The geology of the region shows that the Himalayas are the young mountains in the world. During early Mesozoic times, or the secondary geological period, the land mass now covered by them was occupied by the great geosynclinal Tethys sea . The probable date of the commencement of the elevation of the Himalayas is about the close of the Mesozoic period, but the unraveling of the story of their structure has only just begin, and in many cases no dating of the rocks is yet possible, though they include ancient and relatively recent crystalline intrusive, rocks and sediments allied to the peninsular part of India . The section of the range in the district is deeply cut into by the headwaters of the Alaknanda river, this trunk stream seeming to have reached a latter stage of development than its tributaries. This much, however, is known that there has been intense metamorphosis. In some parts uplift has been considerable since the mid-pleistocene period, in others there are great stretches of high but subdued topography and elsewhere there are the deepest gorges.