definite and orderly arrangement over extended areas. Individual beds of clay thin out rapidly or grade bodily into beds of sand within short distances. In not a few instances data have been observed, which indicate that beds after deposition were partially swept away by shifting currents, before the overlying layers were formed. Within comparatively short distances, also, sand and clay were being deposited simultaneously, so that rapid changes in the character of the deposit have resulted. In these respects the Clay series is in marked contrast to the Clay Marl or Marl series, during the deposition of which uniform conditions prevailed over wide areas, and successive deposits were formed, which can be traced as individual beds across the State. Although it is impossible to establish any divisions in the Raritan series, which can be accurately identified at widely separated intervals, nevertheless, as was long ago pointed out by Cook and Smock,1 in Middlesex county, in the vicinity of Woodbridge, Perth Amboy, South Amboy and South River, where the beds have been extensively opened in many localities, there are certain divisions, which in their general features persist from opening to opening, and so can be traced through all the region. Yet even here, not infrequently many of the minor beds seen in one pit are wanting in the next one a few rods away, showing that variable conditions prevailed, even in this area. The degree, however, to which the Clay series has been subdivided in this part of Middlesex county is probably not due entirely to the distinctness and persistence of individual members. The great number of exposures, both natural and artificial, enable one to trace the beds with much greater detail than in any other portion of the State. Were the formation everywhere so well exposed as in this region, it is highly probable that some similar classification could be made in other districts, and that the formation would not prove to be such a varying complex of clay and sand, as seems to be the case. It is certain, however, that the classification which is applicable to Middlesex county would not apply to Burlington, and it is equally certain that no 1 1 Report on the Clay Deposits of Woodbridge, South Amboy, etc., 1878, pp. 33-75. such definite subdivision would be possible in the case of the Raritan as has been made in the Clay Marls or Marl series. Thickness.-The thickness of the Raritan series varies considerably, as is shown by numerous well borings which have penetrated to the older rocks beneath. Cook and Smock made an estimate of 347 feet from a detailed study and comparison of the various beds in Middlesex county. Our own estimates for this region give 380 to 390 feet. At Asbury Park, 20 miles down the dip from the outcrop, a well penetrated 367 feet of beds belonging to this series without reaching its base; whereas, at Bordentown, the entire thickness of the formation, from top to bottom, as shown by borings, does not exceed 250 feet. At Jobstown, southeast of Bordentown and 8 miles farther down the dip, the Raritan was penetrated for 409 feet, and bottom not reached. At Delair, north of Camden, the base of the Raritan is 162 below tide. Making due allowance for the upper part of the formation not present here, owing to post-Cretaceous erosion, the thickness is 275 to 300 feet. The greatest thickness, however, has been reached in a boring at Fort Dupont, Del. (opposite Fort Mott, N. J.), where 594 feet of the strata belonging to the Raritan were penetrated without reaching its base. These figures indicate that the formation' is thinner along its outcrop than down the dip to the southeast. This conclusion is in accord with what is known of other formations of the coastal plain. Stratigraphic relations.-As has already been stated, the contact of the Raritan and the Clay Marls above is sharp and easily recognized. Wherever seen, its top is a loose sand, or a sand with clay laminæ, whereas the base of the Clay Marl is a glauconitic clay, black when fresh, a rusty brown where weathered, and frequently fossiliferous. The contact is, moreover, frequently emphasized by a bed of ironstone due to cementation of the upper layer of sand. The basal contact is less frequently shown. In Middlesex county, wherever exposed, the Raritan beds rest unconformably upon the eroded edges of the Triassic (Newark) shale, while some well borings show that locally they are underlain by trap rock. From Trenton, southwestward, they rest upon the Philadelphia gneiss and schist, as is shown by a few well borings. So far as known, the lowest layers are always derived from the subjacent formation. At Brinkman's clay pit, Piscataway (96), there is a gradual transition from the undecomposed Triassic red shale to a red and white plastic clay, which is undoubtedly Cretaceous. Since, however, the Triassic beds dip to the northwest, and the nearly horizontal Cretaceous beds lie upon their beveled edges, we know that there was a long period of erosion, accompanied by great crustal movements after the formation of the shale and before the deposition of the Cretaceous Nevertheless, it is here impossible to draw a sharp line between them. The apparent transition is undoubtedly due to a partial re-working of the residuary red clay, which mantled the Triassic at the beginning of Cretaceous time. At other localities there is a distinct alternation of sediments derived from the shale, and from more distant sources.1 In general, wherever the underlying rock is red shale, the lowest bed of the Raritan is a very sticky red clay, evidently derived in part, if not wholly, from it. Where the Raritan rests upon a micaceous schist or gneiss, as is the case at Delair, near Camden, borings have shown that the lowest beds of the Raritan are mica sands, such as would be derived from the subjacent formation. Conditions of formation.—It has been generally considered that the Raritan formation was accumulated under broad estuarine conditions. The rapid alternation of layers, the horizontal variation in character of the beds, and their abrupt changes in thickness, have been interpreted to mean shifting currents and great variations in conditions within comparatively narrow limits. The cross-bedded structure of many of the sand beds, the billowy, eroded upper surface of some clay layers, the bits of lignite, and even trunks of trees and great masses of leaves, all indicate shallow water and proximity to a shore line, as well as shifting currents. The beds of extremely fine clay, however, indicate that still waters must have prevailed a portion of the time, even although the shore was not many miles distant. The few fossil shells which have been found are of brackish water, rather than marine types. In all these respects the Raritan beds stand in 'Cook and Smock, loc. cit., pp. 169–170. marked contrast to the Clay Marl and Marl series, which, by their constitution, indicate deeper water, uniform conditions over much wider areas, marine rather than brackish water, and a tendency to uniform, rather than strongly varying rates of accumulation. Location. The area occupied by the Raritan series is shown upon the accompanying map, Plate X. It forms a broad belt, extending from Raritan bay across the State to Trenton and Bordentown, and a much narrower strip along the Delaware river to Salem county. Its greatest width is something over 8 miles, while for a few miles below Bordentown it is limited in outcrop to the face of the bluff above the river, and the side slopes of the neighboring ravines, the greater part of the outcrop belt being beneath the bed of the river. Over most of its outcrop across the State its surface is more or less covered by later deposits of sand and gravel, the Pensauken or later formations. These are often so thick as to conceal effectually the beds beneath, and in not a few localities to hinder or entirely prevent digging or even prospecting for clay. This is particularly the case in the flat, low-lying portion of the State from Fresh Ponds and Spotswood to Trenton. Within this area it is not only impossible to make out any subdivisions in the Raritan, but it is a matter of some difficulty even to determine accurately its boundaries. Nevertheless, occasional well borings show that extensive beds of clay occur within this area, although not at horizons which render them economically valuable. NORTHEASTERN MIDDLESEX COUNTY. Within the region lying between Woodbridge, South River and Cliffwood, shown in detail on the maps, Plates XI and XII.1 it has been possible to subdivide the Raritan formation into nine. members, which can be differentiated and mapped with reasonable accuracy. These are as follows, beginning at the top: 1 These maps are described in detail in Appendix E. Subdivisions of the Raritan formation in Middlesex County. The Cliffwood lignitic sands and clays. No. 4. Sand-laminated quartz sand. No. 3 Sand-chiefly quartz. The South Amboy fire clay. No. 2 Sand-including beds of so-called "feldspar" and "kaolin." The Woodbridge clays-fire, stoneware and brick clays. The Raritan clays-fire, and terra-cotta clays. Locally, still more minute subdivisions can be recognized, but the above are the only ones which can be successfully mapped. THE CLIFFWOOD LIGNITIC SANDS AND CLAYS. These beds, the upper portion of the Raritan, are nowhere exposed in a continuous section, but are well shown, a) in the cliffs along the Raritan bay from the southeast side of Cheesequake creek to Prospect Grove, near Cliffwood; b) in the various clay pits about Cliffwood, and c) in the cuts of the Long Branch railroad, southeast of Cheesequake creek. Combining these various exposures, as well as possible, we have the following sequence of beds. At Prospect Grove 40 feet of white sand, with seams of black lignite and thin beds of black clay (becoming thicker and more numerous in base of section), are exposed immediately beneath Clay Marl I. At tide level the top of a massive black clay is shown. These beds contain many sandstone concretions which have yielded numerous plant remains.1 The lenses of clay in the sand thicken and thin out variously, as shown in the bluff along the shore. Apparently the basal portion of these alternating sands and clays are exposed in the higher beds at Geldhaus' 1 'Hollick, Arthur-The Cretaceous Clay Marl exposure at Cliffwood, N. J Trans. N. Y. Acad. Sci., Vol. XXI, p. 124. |