premise: class is a property of a rock and includes values of sedimentary / metamorphic / igneous sent2: sedimentary rocks are formed by deposition / cementation sent3: metamorphic rocks are formed by rocks being exposed to extreme heat and pressure sent4: class is a measure of how a rock is formed sent5: limestone is a kind of sedimentary rock sent6: marble is a kind of metamorphic rock.
hypothesis: different classes of rocks are formed by different methods