The results given in this paper are preliminary, but it will be seen by those familiar with such researches that my opinions, although for obvious reasons here considered as provisional and therefore subject to revision in final publications, have been based upon abundant materials. These consist of four different collections: The first was made by Mr. I. C. Russell and by the author and his son in the summer of 1888, and showed the existence of the Lias* and Oolite in mount Jura, near Taylorville, Plumas county, California, and the need of making further researches in this locality. The second was gathered by Mr. J. S. Diller and the author in the summer of 1890, and this, together with a third collection made during the same season by Dr. Cooper Curtice, demonstrated the existence of a distinct fauna in the Hinchman tuff. It is only just to add that . . .