204 
[VOL. X, 
Records of the Geological Survey of India. 
The Blaini Group and the “ Central Gneiss” in the Simla Himalayas, 
by Lieut.-Colonel C. A. McMahon. 
I.—The Simla Neighbourhood. 
On my transfer to Simla from Hissar, the first thing I attempted to do in the way of 
geology, was to trace the outcrop of the Blaini* limestone round Simla; and I proceed to 
give as briefly as possible the results of ray explorations. The Blaini rocks form such an 
important clue to the structure of the region around and beyond Simla, as was pointed out 
in the preliminary sketch of the geology of those hills published by the Geological Survey,! 
that it may be worth while to record a notice of its position as traced over a large area. 
The most convenient starting-point will, I think, be the Lakri Bazaar, Simla. When 
I arrived at Simla, there was an outcrop visible on the mall, a few yards to the north of 
the Lakri Bazaar, and another below it on the road leading to Elysium, hollowing the 
mall round the north of Jako towards Mahasu, there is a good outcrop on the road side 
opposite the house called Snowdon, and the Blaini conglomerate is well exposed on the 
opposite or north side of the road. The limestone crops out again just below where the 
road to Mahasu branches off from the mill, and thence striking across the mall comes to 
the surface on a knoll above the house named Holly Oak at an elevation of 7,600 feet.J Still 
proceeding east along the North Jako road, a good outcrop is seen on the road side at the 
extreme north-east of Jako just where a path descends from the mall to the Mahasu road. 
Between this point and the exposure of the rock opposite Snowdon, the conglomerate may 
bo seen in numerous places both on the North Jako road and on the Mahasu road below it. 
From the point on the north-east of Jako, above alluded to, the Blaini rocks strike down 
the Mad in a south-easterly direction and then curve round the flank of Jako, descending 
by a gentle but steady slope. The limestone passes just above the villages of Sanguti 
(elevation 6,929 feet) and Chanan (6,600 feet), the outcrop being almost continuous. Thence 
it winds round the flank of the Chota Chelsea spur above the village of Balah, and onwards 
through Malka.ua and Kamliali to the east side of the Chota Simla spur. It then rises to 
the crest of the spur and crops out along the top of it until it overhangs some slate quarries. 
From this point the hills drop rapidly to the bed of the Ussan, and the Blaini rocks 
have been removed by the erosion which has carved out the valley of that river. The 
outcrop of these rocks, however, can be traced in a north-westerly direction down to the 
bottom of the ravine between the two spurs into which the Chota Simla spur bifurcates; 
and from thence in a south-westerly direction up the opposite side of the spur, being well 
seen at Chali, Laret, and Jharet. 
A little distance beyond Jharet, at a temple above Ivwalgarh, the Blaini rocks show 
again, and then they are cut off by a fault which runs towards the eastern boundary of 
* I have followed the modern system of spelling adopted by Government within the last three or four years. 
The first vowel sound is hard, as in Blind. 
t Medlicott: Memoirs, Geol. Surv. India, Vol. Ill, where the following classification is given of the rocks of 
this region: — 
( Siwalik. 
V Nahan. 
Tertiary ... -< /'Kasauli. 
/ Subathu •< Dagshai. 
V (.Subathu (nummulitic). 
Krol. 
Infra-Krol. 
Blaini. 
Infra-Blaini (Simla slates). 
Crystalline schists and gneiss. 
J The top of Jako is 8,018 feet. Holly Oak is, according to the Trigonometrical Survey, 7,523 feet. 
