In between Laurasia and Gondwanaland, there was a long narrow and shallow ocean known as the Tethys ocean. There were many rivers which were flowing into Tethys ocean. Sediments brought by these rivers were deposited on the floor of the Tethys ocean. These sediments were subjected to powerful compression due to the northward movement of the Indian Plate. This resulted into the folding of sediments. Once, the Indian Plate started plunging below the Eurasian Plate, these sediments were further folded and raised. So, the Himalaya came into existence as a folded mountain by this process which continues even today.