Bank of black Raritan clay overlain by gravel at S. Graham & Co's. brickyard. The man stands just below the contact, which is sharply marked.

deposit showing 16 feet of clay (Pl. XL, Fig. 2), underlain by white sand and covered by 4 to 6 feet of Pensauken gravel.1 It is black, micaceous, and the clay layers are separated by thin laminæ of white sand. Pyrite concretions are very abundant, and owing to the large amount of carbonaceous matter, care has to be exercised in the early stages of burning, not to push the firing too fast, otherwise the bricks are liable to swell and crack. Drying takes about 48 hours. As a matter of fact the clay is not used alone but is mixed with a certain proportion of surface loam of Pleistocene age.

The black clay (Lab. No. 652) has the following physical characteristics:

Water needed for tempering, 27.8 per cent.; air shrinkage, 7 per cent.; average tensile strength, 168 pounds per square inch.

The addition of the loam improves its color-burning properties and renders it more porous. The material burns to a good red brick, of moderate absorption, but is too coarse-grained to make a good smooth pressed brick.

Kinkora.—At Murrell Dobbins' brickyard the upper portion of the sandy laminated Raritan clays are shown, but most of the clay used comes from the overlying Clay Marl I. An analysis of the laminated Raritan clay was given by Dr. Cook2 as follows:

Sand,

Analysis of clay from Murrell Dobbins' yard, Kinkora.

Combined silica (SiO2).

Alumina (Al2O3),

Ferric oxide (FeO3),

Lime (CaO),

31.80

25.50

17.70

6.40

0.16

1

Since this was written, continued excavation into the hillside has shown a few feet of Clay Marl I on the Raritan clay and beneath the gravel. The contact is distinctly marked by an abrupt change in the character of the deposits and a line of nodules, but owing to the sameness of color of the two formations here it is not obtrusive. H. B. K.

2 Clay Report, 1878, p. 241.

A number of clay works are supported by the Clay Marl deposits in the northwestern part of the county. Some of these use Clay Marl I and others Clay Marl II, while still others have opened pits along the boundary between Clay Marls I and II, and use a mixture.

At many localities the Clay Marl is overlain by a ferruginous sand or gravelly loam, of which a certain proportion is added to the clay. In addition to the worked localities, samples were taken from a number of outcrops of Clay Marl for the purpose of determining the general character of these clays. The worked deposits will be first discussed.

Bordentown.-Clay Marl I is worked in Burlington county at The Bordentown Brick Company's brickyard, near Bordentown (Loc. 109). In the main pit there are 8 feet of a black sandy clay of marly (glauconitic) aspect, with numerous quartz grains and mica scales visible to the naked eye. The upper foot or so is weathered and lean. Above the clay are 2 to 3 feet of Pensauken gravel, with a similar amount of sand and more gravel.

The black clay alone (Lab. No. 600) has a high shrinkage, and cannot be used by itself, hence a clay loam is mixed with it. It takes 23.4 per cent. water to temper it, and it shrinks 8.8 per cent. in drying, which is somewhat high. Its average tensile strength is 251 pounds per square inch. When burned, it gives the following results:

Burning tests of a black clay, Bordentown Brick Company.

On account of the low cone number at which the clay softens care has to be used in burning, so that the bricks do not crush out of shape. This clay shows the highest fire shrinkage of any of the Clay Marls tested and cannot be used alone, but is mixed with considerable top loam (See tables of Pleistocene tests, p. 348). The latter burns to a porous body of low shrinkage, and, therefore, counteracts the undesirable properties of the clay. The bricks show up well when tested.

Kinkora. As noted above (p. 381), Clay Marl I is used for common brick, at Murrell Dobbins' brickyard, Kinkora (Loc. 113), along with some sandy clay from the Raritan and some clay loam of late Pleistocene age. It is a black, very micaceous clay with more or less greensand marl and is from 12 to 14 feet thick in the bank. Samples were not tested.

Crosswicks.-Clay Marl II is worked at Crosswicks (Loc. 110), by J. Braislin & Son, for making hollow bricks (Pl. XXXIV, Fig. 2). The clay bank is about 20 feet high and is one of the best exposures of this formation in Burlington county. The clay burns red, and is probably of low fusibility judging from the behavior of the ware in the kiln.

Maple Shade. The same Clay Marl formation is worked by T. Saucelein, at Maple Shade (Loc. 150), on the north side of the railroad tracks. Here the beds are mostly weathered, but burn to a hard, red brick, and make a good product on stiff-mud machines.

On the south side of the railroad, and just south of the trolley road from Merchantville to Moorestown is A. Reeve's brick-clay pit (Loc. 149, Pl. XLI, Fig. 1), but here the clay dug is at the line of contact between Clay Marl I, and Clay Marl II, both being used. The section exposed in 1902 was about thirty feet high and showed the following layers beginning at the top: