290 THE LAKES BESIDE THE LOWER TARIM.
At first the approaching harbingers of the tempest hung clown like a curtain, with a serrated edge at the top, while the sky was streaked with black bands; but soon they all melted together into one opaque mass. The darkening of the sky in this awe-inspiring way is caused by the fine dust; it is this which gives to such a tempest its distinguishing name of kara-buran, or »black storm». The cloud of dust must rise to a considerable height above the surface of the earth, for the interval which elapsed between the moment when we first saw it to the moment when it struck the lake was only 20 minutes. During this time it travelled a distance of fully 36 km., at a speed of at least 3o meters in the second. During this period the lake was again as calm as a mill-pond, its surface like a mirror, but a grim gloom was gathering in the background. There is an ominous stillness in the air, an oppressive silence everywhere, even the mirk on-coming tempest, which is rapidly approaching,
Fig. 252. A CANOE ON THE BEGEL!K-KÖL.
does not as yet emit a sound. It strikes the outermost crests of the dunes which fence in the lake on the east. Up whirl clouds of tawny drift-sand, contrasting glaringly against the inky-black mass of dust behind them. In a moment the dunes are swallowed up from end to end. Then comes the swish of the tempest as it swoops down upon the lake. Instantly its surface is whipped into foam, and within a few short minutes the waves are racing across it in a panic of mad terror, and we hear the roar of them as they dash themselves against the western shore. We ourselves are swallowed up in the impenetrable gloom. All we can see is a tiny speck of the lake in our immediate vicinity; our eyes will barely reach to the other canoe. The howling of the tempest is deafening.
This storm continued all the rest of that clay, all night, and the greater part of the next day. We only escaped disaster by sheer good luck; but to experience
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