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nent in the Tertiary age was above 50° Fahr, During this period 

 there was a land connection between North America and^ Europe by 

 way of Iceland and the Hebrides, and also with the Asiatic continent 

 by way of Behring Strait. Taking advantage of this opportunity 

 our American flora seems to have marched over and occupied both 

 these continents. In Southern Europe the climate at the beginning 

 of the Tertiary was sub-tropical, and the Indian Ocean communicated 

 with the Atlantic through the Mediterranean. The gradual elevation 

 of the Alps, Pyrenees, etc., during the Tertiary age, resulted in the 

 formation of a barrier which limited the reach of austral influences 

 and gave a temperate climate to the interior of Europe. At this time 

 the American temperate flora descended from the north and occu- 

 pied all Europe ; for we find in the Miocene or Middle Tertiary strata 

 the remains of the deciduous cypress, our magnolias, the tulip tree, 

 sweet gum, sassafras and the American poplars. When the Ice 

 period came on, however, these plants were driven southward but 

 found their retreat cut off" by the Mediterranean, and were thus 

 mostly exterminated. Subsequently, when a milder climate super- 

 vened, the vacant area thus formed was entered and possessed by a 

 flora for the most part of Asiatic origin. In Japan and China, how- 

 ever, our American flora still exists. There is a remarkable similarity 

 between the flora of Japan and that of Eastern America ; many of the 

 species being identical, and others so closely allied that they must 

 have had a common origin. We find, too, in China and Japan some 

 interesting members of our American Tertiary flora, which, once com- 

 mon here, have been by some cause exterminated, while they still 

 exist in Asia. Of these, perhaps the most striking examples are the 

 Salisburia or ginko, a genus well represented in our Cretaceous and 

 Tertiary flora, and the Glyptostrobus, another conifer which was 

 abundant both in Europe and America in the Tertiary age, but, dis- 

 appearing elsewhere, has survived in China. 



I have said that our Tertiary flora was directly derived from the 

 Cretaceous, and was the distinct progenitor of that of the present day. 

 This is strictly true; but, if we may judge by the arborescent plants, 

 our living flora is but a wreck and relic of that which covered our conti- 

 nent before the Ice period. We have already collected from the 

 Tertiary strata in various parts of the country the remains of more 

 specids of forest trees than are now growing on its surface, and yet 

 every vear sees important additions made to the list. Imperfect as 

 is the picture which these fragmentary fossils give us of the Tertiary 

 flora, we find in it an explanation of some facts in the flora of the 

 present day which have long puzzled botanists. For example, our 

 giant trees, the two Sequoias of California, though of enormous size, 

 are confined to very narrow geographical limits, the mammoth tree 

 being restricted to a few groves ; so in our eastern forests the sassa- 

 fras, the sweet gum, and the tulip tree are each a solitary representa- 

 tive of its genus, and it has been a matter of surprise that these noble 

 and striking trees sliould have no living relatives ; but as we turn the 

 pages of the Tertiary herbarium we find each of these genera repre- 

 sented by many species, and the species now living and restricted to nar- 

 row bounds, then having a verv extended range, and existmgin count- 



