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Mawlyngngot (25° 24′ 91° 56′), where the stage is represented by a conglomerate over 50 feet thick overlaid by 50 feet of massive, falsebedded sandstone. Another outlier, east of Phansawrut (25° 28': 91° 53'), rests on a zone of lithomarge.

An unconformity exists between the Cherra sandstone stage (basal Eocene) and the underlying Upper Cretaceous strata, which is well displayed in the cliff sections at the eastern edge of the Cherrapunji plateau. Here the Cherra stage attains its maximum development. The unconformable relationship between the two sets of beds is best studied in the cliff face about three miles north of Cherrapunji. In this section the upper Cretaceous beds dip at 10°-12° and are overlaid by almost horizontal Cherra sandstone; about its base the sandstone contains pebbles and in places becomes conglomeratic. This basal pebbly sandstone becomes conglomeratic in a northerly direction, as at Laitryngew. The basal Cherra sandstone conglomerate was found by Mr. Ghosh on all the footpaths descending from the western edge of the main plateau into the valley of the Umiew river, at one place a 200 ft. thick band of an algal limestone coming below the main Cherra sandstone but above the basal Cherra conglomerate. In a few instances the conglomerate is wanting at the base of the sandstone.

The Cherra sandstone stage is conformably overlain by the Sylhet (Nummulitic) limestone stage, which consists of limestones, sandstones, shale and coal seams. The limestone is sometimes absent, possibly due to subterranean solution, but in places the Cherra sandstone passes imperceptibly into the upper sandstone. In such cases it is difficult to delineate the boundary between the two stages. Mr. Ghosh records that he did not find evidence of the beds of the Sylhet limestone stage north of a line joining Pyngkerdem (25° 21′ : 91° 54') and Sohrarim.

Mr. V. R. R. R. Khedker, Assistant Geologist, left for the field on the 3rd February 1937, for the Garo Hills district, where he worked for a fortnight under Dr. Fox, and then proceeded to the Khasi and Jaintia Hills district, where he worked up to the 10th May, 1937, mapping the south-east portion of sheet 78 0/10 and the south-west portion of sheet 78 0/14. He found that the oldest rocks in this area are the Shillong series. Their general strike is N. E.-S. W., with most of the strata dipping towards the south-east.

Khasi and Jaintia Hills district, Assam.

Mr. Khedker recognises the following sub-divisions in the Shillong series:

(1) Slates and phyllites, which occur between Sohiong (25° 30′ : 91° 43') and Wah Umiam nala, with a N. 40°E. S. 40 W. strike, and dips at high angles, varying between 60° to 80° towards the south-east. These include hornstonelike siliceous bands, felspathic schists, quartz schists, carbonaceous slates, arenaceous gritty laminated slates and phyllites. Locally these beds have been considerably crumpled and sheared.

(2) Conglomerates occur in three isolated outcrops-half a mile west of Sohiong (25° 30′ : 91° 43′), in the vicinity of Kynsew (25° 33′ 91° 44') and one mile E. N. E. of Kynsew. These consist of pebbles and boulders of quartzite, embedded in a schistose micaceous matrix which is also arenaceous in places. The conglomerates occur interposed between a series of quartzites and the slates abovementioned and are seen along the western margin of the slates.

(3) Quartzites--these rocks, which occur largely east of the slates, form the region to the right of the Wah Umiam nala, including Shillong itself and the surrounding plateau. Quartzites also occur towards the west of the slates, in the area between Nongthliw (25° 33′ : 91° 43′) and Dingshit (25° 31′ 91° 41′). They are well bedded, low grade quartzites with thin irregular laminations of sericite and show current bedding. Those which are towards the west of the slates however have more sericite and are often foliated.

(4) Between Mawiong (25° 34' 91° 43′) and Nongti (25° 33′ : 91° 41′) and between Dingshit (25° 31': 91° 41′) and Mawkneng (25° 30′ 91° 40′), there are belts of micaschists.

(5) Between the mica-schists (4) and the masses of intrusive Mylliem granite-to the west of the former and south of the latter-there are belts of supposed paragneisses which, in Mr. Khedker's opinion, are probably connected with the intrusive Mylliem granite. He, however,

believes that the whole series, 1-5, is the Shillong series.

Mr. Khedker has found that the Shillong series have been invaded

by two igneous rocks-(a) a basic rock, now epidioritised, which

is presumably the Khasi greenstone; and (b) granite of the Mylliem type. This is in agreement with long established facts from elsewhere in the Khasi and Jaintia Hills. The epidiorite appears as sills along the bedding planes of the Shillong series. The granite occurs as stocks and bosses in the Shillong series.


A banded granite which covers a large area in sheet 78 0/10 and which has been described as a granite-gneiss' by previous workers, is also present. It is probable that this banded granite is a gneissic type of the Mylliem granite.

The Shillong series and the Khasi greenstone are traversed by quartz in veinlets to large reefs, which reefs are absent from the granites. Two localities of a highly weathered gritty sandstone have been noted by Mr. Khedker as remnants of Cherra sandstones,mile north of Sohiong (25° 30′ 91° 43') and one mile S. S. E. of Laitartet (25° 34' 91° 44').


North-western Circle.

101. Dr. A. L. Coulson continued to be in charge of the North-western Circle during 1937. The following officers conducted field work in this Circle Dr. A. L. Coulson, Baluchistan, Waziristan, NorthWest Frontier Province and Kashmir; Mr. W. D. West, Simla Hills; Mr. J. B. Auden, United Provinces and the Karakoram, Mr. H. M. Lahiri, Punjab; and Mr. P. C. Das Hazra, Kashmir.

