of the Tuscarora formation have been subjected to little alteration and the hard sandstone stands out as ridges upon the surface.

THE CLINTON FORMATION is named from its exposure at Clinton, New York. It is confined to the central Appalachian Region in Maryland, occurring in three, narrow, isolated belts west of Hancock, Washington County, and in three V-shaped areas in Allegany County about the Wills Mountain, Evitts Mountain, and Tussey's Mountain anticlines. It is composed of shales of a grayish-olive to reddish color interbedded with thin sandstones, which give place to thin-bedded limestones near the top of the formation. Two beds of iron ore (hematite) of a deep red color are contained in it, one 6 inches to 30 feet thick occurring near its base, and another about 1 foot thick near its summit. The latter usually overlies a heavy quartzitic sandstone. The original character of these two bands of iron ore was probably that of a highly ferruginous fossiliferous limestone from which the calcium carbonate has been removed by solution. The shale between the iron-ore beds usually suffers much erosion, producing characteristic valleys.

THE MCKENZIE FORMATION consists of interbedded shale and limestone which weathers to a fertile soil. The formation occupies valleys which lie between the hard sandstone of the Wills Creek formation and the top of the Clinton. It receives its name from McKenzie Station on the Baltimore and Ohio Railroad southwest of Cumberland. It is 250 to 275 feet thick.

THE WILLS CREEK FORMATION consists of calcareous shales and argillaceous limestone in addition to which it contains several beds of sandstone. Some of the limestone contains clay in such proportion as to yield a natural cement rock of which four beds are found in Allegany County. The lower part of the formation consists of red sandstone and shale known as the Bloomsburg sandstone which contrasts sharply with the overlying gray rocks. The Bloomsburg sandstone forms a prominent ridge where it outcrops upon the surface. The overlying strata weather to a fertile soil. This formation receives its name from Wills Creek in Cumberland. It is 450 to 500 feet thick.

THE TONOLOWAY FORMATION consists of interbedded limestone and calcareous shale. The limestone is characteristically thin-bedded and weathers to small, hard pieces upon the surface of the ground. The strata give rise to a characteristic reddish soil. This formation receives its name from Tonoloway Ridge in Washington County. It is 600 feet thick.

THE DEVONIAN PERIOD

The deposits of Devonian age enter, together with the Silurian rocks, into the formation of the central division of the Appalachian Region, and together with the Carboniferous deposits, into the formation of the Alleghany Plateau. They consist of sedimentary materials that have been but little altered since they were deposited, although in places subjected to considerable structural disturbances. Three divisions are recognized in the strata of Devonian age known respectively as the Lower Devonian, Middle Devonian, and Upper Devonian.

The deposits of Lower Devonian age comprise two divisions known respectively as the Helderberg formation and the Oriskany formation. THE HELDERBERG FORMATION is named from its exposure in the Helderberg Mountains, New York. It occurs in the central Appalachian Region, being exposed west of North Mountain and west of Hancock in Washington County, and upon the Wills Mountain, Evitts Mountain, and Tussey's Mountain anticlines in Allegany County, in association with the formation last described. It consists of limestones usually purer and more massive than those of the Upper Silurian formation, together with some shales. It comprises three divisions in Maryland, known respectively as the Coeymans, New Scotland, and Becraft members of the Helderberg formation. Of these members, the last is restricted to the region about Cherry Run, West Virginia.

THE ORISKANY FORMATION is named from its exposure at Oriskany Falls, New York. It is confined to the central division of the Appalachian Region in western Washington and Allegany counties. The deposits of the Oriskany formation are typically rather coarse-grained, somewhat friable sandstones, white or yellow in color. At times the materials become very coarse-grained, resulting in a clearly defined conglomerate,

while at other times, especially in the western portion of the area, the materials are fine-grained, with here and there interstratified layers of coarser materials. These deposits afford excellent glass sand.

One division is recognized in the Middle Devonian deposits, known as the Romney formation.

THE ROMNEY FORMATION, So called from its exposure at Romney, West Virginia, is confined to the central division of the Appalachian Region, and occupies very much the same areas as those given above for the Oriskany sandstone. It comprises two divisions known respectively as the Marcellus and Hamilton members of the Romney formation.

The Marcellus member, so called from its typical exposure at Marcellus, New York, consists of thin, fissile, black shales, which weather into thin, flat, black plates. Several thin bands of limestone frequently occur some distance above its base. It contains numerous fossils characteristic of the Marcellus formation of New York. Its thickness is about one-third that of the entire Romney formation.

