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Preliminary Sketch of the Geology of Simla and Jutogh, by R. D. OLDHAM, A.R.S.M.,
ANNUAL REPORT OF THE GEOLOGICAL SURVEY OF INDIA, AND OF THE GEOLOGICAL MUSEUM, CALCUTTA, FOR THE YEAR 1886.
For the past three field seasons Mr. Foote has had the Madras Presidency all to himself. This came about in the course of a perfectly natural selection in the distribution of a limited staff according to the urgency of demand, whether practical or scientific. In the early days of the Survey the whole staff was for several successive years engaged upon the coal-fields, and ever since continuously several geologists have been so engaged, but Madras is not favoured in that line, the Gondwana coalmeasures being only found in a part of the Godavari district. For other reasons, however, Madras very early received our best attention. In taking up a new country the rational method of geological enquiry was to get hold of such formations as offered, through their fossils, the means of establishing correlations with known rocks, and from those fixed horizons to obtain indications as to the ages of contiguous deposits. In this way the best part of the Survey staff were, at the beginning, for several years engaged in Madras; and the proportion was fairly kept up until nothing was left but the immense residuum of fundamental gneiss and the oldest schists that locally accompany it; while other parts of India offered more promising fields of research for the final solution of the total complex of formations in Peninsular India. This accounts satisfactorily for Mr. Foote's recent isolation; but the local authorities only recognised the isolation, and remonstrated against it, so it has been decided to add Mr. Fedden to the Madras party of the Survey. Before going on furlough, Mr. Fedden had finished his survey of Kathiawar, and I had intended him to take up new ground in the Rewa Kanta districts of Guzerat, but he has now begun work on the gneissic rocks of Vizagapatam. Results are very slowly acquired in rocks that are so obscure and so extended. Mr. Foote during last season mapped a considerable area in extension of his previous work in Bellary, both of
gneiss and of his Dharwar schistose series. He suggests a probable correspondence of a large part of the gneiss with that of Bundelkhand, long ago distinguished as older than the prevailing gneiss of Bengal. It was then also shown that the gneiss east of Chaibassa, in Singhbhum, is probably of the same age as that of Bundelkhand (Manual, p. 21).
Mr. Foote resumed his survey in Bellary at the beginning of the current season, but he has since been deputed to report on some gold-fields in Mysore, at the solicitation of the local authorities. Although these interruptions to our regular work are somewhat perplexing, it is right that the best knowledge and experience should be made available for the furtherance of practical objects.
We have now published in admirable form by Mr. Lydekker in the Paleontologia Indica the detailed description of the fauna of the Karnul THE KARNUL CAVES. caves, discovered and so carefully explored by Mr. Foote and his son, Lieutenant H. Foote, R.A. If the results were disappointing in respect of what was most hoped for-prehistoric human relics (though upon this point I believe Mr. Foote has still a word to say regarding certain cut bones)—the general results are of considerable interest. As to the age of the fauna, Mr. Lydekker remarks:-"The comparatively large number of species either totally extinct, or which are not now found living in India, renders it probable that the age of a considerable part of the Karnul cave deposits is not newer than pleistocene; and the fauna, as being almost certainly more recent than that of the Narbada beds, may be provisionally assigned to the later part of that period." The numerous affinities with African types is a feature previously noted regarding the Tertiary (Siwalik) fauna of India. Dr. King's regular work in the hills west of the Chhattisgarh plains was necessarily much interrupted by his having to superintend the coal explorations in the fields far to the east. The results of those trials were published in the Records for November, and it has to be regretted that the Rampur field, which is the one crossed by the new line of railway, does not promise a fair supply of fuel. The trials were all by borings, but the samples of each seam were taken very carefully foot by foot, and separately assayed. The amount of ash in almost every case was prohibitively high, from 30 to 50 per cent. In only one seam, in the Baisandar valley, the average was 21 per cent. of ash, the 5th, 6th, and 7th feet giving only 652, 1208, and 18.68. Thus it may yet be possible to get small local supplies from some of these seams, and no doubt this will be attempted by shafts when the demand comes to be pressing. Meanwhile the exploration is being carried on in the nearest ground to the north, in the Mánd valley. In the remote hill country, far to the north of Korba, a large new coal-field was traced out by Sub-Assistant Hira Lall: it is the western extension of the measures noticed some years ago by Mr. Ball at their eastern extremity as the Lakanpur field.
Mr. Hira Lall.
The relations of the rocks forming the plains of Raipur to those underlying them on the west is still under examination. Dr. King describes the bottom sandstone of the Raipur series (? Lower-Vindhyan) as resting with partial unconformity on shaly beds of the Chilpi series-general parallelism of dip at low angles with local overlap and discordance-a like relation to that described by him between the Karnul and Kadapa formations, or even between the separate groups of the Kadapa
series. It seems as if the chief difficulty would be with the lower members of the Chilpi series in connection with igneous and schistose rocks. Dr. King reported upon Mr. Bose's work as still exhibiting the want of observation and study that had been found fault with in previous seasons; I may however add, that since going to the field this season Dr. King has written less unfavourably of Mr. Bose. I only hope he has not been beguiled.
