In the Himalaya, the Indian continental plate is crashing into the Eurasian continental plate with nearly north-south motion. Therefore, the compression of the rocks in the Himalaya is in the north-south direction. So, folding should occur trending east-west, as is observed. However, it has also been noted that folding occurs in the north-south direction. It was noted that these folds follow the traces of the major rivers, such as the Arun and the Indus. Originally these folds were explained by assuming that the rivers did not form these anticlines, instead the river's course was by coincidence on top of these geologic features, forming by differential erosion. The idea of isostatic rebound was suggested as the best fit mechanism for these north-south trending folds and is now widely accepted.