History of Hunterdon and Somerset counties, New Jersey : with illustrations and biographical sketches of its prominent men and pioneers, Part 47

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 47
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 47

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* Geology of New Jersey, 1868, p. 104.

177

PHYSICAL GEOGRAPHY AND GEOLOGY OF HUNTERDON COUNTY.

region between the earth and the sky. While high up in the air, acted upon by the west winds, the cool- ing masses were carried so far towards the cast that they fell upon sites sometimes two hundred yards eastward of the line of the dike. And we may some- what estimate the activity of the projectile force by the amount and the kind of work it did. Upon A. T. Williamson's farm are several large pieces of trap that lie some one hundred yards east of the dike. The largest of these is fifteen feet in length, eleven feet in width, and five feet in thickness, and the piece would weigh at least sixty tons. To have thrown this so high into the air that the wind could carry it this distance eastward before it returned to the surface must have taken a great deal of force.

Trup of Dike Ridge .- The core of Dike Ridge is a narrow dike of fine-grained basaltie trap. The dike seems to stand vertical, and in many places to con- stitute the entire upper portion of the ridge. In the process of disintegration it breaks up into lozenge- shaped masses, the largest of which have a diameter of not more than three inches. In color the fresh fractures are very dark ; the weathered surfaces, ochreous. It may be seen in place at the south- eastern extremity of the ridge, at the site at which the Sand Brook makes its way out to the Red Shale Valley. Here, on the southwest side of the rivulet, the outerop is a craggy cliff rising to the height of seventy-five feet above the surface of the stream. It may also be seen in place near the erest of the ridge along the side of the road that extends from Higgins' still-house to the Dunkard church ; also near the top of the hill on the north side of Sand Brook; and near the south side of the road which extends from Copper Hill across the ridge to the Sand Brook Val- ley.

Klinesville Dike .- A little north of Klinesville a narrow dike extends, apparently from the Sudo-dike in the brow of the table-land, northeast across the rond. Upon the surface we picked up a number of lozenge-shaped pieces of trap, and the soil is very ochreous. In color the freshly-fractured surfaces are very dark, the weathered surfaces are ochreous. The grain of the stone is very fine. It is not only pos- sible, but highly probable, that this dike formis an anastomosis between the trap of the Sudo-dike and the dike that constitutes the core of Round Monu- tin.

Trap-Dike near Three Bridges,-Less than a mile northeast of the village, across the road that leads from the Three Bridges to Centreville, extends a nar- now dike of basaltie trap. The surface-pieces that we picked up are cuboidal, very dark upon the sur- face, of a fresh fracture, deeply ochreous upon the weathered surface.

Trap of the Merzocken Dike, From Fisher's Peak, a little south of west, extends a narrow dike of basaltie trap that can be traced almost to the Dela- ware. It extends across the road near the summit

less than a mile southwest of Mount Airy. Here, and west of this site for a mite or more, it form- the core of Anastomosing Ridge; about a mile cast of the Delaware it cease- to form the core of this ridge. From this point it is traced along the northern slope of the ridge to the bank of and across the Alex- socken freek. Where crossed by the Mexsocken the walls of the dike are well exposed, but between them no trap is seen. For the distance of a hundred feet the stream, in low water, flows between these walls. They are apart about three feet in the narrowest place. They consist of altered shales that exhibit evidences that at some time they have been heated almost to a molten condition. So much is this the case that the chasm presents the appearance of a miniature extinct volcano, and no doubt such it is.

The shale here, in the process of disintegration. breaks up into small lozenge-shaped masses, the edges of some of which are almost as sharp as a knife. lu color it is very dark,-almost glossy black in some places. No fragments of trap have been found here, but it is reasonable to suppose that the floor of this chasm-or, at the least, the space but a few feet below the floor-is filled with this substance.

At the Alexsocken t'reek the altered shale that forms the walls of this pseudo-dike are very well ex- posed for about a hundred and fifty feet. They trend S. S.P W. The chasm is not exactly vertical ; as it extends downward it inelines a little towards the south.

I have reasons to believe that this dike extends from the Alexsocken to the trap that forms the core of Ciilbo. If so, this too is an anastomosing dike.

Trap neur Van Lien's Corner .- About a quarter of a mile south of Van Lien's Corner, across the road to Hopewell, extends a dike that trends almost cast and west, and may be traced from the road eastward for a mile or more. It seems insular. It is narrow, but it has been very prolific in surface-fragments.

