PART 4.] 
Ball: Mahanadi basin and its vicinity. 
173 
Ishtapali and Jogipali. Its precise area is somewhat doubtful owing to the way in which 
it is covered by superficial deposits. Another of small extent exists in the interval between 
the main Talehir area at Bolunda and the outlier at Terda. South of the Mahanadi and 
opposite to its junction with the Ebe, just close to the village of Easem, is a third. It 
is about half a square mile in extent. Sandstones, shales, and the boulder bed are all re¬ 
presented within these limits. 
In the Pal-jor, a small tributary of the Ong River, to the east of the village of Ganislot, 
the section discloses the existence of a small basin occupied by Talchirs. The rocks consist 
of sandstones, shales, and a well developed boulder bed with rolling bedding. On the south 
they seem to rest directly on the gneiss, but on tbe north the character of Iho boundary is 
uncertain owing to the superficial covering. The exact area has uot yet been ascertained; 
it probably does not exceed three square miles. Still further south, in the bed of the 
Tel River east of the village of Tanigaon, Talehir sandstones are exposed under the bank. 
On the south they are cut off by gneiss, but bow far they may extend to tbe north-east, 
up the valley of the Ebe, is not known. Other localities where rocks of this group 
are reported to exist are at Keutasiugha in Patna and Baisasankar in Boad. 
Vindhyah Series. 
General [lithological resemblance and the relations with other formations are the sole 
data available for correlating the series of azoic sandstones, limestones and shales of 
the Chhattisgarh and neighbouring areas with the Vindhyan series of Northern India. 
Already, in a general way, the Karnul series of Madras has been identified with the lower 
Vindhyan series ; but even though the details of tlia sequence in both are well known it has 
been impossible hitherto to establish even an approximate correlation of horizons. Such 
being the ease where the rocks have been fully examined, it will be readily understood that 
with rocks the sequence of which in the wide area of Chhattisgarh is at present a matter 
of some doubt, no attempt at detailed correlation can be usefully attempted. 
Until some complete standard sections have been locally established, comparison with 
other areas cannot be of much aid in tbe elucidation of tbe history of these rocks. But 
some allusion to the rocks of tbe same age in tbe Chanda and Godavari valley districts 
may become necessary. 
Apparently two great groups of these rocks exist, one (A) consisting of a thickness of 
upwards of 1,500 feet of quartzites, sandstones, and conglomerates resting on shales which 
latter, in some sections, appear to have been considerably disturbed before the deposition of 
the upper beds. The relations between the two seem to be in many respects similar to those 
existing between the upper and lower Vindhyans of tire Vindhyan range. What the rela¬ 
tions may he which exist between these shales and those of the second group is at present 
not absolutely known, as no section hitherto examined contains both groups of rocks in 
their full development; but from their lithological characters and some other considerations 
to be mentioned hereafter, I am strongly inclined to believe that these shales belong to the 
second group which seems to he the elder of the two. This second group (B) consists of 
limestones, shales, and sandstones. The existence of these sandstones interbedded with* 
and in some cases underlying, the shales and limestones, has been the principal cause 
of the difficulty which has been experienced in assigning the rocks to two groups, and 
also establishing the relative position of these groups in the geological sequence. In 
the following pages, however, sections will be described where sandstones occur sometimes 
underlying, sometimes interbedded with, limestones and shales; and, on the other hand, 
sections of what are considered to constitute an upper group, in which there is an unbroken 
thickness of upwards of 1,500 feet of quartzites, sandstones, and conglomerates resting 
