LIBRAR~ 

A Review and Interpretation of 

the Geologic Setting of the 

Watchung Basalt Flows, 

New Jersey 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 864-A 

.. 

I 

~ 

.~ .• 

i 
A Review and Interpretation of 

the Geologic Setting of the 

Watchung Basalt Flows, 

New Jersey 

By GEORGE T. FAUST 

STUDIES ON THE WATC·HUNG BASALT FLOWS OF NEW JERSEY 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 864-A 

A general introduction to the restudy of the 

volcanism in theN ewark basin of New] ersey 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON 1975 
UNITED STATES DEPARTMENT OF THE INTERIOR 

STANLEY K. HATHAWAY, Secretary 

GEOLOGICAL SURVEY 

V. E. McKelvey, Director 

Library of Congress Cataloging in Publication Data 

Faust, George Tobias, 1908-

A review and interpretation of the geologic setting of the Watchung Basalt flows, New Jersey. 

(Studies on the Watchung Basalt flows of New Jersey) (Geological Survey professional paper ; 864-A) 

Bibliography: p. 

Supt. of Docs. no.: I 19.16 :864-A 

1. Geology-New Jersey. 2. Volcanism-New Jersey. Geology, Stratigraphic-Triassic. I. Title. II. Series. III. 

Series: United States. Geological Survey. Professional paper ; 864-A. 

QE141.F38 551.7'6 74-20937 

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D.C. 20402 

Stock Number 024-001-02652-0 
~\bstract -----------------------------------------

Introduction ------------------------------------- Acknowledgments _____________ -------------------

Location and physiography of the Watchungs -------- Geologic setting ____________ ---- _______________ ---

Summary of previous views on the structural 

characteristics __ ----- _..:. ______________________ ---

The continental glaciers over the Watchungs --------

Stratigraphy and geologic age ---·------------------

Local stratigraphic relations -------------------

Timing of fissure eruptions of the Upper Triassic 

in ~ew Jersey ----------------------------- Geologic age of the igneous activity -------------

Regional stratigraphic relations ----------------

The nature and products of the basaltic eruptions -----

Sites of the fissures -------·--------------------

Preeruptive character of the graben floor --------

Surface character of the vesicular tops ----------

Areal extent and volume relations of the 

Watchung Basalt flows ----------------------

Geologic processes responsible for the jointing 

systems _ ---------- __________ --- __ ----- ____ -

Petrochemistry ______________________ ---- ____ _ 

Megascopic characteristics of the basalt ---------

CONTENTS 

Page 

A1 

1 

2 

3 

4 

7 

s· 

9 

9 

14 

16 

18 

20 

20 

20 

21 

21 

22 

22 

24 

The nature and products of the basaltic eruptionsContinued 

Microscopic character of the basalts ------------

The probable character of the pristine gases in 

the Watchung Basalt -----------------------

History of tectonic subsidence and volcanism in the 

~ewark basin as it relates to the Watchung 

Mountains ------------------------------------- Structure of the ~ewark basin at the close of 

the Triassic Period -------------------------

Structure of the ~ewark basin after the postTriassic deformation _______ -----------------

The formation of a regional arch ---------------

Triassic tensional history, its effect on the development of the ~ewark basin and its global 

cause---a summary --------------------------

Supplementary topics ----------------------------- Some characteristics of fissure eruptions ________ _ 

Vesiculation in basaltic magma ----------------

The process of bubble formation and movement ---------------------------------- Bubble formation in a natural lava flow ----

Literature cited ----------------------------------

Index --------------------------------------------

ILLUSTRATIONS 

FIGURE 

TABLE 

1. Outline maps of area -------------------------------------------------------------------------- 2. Map showing southern limit of the Wisconsin ice sheet over the Watchungs ----------------------

3. Stratigraphic columns for the Triassic rocks in the ~ewark basin in ~ew Jersey ----------------------

4. Generalized geologic cross section from west of Pine Brook on Third Watchung Mountain to an exposure 

just north of West Orange on First Watchung Mountain --------------------------------------

5. Diagram showing estimated sequence in time of the extrusion of the Watchung Basalt flows of· ~ew 

Jersey ------------------------------------------------------------------------------------ 6. Diagram showing estimated sequence in time of the extrusion of the Watchung Basalt flows of ~ew 

Jersey ----------------------------------------------------~-------------------------------- 7. Chart showing generalized stratigraphic section of the Triassic of southern Connecticut ---------------

8. Generalized cross section of the Triassic of northeastern ~ orth America showing the postulated arching 

of the crust ------------------------------------------------------------------------------- 9. Diagram showing geometric changes produced by folding horizontal beds to form an arch -----------

10. Schematic representation of a tectonic graben and folds ------------------------------------------

11. Block diagram of the Mount Eccles fissure eruption in Victoria, Australia ------------------------

12. Schematic representation of a fissure eruption showing the linear formation of the late stage vents 

TABLES 

1. Stratigraphic sections of the upper part of the Brunswick Formation of the Triassic System in the ~ewPage 

A25 

26 

26 

26 

27 

29 

31 

32 

32 

35 

35 

35 

36 

41 

Page 

A4 

8 

10 

12 

15 

17 

18 

27 

30 

30 

33 

33 

Page 

ark basin of ~ew Jersey -------------------------------------------------------------------- All 

2. Average chemical analyses and C.I.P.W. normative data of Watchung Basalt from Third Mountain with 

other averages of tholeiitic rocks _______ ------ __________________________________ ~- _ ___ _ ___ _ __ 23 

3. Mechanical strength of selected rocks ------------------------------------------------------------ 29 

III 
STUDIES ON THE WATCHUNG BASALT FLOWS OF NEW JERSEY 

A REVIEW AND INTERPRETATION OF THE GEOLOGIC SETTING 

OF THE WATCHUNG BASALT FLOWS, NEW JERSEY 

By GEORGE T. FAUST 

ABSTRACT 

The Watchung Basalt flows and the thick sedimentary sequences as now exposed in Bergen, Essex, Union, Passaic, 

Morris, and Somerset Counties, New Jersey, are part of the 

remnant of a former. graben. This graben has been largely 

destroyed by erosion. The graben is generally believed on the 

basis of paleontologic evidence to have been formed in the Late 

Triassic. About 21h to 1 million years before the end of Triassic 

sedimentation in the graben, lava flowed out onto the graben 

floor to form the large flood basalts of First Watchung Mountain. Approximately 600,000 to 250,000 years after the first 

volcanic episode a second period of basaltic eruptions produced 

the lavas of Second Watchung Mountain. Following a lapse of 

11h million years to 600,000 years another flood of basalts 

formed the lavas of Third Watchung Mountain. As the lavas 

solidified they accumulated body stresses and most of this stress 

was relieved by jointing. Subsequently, the region was folded 

to form an arch. During the buckling of the arch subsidiary 

border synclines were formed along the contact with the granitic walls of the horsts. This tectonic event produced joints 

whose abundance and distribution are related to the geometry 

of the structure. Late in the history of the Newark basin in 

New Jersey, during the Pleistocene, a continental glacier covered a part of the area. After the disappearance of the glacier, 

decompression of the crust produced sheeting structures in the 

basalt. Thus the jointing systems observed today are the results of the combined geologic processes of volcanism, tectonism, 

and glaciation. 

The history of the events involved in the tectonic subsidence 

and volcanism in the Newark basin bears a parallel relationship to the order of events taking place in the North American 

plate in its location in the ancient continent of Pangaea. It is 

suggested here that ( 1) the rifting to form and develop the 

Newark graben, (2) the deep rifting associated with the volcanism, and (3) the downfaulting of the graben which produced the central arch and the border synclines are the result of the following events in the continent of Pangaea: (1) 

the development of a linear zone of tension, (2) deep rifting 

which separated the North American plate from the adjacent 

parts of Pangaea. 

Basalts form the three ridges known as First, Second, and 

Third Mountains. The feeder dikes from whence the lava welled 

forth are hidden by cover. A feeder dike was observed cutting 

through the lower flow unit of First Mountain, near West 

Orange, N.J. The areal extent of the Watchungs is now about 

500 square miles (1,29·5 km2); they probably covered an area 

of 2,000 square miles ( 6,180 km2 ). The lavas are tholeiites. 

Supplementary topics include a discussion of the characteristics of fissure eruptions and of vesiculation in basaltic 

magma. 

"Watchung Mountains-The trap 

'ridges extending from Bedminster 

and Somerville to Oakland and 

Darlington are known as the 

Watchungs or Orange mountains. 

They are sometimes called First, 

Second and Third Mountain, beginning with the outermost or 

eastern one. 111 

INTRODUCTION 

In 1936-37, the author was teaching ·a course in 

the theory of annealing, as developed by Williamson 

·and Adams (1919) and Adams and Williamson 

(1920), to graduate students at Rutgers University. 

During this course, I became interested in the problems of the cooling of lava flows, such as the nearby 

Watchung Basalt, and I made some preliminary calculations of the heat-flow relations. Subsequent 

field observations of the three Watchung Basalt 

flows disclosed that the problem was more complex 

than the ·simple model. Any theory of cooling of the 

lava flow would have to account for the several 

types of joints present in these flows and the 

obviously unequal frequency of the several joint 

systems. It thus became evident that a preliminary 

stage in the evaluation of the cooling history of these 

flows would be a study of the character of the jointing and its uniformity. 

This report provides a background for ·an extensive study of various aspects of the Watchung Basalt 

flows in New Jersey. F·aust and Murata (1953) and 

Faust, Hathaway, and Millot (1959), in a study of 

the m~ineralogy of the Watchungs, reported on 

1 Kilmmel ( 1898, p. 76-77). 

A1 
A2 STUDIES ON THE WATCHUNG BASALT FLOWS OF NEW JERSEY 

stevensite, the ma-gnesium end member of the montmorillonite group. Preiiminary results on the jointing systems were reported by Faust (in U.S. Geological Survey, 1961, p. A77). Aeromagnetic maps 

were prepared and used as a background for this 

study (Andreasen and others, 1963; Henderson, 

Andreasen, and Petty, 1966; Henderson, Chandler, 

and others, 1962, 1963; Henderson, Tyson, and 

others, 1957a, b; Henderson, Tyson, Gilchrist, and 

others, 1957, 1958a, b; Henderson, Tyson, Wilson, 

and others, 1957a, b, c, d; PhHbin and Kirby, 1964). 

This report is written not only to orient the reader 

with respect to the location, physiography, and 

geology of the Watchung Mountains but to indic·ate 

something of the order of magnitude, direction, and 

time sequence of the several physical geologic forces 

which are responsible for the joint systems in the 

basalt flows as we see them today. Because geologists 

differ in their views on the origin and development 

of the Triassic Newark basin, brief statements of 

these several theories and a short review of fissure 

eruptions are included. 

There has been a revival of interest in the Triassic 

basins of eastern North America. One of the unsolved problems which has attracted much attention 

and is pertinent to this study is the relation of the 

numerous dikes which occur both without and 

within (in part) the basins and whose trend is almost always discordant to the structural trends of 

the basins. King (1961), who has studie~ this problem in detail, has made some comments on the stress 

patterns as deduced from these dikes and the struc-. 

ture of the basins. 

Some matters of nomencla.ture require mention 

at this time. The three ridges that constitute the 

Watchung Mountains have been known for a long 

time in popular and scientific usage as First, Second, 

and Third Watchung Mountains and collectively as 

''The Watchungs." In addition a shorter usage First, 

Second, and Third Mountain has been used where no 

confusion could result. 'The latter usage has been 

adopted in this report. The name "Watchungs" is derived from the Indi·an name "Wach Unks" which 

means "the high hills" (Torrey and others, 1951, 

p, 243). This name was given by the Lenni Lena;pe 

Indians of the Algonkian group, known to the colonists as the Delawares, who inhabited the region 

(Federal Writers Project, 1939, p. 30-31). 

Another matter of nomencl·ature concerns the 

name "trap" and the usage "trap rock" which are 

very old terms that go back to the early history of 

mining and quarrying. Trap was apparently first 

used in Sweden as a roc·k name by Rinman in 1754, 

(Troger, 1935, p. 335). Rinman (1754) was the head 

foreman of a Swedish iron foundry, and he published 

a collection of rock terms amongst whioh was trap. 

The name since then has been applied to various 

rocks, but most commonly its usage has been associated with basalt (Johannsen,· 1937, p. 245). 

Schottler (1908, p. 344) applied the term "trap" to 

basalts occurring in the vicinity of Giessen, and 

which make up part of the large central-type eruption now constituting the V ogelsberg Mountains in 

Hesse, Germany. The immense plateau basalts of 

India are officially known in the stratigraphic nomenclature of India as the Deccan Traps (Washington, 1922; Wadia, 1953). Trap is chiefly a field term, 

and is applied most frequently as a designation for 

the source rock of the mine~al commodity crushed 

bas·alt, which is used in road construction. 

The word "trap," as well as "ba·salt," is used in 

this report because of its long established use in New 

Jersey and elsewhere in the Triassic of eastern 

North America and because no ambiguity arises 

from its retention. Davis (1882) and Darton (1890), 

to mention but a few of the early writers, used the 

term "trap," and Mason (1960) preserves this 

usage in a ·bulletin of the New Jersey Geological 

Survey. 

ACKNOWLEDGMENTS 

I am indebted to m·any colleagues with whom I 

have discussed various problems. In particular, I 

wish to thank Richard C. Erd, U.S. Geological Survey, who worked with me in the early stages of the 

project and contributed much to the field studies, 

the field assistants (Theodore Woodward, Joseph R. 

Houston, John P. Marble, David Y. Moore, Charles 

E. Minard, Frank A. Mooreshead, III, Edward D. 

Frey, L. Robert Gardner, Matthew L. Werner, III, 

Frederick P. Zoerner, Joseph R. Mraz, and Paul E. 

Diehl) who worked during the summer months, and 

Robert L. Smith, U.S. Geological Survey, with whom 

I discussed some of the facets of the problem. 

Various companies that produce crushed stone 

and operate quarries in this area were. very cordial 

in their cooperation. The engineers, superintendents, 

managers, and quarrymen in these companies were 

exceedingly helpful. The engineers and staff of the 

New Jersey Highway Department, and the engineers 

and staff of the various construction companies, who 

were building U.S. Highways 287, 78, and 80, and 

other highways helped in many ways. The farmers 

and property owners in the area have been very 

cordial in extending privileges to me. 
REVIEW AND INTERPRETATION OF GEOLOGIC SETTING A3 

I have benefited from the comments and reviews 

of Thomas L. Wright and Eugene C. Robertson, 

Edwin Roedder commented on the section "Vesiculation in basaltic magma." The former State Geologist 

of New Jersey Meredith E. Johnson and the present 

State Geologist Kemble Widmer have furnished me 

with well data and aided me in other ways, and I 

thank them for their help. 

LOCATION AND I>HYSIOGRAPHY OF THE 

WATCHUNGS 

The Watchung Mountains are in northern New 

Jersey in Bergen, Essex, Union, Pas·saic, Morris, and 

Somerset Counties. They form a crescent-shaped belt 

a-bout 12 miles wide and approximately 40 miles long 

trending in a northeasterly. direction from Somerville and Bound Brook in Somerset County and 

reaching almost to the New Jersey-New York 

border in Bergen County. The W·atch ung Basalt 

flows of New Jersey are exposed in three mountain 

ridges separated from one another by valleys eroded 

out of the less resistant red shales and brownish 

sandstones. The basalt flows are part of the physiographic province known as the Triassic Lowland, an 

area bounded on the west by the Reading prong, on 

the north by the Manhattan prong, on the east by 

the ·Coastal Plain and the Trenton prong, and on 

the south by the Carlisle prong (Davis, 1912). The 

four "prongs" are made up of very old (probably 

Precambrian) metamorphic rocks, while the Coastal Plain is underlain .by sediments of Cretaceous, 

Tertiary, and Quaternary age. ·The Reading ·and 

Manhattan prongs are sometimes referred to collectively as "The Highlands" in Pennsylvania, New 

Jersey, ·and New York and that part of the Coastal 

Plain adjacent to the Triassic Lowlands is sometimes called the Cretaceous Overlap. The physiography of the Watchung Mountains is exceptionally 

well presented both textually and graphically in publications by Lobeck and Raisz (1930), Lobeck 

(1952), and ·Kiimmel (1940). Although the lava 

flows do not crop out everywhere in this belt their 

areal extent c~an be estimated to be about 500 square 

miles (1,295 .kJm:!). The northern and .middle part of 

the Watchung Basalt flows parallel the Palisade Diabase, a stratigraphically correlative intrusive unit, 

which crops out along the Hudson River. New York 

City lies Qlbreast the northern part of the Watchung 

Mountains and is approximately 12 miles (19 km) 

distant from First Watchung Mountain. The New 

Ger~antown trap sheet, a smaller crescent-shaped 

flow with an inner trap knoll has been correlated by 

Lewis (1907, p. 115-117) with the Watchung 

Mountains. It lies in Hunterdon County, near the 

hamlet o.f Oldwick, N.J. 

A sketch map (fig. lA) shows the outline and 

relation of the three mountains which constitute the 

Watchungs and the New Germantown trap sheet. 

It does not include minor fault dislocated trap 

masses such as the structure at Sand Brook, near 

Flemington, N.J. The quadrangle sheets covering 

thi'S area are shown in figure lB. Place names not 

shown in figures 1A and B appear in figure 2. 

First Watchung Mountain rises abruptly, as a 

rocky escarpment 'above the Raritan Valley and 

Coastal Plain, which in this ·area is generally less 

than 200 feet (61 m) ~above sea level. From P.aterson 

to ;below ·South Orange the esc-arpment ranges from 

690 to 550 feet (210 to 168 m) above sea level and 

rises to the north to reach a maximum elevation of 

885 feet (270 m) above sea level, at High Mountain, 

a peak just north of Paterson. The height of the 

ridge drops from 540 to 450 feet ( 165 to 137 ·m) as 

it is followed farther south (Ktim.mel, 1940). The 

continuity of the escarpment is broken by occasional 

notches. The northwest slope of Fi~st Mountain i·s 

gentle and represents the regional dip of the basalts 

except where ·modified by later processes. The valley 

between First and Second Mountains has an average 

elevation of 300 to 200 feet (91-61 tn). ·The escarpment of the Second Mountain parallels that of First 

. Mountain, and it is likewi'Se generally continuous 

except for occasional notches. Its elevation in the 

northern part ranges from 500 to 665 feet ( 153 to 

203 m) •and in the southe.rn part it ranges from 530 

to 635 feet (162 to 194m) above sea level. The valley 

between Second and Third Mountain is again at :an 

elevation of 300 to 200 feet (91-61 m). 

The escarpment of Third Mountain is significantly 

different from those of First and Second Mountains 

in that it is discontinuous (fig. 1). It consists of the 

ridges known as Long Hill; Riker's Hill; the doublecurved, hook-shaped Hook Mountain arid Packanack 

Mountain; together with the upturned and folded 

edge of the sheet ·to the northwest of Long Hillcalled the New Vernon trap sheet. The valley between Third Mountain and the New Jersey Highlands is approximately 300 feet (91 m) above sea 

level. 

The apparently level crestlines of the Watchungs, 

parts of the Palisade Ridge, and the high hills of 

Staten Island led Darton and others (1908, p. 1) to 

the view that these elements define the eastward 

extension of the Schooley Plain. 
A4 STUDIES ON THE WATCHUNG BASALT FLOWS OF NEW JERSEY 

GEOLOGIC SETTING 

The geologic relations of the Watchung Basalt 

flows have been described by Lewis (1908), and the 

geology of the Triassic Lowlands, as a unit, has been 

summarized by Kiimmel (1940) and by Widmer 

(19·64). Wheeler (1939) and Sanders (1963) have 

introduced new theories to account for the tectonic 

history of the region. The summary of the geology 

which follows is based largely on these and other 

sources. 

At the close of the Paleozoic Era the very large 

compressive forces that ;produced the folded Appalachian Mountains had been relaxed. At some later 

time, as a consequence of this change in the mechanical state of the crust, large blocks of the crust 

dropped down to form troughs or grwbens in a region extending from Nova Scotia to North Carolina. 