This dike is, no doubt, but an injection of basalt into a rent into the strata of shale that overlies the trap of the Sourland.

I doubt not that several other anastomosing and in- sular dikes exist in the Triassie portion of Hunterdon County. Indeed, it seems to me that, directly suber- quent to the deposition of the material out of which the strata of shale were formed, some profound com- motion occurred in the fluid that then existed beneath the Arebaran rocks which established a great wave, or a line of waves, along the northwestern border of the trias. The wave or waves, moving southeastward beneath the Archaan rocks upon which the shale rests, fractured these old basement-strata in long lines at right angles to the direction of its motion, a- a wave that passes beneath a sheet of ice break- it up into great slabs which have their longer diameter at right angles to the course of the wave. The space made by these long lines of fracture at once became filled with the molten material. Thus originated the

178

HUNTERDON COUNTY, NEW JERSEY.

great dikes that are conformable to the strata of the shale. And, as the inequality of the surface of a wave in a pond is such as to fracture the lifted slab of ice into smaller pieces, so the wave in the molten basaltie fluid fractured the floating fragments of Archæan rock and its superimposed freight of shale into pieces of various length and of various shape. The spaces affected by these transverse or secondary fractures were at once injected with molten trappean material. Thus originated the anastomosing or in- sular dikes, which are secondary both in size and in time of origin.

When this molten trappean material was injected, the contiguous shale must have been so heated that in many places it assumed the liquid form, and the water it contained must have been quickly converted into steam. And of this there is abundant evidence. All along the dike in the Dike Ridge are beds of amygdaloid or scoriaceous rock that have resulted from reducing the shale to a molten condition and then rendering the molten mass cellular by the ex- pansion of the pent-up steam. Other sites there are that abound in scoriaceous shale.

In chemical composition as well as in physical qualities there is considerable difference in the trap that exists in separate dikes, and even in different parts of the same dike. The difference in chemical composition may be learned by inspecting the follow- ing analyses, published in the "Geology of New Jersey, 1868":

Specimens from

Point Gilbo. Pleasant.

Cemetery Anastomo- Goat

Pickle's

Hill.

sing Dike. Hill. Mountain.

Silica.

50.4

50.6

53,4

50.6

51.4

63.1

Protoxide of iron. 15.4

13.0

122

12.2

7.3

Alumina ..

15.6

12.5

11.2

14.9

18.3

16.7

Magnesia ......

4.9

7.2

6,9

6.0

5.3

1.2

Lime.

7.1

11.1

6.6

11.1

8.0

5.2

Soda .

1.4

1.5

2.3

1.9

1.1

3.1

Potassa

2.0

0.7

1.3

0.6

0.9

Water

1,8

1.6

4.8

2.9

1.9

2.1

98.6

98.2

99.5

100,2

99,1

These analyses show that the trappean rock, wher -. ever found, consists of elements that make good soils. Nor is it possible, in Hunterdon County, to find a belt of soil that is the result of the decay of trap-rock that is not susceptible of the highest culture.

For architectural or sculptural purposes the trap- rocks of Hunterdon County were formerly regarded as almost worthless. But, in the year 1868, Mr. James Murphy, a sculptor of Flemington, began a series of experiments which have shown that the bowlders of trap upon the Sourland Ridge are very valuable for sculptural purposes. At first it was extremely dif- ficult to find a customer who would take a grave- monument worked from basalt, but Mr. Murphy in- forms me that at present about four-fifths of the orders that come to his establishment call for monu- ments of basaltic granite.

With the " wedge and feather" the coarser-grained basaltic rock is readily worked. Sills, cornice, step- stones, and building-stone of any size or shape can

easily be worked out of this rock. The time will come, no doubt, when this will be the material in greatest request for fine edifices. At present, owing to the cost, it is not attracting much attention for this pur- pose. The only structure in Hunterdon that is built of this material is the one in which the author of this chapter now sits writing this article. It was erected by the writer in the fall and winter of 1875.

From Goat Hill much valuable basaltic granite has been shipped to Philadelphia and elsewhere. Upon this site the rock works well, and, the canal being near by, it is easy of transportation. At this place have been split out slabs twenty feet long that were not more than two and a half feet wide and two feet thick. From this site, also, thousands of tons have been shipped for paving material.

