the zone, is medium light gray, silty, limy, and very fine to fine grained. The siltstone and shale are medium light gray to medium dark gray, finely micaceous, and nonlimy to very limy. The limy upper part grades downward to the very limy lower part, which contains crinoids, brachiopods, and gastropods.

Zone B.-Zone B extends from 1,075 feet to 1,728 feet above the base of the Catskill. In the Ransom quadrangle zone B is the only part of the lower part of the Catskill that contains coarse grains and granules of quartz. About 45 percent of the unit is sandstone; the rest is medium-gray slightly limy siltstone and shale. A few pelecypods are present in the shale of the lower half of the zone, and numerous crinoids are present in the sandstone of the upper half. These crinoids are the youngest marine fossils that were found in the formation.

Zone C.-Zone C extends from 1,728 feet to 4,380 feet above the base of the Catskill. Zone C is separable from the overlying and underlying coarse-grained units because its quartz grains are no larger than medium-sand size. The zone is made up of 60 percent mostly crossbedded very fine grained to fine-grained sandstone and a few beds of medium-grained sandstone, 30 percent medium-gray to greenish-gray siltsone and shale, and 10 percent brownish-gray to grayish-brown siltstone and shale. The brownish rocks, the "red" rocks of previous writers, occur mostly in the upper half of zone C. One of the thickest units of siltstone and shale, about 800-900 feet above the base of zone C, is grayish brown in the lower one-third and medium gray in the upper two-thirds. It contains nodules and lenses of light-brownish-gray silty siderite, the only siderite that was noted in the formation.

One minor but notable constituent of zone C and of the overlying zones is the medium-gray to brownish-gray very limy very silty sandy conglomerate that has been referred to in previous reports as "glomerate" (Willard, 1936; 1939). It forms beds and lenses, seldom more than 5 feet thick, and probably constitutes less than 5 percent of this interval. Willard (1936, p. 578) named one of these calcareous beds near the base of the Cherry Ridge Formation the Dyberry Glomerate. Many "pebbles" in these "glomerates" are algal (?) masses, and some are fish scales and bones. The subrounded pebbles in the "glomerate” of zone C appear to be locally derived and are probably a residual coarse fraction left in depressions by the cut-and-fill process. Similar "glomerates" in the overlying coarse-grained units contain quartz granules and pebbles. Thus, the coarsest pebbles available apparently tended to be concentrated in these lenses, and the calcareous cement was probably introduced by ground water that contained dissolved carbonate, which came in part from the surrounding rocks and in

part from the pebbles of algal (?) limestone. Outcrops of "glomerate" have a highly "pock-marked" or "worm-eaten" appearance. The rock is porous and ironstained where decalcified by weathering. "Glomerate" is hard and resistant to mechanical abrasion when fresh; angular boulders of it are locally present in glacial debris. Brown ironstained porous lightweight decalcified rounded pebbles and cobbles of this rock are common in the fluvial gravel along the Susquehanna River.

Crossbedding in zone C, as well as that in the overlying zones of the Catskill, is conspicuous in outcrops of the Ransom quadrangle. Although some layers are much more crossbedded than others, the degree of crossbedding does not seem to be a criterion by which the Catskill can be zoned in the Ransom quadrangle. Both tabular and lenticular crossbedded units are abundant; the lenticular units are more common (fig. 3) and were probably formed by the scouring and filling action of meandering streams. The tabular units may have been deposited in a similar way but by larger streams.

Zone D.-Zone D extends from 4,380 feet to 4,804 feet above the base of the Catskill. It is transitional between zones C and E in that it contains only a few lenses in which coarse grains, granules, and pebbles of quartz are present. About 60 percent of the zone is mostly crossbedded and very fine grained to medium-grained sandstone; the remaining 40 percent is mostly limy grayish-brown "red" shale, claystone, and siltstone. Beds and lenses of limy rock, including "glomerates" similar to those in zone C, and calcite-filled vugs are

common.

Zone E.-Zone E extends from 4,804 feet to 5,840 feet above the base of the Catskill. It consists of about 55 percent mostly crossbedded fine- to coarse-grained sandstone, containing scattered pebbles and granules of quartz, and about 45 percent mostly grayish-brown claystone, shale, and siltstone. The abundance of coarse quartz sand distinguishes zone E more definitely from other zones in the Catskill Formation than from the overlying Pocono sandstone, which also contains abundant coarse quartz sand. Beds and lenses of "glomerate" are less common in this unit than in zones C and D.

