The one i think goes first is the 3. Because its made its way through all the rocks. The one i think goes after 3 is 1 because its on the top and the top ones are the youngest. the one i think goes after 3 and 1, is 6 because its below one and no other rocks have cut through it.  then i think 2 goes after 6 because its made its way through all the other rocks other than 3 1 and 6. Then i think it goes 4 then 5 because those two are that the bottom and the bottom is the oldest.