to compact something means to compress something & sedimentary rocks are formed by sediment compacting together ->  sedimentary rocks are formed by sediments being compressed together  sedimentary rocks are formed by sediments being compressed together & sediment is a kind of small particle ->  sedimentary rocks are formed by small particles being compressed together  sedimentary rocks are formed by small particles being compressed together & sedimentary rocks are formed in layers -> sedimentary rocks are formed by small particles being compressed together in layers