This down;f.aulting was accomplished by displacement of the blocks along ·major faults or chains of 

faults which made up the walls of the trough. According to some geologists (Klein, 1969), the grabens were probably not continuous from Nova 

Scoti·a to North Carolina but consisted of a series 

of discontinuous •basins. ·This faulting must have 

occurred over a period of about 10 million years. The 

Triassic rocks in New Jersey all belong to the upper 

thir.d of the Triassic Period, so that we can conclude 

that this region in New Jersey during the lower 

and middle thirds of Triassic time was at a sufficient 

elevation to be yielding sediments rather than receiving them. The ·basin in New Jersey is referred 

to as part of the N ew·ark basin. 

The geological history of the Newark basin has 

been interpreted in several ways. The theories of 

Barrell (1915), Sanders (1963), and Klein (1969) 

are summarized below for the convenience of future 

reference. 

Barrell's (1915) concept of the formation of the 

Newark basin is sum-marized as follows : 

1. ·The !beginning of the basin was a downsinking 

of a long trough with a tendency to downwarp on one side and upwarp on the other. 

This movement was accompanied by the uplift of neighboring areas. 

2. The rocks of the uplifted areas were eroded to 

produce the sediments, the mud and gravel, 

which make up the rocks formed in the trough. 

In New Jersey, Kilmmel found that "the basal 

beds disappear toward the north and that 

sediment came from both east and west." 

(Barrell, 1915, -p. 28-29). 

3. The continued accumulation of sediments re-

·sulted in a loading over the area of deposition 

74"40' 30' 20' 74"10' 

0 5 10 "MILES 

~ •'• I' ~ ' 1

1

0 KILO~ETRES 

40"L-----~----------L---------~--------~~ 

30' A 

FIGURE !.-Outline maps of area. A, Sketch map showing the 

outline of basalt outcrops of the three Watchung Mountains 

and the New Germantown trap sheet (modified from Lewis, 

1908, pl. 10). I, II, III refer to First, Second, and Third 

Watchung Mountains. B, (see facing page) Index to the 

U.S. Geol. Survey topographic quadrangle maps, scale 

1:24,000, covering the exposure area of the Watchung Basalt 

flows. 

that produced further sinking of the trough. 

The greatest sinking took place along the 

margins where the deposition of the sediments 

was the greatest. The occurrence of conglomerate beds throughout the section indicated 

regrowth of the mountains supplying the sediments for the basin. This necessitated a boundary consisting of a fault wall along which renewed movement took place. In New Jersey 

"These areas were therefore basins facing 

each other and bounded on their outer sides 

·by faults. * * * the western limit of the New 

Jersey area is still on or near this ancient 

boundary. * * *" (Barrell, 1915, p. 29). The 

Triassic section in New Jersey contains at 

least 15,000 feet of sediments and igneous 

rocks, so that approximately " ... three miles 

of sediment w·as deposited in the basin in the 

tract of greatest subsidence. The basin floors 

in those places subsided at least three miles 
REVIEW AND INTERPRETATION OF GEOLOGIC SETTING A5 

NEW JERSEY 

~ ~~ 

~ ~ 

~ ~ 0~ ~0 ~ ~ ~"' ~"' v ~ 0 ~ ~ <f ~<.;; Bedminster 

&' 

<ij ~ Somerville o #> 0 

c§i Bound 

0 

I 

0 

I 

10 

10 

I 

<ij Brook 

I 

20 

during the ~progress of the period, yet the sediment was sufficiently abundant to keep the 

basins continuously full of sediments. Slow 

movements intermittent in nature went forward therefore for a vast period of time, dur-

~~ ~0 ~ ~<.;; 

0 

Oakland 

0~ 

~ ~ 

q,"t' 0 Paterson 

·~ 

~G 

41 °00' 

~c., ~ ~~ 

0~ v~ 0 

~ 

Morris tow 

I 

~ ~ 

<:.i ~ 

~ ~~ ~ q,..Y 

20 

I 

~ 

~ 

~ 

~ 

30 MILES 

I 

30 KILOMETRES 

ing which erosion planed even deeper into the 

folded and metamorphosed rocks of the rising 

tracts of the Appalachian system, the rock 

waste being swept into the intermontane 

basins." (Barrell, (1915, p. 31). 
A6 STUDIES ON THE WATCHUNG BASALT FLOWS OF NEW JERSEY 

4. In the Early Jurassic extensive crustal movement took place in the Newark basin. The 

crust broke into great blocks by faulting and 

these blocks were rotated so that they now 

slope 15° to 20° W. In Connecticut the Triassic 

rocks slope to the east. The opposite slopes of 

the two basins suggest that a wide mountain 

.arch was raised between them. The raising of 

the arch was followed by fracture and settling 

along the sides. "Where the principal movement of the blocks was tilting, rather than 

elevation or subsidence relative to adjacent 

'blocks, the upturned edge of each block would 

form a ridge with a steep face along the fault 

plane and a gentle slope following the dip of 

the strata. * * * The least uplift was on the 

western side of the New Jersey Triassic." 

(Barrell, 1915, p. 27). 

Commenting on the sections in Pennsylvania, 

Johnson and McLaughlin (1957, p. 35) state "The 

availa.Jble facts are not consistent with the hypothesis 

that Newark sedimentation was initiated by downfaulting along the present north border or by the 

form·ation of gra;bens. The first sediments came from 

the south, where no evidence of downfaulting has 

been found. The locations of the Newark basins, and 

especially the New York-Virginia one, suggest instead they were produced by deep erosion of the 

least resistant Paleozoic rocks, the limestones and 

shales of Cambrian and Ordovician age, with some 

down:f.aulting along the northwest border. The more 

resistant crystalline rocks of the present Piedmont 

formed a lofty highland along· the southern border 

of the Newark trough, while an escarpment of resistant quartzite formed much of its northern 

limit." 

Sanders (1960, 1962, 1963) reexamined the Late 

Triassic tectonic history of the northeastern United 

States. His field observations covered the Triassic 

basins from the Connecticut V·alley to the Schuylkill 

River in Pennsylvania, and his study showed that 

the tectonic history of the basin is more complex 

than had been realized by earlier workers. 

Sanders (1963, p. 501) on the basis of the data 

available to him concluded that the isolated basins 

"represent remnants of the filling of an elongate rift 

valley that was 50 to 70 miles wide," and that "the 

stratigraphic thickness of the Triassic rocks is held 

to be approximately 30,000 feet." He recognizes 

four discrete episodes : 

1. Initial graben subsidence, sedimentation, and 

basaltic igneous activity qntrusive and extrusive) .-The basin was formed by downfaulting and not down-warping. Differential relief 

was maintained by recurrent movement along 

the marginal faults. "These marginal faults 

must have originally dipped under the graben 

block at approximately 70° to 75°; now they 

dip 55° to 60° in many localities, but they 

have been rotated 15° to 20° during the longitudinal crustal arching of episode 2." (Sanders, 1963, p. 506). "Three periods of plateau 

basalt outpourings were associated with the 

initial episode of graJben subsidence. * * * 

Dikes and gently concave saucer-shaped intrusive sheets of similar composition to the lava 

flows were also emplaced during the initial 

episode of graben subsidence. * * * The evidence found locally in the Palisades sheet 

proves that these sheets solidified before tilting 

of the Triassic strata. * * * The parallelism 

of the Triassic strata with each other and with 

the three interbedded lava flow complexes, as 

well as the parallelism of the latter to each 

other and with the base of the Triassic indicates (notably in the New Jersey-New York 

belt) that the initial episode of graben subsidence took place without important longitudinal or transverse warping." (p. 508). 

2. Longitudinal crustal warping.-During this episode longitudinal crustal warping in the center 

of the initial graben was responsible for the 

tilting of the New York-New Jersey-Pennsylvania and the Connecticut Valley belts so that 

they now di·p 15° to 20° away from each other. 

The total uplift .may have been as ·much as 

35,000 feet. 

3. Second-generation graben subsidence ·and transverse crustal warping.-"The next tectonic 

episode is related to the formation of the 

transverse folds (or warped structures, as they 

have been previously called) that are so 

prominent in the topography and geology of 

the Hunterdon Plateau, New Jersey. * * * The 

width of the second-generation graben varies; 

the transverse synclinal structures show a corresponding change of size. Hmall synclines occur on narrow parts of the graben and large 

synclines occur on the wider parts of it." 

(Sanders, 1963, p. 510). 

4. Fragmentation of transverse warped structures 

and emplacement of late intrusives (basaltic) 

and mineral deposits.-The final episode of 

tectonic activity displaced the transverse folds 

which had been formed on the second generation graben block. "In New Jersey the faults 

are curved and change trend from northeast-
REVIEW AND INTERPRETATION OF GEOLOGIC SETTING A7 

southwest in the Delaware Valley to northsouth in areas to the northeast. * * * New 

Jersey faults were discussed by Kiimmel 

(1898, 1899) and Wheeler (1939) ." (Sanders, 

1963, p. 512). 

Sanders (1963, p. 514) concluded that the Flemington fault "marks an important tectonic boundary 

in the Triassic outcrop belt. * * * The Flemington 

fault shows an unknown amount of right-lateral 

strike slip displacement as well as more than 10,003 

feet of dip slip displacement." 

Klein (1969) has summarized the availa:ble data 

of stratigraphic and sedimentological studies on the 

Triassic basins, and he concludes that the several 

troughs which make up this basin were all separate 

basins at the time they were infilled. 

The original areal extent and the distribution of 

the present outcrop areas of the Newark Group has 

given rise to two hypotheses (Russell, 1892, p. 101-

107). The local-basin hypothesis suggests that the 

presently existing detached basins represent essentially the original extent of the areas of deposition 

during Triassic time. The broad-terrane hypothesis 

assumes that the presently existing detached basins 

are only remnants of the former areas of deposition 

of the Newark Grou~ and that the missing elements 

have been removed .by erosion. It further claims that 

most, if not all, of the detached areas were united 

into a broad terrane during Triassic time. 

The two .principal objections to the broad-terrane 

hypothesis, with particular reference to the Connecticut and Newark basins, are based on the observations that no trace of the eroded Triassic rocks 

between the detached basins exist and no area where 

eroded sediments could have been deposited was 

recognized. The first objection was negated by the 

observations of Triassic rocks in the downfaulted 

area of the Pomperaug valley in Connecticut by 

Hobbs (1901), and by the recording of Triassic sediments in a well on Long Island by Wheeler (1938). 

The second, by the requirements of sedimentary 

material heeded to form the coastal plain of New 

Jersey (Owens, 1970). 

The implication of the broad-terrane hypothesis 

suggests that the areas and volumes of Triassic 

basaltic volcanism were far larger than those observed today, a point emphasized by Sanders 

(1963). 

There is general agreement amongst most investigators of the structure of the Triassic rocks in New 

Jersey that the Newark basin was formed as a graben. Johnson and McLaughlin (1957) proposed that 

the structure was formed by deep erosion out of 

Paleozoic limestones and shales. Their view has not 

been accepted by later investigators, Sanders (1960, 

1962, 1963), Klein (1969), VanHouten (1969), and 

more recently, Rodgers (1970). The source of the 

sediments is attributed principally to the granitic 

and metamorphic rocks represented in the Trenton, 

Reading, and Manhattan prongs and also to the sedimentary rock of the older Paleozoic formations. The 

direction of transport of the sediments is still an 

unsettled question, and the various proposals on the 

subject have recently been discussed by Van Houten 

(1969). 

SUMMARY OF PREVIOUS VIEWS ON THE 

STRUCTURAL CHARACTERISTICS 

All of the geologists who have investigated the 

volcanic rocks of the Newark basin in New Jersey 

since Darton's study of 1889 and 1890 agree that 

they are flows from fissure eruptions. Darton ( 1889) 

described the flows as follows : 

(1) The extrusive sheets are perfectly conform·able 

to the underlying sediments. 

(2) Their upper surfaces are slaglike and deeply 

vesicula ted. 

( 3) The overlying sediments are totally unaffected. 

( 4) Trap breccias are observed at some of the 

basal contacts. 

( 5) The base of the flows are vesiculated. 

( 6) There is evidence of successive flows. 

(7) There is a general absence of tuffs. 

( 8) No central cone is present. 

Darton reasoned that the general absence of fragmental deposits, excepting a few local beds; the absence of craters; the large areal extent of the Watchungs; and their similarity to the great fissure 

eruptions of the Western United States described by 

Von Richthofen (1868) and Geikie (1882) was sufficient evidence to attribute these flows to fissure 

eruptions. 

Darton's (1890) view that each of the three Watchung Mountains was actually made up of successive flow units was investigated by Lewis (1907, p. 

110-114, and 1908, p. 148-151). Lewis (1908, p. 

150, 152) believed that the composite character of 

the trap sheets "seems to correspond to successive 

flows of lava or to successive pulsations of an irregular eruption." The presence of a ropy and vesicular 

layer at a quarry in First Watchung Mountain he 

suggested indicated two successive flows (here called two flow units). His study of Second Watchung 

Mountain, ·particularly in the vicinity of Bound 

Brook, led him to conclude that it consisted of two 

sheets (flow units). In addition he supposed, with-
AS STUDIES ON THE WATCHUNG BASALT FLOWS OF NEW JERSEY 

out field evidence, that these flow units were separated. by an intertrappean layer of sedimentary 

rocks, a view denied by Kiimmel ( 1898, p. 125), 

whose views on faulting were likewise unsubstantiated. Lewis (1908) was less certain of the composite character of 'Dhird Watchung Mountain, and 

his criteria were admittedly inconclusive. 

Bucher (in Bucher and Kerr, 1948) recognized 

the fact that First Watchung Mountain, in the few 

exposures that he examined, actually consisted of 

two :flow units-a lower flow unit and an upper flow 

unit separated by "a thin layer of reddish argilla- . 

ceous siltstone" and he· gave a columnar section 

portraying these relations for the outcrops in the 

vicinity· of Paterson, N.J. Van Houten (1969) followed Bucher's classification. 

It is im·portant to note that this preliminary 

knowledge of the composite structure of the Watchung Mountains is based entirely on the structure 

as seen at a few widely separated outcrops. Lewis 

made his observations chiefly near the nose of the 

syncline in the vicinity of Bound Brook, while 

Bucher's studies were chiefly in quarries near Paterson. 

The· pillow lavas in First and Second Watchung 

Mountains have been described by Lewis (1915), 

and their outcrop has been delineated in First 

Mountain by Fenner (1908). 

THE CONTINENTAL GLACIERS OVER THE 

WATCHUNGS 

Northern New Jersey was subjected to several 

glacial invasions. Salisbury (1892) reported scattered deposits of pre-Wisconsin drift in New Jersey 

as f~r south as lat 40°35'N. Widmer (1964) has reviewed the recent studies of this glaciation and 

points out that the glacial deposits representing this 

stage lie to the west of Somerville and further that 

the field evidence available is so meager as to permit few ·additional conclusions other than its limited 

occurrence. No evidence of the effects of this glaciation on the Triassic sediments or lava flows h·as 

been reported. The Wisconsin Glaciation, in contrast, 

is well documented. The terminal moraine cuts across 

the Watchungs in a curved line from Summit to 

Morristown. 

The Wisconsin glacier covered the northern part 

of the Watchungs as is shown in figure 2. Salisbury 

and others (1902, p. 67) discuss the thickness of the 

ice sheet and point out that it was thickest over the 

Triassic Lowlands. These authors estimate that the 

average thickness of the glacier in the area considered in this study was about one-fifth of a mile 

45' 

•Elizabeth 

0 5 10 MILES 

I 1'1 r' r'r ' ' ' 0 5 10 KILOMETRES CONTOUR INTERVAL 100 FEET 

FIGURE 2.-Southern limit of Wisconsin ice sheet over the 

Watchungs (from Salisbury and others, 1902, pl. 40). 

(1,056 ft, 322 m). The map shows clearly that the 

northern part of Third Watchung Mountain, Hook 

Mountain and Packanack Mountain, must have borne 

a considerable weight of superincumbent ice. 

When the glacier invaded the area, it caused a 

depression of the crust below it which was manifested in bending of the rock units and settling. 

Since the thickness of the glacier increased slowly, 

there was a gradually increasing pressure applied 

to the crust. Antevs (1928, p. 107) estimates that 

the ice sheet maintained itself for a~bout 2,000 years. 

Recent studies of the retreat of the last ice sheet in 

New England by Schafer (1968), who used radiocarbon dating, suggest that this period may be twice 

as long as Antevs estimates. Accordingly, the vertical component of the stres·s that was impressed by 

the weight of the ice above the rock was maintained 

at its maximum value for a significant length of 

time. The value of this stress varied from an almost 

negligi1ble value at the end of the sheet to the maximum values farther north. The outcrop edge of 

Hook Mountain and Packanack Mountain must have 

been covered by at least an average thickness of the 

ice sheet. If we use the average thickness of 1,056 

feet (322 m) of ice and the weight of a cubic foot 

of ice as 57.2 pounds, (25.9 kg) we can calculate 

that the pressure of a column of ice 1,056 feet (322 

m) high and 1 square foot would be close to 60,400 

pounds per square foot (29.5 kg/cm2 ). These values 
REVIEW AND INTERPRETATION OF GEOLOGIC SETTING A9 

represent the vertical normal component of the 

stress acting upon, and in the vicinity of the outcropping edge of the lava flow of Third Mountain. 

When the glacier disappeared, either by retreating 

or downwasting, a reverse mechanical reaction took 

place, namely uplift, and the crust strove to recover 

from its depression. Evidence for this recovery is 

observed in the postglacial upwarping of the shoreline of glacial Lake Passaic. Reeds (1933) has calculated the changes in elevation for the length of 

the lake; at Hook Mountain it amounted to 3ibout 

35 feet (11m), and at the end of Packanack Mountain to about 67 feet (20 m). The evidence suggests 

that the largest change in altitude coincides with 

the greatest thickness of ice. Additional evidence of 

this upward movement can be seen in the glacial 

clays in the form of small faults with a throw of 

a few feet and in the recorded occurrence of occasional very mjnor earthquakes attributed to the adjustment of the land surface. Sheeting (sheetjointing) occurred in the basalt flows where the ice was 

thickest (Faust, unpub. data). 

STRATIGRAPHY AND GEOLOGIC AGE 

LOCAL STRATIGRAPHIC RELATIONS 

The 'Stratigraphy of the Newark Group was established by Ki.immel (1898). He divided the Newark 

Group into three formations made up of the Stockton Formation, which lies unconformably upon the 

older crystalline rocks; the Lockatong Formation, 

which lies over the Stockton; and the Brunswick 

For·mation, which overlies the Lockatong and is thus 

the youngest member of the Newark Group. The 

three Watchung extrusive sheets (First, Second, and 

Third) were extruded near the end of Brunswick 

sedimentation. Each of these volcanic episodes forming the three sheets consisted of two events, and 

each sheet is composed of two separate flows, here 

designated flow units. The time lag between these 

multiple events was short. The Palisade Diabase was 

intruded chiefly into the upper part of the Stockton Formation and the lower part of the Lockatong, 

but some of the Palisade Diabase intrudes the 

Brunswick Formation. Lewis (1907, p. 120) pointed 

out the presence of the recurved Palisade Diabase 

sheet in the upper part of the Brunswick at .Haverstraw, N.Y., where "it reaches almost to the top 

·of the series." This observation thus dates the Palisade intrusion as near the end of Triassic sedimentation and is evidence for the conclusion that the 

Watchung flows and the Palisade intrusion were 

contemporaneous igneous events. 'rhat the Palisade 

Diabase intrusion is also a multiple intrusive event 

is shown by the studies of Walker ( 1969) , who 

demonstrated its composite character on the basis 

of petrographic and chemical evidence. The first 

intrusion to form the Palisade sill had cooled sufficiently to crystallize and to undergo some differentiation before the second intrusion was emplaced within 

it. The multiple events forming the sill thus show 

a correspondence with the events forming the sheets 

and their flow units. 

The stratigraphic section is given in figure 3 for 

three representative thicknesses. 

