No. V. A reddish quartz sand.

No. IV. Black, laminated sand and clay, strongly glauconitic to the southwest, but less so to the northeast. No. III. Vari-colored sands, locally with thin clay laminæ and

lenses.

No. II. Black clay, weathering to a chocolate color, and nonglauconitic.

No. I. Black, sandy clay, notably glauconitic at top and bottom, weathering to a cinnamon brown.

The total thickness in Monmouth county is about 230 feet.

CLAY MARL V (WENONAH SAND).

This formation is in general a reddish-brown or black sand, sometimes strongly micaceous and often having a peculiar mix-ture of pinkish, brown and gray sand grains, which give it a characteristic color. Locally it is distinctly laminated with thin seams of black or chocolate-colored clay, but these are never, so far as seen, commercially important. It is somewhat ferruginous, and is not infrequently cemented to ironstone, but less commonly so than the lower sand bed, Clay Marl III. It contains a small amount of glauconite (greensand marl), but except near its top, this element is not apparent save upon close examination. Deep exposures, particularly in the upper portion of the formation, often show large pockets of white sand, which are sometimes clean sand, and sometimes contain pellets of a hard white clay giving the sand an arkose appearance. This phase is particularly characteristic of the upper 2 to 10 feet, and renders the sand quite compact. These upper layers generally contain very coarsegrains of quartz sand, and are also not infrequently somewhat cemented by iron, which has been leached from the overlying marl beds.

At the very top of Clay Marl V, in the upper few feet of this "arkose" sand, there is generally found a fossil bed from 1 to 4 feet in thickness composed largely of the large shell Gryphæa vesicularis. The fossils are thickly imbedded in a matrix of clayey sand in which there is an increasing amount of marl

towards the top of the shell layer. Immediately above the latter lie the workable greensand marl beds. The shells occur somewhat sparingly in the sand for some distance below the fossil bed and more rarely individuals occur in the marl above. Inasmuch as this layer is a very persistent feature and can be readily recognized at many localities across the State, and since the beds. above and below are so different in character, the top of the Clay Marl series is a definite and easily recognizable horizon.

The Wenonah sand (Clay Marl V) outcrops along the southeastern side of the Clay Marl belt from Atlantic Highlands to Salem county. It is in part covered by areas of Pensauken gravel, but it forms the surface deposit over considerable tracts in the vicinity of Sharptown, Salem county; over a broad belt between Mullica Hill and Swedesboro, near Chew's Landing; Wenonah, east of Haddonfield, and near Evesboro, in Burlington county. In Monmouth county it forms the sandy belt on the northwest of the Lower Marl from Tennants, Robertsville, and Morganville to Atlantic Highlands. Its thickness is about 50 to 55 feet in Monmouth county, increasing to something over 60 feet in Salem county.

Although locally it contains thin seams of clay, yet these are nowhere of economic value.

CLAY MARL IV (MARSHALLTOWN BED).

This member of the Clay Marl series is more variable in its make up than either of the other four, but the variations are gradual, and there is no difficulty in tracing them from one phase to another. It ranges from a sandy clay to a clayey marl, which at one time was mistaken by all geological workers in the State for the Lower Marl. In Monmouth county it is chiefly a laminated, micaceous clay with thin seams of sand, which locally may be of some commercial importance. In this region greensand grains are wanting in all save the upper portion, in which they are only

'Mr. Knapp was the first to differentiate it from the Lower Marl and make out its true position, although he did not receive proper credit for it in the Annual Report for 1897.-H. B. K.

locally conspicuous. Towards the southwest, however, the marl content increases, and in the vicinity of Marshalltown, Salem county, the bed was once extensively dug for fertilizer. It has also been opened at many other points for the same purpose. The marly portions are abundantly fossiliferous.

This member of the Clay Marl series outcrops north and northwest of the Wenonah sand bed, into which it passes somewhat abruptly. In Monmouth county, where alone it is likely ever to prove of any value for clay, it occurs on the lower slopes of the Mount Pleasant hills from Atlantic Highlands westward through New Monmouth, Morganville, Robertsville and Englishtown. It lies between two thick sand beds, No. V above and No. III below, so that it can be readily identified. Its position for a portion of this distance above mentioned is shown upon the large scale of the Matawan district, Plate XII.

