Colts Neck Township is located near the northern end of the Atlantic Coastal Plain. The relatively unconsolidated rocks underlying the soil, the temperate climate and the moderate precipitation are responsible for the rolling hills, the low gradients of streams and the fertile sandy soils which support good crops, trees and vegetation.
Regionally, the Township is located in a topographic basin (Map III) extending west from Long Branch through the Hominy Hills to Freehold, north to Matawan and east to Highlands. It is located within the Raritan Embayment.
General slope (Map IV) of the topography is southeast. From an elevation of 260 feet in the Clover Hills (Mt. Pleasant Hills) to a low of 40 feet above mean sea level where Hockhockson Brook meets Pine Brook in the easternmost part of the Township, the average slope is about 19 feet per mile.
The Clover Hills, located partially in the northwest portion of the Township, have the highest elevation (260 feet) and generally have slopes of 10 to 15%. Stream valleys are young to mature, but in spite of this, flood plains and dual streams in a single valley are common. The more resistant Navesink formation (Figs. 3 & 4) underlies the more easily erodable Red Bank Sand and the streams have base leveled within the Navesink.
In the southeastern part of the Township the Hominy Hills partially lie within the Naval Weapons Station Earle (Federal) lands. The Hills reach an elevation of 246 feet above sea level, but the slopes are more gentle than those at Clover Hills, because the less-resistant Tertiary Sands (Map IV, Figs. 3 & 4) underly the area.
The Hockhockson Swamp, lying north of the Hominy Hills, is a topographically low area and is generally flat. The high ground water level is caused by the intersection of the ground water table of the Hominy Hills with the topography, which drops to an elevation of 40 feet at the intersection of Hockhockson and Pine Brooks.
Centrally located within the Township and trending northeast-southwest are three hills known, from east to west, as Sugar-Loaf, Stone Hill and Stout Hill. Sugar Loaf, the largest, has a rise of about 70 feet above the surrounding area.
The rest of the Township consists of gently rolling hills and broad valleys. Streams tend to have a steep south bank with narrow flood plains in the upper reaches. Braided streams are not uncommon, with siltation especially heavy just above Swimming River Reservoir where stream velocity is checked. The exception is Hockhockson and Pine Brooks, which flow north into Swimming River, thence into the Navesink River. These two streams originate in the Hominy Hills and wander sluggishly through the swampy area to the north. Siltation is slow, but the streams have developed a well-defined flood plain in the higher areas.
Slope (Map IV) can have great environmental importance with respect to soil stability, sedimentation, water supply, and septic and foundation limitations. As an environmental determinant, it must be considered together with vegetation and soil quality. Together, these factors determine the slope's ability to absorb surface runoff and its rate of erosion.
The general type of soil in the Township is loam or sandy loam (Map V). Most soils do not pose a serious problem in structure support capabilities, but at least 25%, probably more, of the Township (excluding Naval Weapons Station Earle and the Swimming River Reservoir) can be considered to have poor permeability and/or high ground water within the soil (Map VI). Poor permeability soils include those very silty or clayey or those already saturated from a high ground water table.
This area is the southern extent of one of the ice tongues of the Pleistocene glacial period, and patchy remnants of the glacial till still fill some of the old valleys. The resulting poor drainage partly accounts for scattered small swamps.
With the exception of Pine and Hockhockson Brooks, virtually all drainage from Colts Neck enters the Swimming River Reservoir (which is owned by the New Jersey-American Water Company). The Navesink watershed, of which Colts Neck is a part (Map I), is bounded by the Atlantic Ocean to the east, into which it drains, and generally extends west from Long Branch to Freehold, north to Matawan and east to Highlands.
Willow Brook enters the northeastern part of the Township where it joins Hop Brook which flows into the Swimming River Reservoir. With Big Brook and several smaller tributaries, Hop Brook is the principal supply for the 2.6 billion gallon capacity of the reservoir. Willow and Hop Brooks form the northeastern boundary of the Township.
Big Brook runs easterly across the northern portion of the Township. It is a beautiful, generally clear stream with a gentle gradient. It is base-leveled on the Navesink formation causing a wide flood plain and, over much of its course, dual streams within its relatively wide bed.
