THE MULTIPLE RIVER THEORY

An alternative explanation regarding the evolution of the Himalayan drainage has been offered by the Multiple River Theory. The protagonists of this theory find it difficult to accept the existence of a large river like the Indo-Brahma or Shiwalik on geological and physiographic grounds.

This theory postulates that the Eocene Sea (Tethys Sea) extended from Sindh (Pakistan), Rajasthan, Jammu, and Punjab to Lansdown and Nainital (Uttarakhand). The existence of such a sea is evidenced by the presence of shallow water facies indicative of coast near Lansdown (Garhwal, Uttarakhand). This limit also coincides with the eastern continuation of one of the ridges of the Aravalli Ranges which presumably acted as a barrier. At the same time, another ridge extended from the Rajmahal Hills to the Meghalaya or Shillong Plateau (Rajmahal-Garo Gap) which is now occupied by the Ganga Brahmaputra basin.

The sea was broken by the first upheaval of the Himalayas to form an isolated basin in which sediments were deposited. In the next upheaval, a pronounced foredeep all along the southern border of the Himalayas was formed. This foredeep contained numerous lagoons into which flowed streams from the Peninsular area and the newly uplifted Himalayas. These streams brought down sediments which later came to be known as the Shiwalik deposits. The outlet of this foredeep was through the Rajmahal Garo Gap in the Bay of Bengal in the east and the Arabian Sea in the west. Later on, the lagoons got dried up and numerous transverse streams flowing from the Himalayan region formed what is now known the Himalayan drainage.