The Principle of Superposition is a fairly reliable way of determining the older from the younger rock - the older one will usually be at the bottom. This method for relative determination is often...
It can be determined by the relative position and depth of its occurrence compared to other horizontally occurring strata and additionally by the types of index fossils it may contain.
Age is how old the rock is relative to other rocks, position is where the rock is in relation to other rocks. Tectonic motion and other forces can easily turn a portion of the Earths crust upside...