The Bain Boulder-bed: a Glacial Episode in the Siwalik Series of the Marwat Kundi Range and Shekh Budin, North-West Frontier Province, India

Abstract

In October 1934, at the western end of the trans-Indus continuation of the Salt Range of North-West India, extensive outcrops of a deposit possessing all the characteristics of a typical boulder-clay were discovered in the middle of the strongly folded and faulted Siwalik series of the Marwat Kundi hills and on the northern slopes of Shekh Budin. The boulder-clay was named the Bain Boulder-bed, after the frontier village nearest to its most conveniently accessible outcrop alongside the frontier road from Bannu to Tank, through the Bain pass. The occurrence of a glacial deposit in this area and at such an horizon was totally unexpected. Successive studies of Siwalik faunas, made since Falconer's pioneer work, have raised progressively the age of the Siwalik series in terms of the European and American time-scales, but no dating later than Middle Pliocene had been suggested for the thick sandy formation in which the Bain Boulder-bed occurs; neither is there any record of evidence of glacial conditions during the deposition of the Siwalik series (Colbert 1935, p. 11). Prior to the discovery of the Bain Boulder-bed, the age of the formation enclosing it had been regarded as Upper Miocene, following Pilgrim (1913), or Middle Pliocene, following Matthew (1929). The nearest place to Shekh Budin at which fossils had been collected from the formation was the type locality of Pilgrim's Nagri fauna (1913, pp. 267, 318). That fauna lies in the lower portion of the Nagri outcrop cis-Indus, about 100 miles from Shekh Budin. From Nagri