A Note on the Olive Group of the Salt-range,
by R. D. OLDHAM, A.R.S.M.,
Deputy Superintendent, Geological Survey of India.
Records of the Geological Survey of India. 19, 127-131.

The last number of these Records contained a paper by Dr. Waagen on some palaeozoic fossils recently collected from the Olive group of the Salt-range. Dr. Waagen declared his conviction, founded on information supplied by Dr. Warth, that these fossils were derived from concretionary nodules and gave a true indication of the age of the beds from which they were obtained. On the strength of this conclusion Dr. Waagen declared that it would be necessary to divide the Olive series into two portions, one of which was to be regarded as of lower Carboniferous, the other of Eocene age. I was consequently despatched to the Salt­Range to verify on the ground an opinion involving so great a change; the results of my observations, which entirely confirm Mr. Wynne's original mapping, are embodied in the following passages.

On meeting Dr. Warth I was surprised to find that he by no means shared Dr. Waagen's confidence in the concretionary nature of the fragments which had yielded these fossils, and that, though he was not unwilling to allow that this opinion might be correct, and that the fossils truly indicated the age of the bed from which they were obtained, he decidedly inclined to his original idea that they were transported pebbles; on examining the exposures I was able to convince myself that in this he was perfectly correct.

In the first place the bed in which they occur is a thin band of gravel, the last rock in which one would a priori expect concretionary nodules to be formed. Then on examining the so-called concretions I found that in many cases the fossils extended right to the surface, and were there abruptly, often obliquely, truncated, not infrequently they could be seen exposed in section on the abraded surface of  the pebble and occasionally fragments could be found showing on their surface the abraded and more or less obscured impressions of Oonularia or of one of the associated bivalves.

This would in itself  be sufficient proof, but confirmatory evidence is not want­ing. There are associated with this bed some shaly bands lithologically very similar to the matrix of the Oonularia pebbles, but these bands have so far yielded no trace of a fossil: further, near Choah Saidan Shah, where the band is less markedly gravelly and where the pebbles have more the appearance of concre­tionary nodules than near Tobar, there are frequent lenticular masses of an inch or more in thickness and 6 to 12 inches in length which are undoubtedly of concretionary origin and formed in situ, but those, though they have been most carefully searched by Dr. Warth, have yielded no trace of a fossil. Yet another piece of evidence is the occurrence, though very rarely, of pieces of pale micaceous sandstone in this band, and one of these fragments showed obscure impressions of Oonularia. Now this fragment was angular in outline, and is moreover very different in aspect from any concretienary nodule that has ever been seen by me or, I may safely say, any other geologist.

After this it might be thought superfluous to add anything further, but it will at any rate be advisable to notice the arguments on which Dr. Waagen based his final conclusion. Of these, the last, that founded on the homogeneity of the fauna, is without doubt the most important, and when taken in conjunction with the fact that four out of ten species are either identical with or closely allied to species which in Australia are found in beds that also exhibit proofs of glacial action, 1 would seem to make this argument conclusive. Nevertheless, in the face of direct evidence pointing to a different conclusion, this becomes worthless. The peculiarity, however, requires some explanation, and I offer the following hypothesis as one that is at least possible; a careful examination of the fossiliferous pebbles has induced me to believe that for the most part they were originally concretionary nodules, though occurring in their present position as transported pebbles. I base this conclusion on the fact that they are frequently of somewhat irregular shape, and that then it is usual to find the fossils completely imbedded, while those pebbles which show distinct traces of transportation and in which the fossils are truncated at the surface are usually fairly well rounded and water-worn. It will be seen that if this contention is correct, and if shaly beds with concretionary nodules, for the most part formed round fossils, had been exposed in the neighbourhood, it would not be difficult to account for the abundance of pebbles formed from these same nodules.

With regard to Dr. Waagen's first reason, the restriction of the" concretions" to the top of the bed in which they are found, I cannot allow this to pass as a correct description of their mode of occurrence, though, if correct, I do not consider that it would prove anything. Undoubtedly the fossiliferous pebbles do occur more abundantly near the top of the bed than in the lower portions; but this is easily explained by the fact that most of the pebbles in this band of gravel are of quartz or hard crystalline rock, and are of greater specific gravity than the fossiliferous pebbles. In consequence of this, the latter would be swept away by a current only sufficient to transport the former; but as the current died away, it would no longer bring down the heavier pebbles and a layer of the lighter fossiliferous pebbles would be deposited before the current ceased to be able to transport even them. This hypothesis is supported by the fact that, while the crystalline pebble gravel is very distinct near Tobar and Pid, it is almost absent in the exposures near Choah Saidan Shah, and the bed, here very much thinner, contains very few pebbles besides the fossiliferous ones and some of slate and impure limestone.

This thinning out of the bed to the northwards is in contradiction to Dr. Waagen's original supposition, that the fossils came from the Himalayas - an opinion which must have been founded on pure hypothesis, and is not supported by any known fact for, not only have no Himalayan beds yielded fossils similar to those of the pebbles, but all the fragments of rock in the associated boulder beds are of most conspicuously peninsular origin, not a few are of the very peculiar and easily recognizable Malani porphyry. It is consequently to the southwards that we must look for the original source of these fossils; the only locality where any rock is exposed in that direction is the Korana hills, and unless the mother rock of these pebbles is found there or in the Salt-range itself, it must be buried beneath the alluvium of the Punjab.