A local conglomerate that caps the upper 400 feet of Bald Mountain consists of about 40 percent pebble-and-cobble conglomerate, about 60 percent fine- to coarse-grained conglomerate sandstone, and minor amounts of siltstone and shale. The pebbles are mostly sandstone, quartzite, and white to pink quartz; a few pebbles are black chert that weathers white and medium- to dark-gray metamorphic rock. At Pinnacle Rock on Bald Mountain, however, some sandstone cobbles, as much as 6 inches long, and quartz, quartzite, and other rock fragments, as much as 3 inches long, were found. Most of the cobbles and

FIGURE 3.-Typical crossbedding in the Catskill Formation. Upper: Long and short lenticular crossbedding in zone E, near the outlet of the tributary to Falling Springs Reservoir. Lower: Short lenticular crossbedding in zone C in a cliff about half a mile south of Falls, Pa.

pebbles are well rounded, although some are subrounded to subangular. The long axes of some cobbles and pebbles seemingly have a preferred northwest-southeast orientation; however, most have random orientation. The conglomerate is bedded in lenses and tongues that are from 2 inches to 2 feet thick, although a few are as much as 5-6 feet thick. The conglomerate lenses and the sandstone tongues can be traced along the cliff face for distances of not more than 50 feet. A claystone parting 14-2 inches thick was traced for a distance of 30 feet. Fluting, channeling, and other surface features, though scarce, are generally oriented northwest-southeast. The conglomerate was probably deposited in the channel of the main stream, which flowed northwestward across a broad delta. The authors found, by tracing the individual rock units in detail, that the conglomerate sequence on Bald Mountain interfingers northeastward and southwestward along the strike with the more typical sandstone, siltstone, and shale sequence of the upper part of zone E of the Catskill Formation (fig. 4).

The uppermost sequence of zone E is about 138 feet thick and consists of greenish-gray, grayish-brown, and dusky-yellow claystone that contains medium quartz sand, quartz pebbles as much as 2 inches long, and sandstone pebbles, cobbles, and boulders as much as 3 feet long. Sand grains, pebbles, cobbles, and boulders are randomly scattered in the claystone. Sand grains are abundant, but cobbles and boulders are scarce. The entire sequence has almost no bedding, except for lenses of poorly sorted sandstone in the lower part.

The best exposure of this pebbly claystone sequence is at the outlet of Falling Springs Reservoir. (See Powerline B section, units 5-13, p. 48.) Similar rock is exposed along strike to the northeast and southwest just outside the Ransom quadrangle, and a pebble-bearing claystone is present at about the same stratigraphic position in a roadcut south of Wilkes-Barre, Pa. In several other areas along strike

FIGURE 4.-Probable relation of the conglomerate exposed on Bald Mountain to

other strata.

in and near the Ransom quadrangle, this sequence could not be found beneath the Pocono because is is either covered or absent. The lack of both bedding and sorting in the pebble-bearing claystone suggests that this claystone was deposited as a mudflow, but the unit's apparent widespread distribution leaves the exact mode of deposition largely to speculation.

Stratigraphic relations.—The Catskill Formation is apparently conformable and interfingers with the underlying strata. Willard (1939, p. 261-269) described an offlap or interfingering of the Catskill continental facies with marine facies of Late Devonian age. The basal part of the Catskill continental facies ranges in age from early Late Devonian in the eastern part of the State to late Late Devonian in the northwestern part (Willard, 1939, p. 268-269). It interfingers with the Trimmers Rock Formation to the east and with younger marine strata to the northwest. Thus, the basal contact is vague-not always easily recognizable-and transgresses time boundaries. In the Richards 1 well the contact of the Catskill Formation with the underlying Trimmers Rock Formation was arbitrarily placed at the change from medium-dark-gray shale and siltstone (Catskill Formation) to medium-light-gray very fine grained to fine-grained sandstone that contains scattered granules of clear quartz (Trimmers Rock Formation).

MISSISSIPPIAN SYSTEM

POCONO FORMATION

Name and age.-The name Pocono Sandstone was introduced by Lesley in 1876 (p. 221) for the gray sandstone and conglomerate of Early Mississippian age lying below the Mauch Chunk Formation and above the Catskill red beds; it replaced the term Vespertine Series of Rogers (1858, p. 141-146). Apparently Lesley had intended to establish the Pocono Plateau as the type section, but I. C. White (1882) found that most of the Pocono Plateau was underlain by rocks older than the Pocono. Thus, Lesley (in White, I. C., 1882, p. 15) revised the description of the type area for the Pocono Sandstone and implied that the type area was Moosic Mountain on the northwest border of the Pocono Plateau. The Pocono, now called a formation, is considered to be of Early Mississippian age (White, C. D., 1934, p. 269; Read, 1955, p. 1-14).

Griswold Gap Member.-I. C. White (1881, p. 57) recognized a persistent conglomeratic zone in the lower part of the Pocono Formation to which he gave the name Griswold Gap Conglomerate from exposures at Griswold Gap, just east of Forest City, Pa. He traced this conglomerate zone from Griswold Gap to an exposure on the