Notes on the Geology of the Salt Range of the Panjab, with a re-considered theory of the Origin and Age of the Salt Marl; by C. S. MiddleMISS, B.A., Geological Survey of India. (With five plates.)

Introduction.

The Salt Range, since it was first explored in the interests of science, has at several times received a large share of attention at the hands of Indian geologists. In this there is scarcely any room for surprise, owing to its contained mineral and fossil wealth, and to the manner in which the formations are exposed to view. Denudation has used a keen and shrewd scalpel in laying open the anatomy of the rocks in a banding of brilliant rock colours, which there is scarcely any vegetation to hide, or cultivation to disfigure. The inhospitable hillsides, the steeply-carved ravines, and stony wildernesses, though barren and unattractive to the ordinary eye, make up a land of plenty to the geologist the like of which is to be seen nowhere else in India.

So wonderful and vivid, indeed, is the impression made on the mind by a first visit to this region that it will ever be for me an education in itself. Where else in India, or in the world perhaps, can each formation be followed by the eye in its broader lines by its distinctive colour, over hill and hollow, over plateau and ravine, when the range is viewed on a clear day from some commanding height? Where else can be seen a body of horizontal strata comprising members of the Paleozoic, Mesozoic, and Cainozoic groups, lying one above the other in a single cliff section, and apparently as unbroken by great unconformabilities, or by volcanic intrusions, as if they had just been formed? Where else does the geological record, from Cambrian times upwards, present us with a set of rocks unaltered by metamorphism, undisfigured by chemical or dynamical changes, as free in fact from the dust of time as an uncut volume fresh from the binder's hands?

No wonder, then, that the Salt Range, since the appearance of Mr. Wynne's memoir, and during the periodical publication of Dr. Waagen's results in the Palæontologia Indica, has been full of interest for geologists. But, more than all perhaps, the stimulus of controversy has been the agent during the last few years in keeping the interest alive. Dr. Warth, who until recently had been intermittently adding fresh items to our knowledge of the range during holiday rambles undertaken for love, has thrown fresh light here and there into dark places, modified pre-existing results, and necessitated a further examination of the area by the Geological Survey. In 1888 he was successful in finding the first fragments of trilobites that India has yet yielded. Dr. King and myself paid a brief visit to the range in the following spring, when it was determined that I should, in the ensuing cold weather, undertake a thorough overhauling of the subject by the light of the numerous recent discoveries. Another reason urging this course of action was that we saw indications pointing to a theory concerning the origin and age of the Salt Marl entirely different from that which has been hitherto received on the authority of Mr. Wynne. It will be seen to embrace ideas current before the latter undertook his exploration of the country.

Accordingly, in November 1889, I proceeded to take up the work there, assisted by Mr. P. N. Datta, of the Geological Survey.

The Conularia Bed.

Our attention was first turned to the consideration of the Conulariæ-bearing bed. The history of the discovery of the Conularia is well set forth in Mr. Medlicott's Annual Report for 1885 (Records, Geological Survey of India, Vol. XIX, Pt. 1), and in Dr. Waagen's note on the subject in the same number.

These fossils were first found by Dr. Warth, and thought by him to be ordinary pebbles, and therefore of derived origin. Later, he came to the conclusion that they were concretions in situ in the rock, a point of extreme importance at that time, if true, as it altered the age of the lower part of the Olive Series, including the underlying Boulder-bed, from about Cretaceous to Paleozoic.

Mr. R. D. Oldham's subsequent brief visit to the Salt Range once more plunged the matter into obscurity by his decision that they were true pebbles, though probably derived from a concretionary bed, and that, therefore, in their present position, they were of no use in determining the age of the stratum in which they were included (Records, Geological Survey of India, Vol XIX, Pt. 2). In this decision Mr. Medlicott did not entirely agree, as expressed in a note following the one by Mr. Oldham quoted above.

This was the state of the case as regards the opinions for the derived, or in situ nature of the Conularia when Dr. King and I arrived on the ground, except that we had later observations made by Dr. Warth to the effect that the Boulder-bed and Conularia-bed had been found continuous beneath the Speckled Sandstone, and therefore that they were older than the Productus Limestone. Our impressions as to the Conulariæ which we gathered during the short time at our disposal agreed pretty well with those of Mr. Oldham. We found, however, a fossiliferous zone of large bivalve casts between the base of the Boulder-bed and the Conularia zone in the neighbourhood of Dandot, which, if the fossils are sufficiently well preserved and characteristic, should settle the age of the beds irrespective of the Conulariæ.

From a recent paper in the Records (Vol. XXIII, Pt. 1) by Dr. Waagen, it would appear that a bed of the same horizon had been previously found and collected from ; and owing to the mistaken identity of the badly preserved casts, had been temporarily regarded as Upper Cretaceous'; but that on later examination by him in the light of Dr. Warth's discoveries, some of them were found identical with certain Australian Carboniferous species.

