many of which were published in the journal that was published from Ranchi University and some in the journal of Aligarh Muslim University. His initial publications on what developed into the Ahmad theory were first published in the Geographical Outlook and Geographer. One of his first published papers, based on his thesis work, was on human settlements in Uttar Pradesh. He wrote Five Cities of the Gangetic Plain: A Cross-Section of Indian Cultural History in 1950 with Oskar Spate, a geographer, and The Rural Population of Bihar in 1961, both of which were published in the Geographical Review. Contributions The Ahmad theory of Evolution of Himalayan Drainage System The fact that the Himalayan rivers seem to have a longer history as compared to the mountains themselves has been a subject of enduring curiosity. Himalayan rivers like the Indus, Sutlej, and the Brahmaputra have created deep gorges across the mountain range to reach the plains of northern India. They have first flowed parallel to the main axis of the mountain in longitudinal troughs, then they have taken sudden bends towards the south, carving the deep gorges. The gorges created by rivers such as the Indus, Sutlej, Alaknanda, Sarju (Kali), Gandaki River, Koshi River, Teesta, and the Brahmaputra suggest that they predate the Himalayan mountain range. The first known theory to explain the Himalayan drainage system came from Pascoe and also Pilgrim. According to their theory the Tibetan plateau was drained to the west by the mighty Tsangpo-Indus-Oxus combined. Ahmad, on the contrary, had the view that the Tethys Ocean continued as a basin of sedimentation from the Cambrian to the Eocene Periods, while most of the Himalayan region was filled by the Gondwana landmass. During the Himalayan upheaval in the Oligocene period, part of the Tethysian geosyncline and probably, part of the Gondwana Land, were uplifted. Most probably this marked the initiation of the Himalayan drainage. It had earlier been proposed that the Himalayan waters reached the plains through the agency of a single river called Indo- Brahma (Pascoe, 1919), or Siwalik (Pilgrim, 1919) and finally drained into the Arabian Sea. Ahmad (1971) argued that this explanation related only to a part of the period in which the evolution of the Himalayan drainage occurred and fails to explain the drainage within the Himalayas themselves. He writes that "the evolution of the Gangetic drainage, as seen at present, really starts with the