Below this, there is found in Greenland a nearly related species, the _S. ambigua_, Hr., of which the leaves are shorter and broader, and the cones round and somewhat smaller.
The connecting link between _S. Smithiana_ and _Reichenbachii_ is formed by _S. subulata_, Hr., and _S. rigida_, Hr., and three species (_S. gracilis_, Hr., _S. fastigiata_ and _S. Gardneriana_, Carr.), with leaves lying closely along the branch, and which come very near to the Tertiary species _S. Couttsiæ_. We have therefore in the Cretaceous quite an array of species, which fill up the gap between the _S. sempervirens_ and _gigantea_, and show us that the genus Sequoia had already attained a great development in the Cretaceous. This was still greater in the Tertiary, in which it also reached its maximum of geographical distribution. Into the present world the two extremes of the genus have alone continued; the numerous species forming its main body have fallen out in the Tertiary.
If we look still further back, we find in the Jura a great number of conifers, and, among them, we meet in the genus Pinus with a type which is highly developed, and which still survives; but for Sequoia we have till now looked in vain, so that for the present we can not place the rise of the genus lower than the Urgonian of the Cretaceous, however remarkable we may think it that in that period it should have developed into so many species; and it is still more surprising that two species already make their appearance which approach so near to the living _Sequoia sempervirens_ and _S. gigantea_.
Altogether, we have become acquainted, up to the present time, with twenty-six species of Sequoia. Fourteen of these species are found in the Arctic zone, and have been described and figured in the "Fossil Flora of the Arctic Regions." Sequoia has been recognised by Ettingshausen even in Australia, but there in the Eocene.
This is, perhaps, the most remarkable record in the whole history of vegetation. The Sequoias are the giants of the conifers, the grandest representatives of the family, and the fact that, after spreading over the whole northern hemisphere and attaining to more than twenty specific forms, their decaying remnant should now be confined to one limited region in western America and to two species constitutes a sad memento of departed greatness.[DJ] The small remnant of _S. gigantea_ still, however, towers above all competitors, as eminently the "big trees "; but, had they and the allied species failed to escape the Tertiary continental submergences and the disasters of the glacial period, this grand genus would have been to us an extinct type. In like manner the survival of the single gingko of eastern Asia alone enables us to understand that great series of taxine trees with fern-like leaves of which it is the sole representative.