Having shewn that the fossils are of derivative origin and can, consequently, not be appealed to in determining the age of the beds in which they occur, it remains to see whether there is any stratigraphical evidence in favour of the associa­tion of the boulder beds of the Olive group with those of the speckled-sandstone which has been advocated by Dr. Waagen, and to determine whether it will be necessary to draw any line of division in what has so far been regarded as a single group. I may at once remark that I can find no evidence whatever in favour of these hypotheses, but have every reason to agree with Mr. Wynne in associating these beds with the nummulitics rather thiLn with the older beds, and in regarding them as forming a single homogeneous series.

Not the least forcible of these is the fact that Mr. Wynne, a most careful observer, the accuracy of whose mapping it would be impossible to overpraise, and who had most ample opportunities for examining the rocks in detail, was distinctly of opinion that the beds of the Olive group belong to a single conformable series of beds, and that this is more closely related to the overlying nummulitic beds than to the underlying salt-pseudomorph group which he regarded as of triassic age. That this conclusion is correct, is proved by the marked unconformity which can be traced between the salt-pseudomorph group and the Olive group, and the equally marked gradual transition from the latter into the soft white sandstones which underlie the nummulitic coal.

This unconformity is well seen on the main road from Pind Dadan Khan to Rawalpindi just beyond the 8th milestone, where the road runs in a sidelong cutting inthe steeply sloping hill side. Here there may be seen a small lenticular patch of boulder conglomerate apparently interbedded in the red beds of the salt­pseudomorph zone, but this is so exceptional and so much at variance with what is seen elsewhere that I cannot doubt that the interbedding is only apparent and that the appearance is due to slippage, of which there is ample indication just here. But everywhere, as long as the junction is exposed on the road section, the boulder conglomerate is seen to rest on the obliquely and irregularly truncated edges of the beds of the salt-pseudomorph group. Where the boundary runs up the hill side this is of course not so clearly seen, though the unconformity can be detected in the ravines; but here, as in the road cutting, the boulder bed where in contact with the older rocks is full of fragments evidently derived from them.

Dr. Waagen has suggested that the boulder beds of the Olive group and those of the speckled-sandstone are the same. I find it impossible to accept this view, for not only did Mr. Wynne regard them as absolutely and entirely distinct, but the colouration, from which their name was derived, is so marked and so distinct that it is possible to recognize the occurrence and even to trace the boundary of this group from a distance-in fact from as far as it is possible to see the distinction between hill and valley. It is hardly conceivable that this strongly marked feature should be a merely local phenomenon and not indicate a difference of age.

The stratigraphical relations of the beds are thus seen to show that the Olive group is a homogeneous group and must be associated with the overlying numulitic beds rather than with the underlying Paleozoic or early secondary beds. If it should be objected that it is improbable that there should be such a development of glacial boulder beds at more than one geological horizon, I would point out that Mr. Lydekker found beds, of evidently glacial origin, in Ladak, which, like those of the Salt-range, conformably underlie the nummulitic series. This must be taken merely as a suggestion. I do not bind myself to anything except that the fossils occur in derivative pebbles, and that the Olive group of Mr. Wynne is of later origin than the rock from which they are derived.

As regards the speculations Dr. Waagen has based on these fossils, they are very similar to some which I put forward in 1884,1 except that the latter were perhaps more in accordance with the known principles of physical geography, which hardly warrant us in picturing a glacial epoch wandering about the earth like a lion seeking whom or what it may devour. All such speculations, though useful in indicating possibilities, should be used with great caution, and should not under any circumstances be regarded as serious geology.

To sum up : 1st, the fossils discovered by Dr. Warth being of derivative origin, simply prove that the Olive group is post-Carboniferous; 2nd, the stratigraphical relations of the beds prove that it is a homogeneous group which is closely associated with beds of acknowledged nummulitic age ; 3rd, it is in all probability of contemporaneous origin with the infra-nummulitic glacial beds of Ladak; 4th, there is at present neither need nor reason for a revision of Mr. Wynne's survey; and 5th, the question as to the age of the Talchir group of the Gondwana series is left precisely as it would be had these fossils never been discovered.

Memorandum on the discussion regarding
the boulder-beds of the Salt-range,
by H. B. MEDLICOTT, Director of the Geological Survey of India.

The promulgators of an important announcement are bound to give immediate publicity to any doubt that may arise regarding it, and I accept Mr. Oldham's note as throwing much doubt upon the new view of the Salt-range sections expounded by Dr. Waagen in the last number of the Records; but as the note is not completely demonstrative and exhaustive, it is desirable to anticipate further discussion by an appraisement of the present evidence on both sides. Having no personal knowledge of the ground, I accepted the new view on its merits as represented by Dr. Waagen, who next to Mr. Wynne was most familiar with the sections in question, and he was moreover in direct communication with the observer who furnished the immediate data for the change of interpretation. In adopting the view so forcibly presented I had the satisfaction of finding that no discredit was imputed to Mr. Wynne's work. Besides that Dr. Waagen was himself almost as much concerned as Mr. Wynne in any oversight that had been made, it seemed that the oversight in question was of a most venial nature-the not having detected fossils in a particular thin bed of gravel; and I know well how deceptive may be an appearance of natural continuous sequence of strata. On the whole, as represented by Dr. Waagen, the proposed view seemed to me to reconcile some apparent anomalies in the stratigraphy of the Salt-range as represented in Mr. Wynne's memoir, notably the similarity noticed by him in the several boulder-beds placed in very different horizons, although apparently in more or less continuous connexion. I even thought that the new reading would be especially pleasing to Mr. Wynne, as tending to re-vindicate his original view of the occurrence of older palreozoic strata in the eastern Salt-range, which had been the principal point of difference between him and Dr. Waagen. I did indeed perceive a want of due discussion of petrological and stratigraphical evidence in