PART 4 .] 
McMahon : The Simla Himalayas. 
209 
The notion might be best explained by a diagram, but it is quite intelligible in words: 
if a horizontal pressure be set up beneath a deeply eroded surface, any yielding that occurs 
would be determined along the lines of erosion, as positions of least resistance, comparative 
rigidity being maintained elsewhere by the weight of the mountain masses. We should 
thus have extreme contortion in the valleys, extending in diminishing degrees up the flanks 
of the mountain to the summit, where there would he a minimum of effect. This view 
would apply to the “transverse” as well as to the “longitudinal” valleys, for in a yielding mass 
any pressure becomes quaquaversaL The view is, no doubt, opposed to what is often stated 
in geological text-books, even of recent date, as a sort of axiom—that the contortions 
observed in strata must have been produced far beneath the surface; but it has been long 
since shown, in this very neighbourhood, that the extreme disturbance exhibited in the 
enormously thick Siwalik rocks must have been produced at tho immediate surface.* 
I think, then, that the converging dips seen so often in the Simla area, accompanied by 
a rapid increase in the angle of the dip as the valleys are neared, indicate that when the 
last great disturbance, which has left its marks so deeply on the Simla Hills, took place, 
the hill area had been approximately carved out into its present outline. 
II.—JUBAL—TaEOCHE—C lIEFAL. 
The best starting-point for our next excursion will, I think, be the top of Kuper peak, 
in which the Girt takes its rise. A path from Jubal to Chepal passes some hundred feet 
below the top of the Kuper, the path rising to an elevation of 10,650 feet above the sea. 
The rocks exposed along the highest part of the road are the schists above the “central 
gneiss.” Along the ascent from Jubal, the dip is about north-east; near the top it is 
north-ll°-east. On the south side where a spur branches off in the direction of Chepal, 
there is a sudden change in the dip to south-east-ll°-east,i" and this change brings up the 
central gneiss at an elevation of 9,620 feet. 
I hope to show hereinafter that this is the so-called “central gneiss,” but for the 
present I only announce the fact. 
As the slope of the hill side coincides with the dip, the path down to Bamlo (Bomta) 
runs over the gneiss all the way with the exception of two or three comparatively brief 
intermissions where the infra-gneiss mica-schists crop up. Bomta is at an elevation of 
8,000 feet, and the gneiss shows as far as that village. My political duties required me to 
visit Taroche (Tirhosh), and the path from Bomta led me in a north-easterly direction down 
to the bed of the stream. On leaving Bomta, the dip rapidly veered round from south- 
ll°-east to north-east, but the change is masked by grass and trees. In the bed of the 
stream I came upon thin-bedded calcareous schists utterly unlike the crystalline rocks I had 
left behind at Bomta. In the light of facts to be subsequently detailed, I do not think I 
shall be wrong in calling these calcareous schists Krol rocks. 
The path up to Taroche (Tirhosh) soon led me above these rocks (below them strati- 
graphioally expressed), and I passed through mica-schist (answering well to the Infra-Krol 
series) all the way to Tirhosh. After occasional local wavering to the north-north-west 
the strata settled down to a low north-11 -east dip. The stream below Tirhosh was lull ot 
the “central gneiss” boulders, showing the presence of that rock on the southern flank of the 
Kanchu peak. 
From Tirhosh (elevation 6,950 feet) the road to Chepal makes an exceedingly steep 
descent (some 3,000 feet, I should say) to the stream flowing down from the Kanchu peak. 
* Medlicott, 1868: Qtrar. Jl. G. S., London, Vol. XXIV, p. 47. 
j I have not, in any of the bearings I give, made allowance for the variation of the compass. 
