IIIF Color HighRes
National Institute of Informatics - Digital Silk Road Project
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| IIIF Color HighRes |
| Ruins of Desert Cathay : vol.2 |
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Citation Information
14o WESTERN FLANK OF THE LIMES CH. LXII
too, the Surveyor, in the course of his reconnaissance, came upon dry ravines cut by floods into the glacis. The springs which we found rising in marshy beds within the larger bays also supplied proof of such drainage.
But it was equally certain that in forming those curious strings of isolated clay terraces another powerful
agent had been at work, wind erosion. Again and again
I observed how the crest of the narrow but still continuous ridges was being gradually sapped and scooped by wind-
cut trenches mainly starting from the north - east. It
was, of course, the direction from which since the winter we had learnt to expect the most violent gales. The
ridges, stretched more or less at right angles across
the line of the prevailing winds, were thus bound to be gradually broken up into terraces by the cutting force of
the wind and the grinding produced by the driven sand
which it uses for its instrument. But as I looked at the towers and saw how relatively little their bases had
suffered by erosion in the course of two thousand years, I could judge what countless ages were needed even for that powerful agent to carve out those terraces from the hard clay, and finally to plane them away altogether.
I had before me the clearest illustration of that interaction of water and wind erosion which must have
produced the maze of detached clay terraces I had
before encountered, both at the north-eastern end of the ancient Lop-nor lake bed, and again in the terminal basin
of the Su-lo Ho, and around Khara-nor. In the light
of the evidence here gathered I was able to understand better the powerful rôle which wind erosion had played
in this region as a geological factor affecting surface
formations. Its effects upon the work of man were marked with equal clearness. Again and again I noted, in the
course of my surveys on the Limes, how relatively well preserved the wall often rose along those sections which lay parallel to the prevailing direction of the winds, while where the line had been drawn across and in any way barred the progress of dust and fine gravel, wind erosion had badly breached or practically effaced the rampart.
I had ample occasion to convince myself that the winds
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