50 
Records of the Geological Survey of Lidia. 
VOL. IX. 
The special point to bo cleared up was, the discrepancy between tho sections of these 
rocks as described by me in 1862 (Mem. Geol. Surv., Ind., Vol. Ill) in the region of the 
Ganges and the Satlej, and those observed by Mr. Wynne in the country west of the Jhelam. 
I had made out two very marked breaks in the series. One was where the topmost beds of 
the great mammaliferous deposits rested against and upon an inner belt of older rocks. As 
tin; former wero conspicuously the home of the famous Siwalik fossils, I restricted this name 
to that younger group of i - ocks, giving the name of Nahan to the older beds upon which 
they rested unconformably. It was certainly rash of me thus to tamper with a well-known 
name. Although the fauna of tho Nahan rocks is still unknown to us, it presumably will 
include mammalian remains, having more or less of affinity to those known as Siwalik; and 
it may bo paleontologically desirable to make the same name cover all. This, of cours% can 
still be done, if required, substituting some local name in the application I gave to Siwalik. 
The second break in the eastern section occurs where tho Nahan rocks abut against the 
old slaty rocks of the higher mountains, high upon which there rests an extensive rem¬ 
nant of still older tertiary deposits, including at their base the nummulitic beds of Subathu, 
transitionally overlaid by red clays and grey sandstones in distinguishable zones, to which I 
gave the names Dagshai and Tvasaoli. 1 subsequently denoted these three older bands collect¬ 
ively as the Sirmur group, it being desirable to restrict the name Subathu to the nummulitic 
zone proper. There was little direct evidence as to bow far the boundary between the Nahan 
and Sirmur groups might also he an aboriginal unconformity, or altogether due to flexure and 
faulting; but the fact that in tho lowest outcrops of the Nahan baud over a very large area 
no symptom conld be detected of tho very characteristic Subathu zone, nor any specific 
representative of the Ivasaoli beds, which in the contiguous area are repeatedly marked by 
peculiar plant layers, gave strong presumptive evidence for the supposition of aboriginal un¬ 
conformity. 
No trace of these very marked stratigraphical features of the Simla region could be 
detected by Mr. Wynne in the country west of the Jhelam ; although several of the zones 
could be identified with great certainty. The Subathu nummulitics arc very characteristically 
represented west- of Mari (Murree), and over them, at Mari itself, the rocks exactly resemble 
the Dagshai beds; while at the upper end of tbe series tlie Siwaliks are in great force, with 
their characteristic fossils. 
As an unknown quantity between those two contrasting sections there was the remark¬ 
able fact that the axes of flexure in the rocks west of tho Jhelam have a direction at right 
angles to that of the contiguous Himalayan ranges ; the change taking place abruptly along 
the course of the river. It is the junction or confluence, the knee, as it has been termed, 
between tbe lines of the Himalaya proper and those of the Hindu Kush. There seemed 
a possibility that the total disappearance westward of tho boundaries so strongly marked at 
the base of the Himalaya east of the Satlej might be closely connected with this striking 
transverse feature of tlio mountain structure. Such, however, is not the case. These two 
systems of flexure arc continuous and eotemporaneous. 
The difficulty of establishing divisions in the immense series of tertiary strata which 
has so hampered Mr. Wynne in his examination of the trans-Jhelam country, had already 
strongly declared itself to me in the hills between the Satlej and the Itii-vi. On the map 
published with my memoir, it will bo seen that the Nahan-Siwalik boundary and the Nahan 
zone itself is stopped abruptly and arbitrarily at tbe Satlej. I found that the abutting, 
overlapping junction of topmost Siwaliks against low Nahftus had gradually changed into 
vertical parallelism; the ridge of Nahan rocks here taking the form of an anticlinal, sinking 
to the north-west-, round tho point of which the Siwaliks turn over into the inner valley. 
Finding that the several broad duns (flat longitudinal valleys) of the Ivangra district were 
occupied by rocks of Siwalik type, and uot having time to work out their approximate 
separation from the core of Nahan beds in some of the dividing ridges, I coloured tie 
