History of Hunterdon and Somerset counties, New Jersey : with illustrations and biographical sketches of its prominent men and pioneers, Part 135

Author: Snell, James P; Ellis, Franklin, 1828-1885
Publication date: 1881
Publisher: Philadelphia : Everts & Peck
Number of Pages: 1170

USA > New Jersey > Somerset County > History of Hunterdon and Somerset counties, New Jersey : with illustrations and biographical sketches of its prominent men and pioneers > Part 135
USA > New Jersey > Hunterdon County > History of Hunterdon and Somerset counties, New Jersey : with illustrations and biographical sketches of its prominent men and pioneers > Part 135

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* Geology of New Jersey, page 175.

553

THE PHYSICAL FEATURES OF SOMERSET COUNTY.

We will not decide the question of right between the two modes of calculation, except to say that a well in New Brunswick has been sunk four hundred and fifty feet, several in Newark four hundred and six hundred feet, and one in Paterson thirteen hun- dred feet, all in the red sandstone and shale. Perhaps some future observations may determine the question at present in dispute ; until then we will have to wait patiently.

All observations unite in showing that the red sand- stone and shale of New Jersey are of a sedimentary character. The materials composing them must have been deposited in water during the progress of many ages ; and, since an analysis shows so little trace of any of the ingredients of the salt water of the ocean, we add, deposited in fresh water.

In what period of geological history this widely- diffused series of sedimentary strata originated we are not able to determine, but some data may afford an approximation. The organic remains in them are but few. They are certainly not so recent as the green sand, as is proved by their passing unconform- ably beneath that formation ; and that they are more modern than the coal is not less conclusively shown by their reposing unconformably and without signs of disturbance upon the lower members of the Appa- lachian rocks in districts of the country where the uplifting of these and of the carboniferous strata at the top of the same series has obviously been cotem- poraneous. The vast space of time during which the depositions were being made may be imagined by the thickness of the strata, which, as we have said, has only been imperfectly ascertained, but must evi- dently be very great.

Some indications of the period of the formation of the red shale and sandstone formation in New Jersey are also found in the fossils which they contain. There are no marine shells at all, proving that these strata are not upheavals from any primitive ocean. But there are remains of plants, footprints of birds, and fossil fish found in many different places. We are confined to our own small field, and therefore begin by saying that the plants seem to be of the Lepidodendron class, belonging to the lower series of the Devonian period, and cotemporary with the Pittsburgh coal. The fossil plants found in our district, however, are not well defined, and it would be unsafe to place much depend- ence upon any inferences as to the age of the strata made from them,-at least at present.

Fossil fishes have been found in the debris thrown out of the copper mines in Washington Valley, and in several places in the shales at the west foot of the mountain between Bonnd Brook and Pluekamin. Several specimens of these are to be seen among the collection of the Geological Survey at Trenton. There is also an extensive collection in the museum of Columbia College, New York. Footprints of diť- ferent three-toed animals or reptiles have also been found.

In Washington Valley, in a grayish flagstone, there are marks which resemble the bed which the sunfish ( Ichthyosaurus orthagoniscus) makes preparatory to depositing his spawn. It is in the form of a circle from twelve to twenty inches in diameter. The im- pressions are so plain that no one who has ever noticed a sunfish-bed in a clear fresh-water stream can possibly mistake it. It is another instance in proof of the conclusion above indicated, that the strata of the red shale and sandstone were deposited in fresh water. There are many other places outside of our district in which the fossil fish and footmarks have been found.

The sandstone variety of the Triassic formation in Somerset County, as distinct from the red shale, has not yet attracted the attention which its value for economic purposes warrants us in saying that it will attain. It is easily formed into any required shape ; it is durable, resisting the action of the atmosphere in a remarkable degree; it is abundant in almost all the neighborhoods of this county ; it is not generally deeply imbedded, so that little labor is required to ob- tain it; and it can be had in almost all the districts at a comparatively small expense. The brown and yel- lowish varieties are seen in several important edifices in the State. Rutgers College, the Newark court- house, State-House at Trenton, and Trinity Church in New York City are all built of it.

