Section of Raritan clay included in glacial drift. The lighter streaks and spots represent the clay. The upright rod is ten feet long.

or "ironstones" are not uncommon at some horizons, and are locally so abundant as to form an almost continuous layer of stone.

At many banks these layers have to be removed in order to get at the fire clay. They were formerly thrown away in great part, and this is to some extent the case at present, but most of them can be used in hollow brick, fireproofing, common brick, etc., and at many points, particularly near Maurer, Keasbey, Sayreville and South River, they are so used very extensively.

These clays, where uneroded, vary from 30 to 60 feet in thickness, according as it is possible to differentiate certain beds just above the fire clays, or as all beds down to the fire clays are included.

In the area about Woodbridge the black laminated clays are shown in the upper part of the banks worked by M. D. Valentine & Bros. (14), J. H. Leisen (16), Anness & Potter (6), Perth Amboy Terra Cotta Company (7), P. J. Ryan (8), W. H. Cutter (29, 30), and James P. Prall (28, 31), while the banks near Maurer Station, i. e., of the Staten Island Clay Company (33, 43) and of Henry Maurer & Son (36, 34), are entirely in this member.

In the Sand Hills area, the black laminated clays are well exposed in the bluff west of Florida Grove and in the banks of the Perth Amboy Terra Cotta Company (241), the Standard Fireproofing Company (46, 47), the International Clay Company (48, 49), Henry Weber (52), Mrs. John Goodrich (51), Ostrander Fire Brick Company (53), R. N. & H. Valentine (55, 86), D. A. Brown (87), and Charles Edgar (94), near Bonhamtown. South of the Raritan river they occur along the shore from Kearney's dock southwest to Crossman's dock, where the upper beds are dug. At Sayreville, the black clays dug by the Sayre & Fisher Company (71), William F. Fisher (74), Edwin Furman (72), and Boehm & Kohlhepps (73), for common brick, belong to this member. In the vicinity of South River and Milltown, they are found in the banks of Jos. Bissett (85), Yates Brothers (82), Theodore Willets (83), John Whitehead (84), Pettit & Co. (247, 249), National Clay Manufacturing Company (244), N. A. Pyrogranite Company (246), M. A. Edgar (252), and the Sayre & Fisher Company (253, 254).

Fire-clay bed.-A thick, persistent bed of high-grade fire clay occurs at the base of the Woodbridge clay. It is usually a lightblue or gray color, although parts of it are red mottled, due to a larger percentage of iron oxide in these portions. The clay carries more or less white quartz sand, which is generally more abundant in the upper and lower portions of the bed. These are often called the "top-sandy" and "bottom-sandy" clay, respectively. Where not sandy, the clay is hard and brittle and of a high degree of refractoriness. Some of the No. 1 fire clay contains as low as 0.5 per cent. of quartz sand, but the average is 5 per cent., while some of the sandy portion runs over 50 per cent.1 Some portions of the bed contain considerable pyrite in the form of "sulphur" balls or nodules which have to be carefully picked out and rejected in mining.

The best clay, the "fine clay," or "No. I fire clay," as it is variously called, is commonly in the central portion of the bed, but there are frequent exceptions to this. The spotted or red clays are an inferior grade, and most commonly, but not always, occur below the "fine clay." The line of demarkation is never a sharp one, and the two varieties are both parts of a single bed. In some pits the spotted clay does not occur and the whole bed is blue or bluish-white clay. In other pits the spotted clay overlies the blue, in still other localities it passes into the blue horizontally. As is shown in Chapter XVIII, there is considerable variation in the quality of even the "No. 1" clay dug in various banks.

The surface of the Woodbridge fire clay is in places strikingly irregular or wavy, just as was the case with the South Amboy fire clay. Many instances are known where the top of the clay undulates from 5 to 15 feet within a few rods. Where the top of the bed is exposed over considerable areas, this undulatory surface is apparent; "sometimes rising and falling quite gently, forming ridges or dome-like knobs or elevations and irregularly shaped depressions or hollows; at others, marked by exceedingly irregular 'bunks,' as the miners call them, and sink-like holes that succeed each other without any apparent order or system." The irregu

larities are well shown in some of the banks west of Woodbridge. At other localities, on the contrary, the upper surface of the fire clay holds a constant level over somewhat wide areas. Nowhere is this better shown than in the long exposures in W. H. Cutter's banks (29, 30). (Compare Pl. XXI, Fig. 1, with Pl. I, Fig. 1.)

In general, the inequalities of the surface are most marked where the fire clay is immediately overlain by glacial drift or by the yellow gravel (Pensauken) formation (Fig. 35, B). In this case, the irregularities are due to erosion which removed the overlying Cretaceous beds before the much later drift was deposited. In those cases not only has a part of the fire clay been worn away, but also a great thickness of overlying Cretaceous beds, and perhaps a part of the Miocene.

A

Glacial Drift Laminated Clay Fire Clay

Fire Sand

0:

Fig.35.A. Erosion and partial removal of the black laminated clay before the glacialdrift was deposited.

B. Complete removal of the black laminated clay and
erosion of the top of the fire clay, before the glacial
drift was deposited.

C. Complete removal of the black laminated clay and of the
fire 'clay before the drift was deposited.

Locally, erosion may have been so extensive as to remove the fire-clay bed itself. In such cases borings through the drift would strike not fire clay, but the underlying fire sand (Fig. 35 C). Erosion since the deposition of the drift will account for the absence of the fire clay along those streams such as Heard's brook near Woodbridge, where the stream has cut down its valley below the level of the fire clay. In such a case, the fire clay is found on either side the stream at a higher level (Fig. 36, A). In some cases, however, the undulatory upper surface of fire clay is followed immediately by beds of Cretaceous sand or sandy clay. In these cases the irregularities are apparently due to erosion by shifting currents, tidal or otherwise, during the deposition of the