The other sites upon the Sourland at which the surface-trap has been successfully worked are Shep- herd's Hill, Rocktown, Basaltic Cliff, and Pero Hill.

As they exist in the larger dikes, the trap-rocks are stratified. This may be seen in the exposure near Rocktown, in that upon the west side of Goat Hill, and elsewhere. In the main, the layers are thick. In some places are beds that are twenty feet deep; at others not more than one or two feet ; while upon the top of Goat Hill, on lands owned by W. F. Bain- bridge, is a quarry or working of basaltic trap in which the layers are in many cases less than half an inch in thickness. Slabs of basalt four feet long, two and a half feet wide, whose average thickness was less than an inch, are here obtained. This quarry is worked for flagstones and for bridge-covering; and from it, for these purposes, is taken some of the most handsome and substantial material.

In the main, the strata of trap are traversed by two systems of joints that cross each other at such angles as to divide the beds into blocks somewhat lozenge- shaped. Occasionally the blocks are rather cuboidal, sometimes rhombohedral. Be the blocks whatever shape they may, when exposed to the atmosphere they yield to climatic influences, and in the process of dis- integration the course is always the same. The block exposed first loses its corners. Upon examination of the pieces that have fallen we learn that the surface by which it adhered to the parent block is concave; upon examining the surface of that part of the block from which a corner fell, we learn that it is convex. In the process of time, from each of the projecting parts of the remaining portion of the parent block a somewhat meniscus-shaped piece becomes disjointed and falls. In time, from each of the protuberances another meniscus-shaped piece separates, and so the process is repeated, until tlie residue of the block be- comes almost a perfect sphere. Nor does this process of concentric exfoliation cease at this juncture, for meniscus-shaped pieces still separate from thespheroid until the core is in size, in many cases, less than a walnut. The core, however, disintegrates in another way. At first it divides; then it subdivides; and

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PHYSICAL GEOGRAPHY AND GEOLOGY OF HUNTERDON COUNTY.

finally its crystals disjoin and crumble into very small particles.

In many cases, when the process of concentric ex- foliation has progressed only so far as to round off the corners a little, the parent block separates through the middle. Thus are produced two fragments, cach of which has four sharp, well-defined corners and four convex protuberances. But angularity is not allowable by the law that regulates the disintegration of detached basaltic blocks. Ere long the corners of the newly-formed fragments fall, meniscu -- shaped pieces follow, and in a short time the disintegrating block becomes at first irregularly plano-convex, then irregularly ovoid, and finally irregularly spheroid. In many cases where the parent block is very large the meniscus-shaped fragments are correspondingly large, and ofttimes, especially when separated from inferior parts of the parent stone, remain standing, sometimes in a vertical position, but more frequently they are inclined. Occasionally the separation is such that the parent block, while exfoliating, divides into four, right, or sixteen pieces, or any other number that may result from a fission in which the joints are horizontal and vertical. Hence arise so many of those fantas- tir forms seen in the shapes of the trappean bowlers along the Sourland Ridge. Some of these are worthy of mention.

A little north of Pero Hill, on the west side of the road, is a large bowlder projecting its upper surface some three feet above the soil. This table-rock is about twenty-seven feet long and about twenty-six feet wide. Upon it are three irregularly oblong rocks, each of which is about fifteen feet long, five feet high, undl seven feet wide. These superimposed rocks are known as the "Three Brothers."

Along the east side of the base-rock lies a bowkler about one-half the size of one of the Brothers, which within a few years has dropped from one of these su- perimposing fragments, and within a few years more another segmentation will take place with another of the Brothers: in fact it began long since, and is rap- idly completing its work. Now, these five rocks, the table, the Three Brothers, and the fragment which has fallen off, have in an earlier day been but one rock, an immense bowlder almost cubical in shape. At first the segmentation took place horizontally. When the two parts had grown entirely distinct, and their adjacent edges, by the exfoliating process, had become somewhat rounded, the upper rock fractured vertienlly, with joints that extend from east to west. But these several vertical fractures were not all made at the same time. At first was separated the south Brother; after this the northern piece divided in two; and finally, the segment that now lies upon the ground fell from the south Brother.

On the east side of the road, a little way north of the Three Brothers, may be seen specimens of this kind of work on a scale far more grand. But, as they are farther removed from public view, their fantastic

forms have not so much attracted the attention of lovers of the marvelous.

