Sketch of the Metamoephic eocks of Bengal, by H. B. Medlicott, A. B., F. G. S., 
Depy. Supt., Geol. Survey of India. 
From the descriptions of the earliest geological observers in India it has been 
known that large areas are occupied by rnetamorphie and submetamorphic rocks. It mio-ht 
not appear from its publications that the Geological Survey had given to these formations 
their due share of attention. But such an inference would" be tar from correct; coloured 
maps of large districts might long since have been published, with a general description of 
the lithology and of the superficial stratigraphical features; and specious analogies mio-ht 
have been drawn with the ‘fundamental’ rocks of other countries; but any such accounts 
would be illusive without, some definite judgment upon the structure and relations of the 
several rock-groups. The following notice is a brief abstract of observations made by me 
during two seasons (1862-63, 1863-61) spent on these rocks, from the watershed of the penin¬ 
sula near Jubbulpur, in an east-north-east direction, to Monghyr on the Ganges, a direct 
distance of more than 400 miles. Those who have any knowledge of the difficulties attend¬ 
ing the investigation of such rocks will at once understand that my explanations can be only 
tentative. 
The broad promontory round which the Ganges turns at Rajmahal is the termi¬ 
nation of a great expanse of gneissic rocks. Here, throughout its eastern extremity, for 
nearly 100 miles, the gneiss is covered and bounded by the Rajmahal Trap, with its asso¬ 
ciated plant beds (Jurassic), locally underlaid by other members of our Indian Stratified 
Series; and various outliers, of irregular shape and size, of these latter deposits, comprising 
our best known coal-fields, are scattered over the area to the west; but from the Rajmahal 
boundary the gneiss is continuous for 400 miles to the west-south-west to where it passes 
under the Great Deccan Trap (supra cretaceous) of the Mundla plateau. From the south 
extremity of the Rajmahal Trap the general boundary of the rnetamorphie area extends to the 
south-south-west. Across the middle of the area a straight line might be drawn for more 
than 150 miles from north to south, continuously on crystalline rocks. 
Throughout the greater portion of the northern boundary (the region to which my 
observations more especially refer), and with few exceptions wherever rock is more ex¬ 
posed, the gneiss is in coutaet with submetamorphic rocks—slates, schists and quartzites. 
The exceptions are where, only very locally, the Lower Vindhyans lap on to the gneiss, and 
where the crystalline rocks themselves extend through and beyond the otherwise regular and 
continuous run of the schists. This latter case is a most Important one ; it occurs in about 
the middle of the region, and is connected with an interruption of nearly 80 miles in the 
run of the schists, dividing them into two separate areas, and introducing all the doubts 
and difficulties of identification. In the western area the submetamorphies are continuous 
along the south side of the Sone valley and into the Nerbudda valley, and are throughout 
the whole extent bounded on the, north by the great Vindhyan range, the strata of which 
rest totally unconformably upon the schists. In the eastern area, in Behar, the slate series 
appears in detached groups of hills more or less isolated in the deposits of the Gangetic 
plain; the principal of these hills are those of Rajgir, Kurrukpur, Ghiddour, Bheowa, 
andMahabur. There is perhaps a presumption that the analogous rocks in the two divisions 
of this great zone are closely related, but many circumstances combine to complicate the 
question of identification : in the western area the rocks are principally argillaceous, and the 
rnetamorphie products of such; while in the east, quartzose deposits largely predominate. 
Again, this break of continuity is coincident with the eastern extremity of the immense 
spread of the Vindhyan rocks, and thus, through a general analogy of composition, the pos¬ 
sibility was at. first suggested (the crystalline rocks not being necessarily all of one period) 
that the quartzites of Rajgir, &c., might he altered Vindhyans. This supposition may, I 
think, he quite set aside : the Lower Vindhyans near their eastern limit rest quite unaffected 
upon the granitics; and the most peculiar and characteristic beds of the Lower Vindhyan 
series are most extensively developed in this position, yet there are no rocks among the 
submetamorphies of Rajgir that would even approximately represent them specifically. 
There is, on the other hand, no inherent difficulty to the general equivalence of the sub¬ 
metamorphic series in the two regions, in the fact of there being much difference of 
composition at so considerable a distance. It need hardly be stated that only the leading 
relations of the rocks are to be noticed: no fossils have as yet been discovered in any of 
them, and no detailed work has as yet been attempted. 
