After eight days of marching, we reached the delta area of the Keria River. There was no water. Before our eyes stretched the bone-dry river bed, nearly one thousand meters wide. In the evening we saw before us a vast stretch of greenish and black hills. We ran toward them but the hills disappeared; instead we found an enormous forestation. In the depth of the forest we found a small village with a dozen or so families. An old man of the Uigur tribe welcomed us. It was then we found out that we had already arrived at the heart of this great desert, the T'ung-ku-pa-ssu-t'ai [sic].
Source: wiktionary