These facts appear, at first sight, to be inconsistent, unless we suppose the climates of Europe and North America to have been widely different in these early times; but they may perhaps be harmonised, on the supposition of a more uniform and a somewhat milder climate then prevailing over the whole Northern Hemisphere; the contrast in the vegetation of these countries {157}being due to a radical difference of type, and therefore not indicative of climate. The early European flora seems to have been a portion of that which now exists only in the tropical and sub-tropical lands of the Eastern Hemisphere; and, as much of this flora still survives in Australia, Tasmania, Japan, and the Cape of Good Hope, it does not necessarily imply more than a warm and equable temperate climate. The early North American flora, on the other hand, seems to have been essentially the same in type as that which now exists there, and which, in the Miocene period, was well represented in Europe; and it is such as now flourishes best in the warmer parts of the United States. But whatever conclusion we may arrive at on the question of climate, there can be no doubt as to the distinctness of the floras of the ancient Nearctic and Palæarctic regions; and the view derived from our study of their existing and extinct faunas--that these two regions have, in past times, been more clearly separated than they are now--receives strong support from the unexpected evidence now obtained as to the character and mutations of their vegetable forms, during so vast an epoch as is comprised in the whole duration of the Tertiary period.