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At the same time that the ice was doing its work in the north, the streams flowing out from it made deposits of sand and gravel farther south. These are indicated by color number 11 on the map.*
AREA OF THE CAPE MAY FORMATION.
Along the borders of the Coastal plain, from Raritan bay to the mouth of the Delaware and up the Delaware as far as Trenton, there is a low-lying belt of flat country, often somewhat terraciform, having an elevation of 30 to 50 feet. The substructure of this terrace is usually some one of the preceding formations, but it is generally covered by a thin body of loam, sand and gravel of lesser age than any of the preceding formations, except possibly the drift of the last glacial epoch. Occasionally this young formation has a considerable thickness, extending from the surface down to and even below sea level.
The disposition of this formation seems to indicate that when it was deposited, the Coastal plain (of New Jersey) was depressed something like 35 to 45 or 50 feet below its present level, the amount varying slightly in different localities. At the same time the drainage of the Coastal plain was sluggish, and deposits contemporaneous with those along the shore were made by the streams in their valleys. Starting with the debouchures of the streams, the alluvial deposits extended up the valleys, sometimes well toward their sources, and to elevations much above 50 feet. The disposition of this formation is shown on the map, where it is represented by color number 12. It will be seen that it makes a wide, though very irregular border from Keyport to Ocean City, and from Trenton to the mouth of Maurice river. Besides this, it not only covers the whole of Cape May county, but within this county it makes up nearly all the mass of the land which is above the sea. The strict contemporaneity of this formation with the drift of the last glacial epoch is not established, but it is probably at least partly contemporaneous with it, though its later portions may be slightly younger. The approximate contemporaneity of the two is inferred from their topographic relations, especially in the lower part of the Delaware valley, down which glacial drainage coursed, making deposits which are topographically continuous with those of this formation.
* For description of this extra-morainic drift of last glacial age, see Annual Beport of the State Geologist of N. J. for 1892, pages 102-122.
Since it has its best development in Cape May county, the name of that county is an appropriate one for the formation. The name is here used to cover those deposits of late glacial and early post-glacial time, which were made beyond the region directly affected by the ice or its drainage. It includes much of the loam which has heretofore been referred to under the name of the "low level Jamesburg."*
HIGH LEVEL LOAM (NOT MAPPED).
At many points at various high levels in different parts of the State there is a loam, the origin and explanation of which have occasioned much study, but for which no satisfactory explanation has been found. It is not confined to the Coastal plain, though it is there most widespread. It occurs at various elevations up to 200 feet and more, and from this altitude ranges down to the low-lying formations which has just been described. Outside the Coastal plain it lies on the Triassic shale at various points. In its clayey phases, it is used for brick clay. Thus the brick clay south of Pennington, 50 feet or more above the upper limit of the Pensauken formation represents it. Farther south, and at slightly lower levels, it overlies the Pensauken formation, covering it as a mantle three or four feet in thickness. In the vicinity of Trenton Junction, the clay loam mantle has been extensively used for brick, and it might be so used at numerous other points. Loam in such similar positions and relations as to lead to belief in its community of origin, is found up to the elevation of 181 feet in the vicinity of Marlton, 160 feet at Fountain Green, and 200 feet or more in the vicinity of Cream Ridge.
Its physical character varies from point to point, but in the southern part of the State it often contains a goodly amount of marl, even when the immediately underlying formation does not, seeming to make it necessary to suppose that the marl formations were well exposed when it was deposited. Furthermore its position is such as to show that it is younger than the body of the Pensauken formation, representing either its last phase or something subsequent to it.
In the vicinity of Philadelphia, the brick clay overlying the Pen * Annual Report of the State Geologist of N. J. for 1894.
sauken gravel and running to still higher levels, seems to connect itself with the clay loam on the low river terraces which are correlated with the youngest (Cape May) of the preceding formations. If the connection of the high-level loam with that on the low terraces is correct, the former, like the latter, must be much younger than the Pensauken.
Farther north, between Raritan and Pluckamin, there is at some points a surface clay which is highly calcareous. It is a deposit from standing water and seems to have been connected with the glacial waters of the last ice epoch. Clays which may be supposed to have a contemporaneous origin overlie the last glacial gravels and sands at the Plainfield brick yards. These and other facts which will not be here detailed have raised the strong suspicion that there was a deep, but very brief submergence of the State to a much more considerable extent than has been commonly recognized at, or soon after, the close of the last glacial epoch.
The high-level loam here referred to is found at many points in the Coastal plain. In general it is so discontinuous, so thin when it is present, and often so indecisive in character, that it cannot always, and perhaps not generally, be distinguished with certainty from the weathered products of the formations which underlie it; but occasionally it is so distinct as to leave no doubt of its separateness. This is true, for example, where the loam is marly, while the underlying beds are altogether free from marl; it is also true where it overlies the red shale, and where its character is such that it cannot be supposed to have originated from the decay of that formation. This high-level loam is what was designated the "high level Jamesburg loam" in some of the earlier reports.
The formation is too meagre, too equivocal at most points, and the borders of even its best developed areas too ill-defined, to render its mapping practicable or profitable.
THE ABEA8 OF BECENT FORMATIONS. MABSHES, DUNES AND
The youngest formations of the State which cover areas represented on the map, are the marshes, beaches and dunes about the coast. The tide marsh belt has a considerable width from Point Pleasant to Cape May, and thence to Salem. The formation of the marshes, which is still in progress, consists of the fine sediment washed and blown from the land, but chiefly of the remains of the vegetation (peat) growing in the undrained areas. The peat has accumulated until its depth is in many places considerable. The marshes are being gradually filled up both by the sediment and the vegetation, and unless the land be slowly sinking, they will ultimately be converted into dry land.
Outside the tide marsh belt is the so-called beach, or series of beaches. The northern extremity of these beaches is Sandy Hook. This beach is essentially continuous to Long Branch, but is wanting from that point to Mount Pleasant. From Mount Pleasant it is nearly continuous to Cape May, and has a much lesser development, not shown on the map, on the bay side of the Cape. The beach and dune sand are represented together on the map by the black lines (13). The substructure for the beaches was made by waves and shore currents in very recent time; that is, they were originally beach ridges in the proper sense of the term. So soon as the waves had piled up the sand above the surface of the water, the wind commenced its work upon it, and fashioned it in its own way. The continued activity of the waves and currents has furnished new supplies of sand for the wind to work upon, thus giving rise to the well-known dune hills and ridges, rising many feet above the level of the beaches proper, along the larger part of the coast.
Over other parts of the State there is much wind-blown sand, but it is rarely aggregated in such considerable quantities as to constitute dunes which can be shown on a map of the scale of that here used. Dune sand is very prevalent in the vicinity of Old Bridge, especially southeast of the railroad, and along the east side of the Delaware river, especially below Trenton, where it has been blown up out of the valley since the deposition of the last glacial and Cape May formations. Wind-blown sand is also to be found to the depth of a few to several feet in scores, probably hundreds of places in the pine forests. In general, however, the areas of wind-blown sand are too small for representation on the accompanying map.