Kii-mmel (1898, p. 34) based his division of the 

Newark Group into three formations "upon lithologic differences, which imply diverse conditions of 

sedimentation, and which .permit the establishment 

of recognizable horizons." He observed that there 

were no sharply ,marked division planes· and that 

these formations tended to grade into one another 

through transitional zones, but n~vertheless he was 

able to differentiate between them. The paleontologic 

evidence is meager but almost all agree that the 

Newark Group i'S Upper Triassic (Keuper). (See 

Johnson and McLaughlin (1957, p. 33), VanHouten 

(1969).)t 

The lithologic assembly of the Stockton Formation according to ·Kum.mel ( 1898, p. 30) consists of 

"(a) coarse, more or less disinte&"rated arkose conglomerates; (:b) yellow micaceous, feldspathic sandstones; (c) brown-red sandstones or freestones, and 

(d) soft red argillaceous shales. These are interbedded and many times repeated * * *." The Lockatong Formation consists of hard dark-colored shales 

and dark-gray and green flagstones. It also includes 

carbonaceous shales, black and .purplish argillites, 

dark-red shales, almost flagstones, and thin layers 

of limy :shales. The Brunswick Formation consists 

of great thicknesses of soft red shales with ·some 

sandstone layers. Massive fanglomerate beds occur 

along the northwest border of the Newark Group. 

The lithology of these members of the Newark Group 

have been studied by many workers, and a summary 

of their work is given by Van Houten (1969). Van 

Houten (1969) has contributed important studies 

of the Lockatong Formation and shown that the 

Lockatong is a large lacustrine lens-shaped body. He 

has characterized its mineralogy and interpreted its 

chemistry. Picard and High (1963) found the 

Brunswick Formation to be made up of alternations 

of a massive resistant layer rock (chiefly 'Sandstone) 

and of less resistant beds chiefly mudstones and 

poorly sorted siltstones in the .proportion of 43 percent of the massive resistant layers to 57 percent of 

t After this report was completed, studies by Cornet, Traverse, and 

McDonald (1973) of fossil spores, pollen, and fishes from Connecticut led 

them to suggest an Early Jurassic age for the younger sediments of the 

Newark Group. From the youngest sediments of the Brunswick Formation 

in New Jersey, they have recovered similar "Rhaeto-Liassic palyniftorules." 
AlO 

7000 

1-

1.&.1 

1.&.1 

u. 

z 

;i 

t: 

1.&.1 

0 

23,000 

STUDIES ON THE WATCHUNG BASALT FLOWS OF NEW JERSEY 

Kummel (1898) 

20,300 feet (6189 m) 

of sedtmentary rocks 

with 2650 feet (808 m) 

KUmmel (1898) 

11,800 feet (3~98 m) 

of sedimentary rocks 

with 2650 feet (808 m) 

Van Houten (1969) 

16,000 feet (4878-m) 

of sedimentary rocks 

with 2650 feet (808 m) 

of igneous rock 

Second ~,...,:;,;...,;,~,;,;..,...r.;iol· Wa~chung Basalt 

flows 

First Watchung 

.,._,="""""""=""=~=::4 Basal flows 

Top of basement vvvvvvv v 

is at either A or B v ...., v v v v v v 

EXPLANATION 

The symbols for Trb, Trl, and Trs are approximate and indicate ratios 

of sandstone to siltstone and shale layers of 43:57 percent, 60:40 

percent, and 80:20 percent, respectively. The thin layer of the h9rnfels zone under each flow has been omitted. The fanglomerates 

(conglomerates) below the lava flows do not extend for any great 

distance into the basin anti. are close to the graben wall and are 

thus shown as partly underlying the flow by a series of four circles. 

~ 

~ ~ 

~ 

~ 

~ 

0 

1000 

4000 

Fanglomerate conglomerate Shale and sandstone of 

Brunswick F~rmation 

Hard shale, sandstone, argillite, 

flagstone of lockatong Formation 

Arkose, sa·ndstol')e, and shale 

of Stockton Formation 

m w X a v 

v 

Watchung Basalt flows Granite rocks of the basement 

C/) 

UJ 

0:: 

1-

UJ 

~ 

z 

:I: 

1-

a.. 

1.&.1 

c 

FIGURE 3.-Stratigraphic columns for the Triassic rocks in the Newark basin in New Jersey based on the thickness data of 

Kiimmel ( 1898) and Van Houten ( 1969). 
REVIEW AND INTERPRETATION OF GEOLOGIC SETTING All 

the less ·resistant ·beds. Van Houten (1969) has 

evaluated all the lithologic data, correlated it, and 

drawn a schematic block diagram to portray his 

views of the stratigraphy of the Newark basin. 

'The stratigraphic section of the upper part of the 

Brunswick Formation of the Triassic System which 

contains the three Watchung Basalt flows is of particular importance to this discussion and is given 

in table 1; it is also shown in a geologic cross section (fig. 4). On the basis of the mapping that has 

been completed so far in this study, each of the 

three Watchung Basalt flows is shown to be made 

TABLE !.-Stratigraphic sections of the upper part of the Brunswick Formation of the Triassic System in the Newark basin 

of New Jersey 

1:: 

0 

:0 

tiS 

~ 

KUmmel (1897, 1898) 

Alternations of shale, sandstones, and 

fanglomerates (conglomera-te) chie·fly 

along the northwestern wall. 

Third Watchung Basalt 

~ Alternations of shale, sandstones, and ..!1:: fanglomerates (conglomerates). 

·~ 1:: 

e 

I=Q 

1:: 

.9 

~ 

tiS 

E 

Second Watchung Basalt 

Alternation of shale, sandstones, and 

fanglomerates (conglomerates). 

First Watchung Basalt 

~ Alternations of shale, sandstones, and ~ fanglomerate (conglomerates). 

·~ 

~ I=Q 

Picard and High (1963) 

Alternations of "less resistant layer 

rock" of mudstones and poorly sorted 

sHtstones and of more resistant layer 

rock of sandstones. 

Upper flow unit 

Lower flow unit 

Alternations of "less resistant layer rock" 

of mudstones and poorly sorted siltstones and of more resistant layer 

rock of sandstones. 

Upper flow unit 

6ft (2m) of sedimentary rock in north area~ 

Lower flow unit 

Alternations of "less resistant layer 

rock" of mudstones and poorly sorted 

siltstones and of more resistant layer 

rock of sandstones. 

Upper flow unit 

A thin layer of reddish argillaceous siltstone a 

Lower flow unit 

Alternations of "less resistant layer rock" 

of mudstones and poorly sorted siltstones and of more resistant layer 

rock of sandstones. 

11 A provisional estimate of 300 feet is based on field studies and we11-log data (Faust, unpub. data). II This report, p. A18. 3 Bucher In Bucher and Kerr (1948, see p. 110). 

Probable 

thickness 

in feet (m) 

3001 (91) 

300 (91) 

1,500 (457) 

750 (229) 

600 (183) 

600 (183) 

Noteworthy 

occurrences of 

fanglomerates 

Fanglomera tes 

(Kiimmel, 

1897, 1898; 

this report, 

p. A13.) 

Conglomerate at 

Pompton Lakes 

(Kiimmel, 

1898, p. 50; 

this report, 

p. A13.) 

Fanglomerate at 

Oakland 

(this report, 

p. A13.) 

Conglomerate 

Fanglomerate 

in a wall near Paterson 

(Darton, 1890, 

p. 17.) 
1000' 

(305) 

SEA LEVEL 

-1000' 

(-305) 

QO 

c: 

:Jc: 

~.- Ut~~ ........ 

Ill c: 3:::~ 

-co 

... :::!: 

:c 

I 

"" 0 

e 

al 

5000 

(1524) 

10,000 

(3049) 

EXPLANATION 

~-d 

~ 

Shale and sandstone of the 

Brunswick Formation 

Watchung 

~ 

~ 

Basalt 

lava flows 

c: 

~ c: 

:J 

0 

:::!: 

QO 

c: 

:J 

~ 

~ m 

3: 

30,000 

(9146) 

QO 

c: 

:J c: ~ ·- ~!! Ill c: :;:::~ 

0 

~:::!: 

Li: 

I 

Q) 

QO 

c: 

Ill 

0 

35,000 

(10,671) 

Note: The fanglomerates (conglomerates) below the 

lava flows do not extend for any great distance into 

the basin and are close to the graben wall and are 

thus shown as partly underlying the flow as a series 

of four circles. 

1000' 

(305) 

SEA LEVEL 

-1000' 

(-305) 

-2000' 

(-610) 

FIGURE 4.-Generalized geologic cross section from west of Pine Brook on Third Watchung Mountain to an exposure just north of West Orange on First 

Watchung Mountain (compare with fig. 1). The topographic data and the thicknesses of the flows are taken from Darton and others (1908). Most of 

area is covered with glacial materials, but they generally form so thin a layer that they are not shown. 

> 

........ 

~ 

00 

~ 

0 

tj 

joooo4 

t:;r.j 

00 

0 

z 

~ 

!:I: 

t:;r.j 

~ 

> 

~ 

Q 

!:I: 

d 

z 

C) 

t::d 

> 00 

> tot 

~ 

l%j 

tot 

0 

~ 00 

0 

l%j 

z 

t:;r.j 

~ 

~ 

t:;r.j 

~ 

00 

t:;r.j 

~ 
REVIEW AND INTERPRETATION OF GEOLOGIC SETTING A13 

up of two flow units. This multiple character of the 

three Watchung Basalt flows proves that the three 

volcanic episodes producing them were multiple 

eruptive events. The presence of intertrappean layers of ·sedimentary materials in the Watchung 

Mountains had been suggested by Lewis (1907). In 

this ,field study no intertrappean layers were found 

in Third Mountain. Lewis (1907) had suggested that 

an intertrappean layer may occur in Second Mountain in the vicinity of Bound Brook. I did not find 

that the flows were separated by an inte~vening 

lBtyer, except in the northern part of Second Mountain near the Greenbrook, in North Caldwell, where 

a section of 6 feet ( ±) of sediments was measured. 

In First Mountain, in the Upper New Street quarry, 

Fenner (1908) noted intertrappean materials between the upper and lower flow units. This was 

described as a thin siltstone layer by Bucher (in 

Bucher and ·Kerr, 1948) and he gave a detailed 

section. 

Although fanglomerate and conglo~erate beds 

were generally not tied down to particular stratigraphic sections by previous workers their position 

with respect to the three Watchung Basalt flows in 

a few areas is noteworthy, and these are shown in 

table 1, at the top of the column; just underneath 

the Third Watchung Basalt; and just underneath 

First Watchung Basalt. During the mapping of the 

northernmost part of Second Mountain, in July 

1973, a thick fanglomerate bed was found at Oakland, N.J. The contact between this bed and the overlying hornfels zone was covered, but it is probably 

within 50 feet or less. Darton's (1890) observations 

on the fanglomerates below the flows (he called 

them conglomerates) are the most complete. He 

noted (p. 17) "that these conglomerate beds were 

exposed south of Paterson in front of Great Notch, 

and in considerable force several miles north along 

Goffie creek, west of van Winkle's station***" and 

further "The conglomerates are separated from the 

base of the First Watchung Mountain by an inconsidera-ble thickness of sandstones and shales,· and 

are. succeeded eastward by fine grained materials 

which dip gently westward towards the coarser beds. 

At Paterson, a short distance east2 of the conglomeratic outcrop in the gorge of the Passaic, a well 

was bored 2,100 feet through fine grained sandstones 

and shales***." 

The significance of the fanglomerates as marking 

"the intermittent re-growth of mountains whose 

perennial waste kept supplying material for the deposits of the basin" was mentioned by Barrell (1915, 

2 Italics G. T. F. 

p. 29). He further noted that "It is necessary to 

postulate a boundary consisting of a fault wall in 

order that renewed movements upon it may maintain such a long continued supply of coarse, yet 

local waste." 

In the present study we are interested in the relations of the fanglomerates to the lava flows. From 

Darton's (1890) observations that an inconsiderable 

layer of sandstone and shale separates the conglomerate from the base of the flow, we may conclude 

that the volcanic episode forming the lavas of First 

Watchung Mountain took place shortly after the 

faulting along the boundary wall occurred. Similarly 

a fanglomerate bed occurs about 50 ft (15 m) ( ±) 

below the lower flow unit of Second Watchung Mountain. Fanglomerate ·beds occur just under the base 

of the flow forming Third Watchung Mountain. All 

these stratigraphic observations attest to the relation 

that faulting along the boundary wall was followed 

by the formation of a fanglomerate and that shortly 

thereafter the lava poured out. These relations of 

the fanglomerates to the flows show clearly that the 

periods of faulting along the graben walls were 

unrelated to the volcanism (Faust, unpu1

b. data). 

Finally, there exists a dilem·ma over the thickness 

of the Newark Group. Cook (1868, p. 174) originally 

calculated the thickness to be 27,000 feet ( 8,230 ·m) ; 

·but then, because he suspected that hidden faults 

might be present to increase the true thickness, he 

arbitrarily cut the thickness down to 15,000 feet 

( 4,570 m). Cook (1882, p. 12) writes: "A very few 

faults have been found but they are only a few feet 

in extent. ***Taking these data for a !basis of calculation it would make a formation not less than 25,000 

feet (7,620 m) in thickness." Russell (1878) reexamined the problem and calculated 25~000 feet 

(7,620 m) with the reservation that significant hidden faults were not present. Kiimmel (1898) after 

intensive field study calculated the thickness of the 

>Stockton Formation ( 'Rs) to be 4,700 feet (1,433 

m), of the Lockatong For·mation ( lil) to be 3,600 

feet (1,097 m), and of the Brunswick Formation 

( lib) to be 12,000 feet (3,658 m), giving a total 

thickness for the Newark Group of 20,300 feet 

(6,187 m). In 1897, Kiimmel examined two faults 

in the ,basalt of First Watchung Mountain with 

throws of 75 (22.9) and 8 feet (2.4 m) respectively, 

and aware of ·Cook's (1868) earlier suspicion of 

hidden faults, undiscovered in field studies, he reduced his previous estimate to two revised estimates. 

The first attril;mted the Stockton to have a thickness 

of 2,300 feet (701 m), the Lockatong of 3,500 feet 

(1,067 m), and the Brunswick of 6,000 feet (1,829, 
A14 STUDIES ON THE WATCHUNG BASALT FLOWS OF NEW JERSEY 

m), making a total thickness of 11,800 feet (3,597 

m) .. The second estimate made the Stockton 3,100 

feet (945 m), the Lockatong 3,600 feet (1,097 m), 

and the Brunswick 8,000 feet (2,438 m), with a 

total thickness of 14,700 feet (4,481 m). Johnson 

and McLaughlin (1957) reported the exposed Triassic section along the Delaware River to have a 

thickness of 12,000 feet (3,658 m). Sanders (1963) 

restudied the Triassic of the northeastern United 

States, and for New Jersey he calculated a thickness 

of 30,000 feet (9,144 m). Van Houten (1969) arrived at estimates of 16,000 to 20,000 feet (4,877-

6,096 m) after a detailed study of the Lockatong 

Formation and its relation to the Stockton and 

Brunswick Formations. 

The evidence of the recent studies cited above may 

resolve the dilemma, because it supports the greater 

thic-kness calculated by early workers. The oft cited 

hidden faults have not been found and the lower estimates based on this assumption of their existence 

are not supported by field evidence in that part of 

the Newark basin containing the Watchung flows 

and the Palisade sill. Two thicknesses, of 25,000 and 

11,800 feet (7,620 and 3,597 m) respectively, for the 

Newark Group sediments are used here in the calculations because of the uncertainty as to the true 

thickness of the group. 

TIMING OF FISSURE ERUPTIONS OF THE UPPER 

TRIASSIC IN NEW JERSEY 

The timing of the fissure eruptions in the Newark 

Group may be estimated on the basis of some recent 

summaries of the paleontological evidence by Johnson and McLaughlin (1957) and Widmer (1964); 

their studies indicate that the Newark Group is Late 

Triassic in age. Widmer (1964, p. 63) argued that 

because the Triassic Period was 45 million years 

long and the Newark Group was deposited in less 

than one-third of that time that the deposition took 

place in a time span of at lea:st 10 m.y. (See also 

footnote p. A9.) 

Using Widmer's esti·mate of the time span of 

deposition, the thickness of the strata above and 

below the flows ·as given by Darton and others 

(1908), a provisional estimate, by Faust, of 300 feet 

(91 ·m) of s:edi.ments above Third Watchung flow, 

and assuming a total thickness of the Newark Group 

of 11,800 feet (3,597 m), then it may be calculated 

that at least 80 (79.7) percent of the sediments were 

deposited before the First Watchung flow appeared. 

If the greater thickness of 25,000 feet (7,620 m) is 

assigned to the Newark Group, then ~t least 90 percent of the total thickness of the sediments was 

deposited before the flows appeared. These calculations suggest that the outpouring of the lava from 

the fissures started at 21;2 or 1 m.y. before the close 

of the Triassic Period. 

It is thus apparent that the deep fissures from 

which the lavas were erupted were developed very 

late in the Late Triassic Epoch. Sanders (1963) 

believes that they were associated with the initial 

episode of graben subsidence. 

Using an average figure of 600 feet of sediments 

between First Mountain flow and Second Mountain 

flow and a total thic-kness of 11,800 and 25,000 feet 

(3,597 and 7,620 m), a corresponding time interval 

of aibout 600,000 or 240,000 years elapsed between 

these outpourings of the lavas. The thickness of sediments between the Second. and Third Watchung 

flows is approximately 1,500 feet ( 457 m), and this 

value yields a corresponding time interval o{ 11;2 

million or 600,000 years between the flows. These 

estimates are summarized in figure 5. The calculated 

time intervals support the belief that fissuring in 

the graben was intermittent. 

These calculations assume that the overall rate 

of deposition of the sediments was, on the average, 

relatively constant. This assum.ption implies a more 

or less uniform rate of supply of sediments and 

some form of tectonism that will periodically downfault the basin with respect to the source area. 

Krynine (1950, p. 186) pointed out that "The different lithologic types of the Connecticut Triassic are 

due to variations of one fundamental sedimentary 

process: rapid erosion and deposition under savanna 

climate" and that this geologic setting assured an 

abundant supply of sediments at an almost· periodic 

rate of supply. The almost periodic reappearance of 

the fanglomerates along the fault walls is suggestive 

of at least some periodicity to the character of the 

sedimentation between successive periods of faulting. The principal assumption is open to criticism 

by some stratigraphers. Rayner (1967, p. 14-15) has 

discussed the use of rates of sedimentation for the 

rocks in the British Isles and o'bserves that "Rates 

of sedimentation are very elusive, however, and they 

can only be deduced at all reliably either on a very 

small scale or a very large one." 

Sollas (1905), on the other hand, used average 

rates of deposition as a ·method to dispute the calculations of Lord Kelvin on the age of the earth, a 

good example of the use of the assumption on a 

tremendous time scale. Broadhurst and Loring 

(1970) studied rates of sedimentation in the Upper 

Cal"lboniferous rocks of Great Britain, and they emphasize two aspects in the concept of rates of sedimentation, an overall rate and a specific rate. They 
REVIEW AND INTERPRETATION OF GEOLOGIC SETTING A15 

en 10 D:: 

~ >-

u. 

0 

C/) 

z 

0 

::::; 

...J 9 

~ 

~ CJ) 

D:: 

UJ 

.., 

~ UJ 

z 8 

z 

0 

D:: 

0 

(.) 

UJ 

D:: 

(.) 

u; 7 (/) 

< 

0: 

1-

UJ 2 ~ 

1-

u. 

0 

z 

< Q.. 

C/) 

UJ 

~ 1 

i= 

0 

UJ 

1-

< 

~ 

i= 

CJ) 

UJ 

-

-

-

rBased on 11,800 feet (3597 m) of 

Triassic sedimentary rocks 

__ .;...._ __ End of Triassic record 

9.6 Third Mountain basalt 

8.1 Second Mountain basalt 

7. 5. First Mountain basalt 

Onset of Newark Group deposition 

Based on 25,000 feet (7620 m) of 

Triassic sedimentary rocks 

r----- End of Triassic record - _9_._8_ Third Mountain basalt 

I 

9.2 Second Mountain basalt 

9.0_ First Mountain basalt -

-

-

Onset of Newark Group deposition 

o~----~------~------------------------------~--------~----------------~---------------

FIGURE 5.-Es~imated sequence in time of the extrusion of the Watchung Basalt flows of New Jersey. The calculations are 

based on the two estimates of the thickness of the Triassic sections of 11,800 and 25,000 feet (3,597 and 7,620 m), respectively. 

define (p. 1) these concepts as follows: "The overall 

rate of seditmentation is the mean rate of sedimentation during a given unit of time in which ·phases of 

sedimentation may be interspersed with periods of 

non-deposition or erosion (sedimentation remaining 

dominant). The specific rate of sedimentation is the 

rate of sedimentation at any one moment of time." 

