Sentence:  They are huge areas which have been swept by winds for so many centuries that there is no soil left , but only deep bare ridges fifty or sixty yards apart with ravines between them thirty or forty feet deep and the only thing that <WSD>moves</WSD> is a scuttling layer of sand . 
Meaning of the word marked with <WSD> tags:  change location; move, travel, or proceed, also metaphorically