mood had climbed the vertical stone to gain access , feet and hands finding purchase on the merest strands of hapless moss , the cracked shells of pollen grains and the dried husks of spider shit , the dismembered limbs , brittle and hollow , of flies and ants and midges , avoiding the spider 's silky web by concentrating with a stubborn rigidity upon the next lifeless shelf , gripping its time-cut wrinkles , clambering over the battlements by such means , the neck of the sack clenched in his determined teeth and the child within wriggling , perhaps afflicted by vertigo .