156 PHYSIOGRAPHY, GEOLOGY AND MINERAL RESOURCES

their own peculiar types of life; and the several periods are them-
selves divided into Epochs, which vary more or less in character accord-
ing to the region where they are developed. For this reason the
chronological and stratigraphical divisions require an independent
nomenclature, although this duality of geological classification can in
most instances be readily adjusted to the contingencies of each district.
The stratigraphical divisions are usually designated by local terms.

In Maryland we have representatives not merely of the great time-
divisions, but of each of the subordinate periods, as well as of many
of the epochs. This may be best appreciated by referring to the
accompanying geological map and to the table of geological forma-
tions which follows.

TABLE OF MARYLAND FORMATIONS.

		Formations represented in
		Maryland.
	CENOZOIC TIME.
	Pleistocene Period	represented by the Columbia.
	Neocene "	" " Lafayette.
		Chesapeake.
	Eocene "	" " Pamunkey.
	MESOZOIC TIME.
	Cretaceous "	" " Rancocas.
		Monmouth.
		Matawan.
		Raritan. "]
		Patapsco.	Potomac
	Jurassic (?) "	" " Arundel.	Group.
		Patuxent. J
	Triassic "	" " Diabase.
		Newark.
	PALEOZOIC TIME.
	Permian (?) "	" " Frostburg.
	Carboniferous "	" " Elkgarden,
		Fairfax.
		Bayard.	=Coal Measures.
		Savage.
		Pottsville.
		Mauch Chunk.
		Greenbrier.
		Pocono.