102. When he investigated the water-supplies of certain areas in Baluchistan for the military authorities, in December, 1936, and January, 1937, Dr. A. L. Coulson entered that Baluchistan. province from Waziristan by the Tanai-Gul Kach-Fort Sandeman road, thus enabling him to examine, with a view to their tentative correlation with his Waziristan sequence, the continuation into Baluchistan of the thick series of limestones and shales of the Toi Khula area which form part of the Janjal Plant series.

Near Fort Sandeman, the Kapip Khwara has cut a gorge through a series of shales, limestones and sandstones shown as Cretaceous on the 32-mile map of India, presumably following Vredenburg's mapping (unpublished). His published map of the Quetta-Pishin area1 only extends to a short distance east of Hindubagh. Neither Cotter2

1 Rec. Geol. Surv. Ind., XXXI, Pt. 3, Pl. 18, (1904). Op. cit.., LI, Pt. 1, p. 10, (1920).

nor Fermor1 makes any mention of this series of limestones and shales in their summaries published in the General Reports quoted; but Cotter has mapped the "sandstones and shales" of the Jalai Kalai area in sheet 39 E/6 as probably Upper Cretaceous.

Dr. Coulson had tentatively referred the rocks of the Kapip area to the lower part of Dr. M. Stuart's Janjal Plant series in Waziristan, which the former considers as Lower Cretaceous or uppermost Jurassic. But three-quarters of a mile north-east of Nim Parao (31° 52′ : 69° 23′), in rocks which Dr. Coulson had thought in the field to be the same as those cut by the Kapip Khwara, he collected an ammonite which was identified by Dr. L. F. Spath as Didymites, a genus characteristic of the Lower Norian. (Upper Trias). To the east of the Kapip gorge is a broad valley which the stream has carved through thinly laminated black shales with ferruginous concretions, apparently similar to the uppermost stage of the Janjal Plant series. In the rocks of the Kapip gorge are certain bands of ferruginous argillaceous limestones which contain fossil organic remains apparently algal in character.

Dr. Coulson has noted that the fundamental feature of the geology of the Nim Parao, Sambaza and Sri Toi areas to the north of Fort Sandeman is the occurrence of a faulted outlier of Siwalik rocks which has been preserved owing to the fact it has been faulted down into older rocks. The eastern boundary of this elliptically shaped outcrop is a fault, the Sri Toi fault, which, after running north and south through sheets 39 E/5 and 6, turns south-west in the latter sheet towards Zarmat and Khushkhalwai Sar after passing to the east of Sri Toi Post. Naturally, in field work with armed escorts, Dr. Coulson was unable to trace this fault along its entire length. He notes, however, that at Nim Parao, the fault seems to branch northwards and Nummulitic limestones and shales crop out between the two branches. Amongst the fossils collected by Dr. Coulson, Mr. H. M. Lahiri has provisionally identified Nummulites spp., Assilina spp., Assilina granulosa, d'Arch., and Discocyclina spp.

The western boundary of the elliptical outcrop of Siwaliks is also faulted, as? Kirthar limestones and shales with no basal conglomerate are the first rocks met as the boundary is crossed.

1 Rec. Geol. Surv. Ind., XLVIII, Pt. 1, p. 12, (1917). Op. cit., 72, Pt. 1, p. 73, (1937).


There has been very complicated faulting west of Sambaza and Kanikhwa China.

From 1 miles north-west of Sambaza, Mr. H. M. Lahiri has provisionally identified Terebellum cf. distortum, Turritella imbricataria, Stylophoria sp., Turbo sp., Vicarya sp., Fistulana elongata, Trochosmilia sp., Astrococma cf. numisma, a Cidaris spine, Nummulites spp., etc. West of Sambaza Nummulites sp., N. obtusus, and N. exponens occur. Assilina exponens, A. mammilata, Discocyclina dispansa, and Discocyclina sp. occur in the faulted area at Kanikhwa China.

The longer axis of the Siwalik outcrop is at least 20 miles long, stretching from Nim Parao in sheet 39 E5 to well south-west of the deserted militia post of Tungiwar in sheet 39 E/6. The constituent rocks comprise red and grey sandstones and sand-rocks, frequently argillaceous, grits, conglomerates, clays, etc. The more resistant conglomerates, grits and sandstones form ridges which at times have a considerable relative elevation over the general level of the country. Strong grey sandstones, reminiscent of the Nagris, form the Spera Zhara and Khushkhalwai Ghar; the general facies of the rocks is that of the Nagri and Dhok Pathan stages of the Middle Siwaliks. The strike of the Siwaliks is very variable in the Nim Parao region, but becomes north and south and later north-east and south-west in the Sri Toi area. When it is not nearly vertical in the south-western part of the outcrop, the general dip is to the north-west, being at times as low as 45°.

The Siwaliks are frequently covered by a mantle of recent deposits, which are possibly glacial in places. The streams appear to have been rejuvenated at no distant date, the recent deposits forming terraces at times, flat-topped masses capping vertical or highly dipping eroded edges of Siwalik rocks.

The older rocks to the east of the Siwaliks are exactly similar to those of the Toi Khula area in Waziristan. They are generally contorted and highly folded. In the Nawe Oba area, they are intruded by large bosses of peridotite which is now altered to serpentine. Cotter (loc. cit.) has noted two occurrences of chromite in these serpentines. The junction of these rocks and the serpentines is more or less parallel to the road in the gorge of the Torghara Manda for some distance. One or two little masses of serpen

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