POST-PLEISTOCENE CLAYS.

Character. The clay deposits which are to be considered as belonging to the post-Pleistocene or recent period1 are small, impure and of local importance only.

Along some of the streams shallow beds of sandy and often stony clay occur on the flood plains, i. e., those areas subject to overflow in times of high water. They are clearly the result of the deposition by the stream of the finest material it carries in time of flood. Elsewhere swamps and marshes are underlain by clay, which has resulted from the fine mud washed into them by rain and streams. This clay is usually more or less sandy and often contains a large amount of vegetable matter. In still other localities of the State beds of sandy or stony clay have accumulated at the foot of slopes, as the result of the wash, by rain water, of the finest material from the hills above. Since in such locations there has been very little mixing of the material, these deposits often resemble closely the residual clay formed by the decay of rock in place. All these clays are usually either of a mottled yellow or red color, due to iron staining or black, as a result of the large amount of vegetable matter contained in them. They are of limited extent, both in area and thickness, and are rarely of any value save for the manufacture of common brick. For this purpose, however, they often serve admirably and afford workable clay for small brickyards supplying a local demand. Owing to the diverse ways in which these deposits originate, the clay varies considerably in character and the value of each deposit has to be judged separately.

Localities.-Clay of this nature is used at several localities in New Jersey. At Dunellen (235), Rajotte's clay pits are located along the swampy flood plain of Green brook. The clay is 4 to 6 feet thick, covers at least 14 acres, and is underlain by gravel of late Glacial age. The clay is evidently a swamp and flood plain accumulation of post-Glacial or recent time.

It is not possible to estimate accurately geological periods in years, but their length is to be calculated in thousands rather than hundreds of years. 2 These numbers all refer to localities shown on Plates X, XI, XII, XIII.

At Hand & Son's yard (236), North Plainfield, a sticky clay 7 feet thick is used. The clay grades downward into fine sand of glacial derivation. Beneath the sand (7 ft.) is the red shale of the Newark formation. The clay occurs in a slight depression, adjoining a tributary to Green brook, and is perhaps a flood plain and wash deposit of post-Glacial age. It may, however, be connected in origin with the closing stage of the Glacial period, and so more properly belong under the head of glacial clays. Near its borders, where it adjoins a much older gravel formation at a slightly higher level, pebbles from the latter are mixed with it

At Benward's brickyard, Brass Castle, Warren county (279), a sandy, gritty clay containing numerous partially disintegrated bowlders of gneiss, and derived by wash from the steep hillside adjoining, is used in a small way for the manufacture of common brick. A clay formed in a similar manner, but of better quality, is found at Flemington (276), at Pedrick's yard. It is from 3 to 7 feet thick, and rests upon the red Triassic shale. The lower portion of the clay is simply the weathered part of the shale and contains minute shale bits. The upper 4 feet is yellowish in color, contains minute bits of partially decomposed trap rock, as well as some larger fragments of the same rock, and is evidently the result of wash from a steep hill of trap a few rods west of the yard.

Clay loams-At many points in the State there are clay loams, which are used by themselves or in combination with other clays. They occur at all elevations up to 200 feet and more. They are by no means continuous, even within the areas in which they occur, and not infrequently they are so poorly defined as to be indistinguishable from the weathered products of the formations on which they rest. They sometimes occur, however, in such relations, and have such a composition that they cannot be regarded as a part of the underlying formation, nor as the product of local wash, nor as a wind deposit. Their average thickness is 4 or 5 feet; they rarely exceed 8 feet, although thicknesses of 20 feet are not unknown. They are com

'Geol. Surv. of N. J., Vol. V, Report on Glacial Geology, pp. 206-210.

monly pebbly in their basal portion, and not infrequently they are stony throughout.

Certain of them at levels not exceeding 60 feet, contain marine organisms, and are, therefore, positively of marine origin. They rest directly upon deposits made during the closing stages of the retreat of the glacier from New Jersey, and so may be regarded as of post-Glacial age, or at most as marking the very latest stages of Glacial time. Many of the loams at greater elevations are indistinguishable from these low-level loams, and are apparently continuous with them, so that the post-Glacial or very late Glacial age of the highest loams is probable, although not demonstrable. While it is impossible to assert that all these loams have had a common origin, yet many facts in the possession of the Survey point to this conclusion, and suggest, even if they do not prove, the post-Glacial origin of these deposits. In this report, therefore, they will be so considered, although the possibility of other interpretation is not overlooked.

It is impossible to give in a few words their distribution, since they are so widespread over the State, and yet so discontinuous. They may be looked for at all levels below 200 feet. They are extensively used for brick at Trenton and Trenton Junction, and northward to Pennington, where they have been stripped off the surface over many acres, at elevations between 100 and 200 feet. At many points, also, between Trenton and Camden, and in the vicinity of the latter place, there is a loam so clayey as to be used for brick. This is the case at The Bordentown Brick Company's brickyard (109), Bordentown; S. Graham & Co.'s yard (102), near Fieldsborough; Murrill Dobbin's yard (113), Kinkora; Joseph Martin's yard (115), Kinkora, and Budd Brothers (143), Camden. At all of these places, however, other clay is mixed with the clay loam.

Very similar clay loam is also used at Brocklebank's (214), Howell, Monmouth Co., and at Lippincott's (215), near Farmingdale. At B. H. Reed & Bros. (193), Hightstown, one of their pits is in a bluish surface clay, somewhat stony, which may be correlated in age with these clay loams. At other points, too numerous to mention, the clayey loam occurs, but is not worked. The illustrations in Plate XV show the shallow character of the clay.