In Speaking of the terrestrial formations of the Eocene, Chamberlin and Salisbury [1906, Vol. 3, p. 204], when comparing the sedimentation of the Eocene with the present time, say:
Then as now, temporary and permanent streams were doubtless aggrading their valleys, and building fans and alluvial plains where the appropriate conditions were found, while sheet-floods spread debris washed down from the higher lands on the tracts below. The deformative movements which initiated the modern era probably gave rise to basins here and there, in which lakes were formed, and the flows of lava from the unnumbered vents of the time doubtless sometimes obstructed valleys, ponding the streams and giving rise to lakes. Under these conditions, it is probable that much of the debris which was started seaward by the swift waters of the higher lands found lodgment long before it reached the sea, some of it at the bases of steep slopes, some of it on river plains, and some of it in lakes. The wind also made its contribution. The result was an inextricable combination of fluvial, pluvial, eolian, and lacustral deposits.
Terrestrial formations of Eocene age and of fluvial, pluvial, lacustral, and eolian origin are widespread throughout the western interior, occurring even in proximity to the western coast. Many of them are of limited extent, while others are spread over great areas.
Again, in describing the terrestrial deposits of the Miocene, the above authors say [p. 266]:
The terrestrial Miocene formations (the Truckee Miocene[1] of King) are said to reach a thickness of 4,000 feet (King) at some points in the vicinity of the 40th parallel. In general, they are made up of sandstones, conglomerates, volcanic debris, infusorial earths, and fresh-water limestones, overlain by great thicknesses of volcanic tuffs. The John Day series, the upper portion of which is perhaps Miocene, is also thick (said to be 3,000 or 4,000 feet), and is made up largely of volcanic ash and sand, much of which seems to be eolian.[2]
Other areas of deposition, some of them lakes, existed during the Miocene in Nevada and Montana. In the southwestern part of Nevada, the Miocene beds (Esmeralda formation) described as lacustrine, consist of the usual sorts of clastic rocks, pyroclastic material, and workable coal, the latter showing that the formation is not altogether lacustrine. The formation also carries some sulphur. The remarkable thickness of 14,800 feet (which may include Pliocene beds) is reported for this formation.[3]
In the fresh-water Morrison formation of Colorado Mr. Darton notes the presence of 66 feet of limestone [Darton, N. H., 1905, p. 97] in a section 166 feet in thickness.