The speeific rate is very difficult or well nigh impossi-ble to determine in most studies. The overall rate 

of sedimentation is the concept used in these calculations. 

VanHouten (1969) has recently evaluated, on the 

basis of stratigraphic and other measurements in 

sections exposed along the Delaware River in New 

Jersey and Pennsylvania, the rate of initial deposition of the Stockton, Lockatong, and Brunswick 

Formations. The thicknesses are 6,000, 3,772, and 

6,232 feet (1,830, 1,150, and 1,900 m), respectively, 
.A16 STUDIES ON THE WATCHUNG BASALT FLOWS OF NEW JERSEY 

with a total thickness of 16,006 feet ( 4,879 m). The 

fastest rate of initial deposition is 600 mm/1,000 

years ( = 1.97 ft/1,000 yr) for the Stockton, the 

slowest is 215 mm/1,000 years ( = 0.705 ft/1,000 yr) 

for the Lockatong, and the rate for the Brunswick 

Formation is inte:rnnediate, 305 + mm/1,000 years 

(1 .ft/1,000 yr). He also computed the uniform rate 

of basin sinking to be aibout 215 mm/1,000 years 

( =0.705 ft/1,000 yr) during the entire Newark 

time, which is the same as the rate of deposition for 

the Lockatong Formation. From these data he estimates the total Newark episode to have been 22.75 

m.y. in duration. Van Houten ( 1969) also considers 

several other possible interpretations of the data 

and arrives at an estimate for the minimum of 14.75 

m.y. and maximum of 22.75 m.y. for the duration of 

the Newark episode and for a minimum of 215 mm/ 

1,000 years and maximum of 325 mm/1,000 years 

for the average rate of basin sinking and sediment 

accumulation. 

If we use these data of Van Houten (1969) and 

calculate as ;before, we arrive at the following values 

for 16,000 feet ( 4,877 m) total thickness-85 percent of the sed1ments were deposited before the First 

Mountain flow appeared; 3.75 percent of the sediments were deposited after First Mountain flow 

s_olidified and before Second Mountain flow appeared, 

9.375 percent of sediments were deposited· after 

Second Mountain flow solidified ·and before Third 

Mountain flow appeared; 1.875 percent of the sediments were deposited after Third Mountain flow 

solidified. Using the lower time duration of 14.75 

m.y., this yields 12.54 m.y. ibefore the First Watchung flow appeared, 0.55 m.y. between First Watchung flow and Second Watchung flow·, 1.38 m.y. 

between Second Watchung flow and Third Watchung 

flow, and 0.28 ·m.y. before the close of Triassic deposition. If the longer time span of 22.75 m.y. is used, 

the figures ibeconie 19.34 m.y., 0.85 m.y., 2.13 m.y. 

and 0.43 m.y. respectively (fig. 6). The time intervals between the appearance of First and Second 

Watchung flows and between Second and Third 

Watchung flows as calculated from Van Houten's 

(1969) time interval of 14.75 ·m.y. are closely similar 

to those just calculated for a section of 11,800 feet 

(3,597 m) of sediments. 

GEOLOGIC AGE OF THE IGNEOUS ACTIVITY 

·The earliest work on the dating of the igneous 

activity during the Triassic in eastern North 

America is that of Urry (1936). Urry used the 

"helium method"· for age determination and dated a 

specimen of basalt taken from the base of the First 

Watchung Mountain flow in a quarry on Valley 

Road, a quarter of a mile north of Notch Road, 

Great Notch, Clifton, N.J., to be 180±11 million 

years old. He also dated three diabase specimens 

taken from the Palisade intrusion at ·Kings Bluff," 

Weehawken, N.J., at a distance of 5 to 10 inches 

(13-25 em) above the basal contact with the Trias-

-sic sediments; 40 inches (1 m) above the basal contact; and 40 feet (12m) above the basal contact to 

•be 155±8, 165±9, and 165±8, m.y. old. For the 

diabases of the Connecticut Valley he found that 

two specimens of the West Rock sill in a quarry at 

N·ew Haven, Conn., ·gave ages of 170 ± 12 m.y. -and a 

dike in the same quarry had an age of 175±9 m.y. A 

drill-core specimen of basalt from 464 feet (141 m) 

below the surface of the Cape Spencer Flow, Nova 

Scotia, Canada, yielded an age of 160 ± 8 m.y. The 

"helium method" is very sensitive to the loss of 

helium by the host, and as a result it tends to give 

ages which are younger than they should be. 

Erickson and Kulp (1961), using the K-Ar 

method, dated a specimen of columnar basalt .from 

First Watchung Mountain and found the "apparent 

age" to be 79 m.y. For the Palisade Dia:base sill, they 

dated biotite separated .from the upper fine zone of 

the sill and found an average age of 190±5 m.y. 

They attributed the low value for the age of the 

Watchung Basalt to the poor retentivity of the argon 

by the -basalt. Armstrong and ·Besancon (1970) have 

reexamined the problem of dating Triassic mafic 

igneous rocks, and they ·analyzed .by the K-Ar 

method the same sample of biotite from the Palisade 

Diabase studied. by Erickson and Kulp (1961). They 

found an age of 192 m.y. as against the values of 

190 and 196 m.y. measured by Erickson and Kulp 

(1961). The results agree within 1 percent of the 

Lamont-Doherty date. As a result of their study of 

the Upper Triassic Newark Group, however, they 

conclude "The dates for the Palisades diabase, 

although reproducible and internally consistent, are 

all suspect." 

The most recent evaluation of the age data of the 

Triassic igneous rocks of New Jersey 'is that of 

Lambert (1971). He gives (.p. 18) the ·K-Ar dating 

of the biotite from the Palisade sill as a "critical 

point" on the Phanerozoic time-scale with the values 

of 186±5, and 194±5 m.y. and he observed (p. 29) 

that "In any case the stratigraphical assignment 

contains an element of uncertainty, that is, the correlation of the sill with the Watchung basalt." 

The paleomagnetic study of de Boer (1968) in 

which he correlates the three Watchung flows of 

First, Second, and Third Mountains with the Holy-
REVIEW AND INTERPRETATION OF GEOLOGIC SETTING A17 

Based on 16,000 feet (4878 m) Based on 16,000 feet (4878 m) 

of Triassic sedimentary rock of Triassic sedimentary rock 

c;leposited during a time span of deposited during a time span of 

14.75 m.y. (Van Houten, 1969) 22.75 m.y. (Van Houten, 1969) 

23 ~ - ---.....,--- 22.75 m.y. End of Triassic record 

22 f- . ' r 22.3 m.y. Third Mountain basalt -

<n 21 f- - 0:: 

~ 20 > 20.2 m.y. Second Mountain basalt ~ - u.. 

0 19 

19.3 m.y: First Mountain basalt 

~ - (/) 

z 

0 18 

:J ~ - ...J 

! 17 ~ -

~ 16 (/) ~ - 0:: 

w 

.., 15 

~ 

~ 14.75 m.y. End of Triassic record - ------ 14.5 m.y. Third Mountain basalt 

z 14 ~ - ~ 

0 13 - 13.1 m.y. Second Mountain basalt - 0:: 

0 

() 12 

12.5 m.y. First Mountain basalt 

- - w 

0:: 

() 11 ...- - ~ < 10 ~ - ii: 

1-

w 9 ~ - :I: 

1-

u.. 8 f- - 0 

z 7 

< - - a.. 

(/) 

6 w - - ~ 

i= 5 - - 0 

w 

~ 4 - - ~ 

i= 3 (/) - - w 

2 - -

..._ - Onset of Newark Group deposition Onset of Newark Group deposition 

0 

FIGURE 6.-Estimated sequence in time of the extrusion of the Watchung Basalt flows of New Jersey. 

oke Basalt flow of Massachusetts is difficult to reconcile with the stratigraphy. This correlation means 

that the extrusion of the Holyoke Basalt flow, 300 to 

600 feet (91-183 m) thick in Connecticut and 575 

feet (175 m) thick in Massachusetts could have 

occupied as ·much time as the following events in 

New Jersey: 

1. Outpouring of approximately 600 feet (183 m) 

of lava to form the First Watchung flow. 

2. Deposition of approximately 600 feet (183 m) 

of sediments. 

3. Outpouring of approximately 750 feet (229 m) 

of lava to form the Second Watchung flow. 

4. Deposition of approximately 1,500 feet ( 457 m) 

of sediments. 

5. Outpouring of approximately 300 feet (91 m) 

of lava to form the Third Watchung flow. 

This time interval in New Jersey spanned at least 

1 to 3 m.y. Such a correlation would 3Uggest that all 

during this time the area of the Holyoke sheet was 

high land and that there were multiple extrusions to 

form the sheet. Evidence for such a high land in 
A18 STUDIES ON THE WATCHUNG BASALT FLOWS OF NEW JERSEY 

Connecticut would .be extensive erosion within this 

compound sheet or at its upper surface. Van Houten 

(1969, p. 317) voices similar objections to de Boer's 

(1968) interpretation. 

REGIONAL STRATIGRAPHIC RELATIONS 

A comparison of some time intervals between Triassic events in New Jersey and in Connecticut is 

given here -because of its relevance to the problem 

of assessing the state of stress in the graben. The 

rate of relative depression of the graben bloc•ks during Triassic time cannot be accurately calculated. If 

it is a-ssumed that the relative downward movement 

was uniformly continuous, the rate of depression for 

a section of 10,000 feet (3,048 m) of sediments in 

10 m.y. would be approximately a foot ( 0.3 m) of 

depression in a thousand years. For a section 25;000 

feet (7,620 m) thick, it would be a foot (0.3 m) in 

400 years. Van Houten (1969) calculated a value of 

0.7 foot (0.2 m) per 1,000 years based on the duration of Late Triassic time of 15 m.y. and a-ssuming 

a uniform rate of ·basin sinking. The repetition in the 

geological record of fanglomerates (conglomerates) 

at the graben walls against the horst, however, suggests that the relative depression was discontinuous-neither uniform nor a succession of a few 

major movements--but rather spasmodic in response to the unbalance produced by the weathering 

of the horst and the removal and distribution of the 

detritus into the 1bas.in. Such relations between time 

and events .may be descri1bed ·as "almost periodic." 

The best exposed and studied sections of fanglomerates and conglomerates are those in southern 

Connecticut measured and described 'by Russell 

(1922) and Krynine (19·50). Russell (1922) found 

that the fanglomerates had a maximum thickness of 

200 to 300 feet (61-91 ·m) and that they never extend~d more than a·bout half a mile from the fault 

plane. He further observed ( p. 487) the position of 

the fanglomerates with respect to the lava flows to 

be as follows: "The fanglomerate is found below the 

lower ·basalt flow, immediately below the main sheet, 

below the upper ·basalt flow, and above all the flows.'' 3 

If we interpret the appearance of a fanglomerate 

along the fault wall to mark the early stage of the 

weathering cycle in the topographically higher 

granitic horst blocks, then we can equate the number of fanglomerates observed in sections with the 

number of episodes of faulting; for the reappearance 

of fanglomerates means the end of a former period 

of faulting. From the section given by Russell 

3 Italics by G. T. F. 

(1922), we can thus recognize four periods of intermittent faulting bounding the three lava flows. Combining the observations of Russell (1922) with the 

stratigraphic section of the Newark Group in Connecticut as given by Krynine (1950), in figure 7, we 

can observe that the lower ba-salt flow erupted 

shortly after a fanglomerate appeared; there then 

followed a deposition of nearly 1,000 feet (305 m) 

of sediments, and near the end at the top of the 

section a fanglomerate a·ppeared; this event was 

followed by the outpouring of the thick main sheet 

Gl 

c: Aol<ose (med;um to coa<Se) } Q) o ... N c:.,. Ill 

0 ... tic: Subordinate conglomerate 2000±(610±) Gl Ill G 

< 

t 1~.1:1111 «<G Red shale ~ >.~. '0 

c: 

«< ~~~ Arkose (fine ancJ medium) ·'E 0 G.,. N C: ::J } 2000±(610±) ~ ~ .,.~:~ Siltstone ~(!) Fanglomerate 0 

...j Dark shale near base 

Upper basalt flow 50-150(15-46) 

Red shale 100±(30±) Fanglomerate 

~ } .... !! c: Dark shale, arkose, and 

~i-~ 375 ±(114±) conglomerate lenses c: o.e .> O· ~--·- .. '0'0 Siltstone and shale 200±(61±) «< Q) 

E Ill 

~ Arkose and shale 400±(122±) 

c: 

Q) Main sheet of basalt 300-500(91-152) '0 Cl. ·;: ~ Arkose with shaly lenses 600-800 Fanglomerate ::::::> Q) (183.:.244) 0~ ;t2 Dark shale 75 (23) a:: 

(!) ~ ~-~ Limestone 15 (4.6) ...j·-·- :lll:: -o"O a:: Q) Arkose 0-100 (0-30) < Ill 

~ "-! 

z Lower basalt flow 100-250(30-76_1 

Fanglomerate 

Arkose with numerous conglomerate 4000-5000 c: lenses forming two main horizons (1220-1524) 0 

'iii near the top and near the base. 

Q) "> Krynine states (p. 33) " ... the Ill :0 0 .... fanglomerates ... are observed ... .II: 

< Q) 

0. immediately below the lower lava 0. sheet ... in the New Haven Arkose" c: ::::::> Q) 

> 

ftl 

J: 

~ Q) 

z 

c: 

0 Arkose with conglomerate, 2000-3000 (610-915) 'iii 

"> sandstone. and shale 

:0 

... 

Q) Basal conglomerate and 200-300 (61-91) ~ 

0 conglomeratic arkose ...j 

FIGURE 7.-Generalized stratigraphic section of the Triassic 

of southern Connecticut as given by Krynine (1950) together with the position of the fanglomerates as given by 

Russell (1922). Probable thicknesses given in feet (metres). 
REVIEW AND INTERPRETATION OF GEOLOGIC SETTING A19 

of basalt and on it were deposited nearly 1,100 feet 

(335 m) of sediments with fanglomerates near the 

top; thereafter the upper basalt flow appeared, and 

this was followed 1by the deposition of about 2,000 

feet (610 ·m) of the lower zone of the Portland 

Arkose, which contained at least one fanglomerate 

a'bove the lava flow. It is thus apparent that the 

lavas did not appear at the time a given period of 

faulting ended but only after the time interval necessary to allow the disintegration, weathering, and 

transportation of part of the granite rocks of the 

horst to form a fanglomerate at the graben wall. If 

we assume, for ·purposes of estimation, that the 

values calculated for the rate of deposition in the 

Newark basin of 1 foot (0.3 m) of sediment accumulating in a thousand years for the section 10,000 

feet (3,048 m) thick and 1 foot (0.3 m) in 400 

years for a section 25,000 feet (7,620 m) thick, this 

would indicate that approximately a million years 

or alternately 400,000 years elapsed between the 

eruptions of the lower basalt flow and the main 

sheet of basalt and similarly a:bout 1.1 m.y. or alternately 440,000 years ~lapsed between the main sheet 

of basalt and before the upper basalt flow was 

erupted. These time-interval values are of the same 

order of magnitude as those for the stratigraphic 

section in New Jersey, where the corresponding 

values are 600,000 or 240,000 between First and 

Second Watchung, and 1.5 m.y. or 600,000 years 

between Second and Third Watchung. The good 

corres·pondence between the times elapsed between 

eruptive events in New Jersey and Connecticut casts 

doUibts on the paleomagnetic correlations of de Boer 

(1968). 

The Pomperaug valley near South·bury, Conn., is a 

small downfaulted part of the former Triassic section. It is isolated from the principal outcrop area 

of the Triassic in Connecticut and is 15 miles (24 

km) west of it. The area has 'been described by 

Hobbs (1901) and Wheeler (1937). It contains the 

lower part of the section and includes two of the 

lava flows. Hobbs (1901) mapped the South Britain 

Conglomerate, which underlies one of these lava 

flows. It is thus evident from field relations in New 

Jersey, Connecticut, and Massachusetts that the 

stratigraphic position of the fanglomerates (conglomerates) below the lava flows is significantly consistent. This observation suggests that the extrusions of lava did not coincide with the period of 

faulting ·but rather were later than these tectonic 

events .. 

An estimate of the time between successive downfaultings along the wall of the fault system is also 

suggested by these calculations involving the eruptive events. They suggest that the time interval 

between the fanglomerates, for the upper part of 

the Triassic section in southern Connecticut, was of 

the order of half a million years and that an episode 

of faulting likewise was regenerated on the order of 

half a million years with the production of an 

fuplifted' horst block. 

Evidence for this short duration of the periods 

between faulting is also supplied in a study of the 

sediments which was made by Krynine (1950, p. 

186), who concluded from his research on the Connecticut Triassic that the different lithologic types 

of rocks "are due to variations of one fundamental 

sedimentary process : a rapid erosion and deposition 

under a savanna climate." As an index of the rapidity of erosion, transportation, and deposition, Krynine observed that the feldspa·rs are quite stable. He 

further observed that the mafic minerals decomposed 

to form iron oxides and not a montmorillonitic type 

of clay. Concerning the feldspars he states that they 

are generally fresh, but that all degrees of weathering and decomposition are present and that most of 

the alteration is primary-some is postdepositional. 

The feldspars make up on the average 30 percent 

of the Triassic sediments of Connecticut, and the 

fragments are generally angular or subangular in 

shape. This persistence of the feldspars is significant 

as an index of the shortness of the time span that 

these grains could have been exposed to weathering. 

Correns and Von Engelhardt ( 1938) have shown 

that feldspars are relatively easily attacked under 

weathering conditions at pH values in the range of 

3-11 and that at the higher· temperatures corresponding to tropical conditions the feldspars are 

dissolved in solutions that are even in the neutral 

range of 6-7 pH units. Although it is not possible 

at present to quantitatively correlate persistence of 

the feldspars in sediments with their chemical resistance in a geologic environment, their presence 

in large amounts in a relatively stable state does 

support the opinion that the products of weathering 

did not remain for great lengths of time on their 

source rocks. The oft-repeated appearance of large 

quantities of feldspar grains throughout the stratigraphic section attests to their renewed production 

from freshly weathered granitic rocks. Such fresh 

rocks would ·be made available by the postulated 

intermittent, that is, nonuniform and not quite 

periodic movements along the fault walls during the 

process of sedimentation. 
A20 STUDIES· ON THE WATCHUNG BASALT FLOWS OF NEW JERSEY 

THE NATURE AND PRODUCTS OF THE 

BASALTIC ERUPTIONS 

SITES OF THE FISSURES 

The sites of the fissures from which the lavas 

flowed into the Triassic basin have not been located. 

No evidence for their existence, such as lava filled 

feeder dikes, has been found in the underlying Triassic sediments well exposed in outcrop to the southeast. The possibility that they exist here and are 

covered by soil must be considered. The observed 

greater strubility of the basalt over that of the sediments in the Watchungs proper would suggest that 

the dikes should form topographic "highs." No trace 

of such di·kes has 'been observed in th~ sediments of 

the valleys between the flows. The supposed stability 

of the trap dikes has been questioned by Russeii 

(1892, p. 106), who noted that under the climatic 

conditions obtaining in Virginia and North Carolina 

the dikes were frequently deeply decayed, sometimes 

to depths of 50 feet (15 m), and that they did not 

form ridges nor . otherwise manifest their presence 

in the topography. 

Intrusive dikes have been found in the vicinity of 

the Palisade Diabase sill and have been described 

by Darton (1890), Kiim·mel (1898), and Lewis 

(1907, 1908). They all agree that these dikes are 

extensions from the sill itself. 

The difficulty of finding concealed fissures under 

the flows has been emphasized by Geikie (1882) and 

Tyrrell (1937). 'The chief difficulties are first the 

thickness of the flows themselves, which blanket the 

surface and conceal all that is below; and secondly, 

the low probability of finding a feeder dike, of the 

order of 5-feet (1.5 m) width, exposed by erosion 

or topographically expressed in a depression, or 

encountered in excavations or drillings. 

