Formation of Northern Plain:
(i) The Indian Peninsula drifted towards the north and finally collided with the much larger Eurasi plate.
(ii) This caused folding of the sedimentary rocks which were accumulated in the geosynclines (known as Tethys). This led to the formation of mountain systems of West Asia and Himalayas.
(iii) The northern part of the Indian Peninsula got subsided due to the uplift of Himalayas in the Tethys Sea.
(iv) That basin was filled with sediments from the river.
(v) The whole procedure led to the formation of a flat land of alluvial soil, which is known as the northern plains of India.