There remains only one more circumstance of im- portance to be mentioned respecting the red shale and sandstone. It seems to have been subjected, at some period after its deposition, to a process of denu- dation, by which the upper surface of the strata or the outerop has been abraded and worn away, ex- posing them almost naked to the action of the weather. In some localities are found sand-hills, identical in their character with the mass of the same material which forms the surface of a large dis- triet of country southeast of South River, in Middle- sex County, and on the borders of Monmouth. Can this sand have come from our district ? There are also many evidences of a violent and powerful move- ment from the northward. Large rocks of gran- itic gneiss are found lying on the surface of the soil in many places within our district, which must have been transported from the gneiss hills or gneiss forma- tions in Morris and Sussex Counties. Some of these rocks must weigh at least twenty tons, or more. Ser- eral pieces of the variegated conglomerate which is in place on the east side of Greenwood Lake have been found on the trap ranges north of Somerville.

THE TRAP FORMATION.

All authorities unite in affirming that trap is of igneous or volcanic origin. Ordinarily, it is of a greenish gray color, and its aspect varies from that of a fine-grained, compact basalt to that of a coarsely- crystallized greenstone. It contains, in different lo- calities, besides its more essential components,-horn-

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SOMERSET COUNTY, NEW JERSEY.

blend, feldspar, augite, and titaniferous oxide of iron, -various other minerals of more rare occurrence, such as epidote, prehnite, zeolite, stilbite, an alcime, and datholite.

- Trap consists, in its purer state, mostly of feldspar. When united with hornblend it belongs to the variety classed as greenstone. When associated with augite it is called dolerite. When it consists of feldspar, au- gite, and the titaniferous oxide of iron, it is properly called a basalt. A fourth variety is called toadstone,- an amygdaloidal rock composed of a vesicular cement or paste, usually a fine-graiued and rather earthy ba- salt containing small spherical cavities occupied by extraneous minerals. The crystalline structure of the trappean rocks is no less various than their com- position. It presents every gradation from that of a homogeneous paste, in which all trace of a distinct grain disappears, to a coarsely-granular aspect, in which we may easily detect the several other constit- uent minerals.

The structural appearance of the trap rocks is usu- ally that of an amorphous or massive character, des- titute of any greater regularity in its joints than a tendency to a cubical or trapezoidal form in the blocks into which it naturally separates. But in some in- stances it displays a tendency to a bedded form, as if while in a fluid state layer after layer had flowed one over another in forming the mass which was thrown up. In only a few places in this section does it as- sume the true basaltic character, separating into reg- ularly-formed prismatic columns.

Almost every relation which igneous rocks ever pre- sent to the strata intersected by them is seen in the several positions of the red sandstone and trap in Som- erset and Hunterdon Counties. The usual mode is where it reposes unconformably upon the secondary strata. A very striking instance of this is seen in the gorge of Chimney Rock, near Middlebrook. There may be traced the trap above the red shale from the south side of the mass, which at a distance looks like an old dilapidated chimney resting on the shale and conforming to its dip for a hundred and fifty yards, until the falls of the east branch of the Middle Brook are reached, at which point the trap protruded upwards through the red shale, and, being in a semi- fluid state, gradually settled over in a southward direction until it became solid, and so it has remained ever since. A little to the northwest-perhaps five hundred yards-some years since a pit was dug in order to obtain the red shale in a pure form for the purpose of grinding it into paint, and huge broken masses were uncovered, looking as if they had been thrown off in a confused heap when the trap was forced through the strata, previously lying in a per- fectly conformable position as they were originally deposited.

This, with many other facts, appears to us to be conclusive evidence that the trap is, geologically, more recent than the sandstone, but does not point

out the precise period when it was protruded; nor can we determine decisively whether the different trap ridges in Somerset were all upheaved at the same time or at different periods in the Triassic Age of geological science. Evidences of the intense volcanic heat embodied in it when it was extruded to the surface are numerous.

A broad ridge of trap extends from near Neshanic church southwestward until it crosses the river into Pennsylvania. It has an elevation varying from three to five hundred feet. Its length is about seventeen miles, and the average breadth about two miles. The range has a narrow core or dyke of trap rock in its centre flanked on each side by dark indurated argil- laceons shale. At the end near Flaggtown it is so changed in color and baked by heat that it rings like clink-stone when struck with a hammer.

The outcropping trap is seen at Mount Airy, near Rock Mill, and at the northeastern terminus of the range, near Flaggtown. About a mile south of this terminus, on the southeast side of the ridge, there is a remarkable indentation, formed, apparently, by the wash of a small stream of water making its way down to the level land, in which are great masses of rock lying in confusion, one upon another, touching only at the point of contact, and which has been called expressively "The Devil's Half-Acre." A mile farther south a huge mass of rock standing alone is called "Fort Hans;" and still another farther south, similar to the first, is known as the "Roaring Rocks." These localities are favorite resorts for pic- nic parties, and are considered great curiosities by many intelligent people, who, however, have no con- ception of their geological relations and origin.

