According to Sahni, the salt layers accumulated from evaporation of sea water in coastal lagoons, whereas the kallar represented dust and dirt blown on to the drying salt by the wind. Sahni guessed that the kallar might contain pollen and other plant microfossils. When he examined specimens, he found this to be so (Sahni 1944, p. 462): “Every single piece has yielded microfossils. . . . The great majority are undeterminable as to genus and species, being mainly shreds of angiosperm wood, but there are also gymnosperm tracheids with large round bordered pits, and at least one good, winged, six-legged insect with compound eyes.” To Sahni, this meant that the Salt Range Formation must be Eocene rather than Cambrian. Sahni later found plant fragments not only in the kallar, but in associated solid rock layers composed of dolomite and shale.
Around this same time, the Geological Survey of India and an oil company sent a team of geologists to carefully study the Salt Range Formation, and on the basis of their field observations they concluded that it was in normal position below the Cambrian Purple Sandstone and was thus Cambrian in age. This conclusion was announced in a letter to nature (Coates et al. 1945). Among the geologists signing the letter was Gee, previously an advocate of an Eocene age for the Salt Range Formation. The geologists admitted, however, that “our conclusions were arrived at despite certain difficulties, such as the occurrence of minute plant fragments of post-Cambrian age in the dolomites and oil shales, for which we have at present no clear explanation to offer.” In other words, it might be possible to explain the presence of plant fragments in the soluble salt layers, but how did they get into solid rock such as dolomite and shale? This line of reasoning is based on the assumption that land plants did not come into being until the Silurian (about 400 million years ago), with advanced plants such as angiosperms not arising until the Cretaceous (about 100 million years ago).
In his presidential address to India’s National Academy of Sciences in 1944, Sahni (1945) introduced numerous examples of pollen, wood fragments, and insect parts found in samples of kallar, dolomite, and shale from the Salt Range Formation. In his report, Sahni (1945, p. x) said that “stringent precautions” were taken to prevent contamination of the samples with modern organic remains. He also emphasized that samples were taken from locations where the geological evidence ruled out intrusion from younger strata.
The laboratory techniques employed by Sahni and his assistant, B. S. Trivedi, were rigorous. In a demonstration at a symposium, said Sahni (1945, p. xiv) “a piece of carbonised wood was revealed in a tiny block of dolomite . . . which had been cut and polished on all sides to show it had no pits or cracks visible even with a strong pocket lens. The block was, as usual, passed through a flame and then plunged into a jar of filtered dilute HCl.”
In his own address to the National Academy of Sciences, Gee (1945, p. 293) concluded that the Salt Range Formation was a normal sedimentary deposit and in its original position below the Purple Sandstone. This meant it was Cambrian or Precambrian (Gee 1945, p. 305), while Kohat salt was Eocene. This was a change from his earlier opinion that the Salt Range Formation was Eocene (Gee 1934). He saw no compelling evidence for a massive overthrust in the region (Gee 1945, p.
305). Pascoe, formerly a supporter of the idea that the Salt Range Formation was an Eocene deposit covered by an overthrust, placed the Salt Range Formation in the Cambrian section of a new edition of his manual of the Geology of india (Sahni 1947b, p. xxxi).
Gee said that foraminifera of Eocene type found by him in the Salt Range Formation were not in situ, as he earlier believed, but were derived from younger formations. Concerning plant fragments, Gee (1945, p. 296) noted: “Further work on the clay containing plant fragments at Katha led to the discovery of one or two small leaf impressions which were identified by Prof. B. Sahni as belonging to Acacia, a genus still existing in the Salt Range area, whilst in the case of the Khewra mine occurrences, the existence of an important thrust-fault nearby, running roughly parallel to the seams of rocksalt, indicated an alternative explanation for the occurrence of these plant fragments.” Gee thought they might have been introduced into the salt in relatively recent times.
Concerning the Katha finds, Gee relied on the assumption that Acacia is quite recent, and could not possibly have existed in the Cambrian. Concerning the Khewra finds, Gee used the existence of a fault to explain the presence of advanced plants in a formation he regarded as Cambrian. But he did not explain how close the thrust fault was to the exact places where he recovered plant fragments nor whether the stratification showed any obvious signs of local disturbance. The fact that the salt was still arranged in seams, apparently unbroken, leaves open the possibility that the plant fragments were found in situ.
Gee (1945, p. 297) found Anderson’s leaf impressions unconvincing, calling them “unidentifiable brownish markings, possibly organic.” Gee (1945, p. 299) saw signs of organic deposits in the shales and dolomites of the Salt Range Formation, but characterized them as “too primitive to include resistant skeletons or woody tissues such as might be preserved.”
Gee was, however, seriously troubled by the discoveries of Sahni, which were based on careful observation and laboratory work. Sahni had demonstrated the existence of advanced plant remains, including woody tissues, not only in the salt and dolomites of the Salt Range Formation but in other kinds of rock as well, such as shale. About the salt and dolomites. Gee proposed that plant fragments could have been introduced into them by “percolating water.” But this explanation would not, said Gee (1945, p. 307), apply to the extremely resistant oil shales, in which Sahni had also found microfossils. Gee (1945, p. 306) noted that if Sahni, on the basis of his plant fossils, was correct in assigning an Eocene age to the Salt Range Formation, “then it will be necessary to modify our views regarding the essential characteristics of normal sedimentary and tectonic contacts.” According to standard geological reasoning these indicated a Cambrian age.
At the Indian National Academy of Sciences annual meeting for
1945, the Salt Range Formation was once more a topic of extended debate. Sahni (1947a, 1947b) gave reports of additional discoveries of angiosperm and gymnosperm microfossils from the salt marl, the oil shales, and dolomites at all levels of the Salt Range Formation. Microfossils of advanced plants were also recovered from core samples from deep borings in the Khewra salt mine. Sahni (1947b, pp. xxxi–xxxvi) gave convincing evidence that the microfossils were not intrusive contaminations. Furthermore, at scientific gatherings in Great Britain, Sahni (1947b, p. xxxix) demonstrated to geologists his laboratory techniques and obtained “fragments of woody tissue” from samples of the Salt Range Formation’s dolomites and oil shales.
Sahni (1947a, p. 243) added that “in a fragment of Mr. Anderson’s original material several microfragments of wood have been found.” This would tend to support Anderson’s identification of leaf imprints in his material from Khewra Gorge. Sahni had accompanied Gee and others to Anderson’s site, and had found no similar specimens. Sahni (1947b, p. xx) noted that these circumstances “do not by any means cast a doubt upon the identification of Mr. Anderson’s specimen as an oak leaf.” Sahni (1947b, p. xx) also noted: “As it turned out, we had been searching at the wrong place.” Anderson’s oak leaf imprint had come from a spot lower than that searched, and some distance away.