Geologists tend to talk in terms of Upper/Late, Lower/Early and Middle parts of periods and other units, such as "Upper Jurassic", and "Middle Cambrian". "Upper", "Middle", and "Lower" are terms applied to the rocks themselves, as in "Upper Jurassic sandstone," while "Late", "Middle", and "Early" are applied to time, as in "Early Jurassic deposition" or "fossils of Early Jurassic age." The adjectives are capitalized when the subdivision is formally recognized, and lower case when not; thus "early Miocene" but "Early Jurassic." 