During the autumn of 1893 the writer spent five weeks in field work on the Auriferous slates of the Sierra Nevada, chiefly in Plumas, Butte and Calaveras counties, California, in the effort to find some definite horizons that might be identified by fossils. In this he was greatly aided by Mr James E. Mills, under whose guidance he visited many of the localities mentioned in this paper. To Mr Mills is due in great measure whatever success was achieved by the investigations.
The Auriferous slates have long been a puzzle to California geologists, and, on account of the scientific as well as economic interest attached to them, much has been written—hardly any two writers agreeing—about their age.
This paper is intended to present the facts known at the present time.
1858. The first geologist to write about the age of the Auriferous slates . . .