stra·tig·ra·phy 
(strə-tĭgrə-fē)
(strə-tĭgrə-fē)n.
The study of rock strata, especially the distribution, deposition, and age of sedimentary rocks.
strat′i·graphic (străt′ĭ-grăfĭk), strat′i·graphi·cal (-ĭ-kəl) adj.
strat′i·graphi·cal·ly adv.