nessee. 



The Tertiary species common to the flora of both the arctic and the 

 North American Tertiary seem to indicate for the plants of this formation 

 a wider range of distribution than ours have now. But it is not neces- 

 sary to admit that the whole Tertiary land now known on our continent 

 was occupied at the same time by the same class of vegetation. These 

 so-called Tertiary formations may have been in progress at different 

 places during a long period of time, and the land-surface successively 

 invaded by vegetation. Supposing a slow upheaval of the Tertiary land, 

 beginning at the north, with there a relative lowering of temperature, 

 the plants of that region may have by slow degrees migrated south- 

 ward and been introduced upon a more recently emerged land of the 

 same epoch. Even without admitting this hypothesis, which cannot be 

 here suf&ciently developed, and which is not as yet sustained by positive 

 evidence, a comparative wide range of distribution is remarked at our time 

 for some species related to those of our Tertiary. For example, Mag- 

 nolia, Lyriodendron, Liquid amhar, seen as high as the 41° and 42° ot 

 latitude north, descend to South Florida, a difl'erence of about 15°. 

 More common species, especially those which generally inhabit the 

 swamps and bogs, like Prunus Americana, Amelancliier Canadensis, Yac- 

 cinium corymbosum, range from Middle Florida to the northern shore of 

 Lake Superior, on more than 20° of latitude. The same range may be 

 assigned to Acer saccharinum, Quercus rubra, Fagus ferruginea, Corylus 

 Americana, Juniperus Virginica, all species intimately related to species 

 of our Tertiary. The average of latitude of the Tertiary deposits, wliere 

 the Greenland leaves, described by Heer, were obtained, is 70° north. 

 We may place the average latitude of the North American Tertiary, at 

 least for Dr. Hayden's plants, at the 45°. This is 25° of latitude for the 

 distribution of some species of wide range of the Tertiary, a difference 

 of 5° only in comparing this distribution with that of our living plants, 

 and which is easily accounted for by the evenness of the land, together 

 with the greater atmospheric humidity and more uniform climate of the 

 northern hemisphere at tha tertiary epoch. This fact is rendered evident 

 by the great deposits of coal of that formation. 



The land connection of Greenland, Spitzbergen, &c., with our continent 

 during the Tertiary period seems attested by the distribution of the 



