1879. | Distribution of the.North American Flora. 167 
notice; they are those giants of the vegetable kingdom, the 
Sequoias, the red-wood (S. sempervirens), and the “ big-tree” or 
“Wellingtonia ” (S. gigantea). 
The fossil remains of these trees, or species most ahosely allied to 
them, are found in Miocene beds in high latitudes all round the 
globe; in Vancouver’s island, Sitka, on the arctic American sea- 
ceast, in Greenland, Spitzbergen and in arctic Asia, &c. The 
genus, therefore, which first appeared in the Cretaceous times,’ 
was undoubtedly a member of that mixed Americano-Asiatic 
flora that was driven southward during the Glacial period. The 
genus is now confined to Western North America, and to the two 
above-named species, but it is represented in Eastern America by 
the very closely allied genus Taxodium, and in Eastern Asia by 
Glyptostrobus, 
The distribution of the two Sequoias is most instructive. The 
red-wood forms a dense narrow forest tract for about five hundred 
miles, skirting the ocean, along whose warmer shore it crept 
northward after the Glacial epoch. It rivals in height its sister of 
the Sierra, and attains an enormous girth and age, though I can 
find no account of any attempt having been made to estimate its 
age. 
The S. gigantea, or “big-tree” (the Wellingtonia of British 
gardens), again, is a plant of a cooler climate; and hence, having 
survived the glacial cold, was enabled to establish itself in the 
Sierra Nevada under certain very restricted conditions. It extends 
at intervals along the western slope of the Sierra to a little north 
and south of the parallels of 36° and 38° N., that is, for nearly 
two hundred miles in a north-west and south-east direction, at 
elevations of five thousand to eight thousand feet above the sea. 
Towards the north the trees occur as very small, isolated, remote 
groves of a few hundreds each, most of them old and interspersed 
amongst gigantic pines, spruces and firs, which appear as if 
encroaching upon them; such are the groves visited by tourists 
(Calaveras, Mariposa, &c.). To the south, on the contrary, the 
big-trees form a colossal forest, forty miles long and three to 
ten broad, whose continuity is broken only by the deep sheer- 
walled cafions that intersect the mountains ; here they displace all 
other trees, and are described as rearing to the sky their massive 
_ towns; whilst seen from a distance the forest presents the appear- 
ance of green waves of vegetation, gracefully following the com- 
