Arkell.1956.Jurassic..

400 RANGES OF SOUTH-EAST ASIA
the step-like outcropping edges of the Trias after the manner of a staircarpet'
(Middlemiss, 1896, p. 29). Farther south, and in the greater part
of the Attock district, the Spiti Shales in turn are overlapped by the Giumal
Sandstone, which takes on a shelly facies and incorporates at the base,
or rests on condensed representatives of, certain Oxfordian horizons which
belong low down in the Spiti Shales.
The Attock and Hazara districts thus provide a section across the
southern edge of the Himalayan trough and must have been moved bodily
with the underlying shelf of pre-Cambrian rocks if the Indian peninsula
underthrust northward as postulated. A similar marginal section may be
preserved north of Mount Everest (see below).
The following stages have been identified:—
Succession in the Attock District and Hazara
UPPER TITHONIAN AND BERRIASIAN
Ammonites of the genera Spiticeras, Blanfor dicer as and Himalayites
have been recorded in limonitic poor preservation in sandy limestones of
the Attock district wrongly correlated with the Giumal Sandstone of
the Himalaya, and from Hazara is known a Neocosmoceras. These
are all genera typical of the Upper Spiti Shales (Lochambel Beds, see
p. 407) (Spath, 1933, pp. 803-4). Similar rocks in both Hazara and
the Attock district have yielded numerous Trigonia ventricosa Krauss
(Middlemiss, 1896, p. 34; Cox, 1935, pp. 2, 17, pi. ii, fig. 14).
LOWER TITHONIAN
Virgatosphinctes frequens, a species of the Middle Spiti Shales (Chidamu
Beds) is recorded from several places in Hazara (Middlemiss, 1896, pp. 33,
34; Spath, 1933, p. 804).
UPPER OXFORDIAN
In the Attock district, where a condensed, marginal, shelly facies of
the Spiti Shales is overlapping the Kioto Limestone and is itself almost
overlapped by Giumal Sandstone, a highly interesting ammonite assemblage
of the Transversarium Zone occurs. It consists mainly of Perisphinctes
of strong Cutch affinities (though some are cosmopolitan), with
which are associated some Mayaites, including M.pofyphemus (Waagen), the
whole indicating direct sea-connexion with Cutch (Spath, 1934; subgeneric
attributions of the Perisphinctids require revision). With them occur
Gryphaea balli (Stefanini) and Exogyra fourtaui Stefanini, two oysters first
described from Somaliland, and other common pelecypods (Cox, 1935).
UPPER BATHONIAN
The Kuar Bet Beds of Cutch (see p. 391) are represented by a number
of pelecypods preserved in grey rubbly limestone, presumably from the
local top of the Kioto Limestone. Protocardia, Eomiodon and Corbula
have been figured (Cox, 1935).
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