THE NAKTSONG-TSO, ITS SOUND, AND ITS WESTERN HALF. 61
possibly does not reach 2 m., although on my map I have assumed that it does. If we proceed north-west from the deepest point, I I.68 m., we find that the bottom of the basin rises much more steeply. Here however I observed an especially interesting and instructive irregularity in the relief of the bottom, in that a long, narrow ridge juts out at right angles to the north-eastern shore, and consequently runs diagonally across the basin; on this the depth is only 3 m. To the north-west of it the depth is again 5 to 6 m., until the bottom slopes regularly up to the shore. The ridge or threshold in question is thus a formation of precisely the same kind as the moraine ridge at Camp LXXX, the only difference being that the former still lies 3 m. under the surface; and this I suppose was once true of the moraine ridge. This at least is the only way in which I am able to explain its level top, otherwise difficult to account for. Still, notwithstanding the great transparency of the water, it was not easy to determine how far this ridge really is to be regarded as a moraine formation, or whether it is not merely the subaqueous continuation of a mountain-spur; for in point of fact it does occupy the position of the immediate continuation of such a spur. If it really is only the latter, it will of course consist of hard rock, which has possessed sufficient power of resistance to withstand thus far the pressure and friction of the ice. It does not appear to extend all the way across the basin, for on the firm ground on the opposite side there is not the slightest swelling of the surface indicative of a south-western continuation.
In basin No. II the maximum depth was only 3.15 m., and south-east of that I obtained a sounding of 3.05 m. In this basin also the isobathic curves lie nearer together in the north-west and farther apart in the south-east. From basin No. III basin No. II is separated by a very distinct construction, formed by two blunted headlands. Between these there is also a cross-threshold, which of course has nothing whatever to do with moraine formations, but is simply the subaqueous connection between the two promontories that jut out east and west of the sound, and which, it is quite evident, belonged originally to the same continuous range.
Basin No. III reaches a maximum depth of 3.42 m., and this occurs towards the south-east, though towards the north-west I measured a depth of 3.34 m. This exception to the rule which I have pointed out may however be only apparent, for the line of our skiff's passage did not run symmetrically in relation to the shape of the basin. This basin is a good deal more contracted in width than No. II.
The maximum depth in basin No. IV is precisely the same as in the preceding basin, namely 3.42 m., but it occurs in the extreme north-west of the basin; from that point the bottom ascends gently towards the south-east, for our successive soundings were 3.0, 2.1, and 1.3 m. This basin is the narrowest of all. On the north-west it is bounded by a narrow, shallow passage, to the south-east of the moraine-ridge, which of course forms a far more sharply defined boundary than any in the foregoing basins. South-east of the »pier» the lake swells out into basin No. V, and in proportion as it does so the basin grows broad and flat.
In fig. 4o I reproduce a profile drawn through these basins along the line of our route. The vertical scale is purposely made ten times greater than the true scale. From this it is obvious how the sound shallows towards the south-east. This waterway or chain of basins which I have just described bears indisputably a
IIIF Color HighRes
