PART 4.] 
Ball: Mahanadi basin and its vicinity. 
175 
of plateau quartzite at an elevation of 900 feet above the base, and from this amount down¬ 
wards the levels constantly change, different members of the sequence thus occurring locally 
as the bottom beds of the group. Of course sections of these rocks in the scarped sides of 
the plateau are not rare, though many of them are difficult of access. The principal one 
examined was in the gorge of the Jonk River between Maragura and Jumlagor. 
Jumlagor is at the head of a waterfall which is probably 300 feet high. Its elevation 
is about 850 feet above Maragura, and as the beds forming the plateau are slightly inclined 
southwards, the ascent traverses the edges of a thickness of beds somewhat in excess of 
that amount. These beds consist almost exclusively of quartzites exhibiting various degrees 
of vitrification; the exceptions are beds of conglomerate consisting of small, sometimes 
minute, quartz pebbles firmly compacted together in a thin matrix. No slialy beds 
whatever were detected as occurring with these quartzites, which are mostly rather 
thin-bedded, the distinct layers rarely exceeding 3 feet in thickness. As to the chai-acter 
of the beds of the remainder of this group, i. e., those above the horizon of the Jumlagor 
beds, I was not able to examine them in detail, but they seem, so far as is known, to be 
very similar in character to the lower portion. In the internal valley of the Gima River 
to the south-west of Tamot, we find dipping under the quartzites of the plateau a group 
of shales having an extraordinary resemblance to Talchirs, and showing an amount of 
disturbance which is not shared in by the quartzites of the surrounding ranges. No trace 
of these rocks was found at the base of the already described western quartzite natural 
boundary, but on the east they occur in all the deep internal valleys within the outer 
bounding range of quartzite, and are also found in vertical, apparently faulted, contact with 
the gneiss close to the eastern base of the horizontal beds which form a small outlying 
plateau to the east of Tarnot. It will perhaps be sufficient for present purposes to describe 
two sections which exhibit the relations existing between these beds and the quartzites. 
These sections are afforded by the gorges of the Under and Udet Rivers. 
In the accompanying sketch of the former is represented the relations of the beds as 
they are understood by me, but the central part of the section is by no means clearly exposed, 
and may possibly admit of another explanation. The observed facts are as follow:— 
tv. 
Section in the Under Eiver. Horz.: Scale 1 inch = 1 mile. 
The section of the outer range is very clearly exhibited on the southern bank of the • 
river. The beds marked (i) consist of quartzites with very thin Interlamination of red 
and green clays, these clays being more especially abundant in the central portion of the 
thickness exposed. The lowest bed seen outside is a quartzite which is much indurated, 
and which is bent abruptly to the vertical, forming, at least for a short distance, a steep 
outer face on the hill. After a series of rapid contortions, which do not show, to the same 
extent, in the beds on the top of the hill, these lower and central beds dip suddenly vertically 
downwards and do not reappear. Probably, if the rocks were uncovered and visible, we should 
