Arkell.1956.Jurassic..

THE GONDWANA SYSTEM 383
all the coal worked in India. At the base is the famous Talchir boulder
bed, interpreted as a glacial tillite, which is overlain by a marine bed
providing evidence of Permo-Carboniferous date. The next marine
intercalations are of Lower Cretaceous (Upper Neocomian) date. Correlation
of the intervening continental strata from basin to basin and with
the standard geological sequence is difficult and uncertain, since it must
rely largely on palaeobotanical evidence.
The Gondwana system contains only two main floras, the earlier
characterized by Glossopteris, the later by Ptilophyllum. On these grounds
the Geological Survey of India (see especially Fox, 1931) has advocated
a twofold subdivision into Lower and Upper Gondwana. Unfortunately,
FIG. 54.—Sketch-map showing distribution of the Upper Gondwana Series (black)
and the Deccan Traps (shaded). Based on the Geological Survey map of India.
however, the change of floras takes place in the middle of beds (Panchet &
Mahadeva: see the accompanying table, p. 384) proved by their vertebrate
fossils to be Triassic. This did not matter seriously when it was possible
to imagine that the beds with the Ptilophyllum flora represented continuous
sedimentation from Upper Triassic to Cretaceous, and when a whole
series of imaginary Jurassic stages could be written in column alongside
the Indian formations (e.g. Fox, 1931, pi. 9). The position has been
completely changed by Dr Spath's discovery (1933, pp. 826-9) that the
lowest Gondwanas next above the Mahadeva (Maleri) stage are not
Liassic as previously supposed but Upper Neocomian. Geologists have
been slow to accept the implications of this revolution, and the old
imaginary classification still appears in some of the latest text-books
(Krishnan, 1949, pp. 246-7, 272). But now that, in Dr Spath's words,
'it seems probable that there is an enormous gap between the Lower
Gondwanas and the Rajmahal plant beds . . . involving at least the whole
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