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of from one to two thousand feet. This conglomerate is composed of quartz and quartzite pebbles with abundant felspar fragments derived from the Aravalli pegmatite, all much compressed and recrystallised; in certain beds occurs a boulder conglomerate resembling that at Bar. On some portions of the line of unconformity the thin quartzite is eliminated by thrust-faulting; in others it is repeated, and in the south of the area surveyed expands again into a thick felspathic conglomerate like that of Srinagar. Above is a carbonaceous limestone-only locally present-containing wollastonite, and biotite-granulites, succeeded by a thin and very persistent quartzite. Then follows a thickness of about 3,000 feet of biotitic and siliceous limestones, folded in an isoclinal syncline with dips to the north-west. This syncline rises as it is followed to the south-west, and is succeeded further along the strike by other indefinite areas of similar limestone which is complicated folded and intimately associated with calc-schists. The latter are extremely flaggy rocks consisting essentially of tremolite, quartz and felspar, with varying amounts of biotite and calcite, and there is no doubt that their present banding, in endless alternations of layers varying in the proportion of tremolite or calcite with biotite, represents their original stratification and that the tremolitic facies and the biotite-calcite facies are essentially modifications of the same thing. They have a general anticlinal lie, with complicated minor corrugations, and are everywhere injected, to a profuse degree, with tourmaline-muscovite-pegmatites in dykes, sills and masses up to two miles long and a mile wide. This is the pegmatite from the later post-Delhi granite, and it is practically absent from the limestones. From the field evidence however, Dr. Heron is of opinion that pegmatite intrusion is not the cause of the production of the tremolite of the calc-schists; its preponderance in the calc-schists, and even more so in biotite schists, is possibly due to mechanical causes, such as the fissility of the biotite schists, and, due to the calc-schists, reduction of volume, allowing fissuring, due to the crystallisation of amphibole. Along their north-western margin the calc-schists dip under biotite schists, frequently garnetiferous, which with three bands of somewhat irregular quartzites, make up the north-western third of the syncline. In this portion dips are uniformly to the north-west, according to the prevailing habit, and the lowest bed, the boundary quartzite, is thus inverted under the older gneisses of the central Aravalli

belt. The basement quartzite is thin and not notably felspathic, but immediately above it is a considerable development of felspathic schists-originally arkose. In this portion also pegmatite has an enormous development, especially towards the south-west, where the mode of intrusion changes from that of dykes and sills to minute interfoliar injection, resulting in the regional production of "injection gneiss" or "migmatite."

The north-western syncline may be considered as two broad zones running along its length, in the direction of the strike. The south-eastern zone, which is by far the broader, consists of an inextricable complex of-to mention the chief types only-calc-gneisses, biotite-schists and felspathic schists (arkose) with irregular masses of biotitic limestone, talc and chlorite schists, and irregular lenticular quartzites, which are siliceous modifications of the calc-gneiss, and white crystalline limestones near its north-eastern margin. No plan of folding can be made out, but wherever any large surface of calc-gneiss is exposed, the most remarkable crumpling is seen, showing that deep-seated folding has carried this assemblage well within "the zone of flowage," where the rocks have acted as if they were plastic under enormous pressure. No continuity of type is maintained as any given band is followed along the strike, and it is probable that the whole complex is a mass of corrugations, pinched out and pitching steeply. It is believed that this complex is to be correlated with the tremolitic calc-schists and biotitic limestones of the other syncline, with which it has a general resemblance, allowing for the intenser and more deep-seated folding and metamorphism undergone. The term "calc-gneiss" instead of "calcschist" is here used to indicate that the banding of the rocks is on a considerably bolder scale. A quartzite or arkose is present, in places, on the margin with the Aravalli gneisses of the central belt, but, as often as not, this has been obliterated by the thrusting of the syncline on the older system.

Pegmatite veins are, except on its margins, practically absent from the north-western syncline, but the hypothesis that tectonic movements have carried it to a greater depth in the earth's crust than has happened to the south-eastern syncline, is supported by the presence of numerous bosses of intrusive granite, the deeperseated equivalent of pegmatite. In addition, veins of fine-grained aplitic granite are numerous, and there is a great abundance of varied amphibolitic rocks, some of which are undoubtedly intrusive,

while others may be metamorphosed effusives and pyroclastics. To the north-east, where the syncline opens out, dips lessen, and the structure can be seen, an immense thickness of these hornblende schists, is exposed, resting on the mixed rocks of the complex.

The north-western and much narrower portion of the syncline is separated from the assemblage just described, by a persistent, fine-grained, white limestone, without stratigraphic discordance on either side. From here to the south-west base of the syncline much more regularity is apparent, the beds being vertical and the divisions being traceable for about 30 miles along the strike, except in so far as they are obscured by epidiorite intrusions; passing from th limestone they consist, in order, of felspathic schist (arkose) with local limestones, biotitic-schist, biotitic limestone, biotitic-schist and the Bar conglomerate. This last is a remarkable bed, extending along the strike for 30 miles and having a measured thickness of 1,000 feet. It is composed of boulders and pebbles of grey quartzite and of gneiss, derived from the underlying older system, which are flattened and drawn out in an extraordinary way in the direction of the dip so that their greatest dimension is ten to twenty times their least; in shape they are best likened to cuttle-bones.

North of where the Bar conglomerate dies out is a very large intrusion of the post-Delhi granite, 26 miles long by 4 miles wide, which abuts against the Aravalli gneiss on one side and the basal beds of the syncline of Delhi rocks on the other; against the former it has an abrupt margin and is easily distinguished from it by its coarseness of texture, the presence of tourmaline in acid segregations, and other lithological differences.

Sub-Assistants Barada Charan Gupta and L. A. Narayana Iyer accompanied Dr. Heron for instruction and training.

BIBLIOGRAPHY,

The following papers dealing with Indian geology and minerals were published during the year 1923

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AYYANGAR, N. N. and Bearing of Geology on some Engineer

NARKE, G. G.

BROWN, J. COGGIN

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(a) Contributions to the Geology of the
Province of Yunnan in Western
China, 7.—Reconnaissance Surveys
between Shun-ning Fu, Pu-e'rh Fu,
Ching-tung T'ing and Ta-li Fu. Rec.
Geol. Surv. Ind., LIV, 296-323.
(b) Contributions to the Geology of the
Province of Yunnan in Western China.
8.-A Traverse down the Yang-tze-
Chiang Valley from Chin-chiang-kai to
Hui-li-Chou. Ibid, 324-336.

(c) India's Mineral Wealth. Published by
the Oxford University Press.

BROWN, J. COGGIN and The Geology and Ore Deposits of the

HERON, A. M.

Tavoy District. Mem. Geol. Surv. Ind.,

XLIV, 167-354.

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