In the present investigation, a filled fissure, now 

a dike, has ,been found cutting through the basal part 

of the lowermost flow in First Watchung Mountain 

near West Orange, N.J., in the cut for U.S. Highway 

280. This fissure furnished lava to the still liquid 

part of the lowermost flow. Evidence for a probable 

dike was also observed at Moggy Holiow, at the 

southern part of Second Watchung Mountain. 

The diabase dikes which have been found in the 

crystalline rock along the border fault_ system have 

been suggested as possible feeder dikes. ·Unless, 

however, field evidence demonstrates an unequivocal 

relation between the flows and the supposed feeder 

dikes, the assignment of a Triassic age to these dikes 

is unwarranted. De Boer (1967) has studied dike 

swarms in the Appalachians using paleomagnetic 

methods and shows (p. 2237) "that most of the 

extensive dike swarms cutting Triassic and older 

formations probably intruded in a time of regional 

tectonic and magnetic activity. distinct from the late 

Triassic tectogenesis," and he suggests a Jurassic 

age for the dikes. King (1961, p. B95) has studied 

relations of these dikes and shows that (1) "most 

dikes locally have a common trend," ( 2) "that these 

local common trends vary systematically from one 

part of the Appalachian region to another," and (3) 

that "The trends of the dikes are everywhere discordant to the trends of the structures of the enclosing rocks, and they are everywhere straighter than 

these structures." May (1971) has studied the trends 

of these dikes in eastern North America, West 

Africa, and northeastern ·South A·merica and has 

drawn the trajectories of the principal stress indicated by the patterns of the dikes. He considers their 

age to be Late Triassic to Early Jurassic. The conclusion to be drawn from these studies of the diabase 

dikes is that they are unrelated to the principal Triassic volcanism. 

PREERUPTIVE CHARACTER OF THE GRABEN FLOOR 

The nature· of the sedimentary floor onto which 

the lavas flowed may be deduced from a study of the 

contact relations. ·The conformable nature of the 

bottom of the flows with the underlying sediments as 

seen in abundant outcrops on the scarp slope of 

Third and Second Mountains shows that the fissure 

eruptions took place-in open country, a fact deduced 

independently from stratigraphic studies of the nonmarine sediments that contain the flows. More recently Opdyke (1961) has demonstrated by studies 

of the natural remanent magnetization in both the 

sediments and the Watchung flows "that in the 

Newark Group sediments an inclination error of 

paleomagnetic signi,ficance is not present." In other 

words the sediments were horizontal, or nearly so, 

when the flows poured out over them. 

In general, along the scarp slope of Third Mountain the lowermost part of the lower flow unit overlying the Newark sedimentary rocks is heavily 

vesiculated for a distance of about 1 foot (0.3 m) 

a;bove the contact, and thereaJfter the vesiculation 

decreases rapidly as one ascends along the scarp 

slope. Locally, as at the quarry at Millington the 

vesiculation in the lower flow unit overlying the sediments is in a zone of about 20 feet (6 m), but the 

abundance of vesicles varies from the top to the 

bottom of the zone and is heaviest closer to the 

contact. The actual co~tact between the lower flow 

unit and the hornfelsized sedimentary rock is sharp. 
REVIEW AND INTERPRETATION OF GEOLOGIC SETTING A21 

The features recognizable in the contacts exposed 

on Third Mountain suggest that the flows poured 

out during a relatively dry season when the sediments were probably just barely moist or, in places, 

nearly dry. They further suggest that the flow o{ 

lava was la-minar and that there was a constant and 

continuous supply of hot fluid lava. 

The contact of the upper flow unit with the lower 

flow unit of the ~basalt in Third Mountain wherever 

it has been examined is always sharp and shows no 

evidence of intertrappean sediments. The base of 

the upper flow unit is generally vesicular for a short 

distance of several feet ( 1 m ± ) or so above the 

contact. At the quarry in Millington the pahoehoe 

surface of the top of the lower flow,· unit ,is: visible, 

and the total thickness of the vesicular zone consisting of the vesicular top of the lower flow unit and 

the vesicular base of the upper flow unit is possibly 

15 feet ( 4.6 m) with varying degrees of vesiculation. 

The contact relations between the vesicular base 

of the lower flow unit of Second Mountain and the 

sedimentary floor of the graben is variable. Over 

long stretches it is similar to that of Third Mountain, 

but at a number of places there is a slight development of pillows a-s in the cut for U.S. Highway 78 

near the village of PI uckemin. Elsewhere, near the 

tem-porary ends of a flow, or a former surge of lava, 

tongues of lava may form which have a resemblance 

in shape to toes. In some areas both pillows and toes 

may form suggesting that the lava was flowing over 

an area with braided drainage. The appearance of 

the pillows and toes suggests that the flow of lava 

may have ibeen temporarily halted and later resumed 

after overcoming a temporary obstacle. The contact 

between the upper flow unit and the lower flow unit 

is sharp, generally lightly vesicular, but in a few 

areas thin zones of pillows or pahoehoe toes are 

observed. I have observed the presence of an intertrappean layer of Brunswick sediments near the 

Greenbrook in North Caldwell. These Newark sediments are about 6 feet (1.8 m) thick. The lower 

contact of tlie upper flow unit here is vesicular for 

a distance of about 1 foot ( 0.3 m) or so. 

Only a small number of outcrops in First Mountain have I examined, but at Montclair, South 

Orange, and at several localities in Paterson and 

elsewhere the lower flow unit is thinly vesicular and 

rests on hornfelsized sediments. The contact between 

the base of the upper flow unit and the vesicula.te top 

of the lower flow unit is separated at several localities in the vicinity of Paterson by a thin intertrappean layer of argillaceous siltstone, as described 

by Bucher (in Bucher and Kerr, 1948). The base of 

the lava flow above this siltstone is composed of pillow lavas. Lewis (1915) measured thicknesses of 50 

to 75 feet (15-23 m) for the pillow zone at the Upper 

New Street quarry, and he further examined localities in the vicinity of Paterson. Fenner (1908) using 

the occurrence of pillows as indication of the former 

occurrence of a playa lake, mapped the extent of 

this lake which he called Lake Paterson. 

SURFACE CHARACTER OF THE VESICULAR TOPS 

When Ktimmel (1899) made his field studies on 

the Newark rocks, he had the opportunity to see 

many small "farmers quarries," which were opened 

for road metal, and many shallow roadcuts. The 

"farmers. quarries" wer.e commonly dug out of the 

upper vesicular zone O'f the upper flow units because 

it was the easiest rbasalt to quarry. The exposures 

gave Kum.mel (1899, p. 36) the chance to observe 

the pahoehoe tops of the flows and he describes them 

as follows: "Upper contacts have not rbeen observed 

in many cases, but the upper surface of these sheets 

is frequently vesicular, amygdaloidal, and scoriaceous. Locally, a thin layer of waterworn trap particles, intermixed with red ·mud occurs between the 

vesicular trap and the unaltered typical red shales, 

or the vesicles are filled with red mud. The overlying 

shales conform to the slightly irregular surface of 

the trap. In frequent exposures the rolling-flow 

structure named by the Hawaiian Islanders Pa-hoehoe, is visible. Nowhere have any tongues of lava 

been found extending from the main sheet into the 

neighboring shales." 

I have observed a few good contacts of the Newark 

sediments overlying the vesicular top of the flow, 

and these showed the pahoehoe surface and the conforming sediments just as Ktimmel ( 1899) described 

them. Such contacts can best be seen under red shale 

knolls. 

AREAL EXTENT AND VOLUME RELATIONS OF THE 

WATCHUNG BASALT FLOWS 

The areal extent and the volume relations of the 

Watchung Basalt flows are not generally appreciated. Outcrop areas and drilling operations for 

water supplies show the area to ibe at least 500 

square miles (1,295 km2 ). Using an average thickness of 600 feet ·(183 m) for First Mountain, this 

amounts to a volume of 56.8 cubic ·miles (237 km3 ) ; 

an average thickness of 750 feet (229m) for Second 

Mountain, this amounts to a volume of 71.0 cu:bic 

miles (296 kma) ; and an average thickness of 300 

feet (91 m) for Third Mountain, this amounts to 

a volume of 28.4 cubic miles (118 km3 ). The total 

volume for the three volcanic episodes is approxi-
A22 STUDIES ON THE WATCHUNG BASALT FLOWS OF NEW JERSEY 

mately 156 cubic miles (650 km3) as now delineated. 

According to Sanders' (1963) views on the former 

probable width of the graben in New Jersey, this 

volume may amount to only a vestige of their former 

volume. Sanders (1963) esUmates the width of the 

graben in New Jersey to be 50 to 70 miles ( 80.4-

112.6 km). Using a width of 50 miles (80.4 km) and 

assuming for purposes of calculation a length equal 

to the ·present eroded remnant of 40 miles ( 64.4 km), 

these values for the· three Watchung Mountains 

would become 227 cubic miles, 284 cubic miles, and 

114 cubic miles (946, 1,184, and 475 km3) respectively with a total volume of 625 cubic miles 

(2.6 x 103 km3 ). 

The igneous rocks of the eastern Triassic basin 

extend from Nova Scotia to South Carolina over a 

distance of about 1,200 miles (1,931 km). The areal 

extent and volume relations for the lava flows in the 

Triassic basins including Connecticut, Massach usetts, New Jersey, and Pennsylvania together with 

the extensive flows in Nova Scotia and the lesser 

volcanism in Maryland, Virginia, and the Carolinas 

suggests a rather considerable former areal spread 

and a volume of possibly .as much as 3 x 103 cubic. 

miles (1 x 10·1 km3 ). Their extrusion in the Late 

Triassic Period constituted a major geologic event 

in eastern North America. Compared to· the lava 

volumes of the fissure eruptions of the Deccan in 

India, the Columbia and Snake River areas in Western United States, the Brito-Arctic region (Thulean 

province) , and the Parana basin of Paraguay, 

Uruguay, and Brazil, the lava flows of the Newark 

basin were smaller. The volume of the Deccan flows 

is given by Subramanian and Sahasrabudhe (1964) 

as 1.24X105 to 25X105 cubic miles (5.18X105 to 

10.4 x 106 km3 ) ; for the Columbia River Plateau 

by Waters (in Shaw and Swanson, 1970) as 0.5X105 

cubic miles (2X 105 km3 ) and for the Lake Superior 

region by Walter .S. White (oral commun., 1973, 

conservative estimate) as 60,000 cubic miles 

(2.5 X 10n km3 ). 

GEOLOGIC PROCESSES RESPONSIBLE FOR THE 

JOINTING SYSTEMS 

Joint systems were developed in the Watchung 

Basalt as a result of stress fields set up by three geologic processes which acted upon the rocks of the 

graben. Cooling of the lava flows gave rise to the 

"cooling joints." The tectonic forces associated with 

the post-Triassic folding and the accompanying deformation of the graben produced the "tectonic 

joints." During the Pleistocene Epoch the northern 

part of the eroded remnant of the former graben was 

covered by a continental glacier which compressed 

the rocks 'beneath it; and, after the ice melted, the 

resulting decompression orf the basalts is thought to 

have .produced sheeting (Faust, unpub. data). 

PETROCHEMISTRY 

The Watchung Basalt flows and the Palisade 

Diabase intrusion were probably derived from the 

same magma chamber. Accordingly, the chemistry 

of the Watchung Basalt is of prime interest in discussing the course of 'differentiation in the Palisade 

Diabase sill, but surprisingly few analyses of the 

basalt exist.* Lewis ' ( 1908) used eight "superior" 

chemical analyses to interpret the chemistry of these 

rocks. Five of the analyses were for First Mountain 

and three for Third Mountain. He placed these 

samples in their approximate stratigraphic position-designated as lower, middle, and upper 

layers-in order to discuss their significance. The 

analyses of the rocks from First Mountain suggested 

that AbOa and (Fe20 3+Fe0) remained essentially 

constant throughout the thickness of the sheet and 

that Na 2 0 is at a minimum at the middle layer, 

whereas CaO is at a maximum. Silica increased only 

slowly towards the top of the sheet, and conversely 

MgO decreased toward the top. The rocks from 

Third Mountain showed some differences from those 

from First Mountain in that there was a noteworthy 

lower amount of 1Si02; that MgO, Al203, and CaO 

were also lower, but less so; and that (Fe20a + FeO) 

was noticeably higher. The Na20 and Ti02 were also 

higher in the rocks from Third Mountain. Lewis 

(1908, p. 161) suggested that "The striking differences again appear in the ·MgO, ·CaO, N a20 and K20, 

particularly in the higher CaO and the lower MgO 

and Na20 in the 'second layer'." 

The specimens from Third Mountain, that were 

analyzed, came from the quarry at ·Millington, N.J. 

When I examined this quarry in 1948 only the upper 

flow unit, as I characterize it, was exposed, so these 

analyses are from that flow unit. The specimen from 

O'Rourke's quarry, West Orange, N.J., comes from 

the base of the lower flow unit of First Mountain. 

Fenner (1931) made four analyses on two pillow 

lavas from the Upper New Street quarry (Burgers 

quarry) and the Lower New .Street quarry, in Paterson, N.J. He analyzed both the glassy-looking crusts 

and the finely crystalline basalt inside of the pillows 

and demonstrated that the glassy-looking crust is 

not the original glassy selvage and therefore that 

the analysis of this crust does not define the original 

I • Abstracts of papers on chemical studies have been published by Black and Piburn (1973) for the Watchungs and by Smith and Rose (1970) for the Pennsylvania occurrences. 
REVIEW AND INTERPRETATION OF GEOLOGIC SETTING A23 

lava chemistry. According to my interpretation these 

specimens came from the base of the upper flow unit 

of First Mountain. 

It was Washington ( 1922) however, who recognized the relation of the Watchung Basalt to the socalled Plateau Basalts, and he correctly related them 

petrogenetically to the rbasalts of the Thulean province, the Deccan, the Columbia River plateau, and 

elsewhere. He pointed out the chemical similarity of 

the flood tbasalts from fissure eruptions and attri~buted their fluidity to their notahle content of ferrous 

oxide. 

I am studying the chemistry of the major and 

minor elements of these lavas. An average of 36 

analyses ·I from the upper flow unit of Third Mountain at Millington, N.J., is given in table 2, column 1, 

together with the IC.I.P.W. norm. Analyses of Washington's average for the Watchungs, Lewis' (1908) 

average for Third Mountain at Millington, N.J., 

Nockolds' (1954) average for tholeiitic basalts, 

Daly's (1933) average for plateau basalts, Water's 

4 Unpub. data of George T. Faust, Laura Reicben, and Angelina C. 

Vlisidis. 

TABLE 2.-Average chemical analyses and C.I.P.W. normative data of Watchun-g Basalt from Third Mountain with other 

averages of tholeiitic rocks 

SiOu --------------- AlnO:~ -------------- Fe.JO:, -------------- FeO ---------------

]dgO -------------- CaO --------------- NauO --------------

KuO --------------- H~O+ -------------- HuO- --------------

TiOu --------------- PuOr. --------------- ]dnO -------------- SrO --------------- COu ---------------- Other --------------

~ '"' ---------------

Q -----------~----­ or ----------------- ab ----------------- an ----------------- di ----------------- hy ---------------- mt ----------------

il ------------------

ap ----------------- cc ----------------- ThorntonTuttle 

differentiation 

index ------------ Normative 

plagioclase ______ _ 

1 S, 0.06; VI!03, 0.05. 

49.40 

13.58 

5.08 

9.54 

5.65 

9.15 

2.96 

.51 

1.85 

.74 

1.30 

.17 

.24 

.08 

2.26 

3.01 

25.06 

22.25 

17.69 

16.98 

7.28 

2.48 

.40 

30.33 

Abr.:1.u 

An~•.o 

49.65 

13.51 

5.36 

9.39 

5.59 

10.25 

2.26 

.46 

1.13 

.96 

1.31 

.17 

.23 

5.16 

2.72 

19.13 

25.34 

20.02 

15.13 

7.71 

2.49 

.40 

27.01 

Ab.,a.o 

Anr.;.o 

49.52 

13.83 

5.12 

9.88 

5.66 

7.41 

3.40 

.77 

1.76} 

.. 68 

1.47 

.18 

.14 

.01 

99.83 

50.66 

14.28 

3.41 

8.58 

6.92 

8.60 

2.92 

.72 

2.28 

1.30 

.17 

.12 

C.I.P.W. Nonns 

0.99 

4.56 

28.73 

20.18 

12.62 

19.63 

7.43 

2.79 

.44 

34.28 

Ab''"·' 

An,u 

1.34 

4.23 

24.69 

23.64 

14.60 

21.18 

4.92 

2.46 

.40 

30.26 

50.52 

13.76 

3.87 

8.50 

5.42 

9.09 

2.42 

.96 

{ 1.51 

.76 

2.39. 

.26 

.16 

.58 

1.11 

100.31 

7.00 

5.68 

20.45 

23.86 

12.98 

15.93 

5.60 

4.54 

.60 

1.32 

33.13 

Ab11 •. :1 

An~.,.s 

50.83 

14.07 

2.88 

9.00 

6.34 

10.42 

2.23 

.82 

-~=~} 2.03 

.23 

.18 

3.76 

4.84 

18.87 

25.95 

19.83 

17.20 

4.17 

3.87 

.50 

27.47 

Ab,~.n 

Anr.".o 

48.80 

13.98 

3.59 

9.78 

6.70 

9.38 

2.59 

.69 

1.80 

2.19 

.33 

.17 

0.92 

4.06 

21.92 

24.48 

16.50 

20.20 

5.21 

4.16 

.77 

26.90 

A b. ... !! 

An .. ~." 

52.31 

14.38 

2.47 

9.95 

4.46 

8.37 

2.94 

1.26 

{ 

.74 

.39 

2.10 

.36 

.21 

4.47 

7.46 

24.85 

22.30 

14.05 

17.26 

3.59 

3.99 

.81 

36.78 

Abr.2.• 

An~;.a 

51.98 

14.48 

1.37 

8.92 

7.59 

10.33 

2.04 

.84 

.88 

.16 

1.21 

.14 

.16 

2.80 

4.73 

16.92 

28.23 

18.19 

23.60 

2.03 

2.28 

.24 

24.75 

Ah:r..r. 

An.12.r. 
A24 STUDIES ON THE WATCHUNG BASALT FLOWS OF NEW JERSEY 

(1955) average for the basalt of the Columbia River 

Group, and Holmes and Harwood's (1928) average 

analysis for the Whin sill are included in the table 

for purposes of comparison. 

A comparison of the average of 36 analyses of 

specimens from the Millington quarry analyzed for 

this study, column 1, t3!ble 2, with the average of 

three specimens from the sa,me quarry reported by 

Lewis (1908), column 3, table 2, shows reasonable 

agreement for Si02, Al203 , (~FeO+ Fe20a), ··MgO, · 

Ti02, and P 205, with small differences for CaO, 

Na20, ·K20, and MnO. Our studies of the section at 

Millington suggest that these slight differences are 

unimportant and that they probably arise in part 

because two of these rocks may actually have been 

slightly altered. A carefully selected set of 22 analyses of rocks, judged to be the least altered, from 

within the larger set of 36 analyses was averaged 

(table 2, column 2). This average is tentatively considered to ~be representative of the upper flow unit at 

the Millington quarry. 

The average sample for the Watchungs of eight 

analyses given·by Washington (1922) is a very small 

sample, but since it is derived from the average of 

five analyses from First Mountain basalts and three 

from Third Mountain basalts it is more representative than the single set of analyses from the Millington quarry. A comparison of Washington's (1922) 

average with the averages of the Whin sill (5 analyses), Nockolds' (1954) normal tholeiitic basalt, 

Daly's (1933) Plateau basalt, and the ·Columbia 

River basalt (13 analyses) shows its close affinity 

to tholeiites. The conclusion that the Watchung 

Basalt is tholeiitic was reached first by Washington 

(1922). The C.I.P.W. norms, the Thornton-Tuttle 

differ~ntiation index, and the· calculated normative 

plagioclase show the variation within those averages. 

The basalts all carry quartz in the norm. 

As early as 1884, Teall had noticed the close chemical resemblance between the rocks of the Whin sill 

and the basalts, dikes, and dia;base of New Jersey 

and Connecticut. 