During the cold weather Mr. Datta and myself were able to see a good deal of the Conularia-bed, and the results of numerous examinations of different parts of the range, where the Olive beds are exposed, are here given briefly

(1) Many of the Conularia concretions show a rolled and abraded surface, with truncations of the fossils, as described by Mr. Oldham.

(2) Near Makrach the Conulariæ, on the other hand, are very characteristic nodules in shape and figure. They are frequently elongated, pear-shaped, or irregular aggregations.

(3) In the neighbourhood of Choya-Saidan-Shah nearly all the so-called pebbles are not perfectly smooth as to their surface. They are dotted or pitted all over with small marks, which, examined carefully, may be seen to be nothing else than the impressions of grains of coarse sand. This indicates

1 The fossils have not yet been studied in detail by Dr. Waagen.

that at the time of their incorporation with the sandstone they were soft enough to take on the impressions of the sand grains: that they were, in fact, soft clay or marl balls.

(4) At Chel hill, and north-north-west of Khusak, immediately beneath the Conularia pebble zone, there is a layer of soft sandstone with small patches of grey calcareous claystone or marlstone. These patches could not be separated from the rock, and were certainly not pebbles. In, about, and among these patches were Conulariæ and bivalves. Conularia were also found in the sandstone.

(5) Just behind the village of Raturcha the Conularia layer is very suggestive of an origin by concretionary action. There is a concretionary-tabular layer of hard, grey marlstone, that is to say, a layer in which the concretions are not separated from one another. Tracing this along in different directions, it soon splits up into free concretions containing Conulariæ. The whole was clearly one band, but free concretions appeared to have formed only when a Conularia or other fossil was present as a nucleus. The conclusions from these observations seem to be that the Conulariæ are approximately contemporaneous with the stratum in which they are found; that they lived and died on a sandy and marly sea bottom; that after death, marl or calcareous clay collected round them; that after this, whilst still soft, they were in many cases rolled about as clay balls receiving a coating of sand, and then buried in the overlying deposits. The Conulariæ thus become a true index as to the age of the beds in which they are found, which, together with the Boulder-bed, must be regarded as Paleozoic.

Dr. Warth (Records, Geological Survey of India, Vol. XX, Pt. 2) describes a locality in the Nilawan ravine where the Boulder-bed, underlying the Speckled Sandstone of Wynne, includes Conulariæ. In addition to the above, we were fortunate enough to find the Boulder-bed and Conularia-bed in normal appearance and sequence underlying the Speckled Sandstone at the following localities:-(1) A little west of Makrach; (2) Makrach valley, east of Dilwal; (3) on both sides and at the north end of the Sardi glen. As the Speckled Sandstone is older than the Productus Limestone, the cumulative evidence in favour of the Boulder-bed and at least part of the Olive series being Paleozoic is irresistible.

Aspect of the Boulder-bed, Olive Series, and Speckled Sandstone.

Besides the Conularia-bed, our attention was very early attracted to the remarkable aspect of the Crystalline-boulder bed, the whole of the Olive series and Speckled Sandstone, and their inter-relations. Mr. R. D. Oldham (Records, Geological Survey of India, Vol. XIX, Pt. 2) was the first to detect the aspect of unconformability between the basal portion of the Boulder-bed and the Salt-pseudomorph zone near Pid pole-an observation which may stand good in spite of the Paleozoic age of the Boulder-bed and Conularia zone. The following is the additional evidence we were able to obtain in support of this unconformability:

(1) In making a collection of facetted and striated rocks included in the Boulder-bed, and also a typical petrological collection of the crystalline boulders, we frequently came upon largeblocks and included masses of

the Salt-pseudomorph rock surrounded on all sides by the matrix of the Boulder-bed; whilst about one and a half miles north by west from Khusak Fort I obtained two rather large boulders, one of Purple Sandstone and one of Magnesian Sandstone, both grooved and scratched after the manner of glaciated boulders. On the west side of the Sardi glen, a little north of Sardi, there is a local development of the Boulder-bed, 40 feet thick, with Conularia bed above, made up of huge fragments (a foot or more across) of the Magnesian Sandstone, with a few crystalline boulders.

(2) West of Makrach the Boulder-bed oversteps the Salt-pseudomorph zone, and becomes directly superposed on the Magnesian Sandstone. Further west, in the neighbourhood of Malot and Sardi, the Magnesian Sandstone becomes gradually overstepped in the same way, until in the glen south of Nurpur the Boulder-bed rests on the Obolus zone (the latter being well recognized in all its facies, e.g. lumpy purple shales, with worm tracks or fucoid marks, micaceous, and glauconitic, &c.). In the Amb glen and neighbourhood, the Boulder-bed which still forms the base of the Speckled Sandstone is in contact sometimes with the Purple Sandstone and sometimes with the Red Marl.