Looking from the Neshanic Mountain to the south- east, we see Rocky Hill culminating iu Mount Rose, rising to the height of four hundred and thirteen feet, and terminating west of IIopewell. The trend of the mountain is west-southwest from the Millstone River, and it extends about nine miles to Mount Rose. Here it changes to a northwest course, which is preserved until its termination is reached. Neither of the slopes are very steep, yet there is a difference between them. That towards Blawenburg and Hopewell is very much more gradual than that on the south side of the ridge. The outcrop of the trap is only seen near the Millstone, about Mount Rose, and south of Hopewell. Loose rocks and yellow trap soil are characteristic of the whole range. On each side, between the trap and the red shale, may be observed a bluish shale indu- rated and changed in its color by contact with the ig- neous rock, proving, as elsewhere, the heated state of the trap when it was protruded from below.

There is another ridge on a line connecting Rocky Hill and what is called Bald Pate Mountain, known also as Pennington Mountain. It is isolated from the . former merely by an interval of shale, and is about two miles long and half a mile wide. Its south face is very steep and rocky, and rises to the height of two

555

THE PHYSICAL FEATURES OF SOMERSET COUNTY.

hundred feet. Its general direction is northeast and southwest. It is not unlike the other trap formation- in this vicinity, and therefore demands no further notice.

On the east side of the Millstone River is a range of trap elevations which must be regarded as a con- tinuation of Rocky Ilill in its eastern direction. In some places it is covered deeply with drift and but imperfectly visible, yet no one passing over the country can well fail to see how the trap at Green's Pond and at Ten-Mile Run is an integral part of Rocky Ilill. Professor Rodgers says of this forma- tion,-

"Commencing at Its castern termination, bear Lawrence's Brook, wo observe the simle on both sides of the dyke assuming a bluish tint or color and an extremely compact structure. In the southern declivity it is porplish or chocolate color in its tints and excessively hard and tough. It is studded throughout with small spherical koobs or crystalline nodules, consisting of the minerais known as epidote and hornblend in a state of Imperfect crystallization. This belt of nitered shale extends from a point half u mile sootheast of the straight turnpike to the Millstone River, near Kingston. The changes induced in the whole lithoid character and structure of the shale by the intruded igneous rock are finely exhibited elong the canal et both the senthern and northern bases of the Rocky Hill dyke, ovincing a curious grudntion in the crystallico action as we approach the trap."

Large blocks of this altered shale are to be seen along the Millstone as far north as Weston, but in places so remote from the river and so high above its present current as to show some action of flood and iee in former ages not now existing.

East of Neshanic Mountain and not far from Plain- ville, about half-way towards the Millstone River, there is a small outerop of trap, made evident by the broken fragments which completely cover the ground for a circular space of a hundred or more feet in di- ameter. On the bank of the Raritan and Delaware Canal, also, below Blackwell's Mills, another small outerop, not more than six or eight feet in width, ap- pears. It seems to have burst out from below through a fissure of the red shale and remained there, standing alone and producing but little visible effect of any kind except the small blocks which lie on the surface around it, covering a space of several square yards. In excavating the Raritan Canal the hill was so cut away as to expose this little pillar for thirty feet in perpendicular height.

We are now brought to the most prominent of the trap ranges in our district,-viz., the two parallel ranges north of Somerville : perhaps we might more accurately say three. The first range begins near Pluckamin and has a southeastern and castern direc- tion until it reaches the gorge at Middle Brook ; thence it tends east and northeast until it reaches Paterson. At Milburn there is a broad gap, and at Plainfiehl a narrow passage, through which a branch of Green Brook finds its way out towards the Raritan. Be- tween its inner and outer slopes there is a great dif- ference. The inner is gentle; the outer steep, and often precipitous, North of Somerville the red shale in some places rises up almost to the top of the dyke

of trap,-in faet, is immediately contiguous to it. At other places the débris of the trap rests upon it and overlies it, so as to hide it from sight. Always the fact of protrusion is so visibly present as to indicate impressively its origin. The height of the whole ridge is remarkably uniform, ranging from three hundred to six hundred and fifty feet above the sea- level. Washington Rock, near Plainfield, is five hun- dred and eleven feet in height. The top of the range is never broad,-in many places is, in fact, less than a mile in width.

