_The wider the ancient glacier, the wider the corresponding gap in the Sequoia belt_.
Finally, pursuing my investigations across the basins of the Kaweah and Tule, I discovered that the Sequoia belt attained its greatest development just where, owing to the topographical peculiarities of the region, the ground had been most perfectly protected from the main ice-rivers that continued to pour past from the summit fountains long after the smaller local glaciers had been melted.
Taking now a general view of the belt, beginning at the south, we see that the majestic ancient glaciers were shed off right and left down the valleys of Kern and King's rivers by the lofty protective spurs outspread embracingly above the warm Sequoia-filled basins of the Kaweah and Tule.

Then, next northward, occurs the wide Sequoia-less channel, or basin, of the ancient San Joaquin and King's River _mer de glace_; then the warm, protected spots of Fresno and Mariposa groves; then the Sequoia-less channel of the ancient Merced glacier; next the warm, sheltered ground of the Merced and Tuolumne groves; then the Sequoia-less channel of the grand ancient _mer de glace_ of the Tuolumne and Stanislaus; then the warm old ground of the Calaveras and Stanislaus groves.

It appears, therefore, that just where, at a certain period in the history of the Sierra, the glaciers were not, there the Sequoia is, and just where the glaciers were, there the Sequoia is not.
What the other conditions may have been that enabled Sequoia to establish itself upon these oldest and warmest portions of the main glacial soil-belt, I cannot say.

I might venture to state, however, in this connection, that since the Sequoia forests present a more and more ancient aspect as they extend southward, I am inclined to think that the species was distributed from the south, while the Sugar Pine, its great rival in the northern groves, seems to have come around the head of the Sacramento valley and down the Sierra from the north; consequently, when the Sierra soil-beds were first thrown open to preemption on the melting of the ice-sheet, the Sequoia may have established itself along the available portions of the south half of the range prior to the arrival of the Sugar Pine, while the Sugar Pine took possession of the north half prior to the arrival of Sequoia.
But however much uncertainty may attach to this branch of the question, there are no obscuring shadows upon the grand general relationship we have pointed out between the present distribution of Sequoia and the ancient glaciers of the Sierra.

And when we bear in mind that all the present forests of the Sierra are young, growing on moraine soil recently deposited, and that the flank of the range itself, with all its landscapes, is new-born, recently sculptured, and brought to the light of day from beneath the ice mantle of the glacial winter, then a thousand lawless mysteries disappear, and broad harmonies take their places.
But although all the observed phenomena bearing on the post-glacial history of this colossal tree point to the conclusion that it never was more widely distributed on the Sierra since the close of the glacial epoch; that its present forests are scarcely past prime, if, indeed, they have reached prime; that the post-glacial day of the species is probably not half done; yet, when from a wider outlook the vast antiquity of the genus is considered, and its ancient richness in species and individuals; comparing our Sierra Giant and _Sequoia sempervirens_ of the Coast Range, the only other living species of Sequoia, with the twelve fossil species already discovered and described by Heer and Lesquereux, some of which seem to have flourished over vast areas in the Arctic regions and in Europe and our own territories, during tertiary and cretaceous times,--then indeed it becomes plain that our two surviving species, restricted to narrow belts within the limits of California, are mere remnants of the genus, both as to species and individuals, and that they probably are verging to extinction.