Clay Marl IV is not at present utilized for clay at any point, although a black laminated clay, belonging to this bed was formerly dug in a small pit near the railroad one and one-half miles west of Atlantic Highlands. At two small brickyards west of Mount Holly (Loc. 123) a loamy surface clay 2 or 3 feet thick may perhaps be the weathered portion of this formation, although it seems equally likely that it is a late Pleistocene deposit. The clay was, also, noted at Belmar (Loc. 148) and east of Rancocas (Loc. 124). Although not now used, there is no apparent reason, however, why portions of it might not be employed for common brick, equally as well as many of the black micaceous clays now utilized at many points. Its thickness is probably between 30 and 40 feet.

CLAY MARL III (COLUMBUS SAND).

The middle member of the Clay Marl series is a very conspicuous bed of quartz sand. It is white or yellow and sometimes marked by delicate lines of red, giving it a highly variegated appearance. Locally, the iron has cemented it into rather massive beds of stone. Although the bed for the most part is clean quartz sand, often closely resembling the sand on the present

beaches, yet not infrequently it contains thin laminæ of firm brittle clay, which stand in sharp contrast to the adjoining sands, there being absolutely no gradation between the two. The clay laminæ contain no sand or grit, and the sand layers are entirely free from clay.

Towards the upper portion of the formation there is a horizon at which a bed of clay occurs locally. The clay is apparently not continuous, but has been seen at a number of widely separated points. At a few points this clay lense has been utilized for the manufacture of common brick, but nowhere extensively, and it is not likely ever to be of more than local importance. At the present time it is worked, in a small way, only at Thackara's pits, near Woodbury (155).

This member of the Clay Marl series is thickest at the northeast and decreases gradually towards the southwest. In Monmouth county it has a thickness of over 100 feet, on Crosswick's creek it has diminished to 30 or 35 feet, and at Swedesboro it hardly exceeds 20 feet. Farther southwest it seems to pinch out. Its characteristics, however, are the same where it is thin as where it is thick, and it retains its integrity as a distinct bed, so that it is readily recognizable everywhere from Atlantic Highlands to Salem county. It does not become more clayey to the southwest, as has been sometimes asserted, but retains its characteristics unchanged.

It passes upward by a somewhat rapid transition into the overlying glauconitic or sandy clay, so that its upward limit can be well enough defined for purposes of mapping. It is underlain by a well-defined clay bed, into which it passes more or less sharply, so that as a formation it is distinct. It outcrops in approximately the middle of the Clay Marl belt, just to the southeast of the clays indicated on Plate X.

CLAY MARL II (WOODBURY).

Character. The sand member just described is underlain by a thick bed of black clay, which we have designated as Clay Marl

'Clark, W. B. Ann. Rep. 1897, p. 179.

II, or the Woodbury clay, from the fact that it was well exposed in the railway cut at that place. The clay is somewhat micaceous, black in color, not sandy in the lower portion, but slightly so in the upper part, where it is locally distinctly laminated. It does not contain glauconite except perhaps at the very base, and in this respect it is to be distinguished from Clay Marl I, a glauconitic clay which underlies it. It weathers to a dove or light chocolate clay, which, when dry, breaks into innumerable blocks, large and small, frequently with a conchoidal fracture (Pl. XVIII, Fig. 1). In some localities, as at Dobbs' clay pit, near Camden (144), these joint faces are smoothed and polished in a striking manner. In its lower portion it is penetrated by numerous joints. Many of these are filled with crusts of limonite, which sometimes form huge honeycomb masses many feet in diameter and tons in weight. A most striking case of this sort was observed on the north bank of Rancocas creek west of Rancocas, where the clay was found to be so filled with these limonite masses as to render it necessary to abandon an extensive brickmaking plant.

Although the upper portion is more sandy than the lower, it is quite sharply set off from the sand bed above, the transition layer being only two or three feet in thickness at the most. Its base also is fairly distinct, although since the underlying member is also a clay bed, this line is not so sharp as at the top. This clay varies from 55 feet in Monmouth county to something less than that along the Delaware.

Although this member presents slight local variations, yet it can be readily traced across the State and is easily recognized by its characteristic features; i. e., its dove or light-chocolate color when weathered, its many joints, its lack of marl and its position beneath the sand bed (Clay Marl III). Its characters are such that there is no question of its integrity as a definite and distinct bed at any point between the shores of Raritan bay and the Delaware river in Salem county.

Localities. The position of this clay bed in the vicinity of Matawan is shown in detail on Plate XII. Within this area

1

This exposure has recently been obscured by grading, but numerous outcrops occur along the banks of the creek a mile west of Woodbury.