Parallel to this first range is a second, beginning near Bernardsville and running first southwest, then south-southeast and south, following closely the trend of the first. It is more than double the width of the first range until it has passed beyond the limits of Somerset County. Its height is much more variable than that of the first, and its slope more gentle. In fact, the abrupt dyke is seldom visible. Between these two ranges there is an elevated valley known as Washington Valley.

Beyond this second mountain there is still another trap range, or Third Mountain. Long Hill and Bask- ing Ridge are parts of it. Both these formations are less elevated than the other two, and they are narrow and level-topped, with the red shale rising np nearly to the apex of the elevation. Their average height is not more than two hundred feet. Their general aspeet indicates that the protruding force had in a measure subsided when the eruption took place, or, perhaps, being farther from the centre of action, had less power to overcome the resistance opposed to it, and so not only threw up less material, but also less in elevation.

The age of the great geological formation in Som- erset County we do not pretend to fix .* It may have been not only more recent than those which remain to be noticed, but perhaps the most recent of all. It is evidently the result of some great volcanic action which either then expended itself entirely or has since remained dormant.

The next formation to be considered is what Prof. Rodgers calls "the variegated calcareous conglom- erate," forming the northwestern boundary of the red shale and sandstone strata so extensively spread out in our district. Conglomerate, says Dr. Cook, is a rock composed of fragments or pebbles of other rocks. The pebbles may be of quartz, limestone, sInte, or other substances, and they may vary in size from a buckshot to the bowlder of a foot or more in diameter. The cementing material may be oxide of iron, carbonate of lime, or other fine substances, and the color may depend upon the cementing paste or upon the pebbles themselves inclosed in it.

. We have no historical records of these remote times. Man had not then found a habitation upon the surface of this mundane sphere ; and there is nothing by which we can calculato parsing eventa, Wo only know that some things must have been first and others last in the con- solidation of the crust of the globe.

556

SOMERSET COUNTY, NEW JERSEY.

The theory of the formation of the conglomerate is given in Rodgers' report. It overlies the red sandstone and shale, and therefore is of a later origin. There is but little difficulty in explaining both its source and the character of the circumstances attending its form- ation. The fragmentary materials of which it consists can be traced, in every instance, to the older rocks of the neighboring hills, immediately bordering on the conglomerate on the northwest; and we can also dis- cover a relation between the amount of the several kinds of pebbles and that of the strata along the flanks of the formation itself.

In order to account for the violent denudation which has taken place along the range of the old gneiss and granite rocks, we have only to advert to the state of things attendant upon the outburst of the trap ranges. This rock, intersecting and overlying all portions of the red shale and sandstone, as well its earliest as its latest formed beds, was manifestly of simultaneous date through the entire region of our district not only, but of the whole continent. The violent agitation of this whole belt of country, and the vertical rising of the red shale depositions to a higher level, would necessarily set in violent motion the entire body of the waters in the whole basin. These, rushing im- petuously over the shattered strata along the base of the hills, confining the current on the northwest, would quickly roll their fragments into that confused mass of coarse heterogeneous pebbles which we see, and strew them into the detached beds where we now find them. The protrusion of the trap, the deposition and formation of the conglomerate, and the elevation and final draining of the whole red sandstone basin can only be considered to have been consecutive phe- nomena. The whole time occupied by these stupen- dous changes must have been comparatively brief compared with the period which produced the mate- rials of the basin so extensive in range and so vast in depth : we mean the red shales and sandstone of New Jersey and the other States.

In attempting to describe the calcareous conglom- erate, its range and principal localities within the limits of our district, we may say that it constitutes the uppermost member of the middle secondary se- ries. It overlies the red shale along its northwestern margin, not in a continuous belt, but rather in several insulated patches, which range in one general line near the foot of the primary or older formations. In almost every portion of its range its materials are very heterogeneous, consisting of pebbles or water- worn bits of rock of all sizes belonging to most of the older formations existing in the region where it is found. A portion of the motley mass is made up of variously colored sandstone pebbles. Sometimes there is a considerable mixture of small pieces of the primary rocks, and in certain places of the range the strata, throughout nearly the whole thickness, are made up of pebbles of limestone cemented by a lime- stone paste. Usually the cement or imbedding paste

contains a prevailing portion of the red argillaceous shale of the underlying strata. This admixture of red matter in the formation in New Jersey is easily explained. The harder sandstones and limestone have retained their fragmentary state, while the soft red shale has been reduced to powder or mud by the violent action which brought together the mass of water-worn materials, and so became mixed up with them. That they are water-worn is placed beyond a doubt by the form in which they appear in the mass of the conglomerate: nothing else could have ab- raded all the angles which these bits of rock must have had when broken off from their original strata except the friction and wear of water.