A comparison of the average of 22 selected analyses of basalts from the upper flow unit' of Third 

Watchung Mountain (table 2, column 2), with the 

average Palisade basal-chilled dolerite of Walker 

(1969), column 9, shows some important differences. 

The Watchung Basalt has lower Si02, Al20a, MgO, 

Na20, K20, and MnO than the ba.sal-chilled dolerite 

and about the same amount of CaO, Ti02, P 205, and 

MnO. The basalt is significantly higher in total iron 

oxides (FeO + Fe20a). These differences are reflected 

in the norm by the appearance oi more quartz, albite, 

and magnetite; slightly less diopside, and less orthoclase, ano~thite, and much less hypersthene than in 

the basal-chilled dolerite. The ·Thornton-Tuttle differentiation index of the basal-chilled dolerite is 

lower than that of any of the tholeiites listed in 

table 2, and the plagioclase in the norm is much more 

anorthitic. 

MEGASCOPIC CHARACTERISTICS OF THE BASALT 

The basalts of the upper flow unit of Third Mountain are uniformly fine grained, with an average 

grain size of less than 1 mm. Small lenses, comyosed 

almost entirely of crystals 2--3 mm across, appear 

rarely in an excavation near Myersville and at the 

cut near Pine Brook. These lenses occur in the section about two-thirds of the distance up from the 

base of the flow unit. They represent the last liquid 

to solidify, and because of the increased volatile 

content of this last liquid, they have completely 

crystallized. The lower flow unit of .Third Mountain 

is also fine grained, but small phenocrysts aJbout 2 to 

3 mm across oi feldspar and pyroxenes are sparseiy 

distributed in the rock. 

The basalts of ..Second Mountain show much more 

variation in grain size. In the lower flow unit they 

are dense and fine grained near the ·base, but they 

coarsen slowly as one ascends in the section until 

at a zone wbout two-thirds of the way up from the 

base the rock .becomes coarse grained and resembles 

a gabbro. The grain size diminishes rapidly above 

this zone and becomes fine grained to the top. The 

upper flow unit is more uniform than the lower flow 

unit, and it has pockets of coarsely crystallized rock 

above the middle of the unit. These crystals are, 

however, not as large as those in the lower flow unit. 

This coarse facies does not form a continuous zone 

but consists only of a series of discontinuous lenses 

at about the same horizon. The zones of .pillows at 

the base of the flow units appear to ·have their individual pillows coated with a glassy-looking rind. 

These rinds are now however altered, and the rind 

may crumble when handled. 

The basalts of First Mountain, in so far as I have 

examined them, appear to ·be fine grained. Lewis 

(1908, p. 153) made similar observations. 

The color of the basalt is normally black, frequently with a greenish tint, but grayish zones are 

also common. There is considerable variation in color 

in the altered zones. On weathered surfaces ·the 

basalts commonly have a yellow coating of iron 

oxides. The color varies from grayish-orange 

(10 YR 7 /4) to moderate yellowish brown (10 YR 
REVIEW AND INTERPRETATION OF GEOLOGIC SETTING A25 

5/4) .r. On quarry walls which have been undisturbed 

for long periods of time, they ·may have a reddishbrown (pale brown, 5 YR 5/2) coating formerly 

referred to as a patina when quarries were worked 

for dimension stone. In hydrothermally altered 

zones they ~may be greenish, owing to considerable 

quantities of chlorite. 

The tops and bottoms of the flow units are vesiculated. The vesiculation is generally light at the basal 

contact of the lower flow unit overlying the sedimentary rocks. The size and the frequency of the 

bubbles increase as the contact is approached. At a 

distance of 6 inches to 1 foot (0.15-0.30 m) above 

the contact the vesicles are commonly the size of a 

pinpoint and then increase to as much as one-fourth 

of an inch ( 0.6 em) in diameter at or near the contact. Less frequently, the individual bubbles are 

larger in diameter. Locally, the zone of vesiculation 

may be thicker. ·The top of the flow unit may be as 

much as 10 feet (3.0 m) thick, and it is heavily 

vesicular. In this zone the larger vesicles are at the 

top. Locally, the concentration of larger bubbles may 

be so great that clustering produces a scoriaceous 

variety of basalt characterized by coarse bubbles 

forming a cellular structure. 

Bubbles are scattered sparsely throughout the flow 

units, and sometimes they collect into single wavy 

layers, thin zones about one-fourth inch (0.6 em) 

thick, and much more rarely into zones 1 foot (30 

em) or so thick. Such zones of vesicles have been 

observed near the top of the flow unit but well below 

the vesicular top. 

The top of the upper flow unit has a vesiculation 

pattern similar to that of the top of the lower flow 

unit, but the basal part of the upper flow unit may 

be more heavily and ·more thickly vesicular than the 

corresponding base of the lower flow unit. The actual 

tops of the two flow units have the pahoehoe form 

of a ·billowy undulatory surface which in cross section resembles a sine wave. 

Pipe vesicles, tubelike cavities as much as 4 or 5 

inches (10 or 13 em) long and oriented with their 

largest axis (the tube axis) normal to the contact, 

are most commonly observed at the base of the 

upper flow unit where it lies in contact with the top 

. of the lower flow unit. In the Millington quarry, 

where the contact could be seen, the base of the 

upper flow unit conformed to the undulatory top of 

the lower flow unit, and the orientation of axes of 

the pipe vesicles also reflected the curvature. 

My field observations of the pipe vesicles, also 

11 Color designations nrc based on the "Rock-color chart" of the Na- tional Research Council (Goddard and others, 1948). 

called pipe amygdules, at the .base of the lava flow 

where it rests on an underlying flow or on the Triassic sediments of the Brunswick Formation are in 

accord with those of du Toit (1907) in South Africa. 

In his extensive· field studies in South Africa and 

elsewhere, he never observed a pipe vesicle (amygdule) in the upper or middle part of the flows. His 

view of their origin was that the ·gases which formed 

them did not come from the lava itself but rather 

·from air entangled in· the lower lava flow or steam 

formed by the vaporizing of water contained in the 

moist surfaces over which the lava flowed. 

The various vesicles may be empty or filled with 

minerals. When the vesicles are filled with :minerals, 

the basalt is said to be amygdaloidal. 

The Watchung Basalt flows are famous for the 

beautiful zeolite. minerals, prehnite, quartz, gypsum, 

thaumasite, datolite, apophyllite, .pectolite, stevensite, and other associated minerals which have developed in the pillow basalts at the base of the upper 

flow unit of First Mountain in the vicinity of Paterson, in the area delineated by Fenner (1908) as the 

former Lake Paterson. These deposits and their minerals have been descdbed by many investigators but 

in particular by Fenner (1910b) and Schaller 

(1932), and more recently their mineralogy has 

been verified by Mason (1960). This type of mineralization, but not in a pillow basalt environment, 

has been developed on a ,much smaller· scale else-

. where in First Mountain as at the Chimney Rock 

quarry near Bound Brook, N.J., and to a much lesser 

extent in Second and Third Watchung Mountains. 

MICROSCOPIC CHARACTER OF THE BASALTS 

The microscopic character of the Watchung Basalt 

was determined for Darton (1890) by J. S. Diller 

and Whitman Cross. Iddings (in Diller, 1898, p. 254-

255) described the .petrography of the famous columnar basalt from the 1

base of the lower flow unit 

at O'Rourke's quarry on First Mountain in Orange, 

N.J. The first detailed study was made by Lewis 

(1908), and he examined rocks from all three 

Watchung Mountains. Fenner (1910a, b, 1931) 

studied in particular the basalts of First Mountain 

with special em,phasis on the pillow lavas. Clark 

(1916) described a basalt with an ophitic texture 

from the Chimney Rock quarry in First Mountain. 

The only measured mode appears to be that of 

Merwin (in Adams and Williamson, 1923, p. 485), 

who examined a dense, black, nonporphyritic basalt 

from the Hatfield and Weldon quarry, in Scotch 

Plains in First Mountain and found it to consist of 
A26 S"TUDIES ON THE WATCHUNG BASALT FLOWS OF NEW JE'1SEY 

30 percent plagioclase, Ab45An55 ; 50 percent augite; 

and 20 percent glass. 

According to all observers, the normal crystallized 

basalt consists of plagioclase of labradorite composition (Ab4oAnso to Ab45An55 ) occurring as either 

stout, short, rectangular crystals or as slender lathshaped crystals ; of augite usually of irregular fonn 

and commonly colorless or with a brown or greenish 

tint; of magnetite 1present as trellis-shaped or firtree shaped groups or as .dust; and glassy base or 

mesostasis usually green or dark brown. The mesostasis has probably recrystallized. Chlorite and calcite may also be seen as alteration products. In some 

varieties of basalt, olivine occurs rarely, and it is 

usually replaced presumably.-.by serpentine. If the 

space between the laths of feldspar is filled with 

granular augite, the texture is diabasic; if large 

augite crystals or grains enclose many laths of 

feldspars, the texture becomes ophitic. 

THE PROBABLE CHARACTER OF THE PRISTINE GASES 

IN THE WATCHUNG BASALT 

The composition of the pristine gases which were 

probably exsolved as bubbles into the liquid lava 

which later solidified as the Watchung Basalt may 

be approximated from the studies of Shepherd 

(1938). Shepherd examined the intrusive equivalents of the Watchung Basalt. He pumped the residual gases out of two Triassic diabases, one from 

New .Market, Md., the other from Granton, Bergen 

Township, N.J. He found that the unaltered diabase 

yielded a gaseous .phase composed of 90 percent 

water vapor, slightly less than 5 percent H2, 2 percent of S2, 2 percent of N 2' about 0.9 percent C02, 

about 0.3 percent F 2, about 0.2 percent Cl2, about 

0.02 percent CO, and a trace of argon. The total 

volatile content amounted to about 30 cc per gram, 

which is the normal value Shepherd (1938) found 

for plutonic rocks. This analysis of the gases is 

probably representative of the composition exsolved 

into the Watchung Basalt. Freshly collected basalts 

from the Hawaiian Islands contained about 5 to 6 cc 

per ·gram, and this again is the normal value Shepherd (1938) found for lavas. This value would be 

the probable gas content of the solidified Watchung 

Basalt. Shepherd's (1938) data suggest that basalts 

retain a;bout one-fifth of the gaseous constituents 

retained by the contemporaneously intruded diabases. This decrease in gas content is chiefly accomplished by the degassing on extrusion of the basalts. 

The presence of 2 percent of sulfur in Shepherd's 

(1938) analysis may be somewhat surprising, but 

the recent studies of Moore and Calk (1971) have 

definitely confir.med this. They observe on page 485: 

"Hence the main vesicle-forming .phases in deeper 

pillows are probably dominated by the com•pounds of 

S and C." 

HISTORY OF TECTONIC SUBSIDENCE AND 

VOLCANISM IN THE NEW ARK BASIN AS IT 

RELATES TO THE WATCHUNG MOUNTAINS 

STRUCTURE OF THE NEWARK BASIN AT THE CLOSE OF 

THE TRIASSIC PERIOD 

·The inherited geometry of the Triassic basins, in 

their several disconnected parts, is a significant 

structural problem that has been studied by various 

geologists. The geometric outline of the Triassic 

basin in Connecticut was thought .by Emerson (1917, 

p. 48 and 127) on the basis of field studies, particularly of the Bernardston Formation of Silurian and 

Devonian ( ?) age, to have been determined in the 

Devonian Period, and he was followed in this view 

by many investigators. Bucher ( 1933, p. 351) recognized the close geometric relation existing between 

the Triassic basins, extending from Nova Scotia to 

South Carolina, and the earlier Paleozoic folds, but 

he concluded from further study of the geological 

and structural ~aps of the eastern part of North 

America that "the line of Triassic troughs cuts 

across the main axes of the preexisting Paleozoic 

structure" and that these troughs "represent a new 

start dynamically which disrupted the old structural 

lines ***." Movement along the border fiault has 

been estimated by Van Houten (1969, p. 328) to be 

18,000 feet (5.5 km) and by Sanders (1963, p. 510) 

to be as much as· 30,000 feet (9.1 km). Ratcliffe 

(1971, p. 125) made a detailed study of :the Ram·apo 

fault system in N:ew York and New Jersey, and he 

suggests that the fault "has a complex tectonic ancestry perhaps dating from Late Precambrian time" 

and (p. 136) "The relationship of the large intrusive 

Palisades phase to the east :and the Watchung flows 

to the west of the hasin suggests that the border 

fault at depth served as an avenue of magma ascent, 

although m·ag,ma apparently never reached the surface along the fault," rand (p. 131) contrary to 

Sanders (1963), he considers it"unHkely that the 

Triassic sediments extended much further northeast 

than the present exposure of the Triassic unconformity *** ." 

For the Triassic basin of New Jersey, the inherited geometry has ·been described by Lewis (1907), 

Kiimmel (1940), and Wheeler (1939). As interpreted in this study, before deformation took place 

the gross system in the graben consisted essentially 

of a stratiform mass made up of sediments, the three 

Watchung Basalt flow sequences, and included near 

its base the discordant Palisade intrusive. The layers 
REVIEW AND INTERPRETATION OF GEOLOGIC SETTING A27 

of the stratiform mass were essentially flat lying. 

This mass was contained between the walls of the 

horsts. The dimensions of the graben based on 

Sanders (1963, p. 504, 507) estimates were about . 

30,000 feet (9.1 km) deep (approx 6 miles) and 50 

to 30 miles (80.5-48 km) wide. Geometrically the 

mass was bordered •by marginal faults which dipped 

under the graben at 70°-75° and thus formed a 

trapezoidal block which narrowed with depth. 

The geometry of the outcrop areas in Connecticut 

has been discussed ·by Longwell (1933) and Sanders 

(1963), who recognized the importance of the preservation of the Triassic rocks in the Pomperaug 

valley, an isolated outcrop area surrounded by 

granitic rocks and approximately 15 miles (24 km) 

west of the principal outcrop area of the Triassic of 

Connecticut. Longwell (1933, p. 101) comments as 

follows: The general tilt in the Triassic belt a·ppears 

to ·be the result of :broad regional uplift in post-Triassic time, with maximum elevation along a northsouth axis in western Connecticut. In northern New 

Jersey and southeastern New York the Triassic 

strata dip to ~he west, on the opposite flank of the 

regional arch. The Pomperaug area of western Connecticut, preserved from erosion ·by downfaulting, 

indicates that typical Triassic sediments, with included basalt flows, existed on the crest of this arch, 

although they may not have been continuous between 

Connecticut and New Jersey. 

The pres.ence of the Triassic rocks of the Pomperaug valley near the crest of the postulated arch 

is a key point in the argument for the former extent 

of the Triassic sedimentation and thus of the geometry of the Newark basin. 

On the basis of the presently existing geometrical 

relations of the Triassic outcrops of New Jersey, 

Connecticut, and Massachusetts, it has been generally assumed that a suitable structural process 

which could bring about the present configuration in 

the Newark basin from Connecticut to Pennsylvania 

would require : 

1. that during the close of the Triassic Period or 

during the Jurassic Period the Newark basin 

was subjected to a large deformation. 

2. that the period of deformation was of long duration-perhaps slow movement over a long 

period of geologic time. 

3. that the obvious longitudinal symmetry of the 

Newark basin in Connecticut and the Newark 

basin in New Jersey with strata and lava flow 

sequence dipping symmetrically in opposite 

directions indicated uplift over a longitudinal 

arch. 

4. that the "border fault" accompanying the deformation is a normal fault and is indicative of 

tension in the crust. 

5. that compressional forces were ultimately involved in forming the asymmetric syncline 

abutting against the fault scarp of the Precambrian granitic rocks. 

The formation of a wide mountain arch under the 

Triassic graben. was postulated by I. C. Russel 

.(1878) .-.Barrell.. (1915) ... ~oncurred in .this view and 

the relationships were further extended and portrayed by Woodworth (1932). His diagram is reproduced in figure 8. Woodworth (1932, p. 158) observed that the Triassic block faulting, over the · 

arch, illustrated "the association of normal faulting 

with an extended tectonic area***." Barrell (1915) 

further pointed out that the production of the arch 

brought about fracturing and settling along the 

walls and that these processes took place either during the arching or shortly thereafter. The later point 

is of considerable importance to the study of jointing 

in the Newark ·basin. 

STRUCTURE OF THE NEWARK BASIN AFTER THE POST· 

TRIASSIC DEFORMATION 

The geometry of the deformed graben in New 

Jersey cannot be described in detail for much of its 

contents have been removed. The angular relationships of the structure are the best preserved. The 

eroded remnant of this Triassic stratiform mass, as 

observed today, in New Jersey, is tilted about 

15°NW. and strikes northeast. According to Sanders 

(1963) the marginal fault surfaces which originally 

dipped at 70°-75° under the gra,ben were rotated 

15°-20° and now dip 55°-60° in many localities. 

The northwest horst block of Precambrian granitic 

rocks, the Reading prong, is topographically higher 

NOVA 

T:~~:ic CONNECTICUT SCOTIA 

NEW JERSEX,_ ••• .i i---------- ; ~--MASSACHUSETT~----~ Appalachian • •..• ---- ~ ----:·--• ..; ----------------- ~---· 

axis ··c·'"'\ ---;f--- i ; "*"' f&t . i&J \ \ \ ! ! . 0 

.,..,...----. 

-- ~-- ,// 

------------

FIGURE B.-Generalized cross section of the Triassic (patterned) of northeastern North America showing the postulated arching of the crust according to Woodworth (1932, 

fig.l). 
A28 STUDIES ON THE WATCHUNG BASALT FLOWS OF NEW JERSEY 

than the Triassic rocks, and the boundary between 

them is a large normal fault. 6 The Triassic rocks 

form the downthrown block. The dip of the fault 

is to the southeast. 

The linear dimensions and the volume of the 

structure, in contrast, are difficult to estimate. In the 

post-Newark faulting the cumulative movement 

along faults amounted to many thousands of feet. 

In the Delaware River Valley, McLaughlin (1945) 

measured the section of Triassic rocks from the base 

of the Stockton Formation to the great diabase sill 

at Haycock Mountain and found it to be a:bout 12,000 

feet (3,658 m) thick. All of this section is below the 

Watchung lava flows, and thus it must represent the 

.. lower .part of the:.Upper Triassic. Widmer (1964, 

p. 63) points out that "the border fault from Boonton to Stony Point truncates more than 10,000 feet 

(3,048 m) of Triassic rocks." Sanders (1963, p. 507) 

gives a thickness of 30,000 feet (9,144 m) for the 

section in New York and New Jersey. 

The suggested shape of the former structure at 

the close of the period of deformation is that of an 

arch. Approximately 22 miles (35.4 km) east of the 

west wall of the graben, on the east side of Trenton, 

N.J., the Triassic sediments have been exposed lying 

on the granitic rocks, there the 1Baltimore Gneiss. 

The contact dips }5°NW., parallel to the dip of the 

overlying .Stockton sedi-mentary rocks. As the section 

is traversed eastward in wells, the granitic rocks are 

continuously found to lie under the Coastal Plain 

sediments and their appearance in the well logs 

deepens to the east, but little is known of the contact 

of the Newark rocks and the granite. The southeastern horst block of the graben, the Trenton prong, 

has been largely eroded away. It is not exposed in 

New Jersey, and its remnant, as revealed in well 

drilling, lies under the Coastal Plain deposits of 

Cretaceous age. 

The geometry of the remnants of the arch in New 

Jersey, .connecticut, and Massachusetts suggest that 

its former geometric shape approximated that of a 

section of a right cylinder. This broad semicylindrical fold was bounded on ·both sides lby the walls of 

the horsts, and the hinge line of the fold was parallel 

to the walls. Evans (1925) estimated the amount 

of stretching of the surface layers of such a buckled 

structure ·by calculating the length of an equivalent 

arc. He assumed that the neutral surface was halfway between the bottom and top of the stratiform 

mass, that this section was unaltered in length, and 

that the angle of dip, no, was the same on ·both sides. 

He set t, equal to the thickness of the mass and 

o The so-called Great Fault is formed by the coalescence of numerous 

faults. 

calculated the stretch s from the relation 7rtDo /180°. 