A favorable example of the process of concentric exfoliation may be seen in the bank along the road extending from Ringos to Rocktown; a more favor- able one still may be found in a sand-pit upon the northern slope of Goat Hill.

The disjointed corners and the meniseus-shaped spalls, as a rule, are very ephemeral. They soon crumble and moulder to soil. Each is but the result of a step in the process of disintegration. This will be learned upon a careful inspection of any basaltie bowlder that is rapidly disintegrating. Even those masses that are decaying beneath the surface of the soil exhibit this fact in a striking manner. In sand- pits along the Sourland we often see a vertical wall that seems to consist of solid blocks, each of which is formed of a core around which are concentric layers capped with corner. But when this fantastic wall is struck with the pick it yields, crumbles, and, except- ing the cores of the apparent blocks, moulders to sand.

COPPER ORE.

In the altered shale along the northern part of the Anastomosing Dike exists that variety of copper ore known as gray enprie sulphide. This ore occurs mas- sive and is seefile. In color it is a dark lead-gray. Specimens are sometimes found that polish readily by rubbing them with a woolen cloth. This is the kind of ore found in the mine at Flemington ; also in those on Gershom C. Sergeant's farm and at Copper Hill.

Copper ore of the same grade has been found in a digging on the southeast side of Dike Ridge. Indeed, it may be looked for along any of the anastomosing or insular dikes.

Cupro-ferrie sulphide, or copper pyrites, is occa- sionally found associated with cuprie sulphide.

OXIDE OF MANGANESE.

A vein of this ore was found on a hill about equi- distant between Clinton and Lebanon, and somewhat south of the line between them. It is on lands of John T. Leigh and the estate of Gen. tieorge Taylor. The hill is of red sandstone and conglomerate, and the opening> in it are in a northwest and southeast . line at intervals for about one hundred and fifty feet. They indicate a vein about ten feet wide, and the openings have been made four or five feet deep. The ore is quite distinct from the rock, and not at all intermixed. The ore contains between seventy and eighty per cent of oxide, but a portion of it is sesqui- oxide.

It has not been applied to any use, and the open- ings were made on the supposition that it was iron ore.

FOSSILS.

Fossil wood is found in small fragments at almost every point where the shale is quarried. In some places may be found the fruit of the Triassic forest.

180

HUNTERDON COUNTY, NEW JERSEY.

Such is the case in the shale in the bank of the Locatong Rivulet, where it cuts through the brow of the table-land. At this site are some layers of shale that seem to have been formed of sticks, twigs, leaves, and fruit, cemented together by mud. Indeed, the shale of these layers, when pulverized and heated in a retort, gives off abundantly an in- flammable gas, In most places the shale is too soft, if exposed, to retain in a legible condition the fossils it contains, but where indurated it retains its fossil- iferous treasures for a greater length of time.

The only well-defined fossils indicative of animal life are those found by Prof. Smock in the indurated shale along a rill near Tumble's Station, not far from the Delaware. These are the tracks of a reptile whose stride was thirteen inches, and the length of whose central toe was three and a half inches. Doubtless the animal that made these tracks belonged to the Dinosaurs, and at the time of making them was erect, walking upon its feet, with its hands pend- ent. The slabs upon which are the tracks are in the museum of Rutgers College, at New Brunswick, N. J.

In the quarries of Milford tracks are said to have been found, although quite indistinct. The writer has searched all the accessible exposures of shale for the past twenty years, and, with the exception of those upon the slabs in Rutgers College, has seen no tracks.

QUATERNARY AGE.

The rocks of this age belong either to the Glacial Period, or else to the modern era of the Recent Pe- riod.

Glacial Period .- The rocks belonging to this period are unstratified drift. They do not occur in all parts of the county, nor are they very abundant or of great depth at any place. A part of the surface of Leb- anon, Tewksbury, Clinton, and Readington is be- strewn with small bowlders, gravel, and sand of this period. The most southern limit of the drift is in the southern part of Clinton township, between the South Branch and Prescott Brook. Here is a deposit of small bowlders, gravel, and sand that overlies the red shale. From this deposit we have picked up bowl- ders of Medina sandstone, Oneida conglomerate, Pots- dam sandstone, magnesian limestone, fossiliferous limestone, Hudson River slate, Lower Helderberg limestone, Oriskany sandstone, gneiss and cauda-galli grit. Hence, we see that this mass of drift, small as it is, consists of fragments from nearly all the older rocks that lie to the north of it. And perhaps one would express a truth should he affirm that this little tongue of drift contains fragments of every formation that lies within a hundred miles north of it.

