Clay Marl I-the Merchantville clay. Localities where worked. Sand bed, No. 4-Laminated sands. The Cretaceous formations in New Jersey can be naturally grouped into three series, a glauconite Marl series at the top, a Clay series at the base, and a Clay Marl series in the middle. The Marl series and the Clay Marl series belong to the Upper Cretaceous; the Clay series to the Lower Cretaceous. As is implied by the above names, each of these series is characterized by certain deposits of economic importance. The Marl series contains valuable beds of glauconite or greensand marl, which were very extensively dug for fertilizer in former years, and which are still in use to a more limited extent. The Clay series contains important beds of clay, some of great value. The Clay Marl series contains beds of clay and beds of marl, both of which have been utilized economically; but the clays are not so good as the best of those in the Clay series beneath, and the marls are inferior to the greensands of the Marl series. No marl occurs in the Clay series, nor has any workable clay been found in the Marl series. Although the three divisions of the Cretaceous can thus be divided into a Marl, a Clay Marl and a Clay series, it must not be supposed that these divisions are composed exclusively of marl, clay marl and clay. This is far from the case. In each series there are several thick beds of sand, which make up probably more than half of each series. The Marl series is then at succession of interbedded layers of marl and sand; the Clay series, of clay and sand; the Clay Marl series, of more or less glauconitic clays, glauconitic sands and marls. In the case of the Marl series and of the Clay Marl series, these subdivisions are so distinctive, and so sharply marked from each other, and hold their characteristics so continuously, that they can be nearly all traced without difficulty across the State, and their limits accurately defined on a map. In the case of the Clay series, however, there is less regularity, and only in a comparatively narrow area between Woodbridge and South Amboy, where the beds have been exposed in many large openings, can definite horizons be made out and traced beyond the limits of individual exposures. The three major subdivisions here outlined are the ones best suited to bring out the lithological and economic characteristics of the Cretaceous system in New Jersey. They are, moreover, the three subdivisions into which the Cretaceous in this State naturally falls. The lines separating them are more clearly defined lithologically and stratigraphically than any others which can be made, and their boundaries can be fixed in the field with greater accuracy than any of the lines between the individual members into which each series can be further divided.1 THE MARL SERIES. The Marl series can be divided into the following formations, the essential characteristics of which are indicated by their names: The Upper marl (in part). The Limesand [including the Yellow (quartz) sand]. The Red sand (Red Bank sand). The Lower marl (Navesink marl). Glauconite or greensand occurs in all five formations, but only as sparsely disseminated grains in the two sand members. The three marl formations are composed chiefly of glauconite, with small amounts of fine quartz sand and locally thin laminæ of clay or scattered clay pellets. These subdivisions are nearly everywhere readily recognizable in the field. Where their contacts are exposed they are seen to change from one to the other within reasonably narrow limits, usually 2 or 3 feet, and rarely more than 6 feet, so that their boundaries are sufficiently sharply marked to be accurately mapped. This definiteness is further enhanced in the case of the Limesand-Middle marl contact by a marked and persistent fossil bed 2 to 4 feet thick, which can readily be traced across the State. 'Dr. W. B. Clark (Ann. Rep. State Geologist for 1897), has proposed a somewhat different classification for these beds, which on lithological and stratigraphical grounds seems inapplicable in several respects to New Jersey. Whether or not it is the one which should finally prevail for the Cretaceous of the Atlantic coastal plain is believed to be open to serious question, but this point is not here considered. For the purposes of this report, the above classification is more convenient, more accurate, and more readily understood by the non-professional reader. The only exceptions to the above statement regarding the sharpness of contact are these. First, the top of the Upper marl (Cretaceous) passes into the Eocene marl without a break and with but little lithological change. The fossils, however, are decisive as to the age of the beds, although the division between the two formations can be made with difficulty in the field. Second, in Burlington, Camden, Gloucester and Salem counties, the Red sand, which separates the Lower from the Middle marl, is apparently absent, due to thinning out in the vicinity of Sykesville, Burlington county. The Middle marl is, therefore, in these counties superimposed upon the Lower marl, and it is impossible except in a general way to differentiate them. This is particularly the case the farther one passes southwest beyond the point of disappearance of the Red sand. The location of the Marl series is shown in a general way on Plate X, where it lies immediately northwest of the line indicating the boundary of the Miocene. It extends in an ever-narrowing belt from Atlantic Highlands and Long Branch at the northeast, in Monmouth county, to Salem, Salem county, at the southwest. The narrowing outcrop to the southwest is due in part to a lesser thickness consequent on the disappearance of the Red sand, but more particularly to the overlap of the Miocene sands and clays. In the southwest these rest upon the Middle marl, save where the larger streams have eroded them back and exposed the Lime sand. In eastern Monmouth county, on the contrary, the Miocene rests upon the Eocene marls, and the whole of the Cretaceous marl series is exposed. Since the Marl series contains no beds of workable clay, it will not be further considered. THE CLAY MARL SERIES. The Clay Marl series includes beds of sand, marl, and clay which underlie the Marl series, described above, and overlie the Raritan or Clay series. Its base is marked by the contact of a black, glauconitic sandy clay upon a cross-bedded lignitic sand, containing lamina and lenses of black, nonglauconitic, micaceous clay. The glauconitic clay at the base of the Clay Marl series weathers into a very characteristic cinnamon-brown, indurated earth, containing gunpowder-like specks of black or dark-green marl. This weathered phase is totally unlike the weathered phase of any of the underlying beds, and it is thoroughly characteristic of the Clay Marl series. The contact is usually a sharp one, easily identified and readily located in the field, wherever exposures are found from the Raritan river to Delaware bay.1 The top of the Clay Marl series is likewise a definite line-the abrupt passage from a loose reddish sand often very coarse, with grains of quartz the size of small peas to a compact greenish marl. For much of the distance across the State the top of the Clay Marl series is also marked by a fossil bed 1 to 4 feet in thickness, which affords a definite and easily recognizable horizon. The outcrop of the Clay Marls extends from the shores of Raritan bay across the State in a southwest direction to the Delaware river north of Salem. It forms a belt varying in width from 22 to 8 miles. Since the beds dip about 35 feet per mile to the southeast, the belt of outcrop is widest where the slope of the surface is toward the southeast, and narrowest where it is steeply to the northwest. On Plate X the position of the two lower, or clay-bearing members, of this series is shown. Subdivisions. The Clay Marl series can be subdivided as follows, the divisions being numbered from base upward:2 In an earlier report of the Survey (1892), the base of the Clay Marls as mapped by Dr. W. B. Clark, include 90 or more feet of interbedded black clay and lignitic sand, exposed between Cheesequake creek and Matawan creek. These beds should more properly be classed with the Raritan formation for the following reasons: a) they are nonglauconitic; b) they are extremely variable and individual beds cannot be traced any distance; c) they contain a flora which connects them with the underlying rather than the overlying beds, and d) the clay layers, some of which are massive beds, thin out to the southwest and give place to sand, until in the vicinity of the head of Cheesequake creek the Clay Marl series is underlain by 90 feet of loose white sand with comparatively few beds of black clay. If the clays east of Cheesequake creek are included in the Clay Marl (Clark's Matawan series), the base of the latter is not drawn at a constant geological horizon, but rises or falls as the upper portion of the underlying series of beds is sandy or clayey. 2 These subdivisions were first made out by Mr. Knapp and mapped by him in 1893-1895. The following names were at that time suggested by him for these divisions, beginning at the top (V) Wenonah sand, (IV) Marshalltown clay, (III) Columbus sand, (II) Woodbury clay, (I) Merchantville clay. |