For a dip of 10°, and a depth of 2 miles (10,560 ft) 

( 3.2 km) the stretch s would be ·about 0.35 mile 

(0.56 :km) ; for a depth of 5 miles (26,400 ft) (8.0 

km) the stretch s would be about 0.87 mile (1.4 

km). For a graben with an original width of 30 

miles ( 48.3 km), this would amount to an increase 

· of about 1.2 percent for the thickness of 2 miles 

(3.2 km) and an increase of about 2.9 percent for 

the thicker section of 5 miles (8.0 km). Evans 

( 192·5) also gives the following approximate formula 

to calculate the theoretical height of such an arch: 

h . ht-h w(1-cosD0

) _ 1 + ........ 1 D. o e1g - --w l,iai.lJ.-

2 sin no 2 2 

where w is the width at right angles to the strike and 

Do is the angle of dip. For a graben of 80 miles 

( 48.3 km) width and with a dip of 10°, this suggests a probable height of 1.3 miles (2.1 km) at the 

crest. 

Admittedly, this calculated increase in length due 

to buckling is a sim.plified treat·ment, but it giv.es us 

an approximate value for the amount of. stretching 

of the rocks. This extension may be co.mpared with 

that permitted by the tensile strength of the rocks. 

From Hooke's law we have the relation that the 

strain produced in a body is proportional to the 

stress applied to it and that it is represented by the 

equation E= stress/strain where E is Young's 

modulus. In a tensile strength test on a brittle substance the material is subjected to incr_easingly 

higher stresses producing increasingly greater 

strains until e·ventually the material fractures. Thus 

the stress required to rupture the material, the 

tensile stress, gives us a measure of the strain and 

therefore of the elongation at fracture. This may 

be calculated as follows: 

E = stress just prior to failure in a t·ensile test 

elong,ation just oprior to failure 

and 

tensile ·stress Elongation just prior to failure=---

E 

The tensile strength of the stratiform mass in 

the graben may be estimated In the following manner. It will be assumed (1) that the composite 

stratiform mass behaves as a unit, and (2) that for 

the sedimentary rocks the proportion of 43 percent 

sandstone and 57 percent shale is a reasonable distribution. Using the elastic and strength data in 

table 3, other el•astic data, and the thickness data for 

the sedimentary ·rocks, lava, a.nd di~base in the stratigraphic columns in figure 3, .the average ten·sile 

strength is estim·ated to be 340 lb/in2 (24 kg/cm2 ) 

and the average value of Young's ·modulus to be 
REVIEW AND INTERPRETATION OF GEOLOGIC SETTING A29 

TABLE 3.-Mechanical strength of selected rocks 

Rock type Locality Tensile strength 

lbf/in~ kgf/cm:.l 

Granite ------------ 420-710 30-50 

Granite ------------ 1,308-1,800 92-126 

Granite gneiss ------ 854-2,054 60-144 

Schist ------------- Dresser, P~'iic- 1,273-1,330 89-93 

Basalt ------------- 2,290 161 

Basalt ------------- County, Wis. Near Minneapolis, 1,552 109 

Hennepin County, 

Minn. 

Basalt ------------- Champion Copper 

Basalt mine, Michigan. 

------------- Ahmeek Copper mine, 

Diabase, Michigan. coarse Michigan ------------ grained. 

Diabase, fine ____ do --------------- grained. 

Gabbro from Near Duluth, St. Louis 1,305 92 

Duluth Gabbro County, Minn. 

Complex. 

Triassic Hummelstown, Pa --- sandstone. 

Triassic Enst Longmeadow, 284 20 

sandstone. Mnss. Triassic New Brunswick, N.J __ shale (weathered). 

Sandstone ---------- Amherst, Ohio ------- 135 9.5 

Sandstone ---------- Waterford, Ohio ----- 206 14.5 Sandstone ---------- 40-165 3-12 

2.7 X 10° lb/in 2 (1.89 X 105 kg/cm2 ). The unit elongation of such a flat-lying ·block just prior to fracture is: 

3.4X102 

----=1.3X10-·1 unit elongation. 2.7X10° 

This amounts to an extension of 243 inches (21 ft) 

for a 30 mile width. 

A comparison of the estimated increase in length, 

by stretching, of the Newark rocks in the formation 

of the arch of 0.35 mile for a graben thickness of 

10,560 feet with the estimated elastic extension of 

21 feet in 30 miles, for a flat-lying stratiform block, 

shows clearly that, if the composite assem,blage behaved as a single unit, rupture would take place with 

the formation of tensional cracks. Tensional joints 

. would be developed. Actually, in arching, the gr31ben 

assem~blage did not behave completely as a unit, but 

slipping along the bedding planes, postulated by Von 

Bubnoff (1963), must have occurred and tensional 

cracks and joints must have been formed (fig. 9). 

As the upper surface of the arch developed tensional 

cracks, the neutral stress surface would shift downwards toward the compression side. Because the 

flank of the central anticline is no longer avaHable 

for observati.on in New Jersey, .this mechanical behavior cannot he proven. For the complementary 

case of the border syncline, where folding was produced by compression, field observation close to the 

f·ault wall has revealed small d:mgfolds in the shale 

member of the Brunswick Fo:i-mation. These appear 

Shearing strength Transverse strength Source (modulus of ruptqre) 

lbf/in2 kgf/cm2 lbf/in2 kgf/cm2 of data 

2,130-4,267 150-300 1,422-2,844 100-200 Kessler (1927). 

D'Andrea, Fischer, 

and Fogelson 

(1965). 

Do. 

Do. 

Do. 

Do. 

3,800 267 Windes (1950). 

2,500 176 Do. 

4,500-5,800 317-408 Do. 

5,200-5,400 366-380 Do. 

D'Andrea, Fischer, 

and Fogelson 

(1965). 

1,138 80 Kessler ( 1~27). 

2,702 190 Do. 

996 70 Jumikis (1966). 

Obert, Windes, and 

Duvall (1946). Do. D'Andrea, Fischer, 

and Fogelson, 

(1965). 

in the shale beds that are confined by the moore competent sandstone layers. These sandstone layers have 

develOped a type of jointing similar to the ball and 

socket jointing that is sometimes observed in columnar basalt. 

THE FORMATION OF A REGIONAL ARCH 

The formation of the regional arch by uplift from 

below may be treated as a problem in the mechanics 

of buckling. When a system is buckled, it changes 

its geometry; for masses involving large geologic 

structures, this change :may ·be very significant. Von 

Bubnoff (1963) 'has illustrated rather clearly the 

geometry of the change which can take place (fig. 

9), and has emphasized that a slip surface must develop and that most commonly it is the bedding 

plane. His sketch suggests the type of space problems ideally developed at the ends of such a fold. 

The geometric change in a folded slab will depend 

on the ratio of the length to the thickness of the slab 

and the curvature of the arch. 

The estimated geometric change in, the Newark 

graben will depend on the thickness assumed for the 

Triassic section, either 10,000 or 25,000 feet (3,048 

or 7,620 m) and on the width of the :basin. Sanders 

(1963) estimates the width of the ·basin in New 

Jersey to 'be 50 to 70 mil:es (80.5-113 km) across. 

Field observations show that the preexisting fault 

.plane dipped 70° to 75° under the graben and thus 

gave rise to a trapezoidal volume (a truncated 
A30 STUDIES ON THE WATCHUNG BASALT FLOWS OF NEW JERSEY 

I I I I II I I I 

A 

~ ~ Contraction 

~ ---+ Stretching 

FIGURE 9.-Geometric changes produced by folding horizontal 

beds to form an arch. The bed<;ling plane becomes a slip 

surface. (From Von Bubnoff (196.3); published by permission of Oliver & Boyd Ltd.) 

pyramid with its base at the Earth's surface). Field 

observations further show that during the arching 

of the basin a mrajor tension f:ault developed between 

the . horst and the basin and that the displacement of these elements was of a considerable order 

of magnitude. 

An arch may 'be produced in this manner by a 

number of mechanical systems. One explanation assumes that compressive forces were exerted by the 

. granitic walls of the horst upon the layered sequences of the graben in the manner of a vise with 

slipping jaws. Another explanation assumes a large 

heat source to underlie the structure. The rocks 

above the heat source expand and form an arch. 

Murawski (1968) has shown another mechanism by 

which arching may take place. If a region is under 

tension, the weakest structural element may be subject to dislocation. If this element is dropped into . 

a zone where the element is forced to adjust to a 

new geometry, arching may occur. (See fig. 10.) 

If that part of the Earth's crust containing the 

Newark graben and its structural host, the granitic 

horsts, were simultaneously subjected to a strong 

tensional force acting normal to the long axis of 

the graben, then major rupture with dislocation 

would occur in the weakest part or parts. If such 

rupture did take place, then the field evidence should 

show where it occurred. The ·graben was not -serially 

;shear faulted. The only evidence of a major faulting 

is that along the graben-hors:t w·all. Thi.s observration 

suggests that the weakest zones in the system were 

the preexisting faurlt planes between the gvaben and 

the· horst walls, ~and ·rupture and dislocation took 

pl:ace in these zones with the contents of the graben 

dropping deeper into the opening created by the 

pulling apart 9f the walls of the horsts in response 

to the tensional force (fig. 1 OA) . 

This dislocation of the graben probably took place 

over some period of time, and it was a discontinuous 

process. As a consequence of the adjustment of the 

down.faulted block to the limitations of space in its 

new position, it folded into a central major anticline 

and two border minor synclines (fig. lOB) . .If, after 

the forming of this complex structure, erosion takes 

place to remove much of the central anticline, the 

border synclines will become topographically promGrabenrandvenMerlUngen 

A 

FIGURE 10.-Schematic representation of a tectonic graben (A) 

and folds (B). A, Wide open arrows = horizontal tension 

(stretching); narrow solid arrows = vertical relative movement; curved arrows = relative movement on the graben 

fault border. B, Two synclines and one anticline; side open 

arrows = horizontal compression; narrow solid arrows 

vertical relative movement. From Murawski (1968). 
REVIEW AND INTERPRETATION OF GEOLOGIC SETTING A31 

inent features, especially if there are resistant layers 

such as basalt in the layered sequence which compose them. The present topographic expression of 

the basalt flows of Third Mountain in New Jersey 

and its counterparts in Connecticut and Massachusetts fit this model. In figure 1, Long Hill, Riker's 

Hill, Hook Mountain, and Packanack Mountain are 

continuous parts of the southeast wall of the syncline. The New Vern on trap sheet and two small 

outcrops against the granitic wall in the vicinity of 

Towaco, on Hook Mountain, are parts of the upturned edge of the northwest wall of the syncline 

·which are pressed against the granitic wall of the 

horst. It is my opinion that the ~structure of the three 

Watchung Mountains conforms to the structural 

model proposed by Murawski (1968). 

TRIASSIC TENSIONAL HISTORY, ITS EFFECT ON THE 

DEVELOPMENT OF THE NEW ARK BASIN AND ITS 

GLOBAL CAUSE-A SUMMARY 

The history of the ·Newark basin strongly manifests a state of tension in the earth's crust in the 

vicinity of eastern North America during Late 

Triassic and probably extending into Early Jurassic 

time. Three events in particular signalize tension as 

the major factor in the geologic forces which prevailed in determining Triassic events. These were 

rifting with the development of the rift zones and 

the formation of the gra•ben, deep rifting in the graben which permitted volcanism with the outpourings 

of the flows and the intrusion of the diabase sills, 

and finally downfaulting of the contents of the graben with the deformation of the block into an arch 

with border synclines. 

The oft-repeated cycle of downfaulting followed 

by basin filling suggests a region in a state of isostatic unbalance constantly striving to achieve balance. 

As a result of the gravitative adjustments in the graben, the sialic roots of the crust in this region were 

being forced deeper and deeper into the underlying 

sima, and it in turn was being laterally displaced. 

Near the end of Triassic time major deep rifting 

took place throughout the Newark basin. These rifts 

were multiple and long and the rift zones extended 

from Nova Scotia to at least as far south as North 

Carolina. They were also deep-seated rifts, for they 

tapped locally molten basaltic layers that were 

probably located in the vicinity of the Mohorovicic 

discontinuity at a depth of about 20.5 miles (33 

km). The multiple character of the volcanicity 

proves that the rifting was not a single event. It 

probably consisted of three major periods of rifting, 

each period in itself being a multiple event. The time 

relations for these events in the Watchung have 

already been given. 

In seeking a cause for the tensional processes operative in the Newark ·basin during the Triassic, and 

probably into the Jurassic, a parallelism between the 

results of these processes and the ·major disruptive 

events involving the breakup of the continent 

Pangaea is clearly apparent. It is suggested here 

(1) that the period of graben formation in the 

Newark basin is a reflection of the state of tensional 

stress in the continent Pangaea at that time, and (2) 

that the development of the rift zones which permitted the outpouring of basaltic magma and the 

major event to affect the Newark basin (downfaulting)' occurred during the events leading up to 

and including ·the breaking apart of .the landm·ass 

formerly composed of the then new continents of 

North America, Europe, and Africa. 

It should be noted that Du Toit (1937) was 

proba-bly the first to point out the connection between 

the voluminous outpourings of basalt in many regions of the Earth and the timing of continental 

drift. His views on this subject of volcanism are 

now generally accepted. 

The suggestions, proposed in this publication, 

concerning the events in the Triassic of eastern 

North America agree with the interpretations of 

geophysicists on the subject of the breakup of 

Pangaea and the formation of the North Atlantic. 

Roy (1972, p. 103) on the basis of paleolatitude 

studies concluded that "the rupture of the block and 

the opening of the North Atlantic did not follow each 

other closely in time" and on p. 104 "In fact the 

block could have ruptured without creating an appreciable longitudinal opening, as the paleomagnetic 

data presented here seem to indicate" and again on 

page 113 "The best estimate is that the time of rupture is pre-Upper Triassic * * * [and] that the time 

of the opening of the North Atlantic was probably 

Jurassic." Wilson (1963, p. 99) has proposed that 

the rift that formed the Atlantic developed before 

the start of the Cretaceous about 120 million years 

ago. 

These data from paleolatitude studies-rupture, 

and some separation-would correspond to the 

periods of strong tensional stress in the history of 

the Newark ba;sin. 
A32 STUDIES ON THE WATCHUNG BASALT FLOWS OF NEW JERSEY 

SUPPLEMENTARY TOPICS 

SOME CHARACTERISTICS OF FISSURE ERUPTIONS 

Fissure eruptions are one of the i~mportant types 

of volcanic phenomena and are so-named because 

they originate from fissures-long cracks rending 

the surface of the earth. The lava ascends to the surface along the crack or system of innumerable cracks 

and wells forth for the most part as a quiet steady 

stream or sheet. As Sapper (1931, p. 8) has put it 

"Still more tremendous than fissure eruptions on 

steep slopes are such eruptions in the open country 

where the whole fissure becomes a volcano." The 

ter.m "fissure eruption" as used in this study thus 

refers to those eruptions which take place from fissures of great length, com,monly many miles long, 

and is not concerned with flank eruptions, or fissure 

eruptions on shield volcanoes. 

The considerable fluidity of the lava that issues 

from fissure eruptions has attracted much notice 

and has been attributed to their chemistry and 

volatile content. Washington (1922) has reiterated 

the observation that these lavas are exceptionally 

fluid at the time of extrusion, and he attributes the 

low viscosity to their chemical composition-they 

contain a notably high percentage of iron oxides, especially ferrous oxide. He based his opinion on the 

well-known fluxing ·action of .ferrous oxide and 

manganous oxide in metallurgical slags (Fulton, 

1910). Washington emphasizes the field observation 

that fissure eruptions, in general, show slight explosive activity and concludes that the ·magmas were 

not rich in a gaseous phase. It has also been suggested that the fluidity of the .magmas giving rise 

to fissure eruptions has been maintained because of 

the rapid rate at which the magma moves from its 

chamber to the Earth's surface. If this is true, then 

the ascent of lava on a system of innumerable fissures would greatly influence the maintenance of the 

fluidity and by providing many paths of travel to 

the surface would allow a larg.e volume of molten 

rock to be moved quickly. 

The eruption and flow rate of basalt from fissure 

eruptions have ·been studied by Shaw and .Swanson 

(1970, p. 292) with particular reference to the 

basalts of the Columbia River Group. They have 

calculated the probable total time of emplacement 

of such flows and find that "For exam.ple, the 3 m 

conduit with 3 km strike length gives a total flow 

rate of about 0.6 km3/hour for a hydraulic slope of 

0.1. A reference volume of 100 km3 for a 'typical' 

Yakima flow would then imply a total emplacement 

time of about a week (2 days for the 5 m conduit, 

etc.)." 

The possibility of even slight explosive activity 

initiating a fissure eruption has been questioned by 

Thorarinsson (1966) on the basis of recent field 

studies. He thinks that the tephra produced at the 

Eldj a fissure eruption in Iceland "resulted mainly 

from a very vigorous lava fountain activity and not 

from explosive activity." The geometry of the surface formed by the intersection of a fissure and the 

surface of the Earth would be similar to that of a 

long ribbon, and this surface would have a tremendous area. Lava welling forth from this vent and 

presented, at every instant, with such a large surface would be capable of discharging any sign.ificant 

excess of gaseous phase, and thus there would be 

no tendency to buildup explosive energy; Iddings 

(1914, p. 263) has expressed a similar view. 

Geological descriptions of the fissure eruptions in 

the Columbia River .plateau (Von Richthofen, 1868, 

1901, p. 542; Geike, 1882; Fuller, 1927), the Watchungs (Darton, 1889, 1890 ; Faust, unpub. data)", 

in Britain (Geike, 1882), the Deccan of India 

(Wadia, 1953, chapter 10), in Iceland (Thorar.insson, 1966), and elsewhere indicate that a fissure 

eruption proceeds as follows : The fissure or fissures 

form, followed -later by very minor explosive activity, and then the molten lava pours out of the fissure 

system as a great flood. The lava fills all the depressions in the land surface and levels the topography 

which it covers in a manner ana.log'ous to water 

flooding. It is possible in examining a lava field of 

some recent fissure eruptions to actually map the 

flowlines on the surface of the lava sheet as was 

done at Mount .Eccles (Boutakoff, 1963). If the 

eruption takes place over a flat land-surface, the 

flood pours out over vast areas, and the flows may 

attain great thicknesses. There .may be a succession 

of flows so that one sheet lies directly above another, 

or the flows may alternate with sediments deposited 

during an interruption in the volcanism. During an 

eruption, the fissures may lengthen. If a fissure is 

closed with solidified lava, it may reopen to permit 

the flow of Ia va again. This passage of several flows 

of lava through the sa·me fissure gives rise to multiple dikes. Old fissures may be paralleled by new 

fissures from which the lava· flows. Some lava-filled 

fissures never opened at the surface. 

Regarding the fissures he observed, Geikie (1882, 

p. 282) writes: "These fissures, whether due to sudden shocks or slow disruption, were produced with 

such irresistible force as to preserve their linear 

character and parallelism through rocks of the most 

diverse nature, and even. across old dislocations having a throw of many thousand feet. Yet so steadily 
REVIEW AND INTERPRETATION OF GEOLOGIC SETTING A33 

and equably did the fissuring proceed over this 

enormous area, that comparatively seldom was there 

any vertical displacement to the sides. We rarely met 

with a fissure which had been made a true fault 

with an upthrow and downthrow side." 

The closing stage of a fissure eruption was interpreted by Tyrrell (1937, p. 103) to be indicated 

by the presence of cones along the fissures, which 

"merely mark the sites of the feeble final spasms of 

activity." It is obvious, as Tyrrell points out, that 

the preservation of these fragile cones, almost intact; after tremendous volumes of lava have poured 

out, 3 cubic miles (12.5 km3 ) at Laki in 1783 (Helland, 1886) is testimony to their very late development in the dying stages of the eruption. The closing 

phase of the fissure eruption at Mount Eccles in 

Victoria, Australia, is iUustrated in figure 11, where 

a line of small cones traces the position of the fissure 

from which welled the large volume of lava. It is 

also apparent from these illustrations that, owing 

to the vast areal extent of fissure eruptions, the 

detection of the fissures may be very difficult. This 

is particularly true in an area whose topography 

was relatively flat previous to volcanism and where 

erosion has removed the surficial evidence of the 

fissure. Fuller (1~27) has described the field appearance of such a filled fissure, which is now exposed as a dike in a tributary to the Salmon River 

in western Idaho, and he points out that the formation of this dike marked the closing phase of a fissure eruption. 

