A History of Agriculture in India v1.c7.15

v1.c7.15

The continued sinking of the Tethys is presumed to have been caused by crustal weakness. During the sinking of the seat, there was a lateral thrust which narrowed the basin. The narrowing of the basin upheaved the sediments, and surplus sedimentary materials were forced up into folds above the basin to form the Himalayan chain. The margin of the upheaved mass also yielded under strain, developing fractures in many places. As the sinking sea floor reached deep into the region of higher temperature and pressure, the lower layers of sediments were melted into "magma", which invaded the crumpled and crushed the overlying sediments as intrusions or as lava flows. These now form the central axis of the Himalayas. Some of the rocks have been squeezed up and out by the lateral forces from two sides and thrust into overturned folds and faults. Many of the overturned limbs are displaced as flat-lying folds known as nappes.