Yellow Brook and its tributaries, principally Mine and Slope Brooks, drain the southwestern and central part of the Township and drain east into the Swimming River Reservoir. Excepting for the upper reaches of Yellow Brook and tributaries, the stream is narrowly confined with steep banks, narrow flood plains and few swamps. Its course drains much of the soft Tertiary and uppermost Cretaceous unconsolidated sediments and is, except during the dry season, rapidly eroding the area of its drainage.
Hockhockson Brook originates in a swamp of the same name which lies principally within the Naval Weapons Station Earle. Its flow northeasterly joins Pine Brook, where both flow into Swimming River below the Reservoir Dam. Hockhockson Brook has a low gradient and, because it drains a topographically low area, is sluggish with low-lying, marshy banks over most of its course.
Pine Brook, with Swimming River, forms much of the eastern boundary of the Township. It, like Hockhockson Brook, originates in the swampy areas of Naval Weapons Station Earle, where it flows north into Swimming River. Characteristics of the two streams are quite similar.
Since most of the streams traversing the Township originate in or near the Township, and because Willow-Hop Brooks are controlled by the Swimming River Reservoir, the Township cannot be considered flood prone. Although flood plains are well developed along many streams, only a few structures have been built where they could be endangered by even the highest recorded flood level (Map VII). The most damage involved would be flooded basements or partially inundated sheds and outbuildings. Township ordinances no longer permit building on flood plains.
The average maximum flow of water at the Swimming River Dam for the period 1923 through 1971 is about 1,800 cubic feet per second. Maximum annual flows of 7,370 cfs (1938), 8,910 cfs (1960) have occurred since 1923 when continuous gauging was put into effect. However, in 1919 a peak flow was recorded of 11,800 cfs -- 32.5% greater than any flow since recorded.
Gauges of Swimming River above the Dam range from a maximum annual height of 9.31 feet in 1961 to a minimum of 1.87 feet in 1925, with an average of 4.74 feet for the 1923 through 1971 period.
Although adequate information is not at hand and further study is needed, it appears that development of Colts Neck Township has not resulted in an increase of runoff peaks from precipitation. Dozens of small dams and man-made ponds appear, on the contrary, to have reduced peak flow gauges in relation to volume by reducing flash floods -- particularly in the period 1963 to 1971.[L.C. Lamar, Colts Neck Environmental Commission, personal study.]
The official "Flood Insurance Rate Maps" for the Township of Colts Neck were published in 1982. [Flood Insurance Rate Maps, Township of Colts Neck, Monmouth County, Community-Panel Numbers 340291 0001 to 0010, Federal Emergency Management Agency, Effective Date: April 15, 1982.]
The Township of Colts Neck lies in the northernmost portion of the Atlantic Coastal Plain, which extends south as far as Florida. Both the underlying metamorphic "basement" and younger rocks dip to the southeast. Dips range from 70 feet per mile in the "basement" to 10 to 20 feet per mile at the surface (See Figs. 3 and 4 and Maps VII and VIII.)
The highly indurated pre-Cambrian gneiss and schist of the Wissahickon formation, both over 600 million years old, are the eroded remnants of a pre-Cambrian mountain range which was leveled during the Paleozoic and lower Mesozoic Eras. The upper Cretaceous Raritan-Bass River formations were deposited on the old surface, which had subsided, followed by uplift and deposition of continental sand, silt and clay. Following erosion of most of the continental deposits, the area was again submerged and the Magothy sand and clay was deposited.
As the Coastal Plain continued to submerge, the younger Cretaceous and Paleocene sediments, with local unconformities, were deposited. Some uplift and erosion and/or non-deposition was followed by deposition of beds of lower Miocene-Pliocene age. The principal unconformities occur at the pre-Cambrian-Upper Cretaceous and Upper Cretaceous-Miocene contacts (See Figs. 3 and 4.)
If younger formations were deposited over the Cohansey in the Colts Neck area, the record has been lost by erosion which would have occurred prior to deposition of the Quaternary Pleistocene Pensauken glacial till. The Pensauken was deposited during the "Ice Age" about 1.8 million years ago when tongues of ice extended from the glaciers which covered most of America to the north. These sediments have been mostly eroded from the area, but some, largely gravel, sand and silt, fill some of the valleys and cap some of the hills in the Colts Neck area.
