86 RICHTHOFEN — NATURAL SYSTEM 
accumulation of Paleozoic and Mesozoic sediments, and the subsequent denudation of 
these, though grand in the extreme, has only been sufficient to expose to view the 
ancient granite in some localities, among which we mentioned that on the Colorado 
River. Other masses of ancient granite are visible at the surface in numerous places in 
the Great Basin, but their exact relations still remain to be determined, while in the 
Rocky Mountains they are one of the prominent features, partaking largely in their 
structure. 
The next period of interest, in regard to the occurrence of eruptive rocks, is that 
of the deposition of Triassic and Liassic sediments in great aggregate thickness, which 
were found by Whitney to extend from the Pacific coast far into the Great Basin. They 
prove that all this country was then still submerged beneath the sea, while the Rocky 
Mountains formed probably a broad belt elevated above it. It is in this period that 
were ejected the quartzose porphyries of the County of Plumas, in northern California, 
almost contemporaneously with those of the southern Alps. Whether this event, which 
was probably not limited to the region mentioned, was attended by any changes in the 
configuration of the surface, cannot yet be decided. After it, however, they must have 
taken place on a grand scale, reminding one of the emergence of the central body of the 
Alps from the sea after the deposition of the infra-Liassic limestones. The ejection of 
granite found, it appears, almost the whole country embraced between the western 
slope of the Sierra Nevada and the eastern slope of the Rocky Mountains lifted out of 
the sea. But changes greater than those which had preceded them, appear to have 
attended and followed those gigantic outbreaks. They were probably due, in a great 
measure, to the intense metamorphism which was connected with them, and has com- 
pletely changed the petrographical character of the preceding sedimentary deposits. 
When the volcanic era commenced, which was probably in the Miocene epoch, all the 
ancient formations of the Sierra Nevada were nearly turned upon their edges, and the 
depressions of the surface in the Great Basin were filled with salt water. But the alti- 
tude of the entire plateau above the level of the sea was probably insignificant at that 
time compared with what it is now, as may be inferred from the fact, that rivers did then 
flow on the present western slope of the Sierra Nevada, parallel to its crest, which they 
could not have done if that slope had had its present inclination. We must imagine 
that where the great mountain range raises now its lofty summits, a hilly country ex- 
tended then, ascending slightly to the east. The first outbreaks of voleanic rocks found 
those rivers still flowing in their beds, as is proved by the higher sediments in the old 
river-channels, which consist of voleanic tufas. But great changes occurred after the first 
commencement of the voleanic era, changes which contributed probably more towards 
imparting tothe western portion of North America its present features than any which 
had preceded them. The voleanic belt extending along the entire western coast of 
America, had its greatest breadth between the coast of California and the Rocky Moun- 
tains, and the eruptive activity has been violent over that vast region. It appears that 
to that era is due the principal part of the elevation of the high table-lands. Such, at 
least, is the case in their western portion. The crest of the Sierra Nevada must have 
been elevated at a quicker rate than its western foot, as distinc. traces are left in the 
gravel deposits that those ancient rivers which were flowing parallel to its crest have 
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