Since Dr. Warth's discovery in the Nilawan that the Boulder-bed there was the same as the Boulder-bed in the more eastern parts, it had of course been assumed that the different Boulder-beds deemed to be distinct by Wynne were one and the same, and marked a line of unconformability or overlap running the whole length of the Salt Range. Hence evidence under head (2) is merely confirmatory of what has been conjectured by Dr. Waagen (see Pal. Ind., Geological Results, pp. 47-48).

It being understood, therefore, as proved that the Boulder-bed, Olive series, and Speckled Sandstone form one series unconformably overlying the subjacent rocks, I will now proceed to mention a few facts that we were able to glean with regard to them, and to give one or two vertical sections and sketch sections through the series at different points of the range.

First, with regard to the facetted, striated, scratched, and polished crystalline pebbles found in the Boulder-bed, although there has been some controversy on the subject,' I am able to state that, after a large acquaintance with the boulder clays of the eastern parts of England, I can detect no essential difference between them and the Boulder-bed of the Salt Range, except that the latter has lost its clayey consistency and become a dark shale, sandy shale, or sandstone, as the case may be. The similarity is not a strained resemblance, but a complete similarity, carried out in every detail as to shape, size, sub-angularity, and scratching of the pebbles, and their condition merged in and completely surrounded by the finer matrix. The character of the boulders, consisting, as they do, of crystalline rocks (chiefly granites, microgranulites, felsites, schists and quartzites) is very unique, owing to the complete absence of crystalline and igneous rocks in the Salt Range as rock masses with the single exception of the Khewra trap. I hope at another time to give a microscopical description of slices taken from fourteen typical boulders.

Vertical Section No. 1, Plate I, is taken through the Boulder-bed and Olive series, a little west of Pid pole. It explains itself.

1 Referred to by Mr. R. D. Oldham, Records, Geological Survey of India, Vol. XXI, p. 160.

Horizontal Sketch Section No. 1, Plate II, is taken across the valley west by south from Raturcha, and shows a 30-feet bed of reddish, speckled, fine sandstone, which already in this eastern part of the range begins to foreshadow the ultimate large development of the Speckled Sandstone.

Horizontal Sketch Section No. 2, Plate II, is taken across the Makrach valley east of Dilwal, and illustrates, among other things, the first in-coming of recognizable Speckled Sandstone above the Olive Series.

Vertical Section No. 2, Plate I, is taken at the head of the glen above Sardi, and shows the Speckled Sandstone as having now attained a marked thickness, slightly exceeding that of the Olive series. As the section on the east side of the head of the glen observed by us differs in some important respects from that given originally by Mr. Wynne in his memoir (Memoirs, Geological Survey of India, Vol. XIV, p. 180), I extract the following from my note-book :-"The Salt Marl and Purple Sandstone are in their normal positions, though the former is not seen in this part of the glen but lower down. Above the Purple Sandstone we found that the shales, marked by Mr. Wynne on his map as Silurian, undoubtedly belonged to the Obolus beds, for there were the same characteristic purplish, lumpy shales with worm (?) or fucoid markings, glauconite grains, and mica flakes. We found the B zone (for explanation see on) with some specimens of Hyolithes wynnei. Above that we got the Magnesian Sandstone in normal order, apparently superposed conformably. After a fair thickness of this, though thinner than at Khusak fort, we came upon the Boulder-bed, of small thickness, but perfectly recognizable, being formed of crystalline boulders of rather small size in a dark shaly matrix. Next above this, in some olive sandstone, came the Conularia-bed, as recognizable as before, and above this a normal section in the Olive series for some way, until it gradually merged into the Speckled Sandstone. The latter is fine-grained in its lower parts, but the grains of sand are always angular or sub-angular. In its upper part it becomes very coarse-grained and conglomeratic. The pebbles are angular or sub-angular, and composed, the smaller ones chiefly of vein-quartz and a compact felsite, or some allied rock, the colour being light red. The larger pebbles, which generally average 1 to 2 inches across, are chiefly composed of the compact red felsite. There are also sundry pebbles of a limestone, or calcareous sandstone, resembling the Magnesian Sandstone, and others of dark quartzite. In this conglomerate there are none of those coarsely crystallins red granites so common in the Boulder-bed. Above these slightly conglomeratic beds come some chocolate-coloured shales, or hardened clays, alternating with coarse sandstones not conglomeratic at all. In the uppermost parts of these beds there are some few shales of a paler tint, which may perhaps be called lavender. The section then becomes obscured by talus from the nummulitic scarp."

It will be noticed that Mr. Wynne, in his section referred to above, does not acknowledge identifying either the Obolus Shales or the Boulder-bed. His black shale band No. 3 he by inference regarded as the representative of the Obolus Shales, though he does not say so. At page 92, however, he mentions generally that the "lower part of the group [Speckled Sandstone] is often seen to consist of brownish and light-coloured sandstones with some whitish flags and dark shales as well as bands of conglomerate, the pebbles in which are of granite, syenite, and other crystalline trappean or metamorphic rocks, this portion having a general resemblance to some beds of No. 10" [i.e. the Boulder-bed and Olive series]. Considering the wonderful