292 RESUME AND THEORETICAL DISCUSSION. 
endeavor will be made to set forth that which may now be considered as 
quite clearly established in reference to the original mode of deposition and 
character of the auriferous gravel deposits of the Sierra. After that has 
been accomplished, the way will be clear to take up some of the more difficult 
and controverted points, the writer hoping that im thus doing he will be able 
in the discussion to throw light on some of them. 
After these preliminaries, the remainder of this chapter will be devoted to 
a résumé of certain portions of the investigations embodied in the present 
work, in regard to which it seems desirable that the salient points should be 
brought together into a convenient form for a rapid review, for such persons 
as would not desire to make themselves acquainted with the mass of local 
details with which some of the essential facts are encumbered in the descrip- 
tive parts of this volume. 
Section Il.— What may be assumed as having been clearly established in Regard to 
the Theory of the Gravel Deposits. 
In a previous chapter there has already been given a partial discussion of 
some of the more prominent points connected with the theory of the occurrence 
of the gravels.* This was done in order that the reader might have the pre- 
liminary information necessary for understanding the details which were to 
follow in regard to the nature and distribution of the various formations, to 
the special study of which this volume is devoted. It now remains to take 
up the more doubtful points suggested in the course of the investigation, and 
to devote especial attention to such of these as seem to require such treat- 
ment, and which the reader who has gone over the details embodied in 
the preceding chapters and Appendix A will now be better prepared to 
understand, 
The present section is introductory to such a review and general discus- 
sion, its object being to clearly distinguish between those points in regard 
to the theory of the gravels, which are so well made out that it is proper 
to assume that there will be no difference of opinion about them, and, on 
the other hand, those which are more obscure and which therefore may 
suitably be laid before the reader at some length, and not without admitting 
that there are certain things which cannot yet be made so perfectly clear as 
to warrant the expectation of entire unanimity of opinion in regard to them. 
* See ante, pp. 53-78. 