Modern Era of the Recent Period .- In this county, during this cra, no extensive beds of rock either have formed or are now forming. Since within the county there are no estuaries, bays, or lakes into which streams flow, we seem almost barren of opportunity for the deposition of rock of this cra. However, de-

posits have taken place upon a small scale, and are still taking place. These deposits are confined almost exclusively to ponds of water the result of art,-mill- ponds and the like. Of these there are none so large or so important as to deserve a special description.

But, while there are but few areas over which rocks are now forming, excepting these small areas, the en- tire soil of our county is suffering change-disintegra- tion and transposition-to effect the formation of de- posits upon the bottoms of the bays or estuaries into which, beyond the limits of our county, our streams flow. This change is immense, and the amount of material annually transported from the surface of our county to the Delaware Bay and to Raritan Bay is enormous. But so silently is this change effected, and so commonplace are the agents employed in effecting it, that the commonalty of people scarcely notice it.

At each rainfall the rills, rivulets, and rivers are swollen. The pluvial waters saturate the surface of the ground, flood the soil, and flow off to the sea. At each rainfall some substances are dissolved from the soil, others are held in suspension, others are pushed along at the bottom of the flow ; all are transported seaward. In this way, during every considerable rain, tons of the soil are carried from our fields and de- posited upon the bottoms of the estuaries of the. streams that drain our land.

About twenty-five years ago the writer began to make systematic observations upon the Wickecheocke Rivu- let and its basin. As this stream has a rapid flow .- about eighty feet in a mile,-it is favorable to this kind of study. The observations that have been made show the following: Since the observations began, between Sergeant's saw-mill and the bridge that spans the stream some quarter of a mile above, the rivulet has eroded the solid rock to a depth of two and a half feet; between the bridge and Pine Hill Pond it has excavated a channel about five feet deep. Twenty- five years ago a little way below the saw-mill was a pond, about four and a half feet deep, with solid, smooth rock floor; at present there is a riffle about where the middle and the deepest part of the pond formerly were. By eroding the bed of the channel below the pond the stream has drained the pool, and now the area of rock previously covered with water is as dry, and exhibits its joints as plainly, as the rock in any well-worked quarry. Nor is the change respecting the altitude and condition of the stream here greater than at any other place for a full mile down the stream.

At the point where the stream from Sergeantsville flows into the Wickecheoche was some time ago a pond. It was about fifty yards long, about twenty-five yards wide, and about four and a half feet deep,-a favorite resort for the young who were learning to swim. Upon the south side the bank was steep, formed of rocks that well preserved the mark made by a chiisel. Upon these rocks the writer used to keep his mark-

181

PHYSICAL GEOGRAPHY AND GEOLOGY OF HUNTERDON COUNTY.

ings, But now the pond is gone, and the rocks have been eroded and removed. Here now is a riffle which is at least ten feet below the altitude that marked our old swimming place. Farther down, where the stream flows through what was formerly B. Larison's farm, the surface of the water, upon an average, is fully five feet lower than it was twenty-five years ago.

In this way we might take up section after section and show that from Pine Hill to the canal at Pralls- ville the Wickecheoche is rapidly deepening the bed of its basin and transporting scaward the material of its banks.

While this rivulet is excavating its bed, the pluvial waters are washing from the slopes that form its basin silt, detritus, and debris to lower the level of their surfaces. To be sure, this lowering of the altitude of these slopes is less than the lowering of the altitude of the bed and banks of the stream. Yet, from mark- ings upon pillars and the like, it is evident that from the face of the farm on which the writer was raised so much detritus has been transported that the surface, upon an average, is fully twelve inches below the sur- face of the sod which he used to plow. Indeed, he who farms the okl homestead now plows not the soil which the writer used to turn twenty-five years ago. That which he now tills was the subsoil then, beneath the reach of the plowshare. Similar changes are, and have been, effected everywhere. The surface of our fields is removed, our hills are lowered, our valleys deepened, the estuaries of our streams filled.

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History of Hunterdon and Somerset counties, New Jersey : with illustrations and biographical sketches of its prominent men and pioneers, Part 47

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