Mr. Hughes' deputation in charge of the Umeria colliery did not terminate till the
end of December (1885), and for the rest of the season he was SOUTH REWAH. engaged in examining the rocks above the coal-measures, Mr. Hughes. and succeeded in finding some new localities for fossils in them. At a few miles to the west, on the Son-Máhánadi, the Jabalpur beds (top Gondwána) are typically represented, and the problem is to make out some distinctions in the variable thickness of sandstones shales and clays between those beds and the coal-measures, representing what in other fields constitute quite two-thirds of the Gondwana system. The most marked stratigraphical boundary in the whole basin is that just above the coal-measures, as was formerly observed in the WardaGodavari basin; yet in neither case does it seem to involve a correspondingly marked change in the fossils, for a considerable thickness of beds above that boundary still contain distinctively lower Gondwána forms. Mr. Hughes has already seen a great deal of those upper rocks, having been at work in Rewah since 1879; and in the north-central portion of the basin he hit upon some fossils marking distinctly the Kota Maleri and Denwa horizon; so it is altogether very disappointing that he has not yet offered any clue to an interpretation of the stratigraphy where it presents any difficulty. On this account, lest we should hopelessly lose any benefit from the extensive acquaintance Mr. Hughes should have acquired of that ground, it was with much reluctance that I recently consented to his deputation for the present field season to the Nizam's territories, to conduct exploration for minerals; but practical objects must, I suppose, claim precedence.
During the past season Mr. Jones completed the survey of the southern coal-fields
of the Satpura Gondwána basin. There are altogether eleven separate areas where the coal-measures group is exposed, seven of them being in the Chhindwara district. The four adjoining areas in the Betul district were mapped and described some years ago (Rec., VIII, 1875). The intended exploration of the seams by trial borings in connection with the survey not having been carried out, the information regarding the prospects of the field is little better than before, the principal outcrops having been already reported on long ago. Mr. Jones has now given a full account of all the exposures and defined the limits within which there is any chance of finding coal. On the whole, the quality of the coal, so far as it can be ascertained from outcrop samples, is not very encouraging. The report and maps are now at press. As a geological study of a very interesting region, Mr. Jones' report is disappointing, through defect of critical observation and discussion on the ground, for it is futile to expect to solve stratigraphical puzzles by the colligation of field notes; the problems must be stated, and to a great extent solved on the spot; the description of them is then a simple matter. The failure to find a single recognizable fossil during two seasons' work on these coal-measures is similarly unsatisfactory.
This piece of work corresponds to Mr. Hughes' description of the southern coalfields of the Rewa Gondwána basin; and here, as there, the chief puzzle remains— to put in order the main mass of Gondwána strata above the coal-measures. A preliminary attempt at this was made in 1873 (Memoirs, Vol. X).
For a great part of last season Mr. Hacket was engaged in endeavouring to clear up the perplexities of the Arvali rocks by a further study of them on their eastern margin, about Chitor and Neemuch, where they are in contact with an archæan gneiss. In this ground in 1881, as was noticed in the annual report for that year (Rec., XV., p. 3), Mr. Hacket made out that the sandstone of Mundsaur, which had originally been taken to be Vindhyan, as occurring close to these rocks and quite like them petrologically, was really identifiable with the highly metamorphic Delhi quartzite (see Rec., XVII, 103) so extensively exposed in the north-east of the Arvali region. This implied a wide distinction of this member from the schists with which it is generally associated throughout the region, and of course a complete separation from the Vindhyans, which are elsewhere quite unaffected in immediate proximity with the Arvali slates. Mr. Hacket now extends this identification so as to include the Arvali schists: the sandy calcareous conglomerate resting on the gneiss near Dhaulapani (20 miles south-west of Neemuch) and containing pebbles of that rock, passes below the limestone and shales that underlie the Mundsaur sandstone, and these also are traceable to the north continuous with the slates, schists, and limestones of the Arvali series. Thus the partial break in that series, as established in 1881, is a good deal modified, and we now seem to have representatives of the whole metamorphic series of the Arvalis (so far as at present made out) in unaltered original contact with an archæan gneiss of the peninsular area, as if sheltered in a bay of that most ancient land from the contortion and metamorphism that took full effect upon the same deposits in the main area to the westward. The western boundary of this old gneiss is very obscure, owing to the changed condition that rapidly supervenes in the newer rocks on that side, where they are extensively transformed into a schistose gneiss. In confirmation of this distinction of two gneissic formations, Mr. Hacket describes the occurrence of boulders of gneiss in the schistose gneiss at the village of Mandkhola (Lon. 74°34', Lat. 24°-7), but the observation needs critical petrological confirmation. The re-connexion of the Delhi quartzite with the Arvali series is more in harmony with the fact of their association over so large an area; but Mr. Hacket considers that there is probably some unconformity, for the massive quartzite is locally in contact with different rocks of the underlying series; this, however, might be due to faulting where the strata are so greatly disturbed. The gradual change from the quartz veins so abundant in the slates of the eastern part of the region (as east of Deoli) to the granite veins that similarly pervade the schists of the central zone, is a noteworthy feature. On the other hand, Mr. Hacket notices patches of comparatively unaltered slates within the area of the schistose gneiss, as close to the east of Oodeypore, and again on the west side of the Arvali range east of Mera (close to the north of Abu); but these may only be, as Mr. Hacket suggests, freaks of partial metamorphic influence within the same rock series.
The stratigraphical relation now brought forward of the Arvali series to the old