Ustun-tagh, which appears on Stieler's map as an alternative name for Altyn-tagh, means Higher or Farther Mountains, and though not used locally of any specific range, would be appropriately employed to designate the higher and more southerly of the twin border-ranges of the Tibetan plateau.
But there exists a striking difference between the crests of the Astin-tagh and those of the ranges which give rise to the gigantic ridge and furrow arrangement on the Tibetan plateau.
On the other hand, the precipitation on the Tibetan plateau is so copious, and so uniformly distributed, that it is able to retain the loosened material in situ, and causes it to heap itself up in rounded masses on the flanks of the mountains that are its primitive source of origin, these projecting in great part like skeletons from the midst of their own ruins."
At the same time the Arkatagh is the actual border-range of the Tibetan plateau properly socalled; to the south.
Hence these ten parallel ranges of the middle Kuen-lun system may be grouped in three divisions - (1) the more strictly border ranges of the Upper and Lower Astin-tagh and the Akatotagh; (2) the three ranges of Chimen-tagh, Ara-tagh and Kaltaalaghan, which may be considered as forming a transitional system between the foregoing and the third division; (3) the Arka-tagh, which constitute the elevated rampart of the Tibetan plateau proper.
