With our present knowledge of the Transhimalaya it is impossible to draw any absolute and definite boundaries to that system. Nobody would be able to tell where its last, easternmost ranges sink into mere hills and finally dip beneath the surface. In the far west it is very likely, though not proved beyond doubt, that the Transhimalaya belongs to the same system of crustal folds as the southern, and highest Kara-korum ranges. To the south, the upper Indus from Rupshu, the Gartang, the Manasarovar, the Gunchu-tso, the Tsangpo, at least to Latse-dsong, may be regarded as a very natural boundary line. To the north I regard the chain of great lakes, from Tengri-nor to Nganglaring-tso, as a not less natural boundary of the Central Transhimalaya, that portion of the system of which I can express an autoptic opinion, for these lakes are all situated in one great depression or latitudinal valley, and one can travel from Tengri-nor to Nganglaring-tso without crossing a single high pass. To the south of this depression is the Central Transhimalaya; to the north a system of smaller ranges, which, at the present date, is difficult to define nearer, as I have crossed it only on two lines. It has, however, to be regarded as situated between the Transhimalaya and the Tibetan Kara-korum, and could, perhaps, be called the Central Tibetan System. This system no doubt at many places stretches out apophyses both into the Kara-korum and the Transhimalaya, and is thus in direct and intimate connection with its two great neighbours. As a rule it is, of course, impossible and unnecessary to draw absolutely sharp boundary lines
between the different mountain systems of Tibet.
I will now try to give a description of this depression so far as I have had
an opportunity to examine it myself.
My routes in and across the depression begin at Ngangtse-tso, and proceed westwards to Nganglaring-tso. East of Ngangtse-tso I have only seen Marchar-tso from a distance. The lakes farther east, as Kyaring-tso, Mokieu-tso, Pul-tso, etc., have only been seen by Nain Sing, and are very little known. Tengri-nor or Namtso, at a height of 4 609 m, is the best known, as it has been visited by several
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