Within Colts Neck Township, surface outcrops, with the exception of Pensauken, form northwest-southeast bands and range north to south (Fig. 3) from the oldest Mt. Laurel to the youngest, Cohansey. In the north portion, deeper valleys expose the Navesink formation which overlies the Mt. Laurel.
Structurally, the entire northern portion of the Atlantic Coastal Plain is generally monoclinal, but minor folding is shown by structural maps (base Navesink and top Englishtown). Whether the structural variation is due to tectonic movement, depositional changes, or a combination of both is unknown. Little is known of the structure of the "basement", but it is likely highly folded and faulted.
Although minor earth tremors have been recorded in the Perth Amboy and Cape May areas and offshore, the land area is believed seismically stable. Seismic surveys offshore, however, indicate structural movement, including much faulting, has occurred there.
Several locations within the Township are well known as fossil collecting grounds. The Navesink formation in Big Brook is famous for a wide variety of sharks' teeth, the best known being Isurus and Scapanorhynchus. A cephalopod, Belemnitella Americana, is also plentiful there. Present in the overlying Red Bank sand, as well as the Navesink, are the pelecypods Exogyra Costata and Gryphea. Bryozoa, foraminifera, echinoids and similar microfossils are present in the younger Tertiary sediments; especially in the greensands of Vincentown. Paleontologists report finding fossilized remains of the mammalian ground sloth and the reptilian Mosasaur and Plesiosaur, which roamed the land during the Cretaceous period.
Monmouth County is not richly endowed with mineral wealth. Within Colts Neck Township there are no known deposits of economically significant minerals. Elsewhere in Monmouth County, relatively small quantities of sand and gravel are taken for building and road work. However, historically, the mineral industry in the county was once far more active than today.
The greensand marls of the Cretaceous strata were once used extensively as fertilizer. Its value as a soil conditioner was first discovered on the farm of Peter Schenck near Marlboro in 1768, after material dug from ditches was spread over the fields. When a marked improvement in yield was observed on these fields, the practice of spreading marl gained acceptance, until by the middle of the 1800's the use of marl was common throughout the Coastal Plain. It was even used to allow farming on the infertile soil of the Pine Barrens. The primary value of the marl was as a source of lime, phosphoric acid, and potassium. All the greensand formations were not of equal value.
Some marls, high in sulfates of iron, were unfit for use without treatment, although even this "poison marl" was used after composition with lime. Too much clay in the marl will cause the development of a hardpan which is also undesirable.
Ground water in the coastal Plain frequently contains high concentrations of iron, as is well known to homeowners with private wells. Since most of the streams in the Coastal Plain are fed by ground water, they too are frequently iron rich. Contact with the air causes the ferrous iron carried in solution to precipitate as iron oxide. Because the iron oxide collects in low swampy areas, it is known as "bog iron". Most of the bog iron in New Jersey is found further south, where it once formed an important industry, although some was produced in Monmouth County. In fact the first known iron works in the state was operating in 1685 at Tinton Falls. Another iron works was started at Imlaystown, in Upper Freehold Township in 1716. The bog iron industry was made uneconomical many years ago by the development of higher grade ores. One feature of the industry is of interest in this present age of scarce resources - bog iron is a renewable resource. It can be "harvested" from different parts of the bogs each year. After the limonite was removed, precipitation of the iron oxide began anew and in only 20 to 30 years a new "crop" was ready for production.
In the 1950's, a new important mineral resource was discovered in the Coastal Plain. Ilmenite, or iron titanium oxide, was found in economic concentrations in parts of Ocean and Burlington Counties, where it is now being produced. Some deposits extend into southern Monmouth County, although these are not being worked. Ilmenite is used as a source of titanium, primarily for the manufacture of paint pigment.
The source of the ilmenite now found in the Coastal Plain was the Precambrian crystalline rocks now exposed in the northwestern part of New Jersey. Thousands of feet of these rocks were eroded over millions of years, providing sediment for the Coastal Plain formations. Because the ilmenite is a heavy mineral, it tends to be concentrated by wave and stream action. The ore bodies in New Jersey are found in the Kirkwood and Cohansey formations. In the Kirkwood, the ilmenite was concentrated by wave action in the retreating Miocene seas. Later, streams which deposited the Cohansey formation concentrated ilmenite in several areas along their paths.
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Reference: "Geology of Monmouth County in Brief," Bureau of Geology and Topography, NJ Department of Environmental Protection, August 1977.
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