The following paper embodies the results of some studies which were begun by the writers in 1897, while students in the department of geology at Leland Stanford Junior University, and which have been continued intermittently ever since. The analyses were made by the junior author in the laboratories of the university. The writers are indebted to Dr James Perrin Smith, of Stanford University, and to Dr Waldemar Lindgren, of the United States Geological Survey, for helpful suggestions relating to the preparation of the paper.
The San Gabriel mountains are a group of more or less intimately associated ridges and peaks occupying the territory between Cajon pass, in San Bernardino county, and the Santa Clara river, in Los Angeles county, their greater portion lying in the latter. They comprise an area of about 50 by 25 miles, nearly all of which lies within the . . .