66 THE HEART OF A CONTINENT. [CHAP. IV.
We used, too, to have very 'cold winds blowing from the northward—from the direction of the high plateau of Mongolia. These blew with great force, and clouds of gritty, sandy dust from the desert and from the bare hill ranges which border it were carried along with them. This well accounts for the dull, hazy atmosphere so common at Peking, which is seen also in Chinese Turkestan. It was this wind which had produced the loess formation, which is met with in many parts of Northern China. It carries down all the dust of the desert and deposits it layer upon layer, till in some places it reaches a thickness of several hundred feet upon the plains of China. Counter winds meet the desert wind, and from that and other causes it is brought to a standstill, and down fall the particles of dust it has been hurrying along with it on to the ground below. In this way large tracts of China to the south of the desert are covered with the loess formation. It makes a light, very friable kind of soil, which crumbles away on the least pressure being put on it, and has a tendency to cleave vertically. In consequence of this, the roads through a loess formation present a very remarkable appearance. A cart passes over the loess. The soil breaks away, the wind blows off the dust thus formed, and a deep track is the result. Other carts follow, more loess is broken up, more dust blown away, the track gets deeper and deeper, till in the course of centuries a road is made one or two hundred feet below the level of the surrounding country ; and this road is bounded on each side by perpendicular cliffs, for, as mentioned above, the loess has a vertical cleavage.
In the valley of the Yang-ho, which we were now ascending, we passed along roads of this description. They are only wide enough for the passage of one cart, and consequently, before entering the defile, we had to send on a man to shout and stop any cart coming from the opposite direction.
Donkeys I note as having been particularly fine in this
IIIFカラー高解像度
