Page:The Journal of geology (IA journalofgeology21894univers).pdf/64

the same way the gold, being heavy, and associated with the quartz originally, accumulated in the same channels, while the fine light detritus was carried directly to the Sacramento valley.

In his paper on the ancient river beds of the Forest Hill divide,^[1] Mr. Ross E. Browne classifies the auriferous gravel channel systems into three periods. The first period was prior to the first important flow of volcanic cement, the second was contemporaneous with the series of volcanic cement flows, and the third following immediately after the last important flow of volcanic cement extends to the present time. He has called attention to the predominance of quartz gravel^[2] and sand in the ancient channels of the first period,and remarks that "quartz is the only important material contained in the belts (of slates) which is hard and permanent enough to resist the destructive action of the current." This is especially true when the auriferous slates are disintegrated. It is possible therefore that the predominance of quartz in the earlier gravels may indicate an earlier period in which the slopes had less declivity and disintegration exceeded transportation.^[3] The fact that in the Light's cañon region of Plumas county the gravel is underlain by a sheet of residuary material which was formed before the deposition of the gravel is evidence in the same direction. Furthermore, the sand deposited with the gravel is rough, angular and unassorted, such as is derived from residuary material near at hand, and records a period of gentler declivity during the next earlier epoch.

The old channels of auriferous gravel of the first period are in a measure characterized by the large size of the deposits. Ross E. Browne states:^[4] "In a general way it may be said that the channels of the second period differ from those of the first as