The Hamilton member, so called from its typical exposure at Hamilton, New York, consists of black shales containing, usually, two heavy beds of sandstone, one of which is near the middle and the other near the top of this division. The upper part of the shales weather into yellow to brown, hackly fragments which are highly characteristic of the Hamilton. The lower part weathers into thin, dark plates, often closely resembling those of the Marcellus shales. Eastward near Elbow Ridge a conglomerate develops in this member, while west of Wills Mountain the entire Romney formation thins, the sandstones becoming greatly reduced in volume.

Fossils abound in this division, especially in its upper half, including many species characteristic of the Hamilton of New York. Its thickness is about two-thirds that of the entire Romney formation.

The strata of Upper Devonian age contain two divisions termed, respectively, the Jennings and the Hampshire formations.

THE JENNINGS FORMATION, so called from its development at Jennings Gap, Virginia, is found both throughout the central and western divisions. of the Appalachian Region. Within the Appalachian Mountains proper

it is frequently repeated throughout western Washington and Allegany counties and occurs as the oldest formation represented in the Allegany Plateau of Garrett County. It underlies the well-known "glades." It comprises three divisions known respectively as the Genesee, Portage, and Chemung members of the Jennings formation.

The Genesee member consists of a deep-black, fissile shale weathering into flat, black plates, and often exhibits pronounced jointing.

The Portage member consists of olive-green to gray shales, alternating with thin, fine-grained micaceous sandstones. The shales weather into thin, flat plates which contrast with the hackly fragments of the Romney shales below, while it is also more resistant to weathering.

The Chemung member consists of olive-green to brownish-red shales and sandstones. A conglomerate occurs near its base in Washington County, while a second conglomerate is found 500 to 600 feet below its summit in numerous localities, forming well-marked ridges.

THE HAMPSHIRE FORMATION (Catskill in part).-The Hampshire formation, so called from Hampshire County, West Virginia, occurs both in the central and in the western portion of the Appalachian Region. It is best developed in the western portion of Allegany and Garrett counties. The deposits of the Hampshire formation consist principally of thin-bedded sandstones, separated by fine-grained shales, although at times the sandstones become thick-bedded, and may merge gradually into the shales. Shales predominate in the upper portion.

The rocks of the Carboniferous period are confined to the western division of the Appalachian Region, where they largely constitute the Alleghany Plateau, and are found in western Allegany and Garrett counties. Two divisions are recognized, known respectively as the Mississippian. and the Pennsylvanian.

The Mississippian

Three divisions are represented in the deposits of Mississippian age, known as the Pocono, Greenbrier, and Mauch Chunk formations.

THE POCONO FORMATION.-The Pocono formation, so called from Pocono, Pennsylvania, is the basal member of the Carboniferous and directly overlies the Hampshire formation above described. It occurs in a series of narrow belts which extend from northeast to southwest through western Allegany and Garrett counties. The Pocono formation consists mainly of hard, thin-bedded, flaggy sandstone, which is seldom coarsegrained, although in a few instances slightly conglomeritic. Thin layers of black shale and coaly streaks, in which plant remains are sometimes preserved, occur in some localities, although not a conspicuous feature of the formation.

THE GREENBRIER FORMATION.-The Greenbrier formation, so called. from Greenbrier County, West Virginia, occurs in very much the same areas in western Allegany and Garrett counties. The deposits consist mainly of limestone strata in which are interbedded shales and some sandstones. The limestones are more sandy toward the base.

THE MAUCH CHUNK FORMATION (Canaan).-The Mauch Chunk formation, so called from Mauch Chunk, Pennsylvania, flanks the ridges of western Allegany and Garrett counties and grades gradually downward into the Greenbrier deposits. The strata consist chiefly of red shales, interstratified with flaggy, red-brown, fine-grained sandstones. The sandstone is at times micaceous. Thin beds of dark carbonaceous shales occur at times near the top of the formation.

The Pennsylvanian

Four divisions are recognized in the strata of Pennsylvanian age known as the Pottsville, Allegheny, Conemaugh, and Monongahela formations. THE POTTSVILLE FORMATION, so called from Pottsville, Pennsylvania, is the lowest division of the Coal Measures and forms the mountain ridges which border the coal basins. The Pottsville formation consists of beds of sandstone and conglomerate interstratified with sandy shales in which thin beds of coal are locally developed. The sandstones and conglomerates are mainly composed of fine quartz grains and pebbles which are commonly cemented by means of siliceous materials. These coarse deposits