CHAPTER VI. PLEISTOCENE CLAYS. CONTENTS. Glacial and aqueo-glacial clays. Origin. In the Hackensack valley. In other localities. Cape May clays. Origin. Localities. Pensauken clays. The Fish House clay. The Bridgeton formation. The Pleistocene formations, as at present recognized in New Jersey, may be subdivided as follows: A. Glacial and aqueo-glacial.1 1. Late deposits (Wisconsin age). 2. Earlier deposits (Kansan (?) age). B. Non-glacial. 1. Cape May. 2. Pensauken. 3. Bridgeton. Extensive clay deposits of late-Glacial age occur at several points in northern New Jersey. In southern New Jersey, both the Cape May and Pensauken formations contain beds of workable clay, and thin seams occur in the Bridgeton formation. 'These deposits are described in full in Vol. V, Report on Glacial Geology. GLACIAL CLAYS. Origin. During the Glacial period a mantle of debris of varying constitution and thickness was spread over the surface by the ice. This deposit, termed till, is commonly very stony and gritty, although containing so large a percentage of clayey material that the whole deposit has often been called bowlder clay. Locally, however, it is so free from stones, comparatively speaking, and so largely made up of clay that it is used for the manufacture of brick, the few stones being previously either screened out or crushed by grinding. This finer ice-deposited material may be called a glacial clay. The streams issuing from the edge of the great ice field which covered northern New Jersey carried vast amounts of rock debris. Most of this was gravel and sand, but a considerable quantity was fine, impalpable rock flour, the finest product of the glacial grinding. This extremely fine material was the last to be deposited by the streams, since it was the most readily transported, and, for the most, it was carried far out to sea. But, under favorable circumstances, it was deposited in lakes of more or less transient character, near the edge of the ice, or in estuaries which now, by reason of a slow elevation of the land, are wholly or in part above the sea. Wherever deposited by streams, this rock flour gave rise to beds of clay of variable thickness and extent, which may be classed as aqueo-glacial clay, since both water and ice were concerned in their formation. Since the glacier covered only the northern part of the State, clays of glacial or aqueo-glacial origin are not to be looked for far south of the line of the terminal moraine, as shown on Plate X, in pocket. Clays of the Hackensack valley.-"Beneath the stratified sand and gravel of much of the Hackensack valley there is a considerable body of laminated clay. It is well exposed only about Hackensack, especially in the pits at the brickyards below the city, on the west side of the river, and at a few points in the river bank north of the city. It is known to occur at Riveredge and New Milford, on the Henry Bartch place; is reported to lie beneath Oradell, and is present just south of Old Hook. It is not known north of this point in the valley of the Hackensack itself, but it is said to occur north of Closter, at Norwood, and at Neuvy. At Neuvy the clay was formerly worked, and its thickness is said to be 28 feet. The clay at this point is not now accessible. "In the valley of Overpeck creek the clay is also present as far north as Englewood, and probably beyond. "This laminated clay was deposited in standing water, which was moderately quiet. Into the water, masses of ice carrying bowlders were sometimes floated, as shown by the occasional large, glaciated bowlders in the clay. "The clay is known to overlie til at many points, and its deposition is therefore later than the occupancy of the region by the ice. At the north the surface of the clay is some thirty feet above sea level, while at Little Ferry its surface is about at sea level. Its surface, therefore, declines slightly to the south. "The depth of the clay is one of its most remarkable features. The following data on this point have been reported: "At Neuvy, surface elevation 20 to 30 feet, 28 feet of clay. "North of Closter, surface elevation about 40 feet, 10 feet of clay. At Oradell, surface elevation about 30 feet, 185 feet of clay, beneath 15 feet of sand.1 "At Hackensack numerous borings have tested the depth of clay, which varies from a few feet at the more northerly brickyards to 85 feet at Mehrhof's lower yard, and at the gas works. "West of Bogota, on the east side of the river, the clay is reported to be 215 feet thick. These figures make it clear that the surface of the rock east and north of Hackensack is far below sea level, and that, if the drift were removed, or even that part of it