Century Magazine 1904, vol.lxviii, pp.

680-694.

Reprinted by permission.] [Footnote 21: At this time the Union Pacific Railroad directly passed the bluffs; in the recent improvement of the grade the main line has been moved to the south .-- H.F.O.] [Footnote 22: A different interpretation of this contraction is given upon p.

68.] REFERENCES.
The published literature on this subject consists chiefly of technical descriptions and researches scattered through the files of numerous scientific journals in Europe and America.

Only the more important titles are cited in this list.