28 
Records,of the Geological Survey of India. 
[vol. VI. 
Talchirs in Mdhrtn valley. 
From the eastern corner of tlie field, a long irregular strip of Talclnrs runs with the 
valley of the Mahan towards Uphia, near which place it probably 
disappears under the sandstones exposed on the southern face of the 
Mailan pat. So far as it could be traced between Uphia and Barbaspur, it appears to be 
unbroken for about fourteen miles. When it does not occupy the present bed of the river, it is 
often much obscured by alluvium and jungle. The boundaries of this strip are frequently in¬ 
dented by noses of metamorphics and submetamorphies, and there are also several inliers 
of the same rocks. 
The bottom rocks of the Talchirs in the sections exposed in the M aban are the boulder 
bed with very irregular bedding and a hard grit sandstone. Overlying these is a considerable 
bed of yellowish-green sandstone, which, near Barbaspur, has been thrown by a cross-fault 
against the edges of the Barakars. In the Mahan itself shale beds are of comparatively rare 
occurrence, but they are exposed in some of the sections in the streams which join it on the 
south. 
One point in reference to the boulder bed, which plasters over quartzites and slates in the 
river south of the Ranchi and Partabpur road-crossing, is deserving 
Origin of boulders. „ . , ... . . 
ot especial notice, as it, has an important bearing on the origin 
of that rook. The principal proportion of the boulders are derived not from the underlying 
rocks, hut from the granitic gneisses which occur three miles to the north. One rock, 
a pink porphyritic granite, which is seen in situ north of Tarki, seems to have been a prolific 
source of these boulders.* 
A branch from the strip of Talchirs above described borders the Barakars southward 
as far as Karnji. This branch is traversed by the Gehur river, 
in which there is a section of sandstones and boulder bed, which 
continues up to the mouth of the Doldoa stream, where slates and quartzites strike into 
the river and continue in its bed for several miles. 
Talchirs on eastern boundary. 
In the Gagnr river west of Karnji there is a very intricate section in which Barakars, 
Talchirs, Slates, Talchirs, Slates, and Barakars are successively exposed. 
The jungle on the banks is very dense, and the map is, probably from that reason, 
deficient in detail, so that it is difficult to trace out the geological boundaries. The accom¬ 
panying map may, however, be taken as affording a fair approximation to the true state of 
things. The second appearance of the slates is due to the same cross-fault as that above 
mentioned at Barbaspur. They occur as a very small iulier in the base-beds of tbe Talchirs, 
whose ends are against the Barakar Sandstones. 
As to the continuation of this fault further south, I could see no satisfactory evidence. 
Possibly it bounds the Talchirs south-east of Udukatra, but with 
the streams, in which the Talchirs are exposed, inclining, accord¬ 
ing to the map, to the westwards, it is impossible so to represent it. 
Between Karnji and Chargar there is a very small patch of Talchirs exposed in the 
low ground. 
K or ill-east of Sidma there appears to he a nai’row strip of Talchirs cropping out from 
Talchirs north-cast ofSidml uude ™eath the Barakars, but the evidence of its existence is 
afforded rather by debris in the stream, than from rocks in situ. 
* In some of the boulder beds which eceur in tbe country west of the Rohr, a considerable proportion of the 
boulders consist of a reddish quartzite saudstone, probably of Vindyan age, which, if that supposition be correct, 
must have been transported to their present position from the neighbourhood of the Sone. This could only have 
been effected through the agency of ice. 
