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THE JOURNAL OF GEOLOGY.

Peak, beneath whose lavas it disappears, makes it very probable indeed that they are connected with the Ione formation that disappears under the opposite edge of the same lavas bordering upon the eastern side of the Sacramento valley. If this could be definitely established it would show that the northern end of the Sierra Nevada has been elevated 7,000 feet since the gravel period of that region. It is possible that the increased elevation does not extend far to the southward, for beyond the 40th parallel the eastern crest of the range retreats to the escarpment of the main block of which the Sierra Nevada is composed.

In connection with the upheaval of the northeastern portion of the range a fault was formed along the eastern base at least beyond Honey Lake. A short distance above Janesville the gravels are displaced by a fault in which the throw is about 3,000 feet. On the very crest of the range, seven miles northwest of Janesville, the gravel rises to 7,400 feet, while at the foot of the steep slope which it caps the same gravel occurs in Mr. Weisenberger's mine at an elevation of about 4,300 feet. To the northwestward the fault runs out apparantly in a monoclinal arch, later than the volcanic eruptions on the crest of the range at that point,[1] but before the final eruptions of the Lassen Peak region were completed. Mr. Lingdren has shown[2] that further south the eastern slope of the range was formed before the eruption of the andesitic lavas. There is some evidence of a similar character in the Honey Lake Region.

Origin of the earlier auriferous gravels.

The Tejon epoch appears to have been brought to a close, and the Niocene initiated, in northern California, without any marked change of level, unless a general subsidence,[3] so that the influences in operation during the Tejon continued into the Miocene. The old streams still carried on their enfeebled erosion, and in some places the land was completely reduced to

  1. ↑ See also Eighth Annual Report U. S. Geological Survey, p. 429.
  2. ↑ Bull. Geol. Society of American, Vol. 4, pp. 257-298.
  3. ↑ Dall and Harris: U. S. Geol. Survey, Bull. 84, p. 278.
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