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STRATIGRAPHY

Mint Capyon Formation:

The Mint Canyon formation, of both laoustrine and

fluviatile origin, consists, in the Humphreys Station area,

predominantly of sandstone and siltstone, with interbedded

conglomerate, fanglomerate, clay, shale and tuff beds.

The conglomerates and fanglomerates are composed

chiefly of igneous and metamorphic cobbles and pebbles. They

vary in color from red-brown to buff to grayish. Most of the

sandstones are buff. Brown-buff members are common and a few

gray beds are present. Both these and tba conperates are

well consolidated. The siltstones, of a greenish cast, are

relatively incoherent and grade locally into shaly and clay-

rich members.

The tuff beds have been described in detail by

Wallace (op. cit.). They are interbedded with the above mem-

bers and in places are gradational both vertioally and later-

ally into sandy tuff and tuffaoeous sandstone and siltstone.

The entire assemblage varies latelli.ly and is cross-bedded.

Ripple marks are common in the lacustrine facies, especially

in some of the tuffaceous siltstones.

Subaerial deposition seems indicated for most of the

formation here exposed although some subaqueous deposition

undoubtedly occurred. A fluviatile origin for part 1s pro-

bable, judging from the sharp lateral and vertical variability,

the prevalence of lenticular, often oxidized, conglomerates,

and current ripple marks. Most common evidences for lacustrine