A large portion of the conglomerate, in its course through New Jersey, exhibits all the characteristics of the rock from which the pillars of the Hall of Representatives in Washington are made, known as Potomac marble.

The relation of the red shale to the conglomerate as underlying strata is also clearly seen on the road to Peapack, east of Lamington River. The rock is generally of a silicious character in this locality, re- sembling a coarse arenaceous sandstone, and the shale dips to the northwest. At New Germantown the red shale has been changed near the brook to a greenish gray color by the vicinity of the trap cropping up here in a narrow dyke.

COPPER.

It is found in the red shale and sandstone of New Jersey, and has been known to exist there since the earliest settlement of the country. Mines were opened before the Revolution at Belville and New Brunswick. We confine our notice to Somerset County. It exists in almost a pure native form as a red oxide, as a basilicate, as a gray sulphuret, and as pyrites or yellow copper ore.

Native Copper has been found in the vicinity of Somerville in several places. Notably onc large piece, nearly all pure, weighing seventy-eight pounds, was taken out of a small ravine three or four feet in depth on the north side of the First Mountain, about twenty-five years since, by a farmer, and was in pos- session of Albert Camman. It had the appearance of having been acted upon by heat, was mixed with the gray oxide in a part of it, and incrusted with the green carbonate in some other parts.

Red Oxide, as it is found near Somerville, in the Bridgewater mine, varies in color from purple to brick-red, has a compact structure, and is nearly des- titute of lustre. It occurs mostly in the altered red shale immediately in contact with the trap rock, as if it had been diffused by its upheaval and heat, and suggests the idea of having come up with the trap from a lower depth.

There is also a compound of the carbon and oxide of copper found near New Brunswick associated with the red oxide. It resembles some dark earthy sub-

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THE PHYSICAL FEATURES OF SOMERSET COUNTY.

stance, and is easily crushed between the fingers. On examination with a microscope small black shining particles were discerned diffused through the mass, found to be carbon, probably anthracite. Heated in the flame of an alcohol-lamp, it burned and continued in a red-hot state until the carbon was consumed. Heated to three hundred degrees, it loses seventeen per cent. of its weight. When treated with nitric acid, after being ignited, a residuum of twenty-five per cent. was found to be silica. It is an important fact that so large a portion of carbon-35.50-should be asso- ciated with this copper ore. This is unusual.

Carbonates of Copper .- Some of the native copper ores are incrusted with the blue and green carbonates. A locality of this ore has been found on the banks of the Delaware and Raritan Canal, about a mile north- west of New Brunswick. The strata of shale where it occurs are all nearly horizontal, and alternate with a gray shale containing particles of mica. In the cleavage and fissures of this shale the blue carbonate is found in the form of crystalline incrustation. The locality is near the bed of a ravine, and when it is re- membered that the red oxide is common in the vicinity, it will not be difficult to account for the for- mation of these carbonates, which seems to be con- tinually going on. Water charged with carbonic acid dissolves a portion of this oxide, and whenever circumstances favor the escape of the excess of the carbonic acid these salts, as a residuum, are deposited. The mineral is manifestly the product of precipitation from an aqueous solution, and to find the above result it is only necessary to admit that the carbonates of copper are rendered soluble by an excess of earbonic acid. The color varies from a light to a bluish green. It can be scratched with a knife, and is easily broken. The fracture is uneven and slightly conchoidal. In structure usually it is opaque, but sometimes translu- cent and having a vitreous lustre.

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History of Hunterdon and Somerset counties, New Jersey : with illustrations and biographical sketches of its prominent men and pioneers, Part 135

Author: Snell, James P; Ellis, Franklin, 1828-1885 Publication date: 1881 Publisher: Philadelphia : Everts & Peck Number of Pages: 1170

Author: Snell, James P; Ellis, Franklin, 1828-1885
Publication date: 1881
Publisher: Philadelphia : Everts & Peck
Number of Pages: 1170