PART 2 .] 
Medlicott, Met amorphic rock* of Bengal. 
The superficial relation of position—a great spread of crystalline, fringed by sub- 
metamorphic rocks—is already variously suggestive : the rival leading questions would 
be—to what extent are the crystallines granitic and intrusive, thus determining the pre¬ 
sent limit of the schists ? or, if the crystallines are in the main gneissic and themselves 
metamorphic, how far may the present limitation of the snbmetamorphic series as a fringing 
deposit be an original feature? No satisfactorily one-sided answer can be given: the facies 
of the crystalline rocks is emphatically gneissic (metamorphic); there is also ample evidence 
of granitic intrusion in the rocks of both series; yet, owing to theoretical scruples, 
and to deficiency of data, the residual phenomena are so numerous that no approxi¬ 
mately final judgment can be put forward even as to the main relative ages. It is time, 
however, that our difficulties should he ventilated. The lie of this great, hand of slaty 
rocks, on the south of the Gangetic valley, and followed up, as it is, by the next suc¬ 
ceeding deposits of the Yindhyan series, suggests at first sight inferences as to the possible 
substratum of the great alluvial formation, as to the inducing conditions for the great area 
of erosion or of depression, and as to possible relations to the rocks on the north of the plains, 
in the Himalayan region. But, whatever independent interest these large structural feature- 
may retain, such speculations as those mentioned are in a great measure negatived by the 
appearance to the north of the Vindhyans in Bundelkund of a large area of thorough 
gneissic rocks; and again, in Behar, in the small group of the Barabar hills, well to the 
north of the Raj gi r range, we find very massive gneiss of most ancient aspect. 
I must here briefly recall to notice some observations I made in 1S5G-57 in a 
neighbouring part of India (published in the 2nd Vol. of our Memoirs) as bearing upon 
the question before us. To the north-west of the Sone valley, and separated from it by 
the long eastern px-olongation of the Vindhyan formation, there is the large area of crystalline 
rocks of Bundelkund; it is hounded on three sides by the Vindhyans and on the fourth 
by the Gangetic plains. Along the south-east border of that area there appears a strip 
of semimetamorphic rocks—quartzites, limestone* and slaty strata, with contemporaneous 
trap, rising from beneath the Vindhyans. I described them as the Bijawur formation. 
They are in many places seen to rest abruptly upon a flatly denuded surface of the gniess 
of that area. The bottom rocks in this position are peculiar quartzites, often compact and 
brecciated, and massive cherty limestone; but along portions of the boundary the usual 
Bij awur strata are underlaid, with at least approximate parallelism, by very non-dcscript 
gneissoid strata. The demarcation bet ween these and the true gneiss is, naturally, very obscure ; 
and it was not then possible to work it out; but there are locally some intercalated 
beds of quartzite-sandstone that effectually betray the stratigraphical affinities of these 
indeterminate strata to be towards the Bijawur rocks, and totally distinct from the true 
gneiss, to which they seem in the relation of an ancient superficial covering. We shall sec 
that probable representatives of the Bijawur rocks occur both in the Bone valley and in 
Behar; and that thus we may' at least get a hint as to the relative ages of the gneiss of the 
two areas. 
A large part of the subrnetamorphic area of the Sone valley is occupied by rocks 
that would well represent the Bijawurs—ferruginous slaty schist with quartzite, limestone, 
and much contemporaneous trap. They are much more disturbed than in Bijawur; it is 
even probable that they are affected by certain granitic intrusions. The uncertainty upon 
this and upon other unsettled points regarding their relation to the main crystalline area to 
the south is largely owing to the presence of another older series of slaty rocks in the Sone 
area. Thy Bijawur deposits are known to be somewhat fickle, but unless they are so boyoml 
all possible conjecture, there can be little doubt of the existence of this older series. In 
some of the best sections, notably in that of the Rebund, there is a clear transition from the 
coarse felspathic gneiss, through well marked stages of crystalline metamorphism, into a 
series of fine clay-slates, with plenty of intrusive greenstone, but in which none of the 
characteristic Bijawur rocks can he recognised. Where decided Bijawur rocks come in 
contact with the gneiss there is no such intimate relation between the two. Now that 
maps of this ground are available there is some prospect of our being able to unravel these 
obscure questions. 
The hills formed of the subrnetamorphic rocks in Behar appear generally as 
precipitous ridges of quartzite, either singly or massed together in groups. Even in the 
* The limestone of Der^oan, which I had doubtfully described as an outlier of the Lower Vindhyan limestone 
lias since been shown by Mr, l 1 ’ K, Mallet to belong to the Bijawur series. 