which lies above the till, a great bay would cover the Hackensack meadows, and extend far to the north. A branch of the bay would run up the valley of Overpeck creek, for the surface of the rock at Englewood is known to be locally as much as 60 1It is suspected that the boring here may have been in soft shale, not distinguished in the drilling from clay. feet below sea level. Even as far north as Closter the surface of the rock is at least 20 feet below the sea level, according to the records of wells. "The records of borings in the vicinity of Newark are in keeping with the above figures. "This clay was deposited in standing water. Such a body of water, therefore, covered the lower lands west of the Palisade ridge, probably as far north as Neuvy, after the departure of the ice. The surface of the clay at the north is about 30 feet above sea level. The surface of the water in which the clay was deposited was, therefore, at least this much above present sea level in the latitude of Neuvy. Not only this, but the water in which the clay was deposited was probably not extremely shallow. While no considerable depth need be assumed for it, it is safe to conclude that the surface of the clay is somewhat below the surface of the water in which it was deposited. Furthermore, the clay was deposited after the ice was sufficiently far north of the site of deposition, so that coarse materials were not readily available. It is not certain that the clay at Hackensack and below was strictly contemporaneous with that at Neuvy. The deposition of clay to the south may well have begun earlier than its deposition to the north. "It is commonly believed that the ice sheet depressed the surface on which it rested, and that, as it melted, the unburdened earth crust reacted by rising. Before the deposition of the clay in the northern part of the Hackensack basin, the land may have risen, so as to make the water shallower than at an earlier time. At any rate, there is good evidence of post-Glacial submergence to the extent of fully 30 feet near the northeastern corner of the State. Considering the depth of water necessary for the deposition of the clay, and the rise which may have taken place as the ice melted back, it is not unreasonable to suppose that the region about Westwood was submerged to the extent of 60 to 80 feet, the height of what appear to be delta fronts, at the time the ice was retreating; for these deltas, if such they are, were probably made while the edge of the ice was in the immediate vicinity, and somewhat before the deposition of the clay. "The hypothesis that the water which covered this area was a lake, rather than a bay, is worthy of consideration, though it is, on the whole, less satisfactory The moraine and other drift deposits may have blocked the southern outlet of this region to the height of 25 or 30 feet, between New Jersey and Staten Island. If a similar dam obstructed Kill van Kull, or the Narrows and East river, a lake would have come into existence in the tract where the clay is. As the outlet was cut down, the lake was drained. But even on this hypothesis, differential movement of the surface must be supposed, for the surface of the clay is higher to the north than to the south. "It may here be added that there is abundant evidence of a late submergence, at least to the extent of 40 feet, at various points about the coast of southern New Jersey. The date of this submergence was not earlier than the close of the last Glacial epoch. "The clay of the Hackensack valley is everywhere covered by sand, generally 8 to 15 feet in depth. At some points the surface of the clay below the sand is leached and oxidized. It is, in most places, not possible to say whether this leaching and oxidation is the result of exposure before the deposition of the sand, or whether it has taken place beneath the sand. The latter would be somewhat out of keeping with the extent to which the drift so far beneath the surface has generally been altered since its deposition. "At two points specific evidence on this point has been obtained. In 1893 one of the clay pits below Hackensack showed the following section: "(5) 8 feet of fine, stratified sand, containing a few gneiss bowlders. "(4) Stratified sand, 2 feet in depth, overlain by a few inches of blue clay containing fragments of leaves and woody stems. "(3) I foot of black soil. "(2) 6 feet of laminated clay, containing an occasional bowlder, calcareous up to within a foot of its upper limit. "(1) Till, seen in the bottom of the pit on its west side. "The old soil (3) was not far from sea level. A similar section, so far as the old soil was concerned, was seen by Mr. Peet, |