The upper foot or two of the clay not infrequently contains scattered pebbles, and the whole is usually covered by several feet of sand or gravel or both. Locally, the change to the overlying sand or gravel is abrupt and sharply marked, and the upper limit of the clay is apparently an erosion surface on which the sand and gravel were later deposited (Plate XVII, Fig. 2). When this is the case, the upper part of the clay is without stones. Elsewhere, there is, for a space of a few inches or a foot or two, an alternation of sediments, laminæ of clay being contained in the overlying beds. In a few instances these clay laminæ continue for several feet above the main mass of the clay.

There seems little reason for doubting that the clay and the underlying sand were successive deposits, formed without interruption. In those cases, where the clay is somewhat sharply separated from the overlying sand and gravel, the former is best referred to the Cohansey, and the latter to the Bridgeton or Pensauken, or regarded as a secondary deposit derived from them by weathering and washing. Where the clay is apparently commingled in its upper part with the overlying gravel, the latter may still be a much later deposit, the commingling of the two being due to re-working of the upper portion of the clay as the gravel was deposited. In this case the bulk of the clay might be Cohansey, with its upper portion re-worked in Bridgeton or Pensauken time. In a few rare instances the clay, by its interlamination with the overlying sand and gravel, seems to be of the same age as the gravel, rather than older. Although in the light of our present knowledge it seems best to regard all these clay lenses as belonging in the Cohansey sand, yet the possibility that some of them may be later in age (perhaps Bridgeton) must be kept in mind.

THE SHILOH MARL.

A gray, highly fossiliferous marl is found in a limited area in Salem and Cumberland counties along the tributaries of Stow creek. In the region in which it occurs this formation next underlies the clay-bearing Cohansey sands. Since it contains fossils of undoubted Miocene age, the overlying sands and clays cannot

be older than late Miocene, and, as above noted, they may be younger. It likewise enables us to fix the age of the thick bed of clay which occurs beneath it, so that, although it contains no clay itself, it is an important stratigraphical bed.

THE ALLOWAY CLAY.

Occurrence. The clay bed, to which we have given this name, is continuously traceable from near Swans Mills, south of Mullica Hill, in Gloucester county, southwest to a point 2 miles south of Alloway, in Salem county. Isolated outcrops, where the overlying beds have been removed, have been observed as far south as Stow Creek township, in Cumberland county. The clay undoubtedly continues south of Quinton, towards Canton, and perhaps southeast to Bacons Neck, near Cohansey creek, but in this direction it is deeply buried beneath the later Cape May sand and gravel. Within the area between Alloway and Ewans Mills, its outcrop forms an exceedingly irregular belt, several miles in width. Within this belt, however, there are considerable areas where the overlying Bridgeton formation is so thick as to effectually conceal the clay which lies beneath. The map on Plate XIII (in pocket) shows the areas (1) in which this clay appears on the surface or is buried by not more than 5 or 6 feet of cover; (2) the areas in which it is so deeply buried as to be inaccessible, and (3) the areas from which it has been removed by erosion. Since the clay bed slopes gently towards the southeast, the northwestern border of this deposit is formed by the outcrop of underlying beds from which the clay has been eroded. Attempts to find this clay to the northwest of the area indicated on the map by boring or otherwise will, therefore, prove futile. On the southeast and south, however, the Alloway clay passes beneath younger formations of various ages. These rapidly attain considerable thickness, particularly to the southeast, owing to the rise of ground in that direction, so that, although the clay there continues an unknown distance to the south and southeast beyond the limits given on the map, yet it is discoverable only by

deep borings.1 Northeastward towards Ewan Mills the clay apparently thins out. At Haines & Son's brickyard, south of Yorktown, it has a thickness of 50 feet, as determined by boring. Along Salem creek it is exposed in frequent outcrops from Fox's mill, near Pittsgrove, nearly to Woodstown, a distance of 4 miles, in which the entire thickness of 75 or 80 feet is crossed. It is apparently a continuous bed of clay, without sand beds of sufficient extent to show themselves in outcrop. Northeast of Harrisonville, however, it rapidly thins out, giving place to sand, and towards Ewan Mills, a thick bed of sand apparently occupies its middle portion. A mile southwest of Five Points (Richwood) and one and one-half miles north of Ewan Mills a clay bed 4 to 6 feet thick apparently corresponds to the basal portion of the Alloway clay. No further trace of it has been found to the northeast.

At present this clay bed is being worked only in one localityHaines & Son's brickyard-south of Yorktown. At Fenwick (169) a secondary surface clay derived largely from this clay bed was formerly utilized in a small way. This clay is available over wide areas, some of them advantageously located, as regards railroad facilities. It is finely developed on the lower slopes of Big Mannington hill, about a mile from the railroad, and also in the railroad cuts at Riddleton Junction and at Alloway.

Character. It is usually a light-brown color, although some portions are white, yellow, or even black. Where weathered, it is traversed by many joints, breaking it up into small pieces, with conchoidal fractures. These joints are locally filled with iron crusts, Plate II, Fig. 2, which diminish greatly its value. The rich farming country underlain by this clay bed is shown in Plate V, Fig. 2. Samples of the clay were taken at many localities

1

At Glassboro it was penetrated at 90 feet from the surface, at an elevation of 50 feet A. T., where it was 55 feet thick (Ann. Rep. '93, p. 407); at Clayton, 98 feet from the surface at an elevation of 46 feet A. T. (Ann. Rep. '95, p. 89); at Williamstown 5 feet of black clay 66 feet below the surface between elevations of 84 feet and 79 feet A. T., may, perhaps represent it (Ann. Rep.., '97, p. 255); 1 mile south of Daretown it apparently occurs 80 feet below the surface from 60 feet A. T. to 35 feet A. T. (Ann. Rep. '97, p. 250).