Gandak, and Tirsuli Gandak, have their sources in the Central Eange, while the others drain the slopes of the Southern Himalaya only. There are three passes over the Central Chain into Tibet by the gorges of the Gandak rivers, namely, the Muktinath pass, by the river Narayani to Mantang (Mustang?); the No-la, by the Buria Gandak ; and the Taku-la pass, by the Tirsuli Gandak. The country of the Gandaks is that of the former Chaubisi (twenty-four) Rajahs.
Eastern Nepal is drained by the Kosi river system, consisting, like the Gandak, of seven main streams: the Milamchi, the Bhotia Kosi, the Tamba Kosi, the Likhu, the Dúd Kosi, the Arun, and the Tambur or Tamor. Their sources are included between the Dayabung (23,762 feet) and the Kangchan (28,158 feet), while Mount Everest (29,002 feet) towers above the left bank of the Arun. The Kosi rivers, after draining the Kiranti country in Eastern Nepal, including the districts of Khatang and Chayanpur, unite within the hills into one stream, which flows through the Murung, or Terai region, and past Bijapúr, places often mentioned in Bogle's narrative. The Bhotia Kosi and Arun rise in the Central Chain, and the Arun has a long Tibetan course before it bursts through the Southern Himalaya, and flows down to the Ganges. There are four passes from Nepal to Tibet by the Kosi rivers: one up the Bhotia Kosi, and by the Nilam pass and Kuti, a place mentioned several times by Mr. Bogle; a second up the Arun river and by the Hatia pass; a third up the ravine of the Tambor river by Wallanchiin, and over the Tipta-la; and a fourth leads up the gorge of the Yangma, an alpine tributary of the Tambur, over the Kanglachan pass.
The three Nepal basins drain the Indian slopes of the Himálaya for a distance of 800 miles. But the rivers which unite to form the Gogra, Gandak, and Kosi, must necessarily converge to three separate centres, leaving intervals on the lower slopes. In that between the Gandak and Kosi is the beautiful valley of Nepal, with the city of Kathmandu, watered
