PART 1 .] 
Annual Rejjort for 1877. 
3 
downwards into crystalline scliist and gneiss, wliicli certainly implies that the 
conversion of this gneiss is of later date than the deposition of the slates. Yet 
there are observations in this region shewing most indabitahly that, duiing the 
ileposition of the slates, a gneiss was undergoing violent denudation, and at no 
great distance: throughout a considernhlo thickness of strata in Pangi, largo 
blocks of gneiss are imbedded in the unaltered slato.s. From the circumstances 
Mr. Lydekker conjectures that they were ico-hoi-no; but, however this may bo, 
the immediate difficulty is, that they seem to be of Himalayan gncis,s, as they 
resemble it, and are not like any known gnoi.ss of the nearest j'egion to the south. 
If they were derived from any gneiss now exp(jsed in the Himalaya, we may 
surely say that it must be of vei'y diffei'eut iige from the gnei.ss cimformably 
underlying and transitional with tliese same slates; and that the unconformity 
betw^een the two series must, at least oilginally, have been of a very striking 
character, so that the non-recognition of such a featui-c would vitiate any in¬ 
dependent interpretation of the rock-structure. The question radically affects 
the view to be taken of the mountain-formation; but we are still in uncertainty 
regarding it, no such distinction having been as yet detected in the gneissic masses 
of this region. The great gneissic mass of the Zanskar range is certainly to 
some extent composed of a gneiss associated with the slates; the so-called 
“central gneiss” has also been provisionally identified in it; hut no minera- 
logical criterion or stratigraphical demarcation has as yet been attempted 
between them. An account of Mr. Lydekker’s observations is published, with a 
skeleton map, in the current number of the Records. 
In this connection I am glad to have to notice the work of a geologist who is 
not on the staff of the Survey, although liis observations have been published 
in our Records for the past year. Workers for love of geohjgy have become so 
rare in India that the appearance of one is quite an event; and Colonel McMahon’s 
paper is in good form, representing much hard work in the field and the study, put 
together rationally, without random spectilation. His map of the Simla region 
indicates a clue to the structure of the most difficult region of Himalayan geology, 
and an interpretation that may pi-ove of great servico is suggested. The ground 
sketched by Mr. Lydekker, although adjoining the groat fringing zone of tertiary 
rocks, is strictly on the prolongation of the groat central Himalayan range, and 
the structure is on a reduced scale of the same type. The Simla region is 
quite different: it belong.s to that broad as-ea of lower mountains -which to the 
east of the Satlej separates the snowy range from the plains, and is made up 
of metamorphio and slaty rocks in a very irregular and incomprehensible 
mode of distribution. In the midst of the slate series there is one well-marked 
group, affording the most certain guide to the disturbance of the strata. 
Colonel MciMahon has mapped its outcrop over an extensive tiuct of rug'ged 
mountains. Ho has also iiidicatcil for this region a probable solution of the 
difficulty noted in Mr. Lydckker'.s work regarding the gneissic rocks. He shows 
that the massive gneiss t'orming several ^U'ominent ridges in the lower mouTitaivis 
must be the same as the “central gnei.ss” of the main range; he describes the 
upper members of the slate series to ho so related to this gneiss as to involve 