The shape of a fissure eruption in open country, 

where it is unlimited by topographic barriers, tends 

FIGURE 11.-B!ock diagram of the Mount Eccles fissure eruption in Victoria, Australia, showing the late-stage vents 

which trace the course of the fissure. From Boutakoff 

(1963) , with permission of the Director of the Geological 

Survey of Victoria. 

to be pseudorectangular with its longest dimension 

parallel to the fissure system. This is illustrated in 

the schematic diagram of Von Knebel and Reck 

(1912) given in figure 12. It is for this geometric 

reason that fissure eruptions are called linear eruptions by some petrologists and volcanologists (Von 

Wolff, 1914, seep. 304, 306, 409). 

The concept of lava flowing out in the manner of 

a flood had been envisioned by a number of geologists in addition to Von Richthofen, (1868). Powell 

(1875, p. 196), in his explorations of the Colorado 

River observed "The fissure of this fault has been 

the channel through which floods of lava have been 

forced from depths below into the upper world." 

Dutton (1880, p. 176) observed in his discussion of 

the history of the Tushar "while the grander floods 

poured out over everything and spread out over 

great expanses of the mountainside." Geike (1882), 

aware of the work of these authors, used the term 

"flood basalt" to designate the rocks formed by a 

fissure eruption in allusion to the manner of emFIGURE 12.-Schematic representation of a fissure eruption 

showing the linear formation of the late stage vents in the 

closing phase (A and B) and after the eruption has ceased 

(C). Taken from Von Knebel and Reck (1912). 
A34 STUDIES ON THE WATCHUNG BASALT FLOWS OF NEW JERSEY 

placement of the lavas. Although such rocks have 

also been called plateau basalts, because some plateaus are for,med of these rocks, Tyrrell (1937) remarked that the occurrence of these lavas as plateaus 

is due solely to geologic changes unrelated to volcanism. Schneider (1911, p. 48, 50, 66) called fissure 

eruptions "pedionites" ,based on the Greek word 

pedion meaning flat. He regarded such eruptions as 

producing the .}east limited type of volcano. 

The actual time span of fissure eruptions and their 

geometric extent are known for only a few of these 

events. Data given by Barth (1950) and Rittmann 

(1962) for eruptions in Iceland are sum·marized as 

follows: 

Laki eruption : 

Length of fissures=25 km (about 15.-5 

miles) 

Volume of lava= 12 km3 (atbout 2.88 cubic 

miles) 

Volume of fragmentary material= 2 km3 

(about 0.48 cubic miles) 

Flooded area= 565 km2 (about 218.1 square 

miles) 

Climax of the eruption= 41;2 months after 

it started. 

Date of eruption= 1783-85 A.D. 

Eldja eruption: 

Length of fissure=30 km (wbout 18.6 

miles) 

Volume of lava=9 krn3 (,wbout 2.16 cubic 

·miles) 

Volume of ash not known. 

Flooded area= 700 km2 (about 270.3 square 

miles) 

Date of eruption= Around 950 A.D. when 

Iceland was first settled. 

Fissure eruptions were first called massive eruptions, and it is of interest that the first recognition 

of the importance of fissure eruptions was made on 

the Pacific coast in 1868 by Ferdinand Baron Von 

Richthofen. Von Richthofen's (1868) work was 

ridiculed in England by Scrope ( 1869) and did not 

find favor in Europe until 1881-82 when Sir Archibald Geikie after his return from field study in the 

western United States affirmed the field observations 

on massive eruptions made by Von Richthofen and 

exposed the error· of Scrope. Scrope had made extensive geomorphological studies of the volcanoes in 

the Auvergne region of France, and he had observed 

the results of the erosion of the cones and craters of 

central-type volcanoes; on this basis he concluded 

that Von Richthofen had erred and that he 

had examined the erosional remnants of the 

former loci of volcanism (Geikie, 1882, p. 276). 

Geike was an admirer of Scrope's work, but he was 

troubled by his own observations of the lava flows 

in the British Isles, specifically in the basaltic plateaus of Ireland and Scotland, where he found the 

abundant related dike swarms and no connection 

whatsoever with any central type vents. Hei·kie in 

order to satisfy his own doubts of Scrope's (1869) 

aggressive condemnation of the work of Von Richthofen (1868), traveled to the Columbia River plateau and made extensive studies in the area, and 

he described his conclusion as follows ( Geikie, 1882, 

p. 277-278) : "A recent journey in Western America 

has at last lifted the mist from geological vision. 

Having travelled for many leagues over some of the 

lava-fields of the Pacific slope, I have been enabled 

to realize the conditions of volcanism described by 

Von Richthofen, and without acquiescing in all his 

theoretical conclusions, to judge the reality of the 

distinction which he rightly drew between 'Massive Eruptions' and ordinary volcanoes with cones 

and craters." 

Although Geikie (1882) accepted unequivocally 

Von Richthofen's (1868) concept of massive eruptions, some of his English colleagues, still influenced 

by Scrope, were more reserved; 17 years later, for 

example, Bonney ( 1899, p. 133) wrote "Before pre .. 

ceeding further in the study of natural dissections 

of a volcanic .mountain we may pause to examine 

one ·rather abnormal form of eruption, traces of 

which may be occasionally Tecognized. 7 Fissure eruptions, as discharges of this kind are called, are 

characterized by the general absence of cones, at 

least of any importance, and by the large area which 

is covered by the lava-flows." Bonney then gave an 

account of fissure eruptions including Geikie's 

(1882) descriptions. Harker (1909) on the contrary 

recognized the importance of ·von Richthofen's discovery and noted its wide application in volcanology. 

American geologists were, in general, quick to 

recognize the concept of massive eruptions, as, for 

example, Darton (1890, p. 16) and Russell (1897, 

p. 252), who specifically credit Von Richthofen with 

the discovery. 

As Tyrrell (1937, p. 100, 102) has put· it "The 

fissure eruption theory, promulgated by Von Richthofen and popularized ·by Sir Archibald Geikie, has 

been almost universally accepted * * * ." 

Several volc·anologists urged that a distinction 

should be made between fissure eruptions and flank 

eruptions on central-type volcanoes. Sapper (1931) 

and Rittmann (1962, p. 46) have both made such 

7 Italics by G. T. F. 
REVIEW AND INTERPRETATION OF GEOLOGIC SETTING A35 

statements. They emphasized the two major points 

of difference-firstly, flank eruptions are fissures on 

central-type volcanoes, whereas fissure eruptions 

have no relation to central-type eruptions, and secondly, the length of the fissures in fissure eruptions 

is of a much higher order of magnitude than the 

short fissures forming the vent of flank eruptions. 

The possible relationship between fissure eruptions of the massive type and the domes of the 

Hawaiian type have been considered by Stearns and 

Clark (1930, p. 139) and Cotton (1952). 

VESICULATION IN BASALTIC MAGMA 

THE PROCESS OF BUBBLE l<"ORMATI.ON AND MOVEMENT 

Vesiculation is the process by which a very viscous 

liquid, such as a basaltic magma, exsolves a gaseous 

phase to form bubbles. The interfaces of these bubbles with the liquid are commonly spheroidal. Their 

former presence in the magma is attested to by the 

presence of cavities in the basalts called· vesicles. 

The formation of bubbles in silicate melts has been 

studied extensively by glass technologists, and especially reported by the Deutschen ·Glastechnischen 

Gesellschaft (1955). To a lesser extent it has been 

investigated by sil,icate chemists concerned with 

metallurgical slags. Their experimental studies and 

particularly their large-scale industrial pla11t practices show that: 

1. If a molten silicate melt flows over a rough surface, bubbles will form. When the melt wets 

the surface, bubbles are nucleated by the air 

entrapped between the melt and the rough surfaces. 

2. Large bubbles will move more rapidly than small 

bubbles-this follows from a consideration of 

the term r~ in Stoke's law 

2r2 · g (pmelt - pgas) 

v=-------

9,., 

where v =the rising velocity of the gas, r = 

radius of the bubble, (pmeit - pgm~) =difference 

in densities, g =acceleration of gravity, and ,.,, 

the viscosity. 

3. A decrease in viscosity of the melt will increase 

the rising velocity-also apparent in the above 

equation-as ,., gets smaller, v increases. 

4. As a bubble rises through zones of supersaturation, it grows ~by diffusion of gases through the 

melt, and, as its radius increases its rising 

velocity increases. ·The converse situation obtains if the bubble enters zones of undersaturation. 

5. Bubbles that reach the surface of the melt may 

burst-this ·will depend on the thickness of the 

film of glass containing the bubble, the internal 

pressure of the bubble, and the surface tension 

of the melt. 

It had formerly been assumed that the large 

bubbles grew chiefly through the coalesence of small 

bubbles as they collided on their ascent in the melt 

and that the larger bubbles served as collectors of 

small bubbles which they then dragged along with 

them. Modern studies show that this mechanism 

plays only a minor part in the growth of bubbles. 

Bubbles grow by diffusion of gases from the melt at 

the level where the bubble temporarily rests. As the 

bubble moves to higher levels in the melt, more gases 

diffuse to it and its size increases; this growth goes 

on until the bubble reaches the surface of the melt 

or another interface. 

Experimental studies on glasses indicate that thermal shock may aid in the nucleation of bubbles. A 

system is said to be in thermal shock when it, or 

any part of it, is suddenly subjected to a drastic 

change in temperature. 

BUBBLE FORMATION IN A NATURAL LAVA FLOW 

The basalt magma when it is in the earth, before 

extrusion, will have its internal pressure (=the 

vapor pressure) at a much lower value than that of 

the external pressure. If, as the magma ascends to 

the surf·ace, its vapor pres,sure exceeds the external pressure upon it (sum of hydraulic pressure 

of overlying lava and the atmosphere), then gases 

will be exsolved to form ·bubbles. 

As the lava continues to flow over the rough and 

·porous sandy floors, this movement could supply considerable trapped air and steam which could be incorporated as bubbles in the flow. 

The process of bubble formation and movement 

is thus regulated by two phenomena-the equilibrium process and the rate processes. The equilibrium 

process is controlled by the vapor pressure of the 

melt. If, as during a volcanic eruption, the external 

pressure is reduced, then vesiculation of the lava can 

take place. The vapor pressure of a melt is generally 

not constant, and it can be increased by crystallization of volatile free silicates. The rate processes 

operating in a melt are nucleation of bubbles, gas 

diffusion to the bubbles, and the rise of the bubbles 

in the melt. 

The addition of bubbles at the base of the flow 

when it pours out over rough surfaces is an aid to 

the rate processes in that it probably provides nuclei. 

As the bubbles ascend in the liquid part of the 

flow their shape may vary, and this characteristic 

will be dependent upon a number of factors but the 

most important will be the velocity with which they 

ascend. 
A36 STUDIES ON THE WATCHUNG BASALT FLOWS OF 'NEW JERSEY 

After the flow has come to rest, it continues to 

evolve bubbles and begins to cool. The natural system is complicated by the fact that the system. is 

losing a gaseous phase to the atmosphere in significant amounts only so long as the surface is still 

liquid. After the surface of the flow hardens, the loss 

by escape into the atmosphere is greatly decreased 

and is probably chiefly limited to escape along the 

joint systems in the vesicular tops of the flow. After 

the vesicular top has for.med . to a depth of a few 

feet, the bubbles that rise to the liquid-solid interface at the base of the hardened top will accumulate 

there. 

The evolution of bubbles in the lava flow as a result of the exsolution, after it has been emplaced, 

is a continuous process, but the rate of bubble formation may be changed significantly by a number 

of other physical factors. 'These factors may operate 

so as to produce unusual concentrations of bubbles 

in the later stages of solidification of the lava flow. 

As the lava .flow continues to solidify the residual 

liquor will be richer in volatiles, and these will decrease the viscosity thereby aiding the formation 

and growth of bubbles. 1Concomitant with these conditions there will be developed a gr.eater tendency 

for the system to form larger crystaJs. 

Some of the bubbles which migrate to the upper 

surface of the liquid flow will burst and release the 

gaseous phase to the atmosphere. Tlie pressure 1n 

a bubble is the sum of three pressures, the atmospheric pressure, hydrostatic pressure, and the pressure· oaused by surface tension. ·The internal pressure within the bubbles of various ,sizes caused by 

the surface tension can be calculated from the formula given by Widtman (1956, p. 498) which 

states that 

2u 

p= ' 

rx10- 6 

where u is expressed in dynes per centimeter, the 

radius (r) is in centimeters, and the pressure (p) is 

in ·atmospheres. ·The surface tension of the W·atchung 

Basalt has been calculated using the average composition of the 22 specimens (table 1, column 2) 

the surface tension factors for the oxides given by 

Morey (1954, p. 198,. 206, 207), and taking the factor for FeO as the same as MgO. This gives a value 

of 405 dyn/cm for the surface tension at 1,200°C. 

Using the formula for the internal pressure at 

1,200°C for bubbles of 1/1,000-mm, 1-mm, and 6-mm 

radius, the respective pressures are 8.1, 0.0081 and 

0.00135 atmospheres. These values show that the 

pressure caused by surface tension in the liquid lava 

of the Watchung flows becomes negligible for bubbles 1 mm in radius and larger compared to the 

atmospheric pressure and the hydrostatic pressure. 

From Widtmann's (1956) equation it is apparent 

that the pressure to form a new bubble is tremendously large, and he has pointed ou't (p. 498) : "One 

can, therefore, assume that one is dealing here primarily with a spontaneous growth of seed nuclei due 

to 'thermal fluctuations' and that these nuclei can 

continue to grow later on." Those bubbles that do 

not burst will retain their gas, and · this gaseous 

phase will probably react with the walls of the 

vesicles as the temperature drops in the system. 

Some of the gas may redissolve in the melt. Any _gas 

not used up in such reactions will later escape in the 

process of weathering. 

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A38 STUDIES ON THE WATCHUNG BASALT FLOWS OF NEW JERSEY 

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A 

Abstract 

Acknowledgments --------------------

Adams, Leason H ---------------------

Andreasen, Gordon E -----------------

Antevs, Ernst ----------------------- Armstrong, Richard L. quoted 

B 

Page 

A1 

2 

1, 26 

2 

8 

16 

Barrell, Joseph quoted --------- 4, 6, 6, 13, 27 

Barth, Tom F. W. quoted ------------- 34 

Basalt flows, chemical analyses ---- 22, 23, 24 

composition of pristine gases ------ 26 

fluidity --------------------------- 22 

megascopic character ------------ 24 

microscopic character ----------·-- 25 

petrochemistry ------------------- 22 

structural characteristics ---------- 7 

vesicles --------------------------- 22 

Bayley, William S --------------------

Besancon, James quoted -------------- 16 

Black, William W -------------------- 22 

Bonney, Thomas G. quoted ------------ 34 

Boutakoff, Nicholas A ---------------- 32 

Broadhurst, Frederick M. quoted ------ 14, 16 

Broad-terrane hypothesis -------------- 7 

Bucher, Walter H. quoted ------------- 8, 26 

cited ------------------------- 13, 21,26 

c 

Calk, Lewis quoted ------------------ 26 

Chandler, Evelyn J ------------------- 2 

Chemical analyses, basalts -------- 22, 23, 24 

pristine gases --------------------- 26 

Clark, Robert W --------------------- 26 

Clark, William 0 --------------------- 36 

Connecticut, Triassic basin ----- 18, 19, 26, 27 

Cook, George H ---------------------- 13 

Cornet, Bruce ------------------------ 9 

Correns, Carl W --------------------- 19 

Cotton, Charles A -------------------- 36 

D 

Daly, Reginald A --------------------- 23, 24 

Darton, Nelson H. quoted ------------- 7, 13 

cited --------- 2, 3, 11, 13, 14, 20, 26, 32, 34 

Davis, William Morris ---------------- 2, 3 

D'Andrea, Dennis V ------------------- 29 

deBoer, Jelle --------------- 16, 17, 18, 19,20 

Deutschen Glastechnischen Gesellschaft- 36 

Dickinson, Robert L ----------------- 2 

Dikes _ ------------------------------- 32 

post Triassic --------------------- 2, 20 

Diller, Joseph S ---------------------- 26 

Du Toit, Alexander L ----------------- 26, 31 

Dutton, Clarence E. quoted ----------- 33 

Duvall, Wilbur I --------------------- 29 

INDEX 

[Italic page numbers indicate major references] 

Page 

E 

Emerson, Benjamin K ----------------

Erickson, Glen P. quoted --------------

Evans, John W ----------------------

F 

A26 

16 

28 

Fanglomerate ------------------- 9, 11, 13, 18 

Faust, George T ------ 1, 2, 8, 11, 13, 14, 22, 32 

Federal Writers Project --------------- 2 

Fenner, Clarence N ------ 8, 13, 21, 22, 24, 26 

Fischer, Richard L ------------------- 29 

Fissure eruptions, closing stage ------- 33 

flow rate ------------------------- 32 · 

pre-eruptive character of floor ---- 20 

shape of ------------------------- 33 

sites -----------------------------· 20 

structural characteristics ------- 7, 32, 33 

time span ----------------------- 34 

timing -------------------------- 14 

vesicular tops -------------------- 20 

Flank eruptions ---------------------- 34, 36 

Flood basalt -------------------------- 33 

Flow units ---------------------- 7, 9, 11, 13 

Fogelson, David E ------------------- 29 

Fuller, Richard E -------------------- 32, 33 

Fulton, Charles H -------------------- 32 

G 

Geike, Archibald quoted ----------- 32, 33, 34 

cited --·-------------------------7, 20, 32 

Geographic locat~on ------------------ 3 

Geologic age, helium method ---------- 16 

igneous activity ------------------ 16 · 

Newark group -------------------- 9 

paleomagnetic method ------------ 16, 17 

potassium-argon method ----------- 16 

Geologic cross section ----------------- 12 

Geologic setting --------------------·-- 4 

Gilchrist, $ybil ----------------------- 2 

Glacier, continental ------------------- 8 

Goddard, E. N ------------------------ 26 

H 

Harker, Alfred ----------------------- 34 

Harwood, Henry F ------------------- 23, 24 

Hathaway, John C ------------------- 1 

Helland, Amund ---------------------- 33 

Henderson, John R ------------------- 2 

High, Lee R ------------------------- 9, 11 

Hobbs, William H -------------------- 7, 19 

Holmes, Arthur ---------------------- 23, 24 

Iddings, Joseph P -------------------- 26, 32 

Intertrappean layer ---------------- 8, 13, 21 

Page 

J 

Johannsen, Albert -------------------- A2 

Johnson, Meredith E. quoted --------- 6 

cited -------------------------- 3, 7, 9, 14 

Jointing in basalt --------------------- 1 

Jointing systems --------------------- 22 

Jumikis, Alfreda R -------------------- 29 

K 

Kessler, Daniei W -------------------- 29 

King, Philip B ----------------------- 2, 20 

Kirby, John R ----------------------- 2 

Klein;~ George De Vries ---------------- 4, 7 

Knapp, George N -------------------- 8 

Krynine, Paul D. quoted -------------- 14, 19 

cited ----------------------------- 18 

Kulp, J. Lawrence quoted ------------ 16 

Kiimmel, Henry B. quoted ------------ 1,9 

cited ------------- 3, 4, 8, 11, 13, 20, 21, 26 

L 

Lambert, Richard St. J. quoted -------- 16 

Lewis, J. Volney quoted ------------- 7, 9 

cited ------- 3, 4, 8, 13, 20, 21, 22, 23, 24, 26 

Lobeck, Armin K -------------------- 3 

Local-basin hypothesis ---------------- 7 

Longwell, Chester --------------------- 27 

Loring, Douglas quoted --------------- 14, 16 

M 

McDonald, Nicholas G ----------------- 9 

McLaughlin, Dean B. quoted ----------- 6 

cited -------------------------7, 9, 14, 28 

Mason, Brian H --------------------- 2, 26 

Massive eruptions -------------------- 34 

May, Paul R ------------------------- 20 

Merwin, Herbert E. ------------------- 26 

Millot, Georges ---------------------- 1 

Moore, James J. quoted --------------- 26 

Morey, George W --------------------- 36 

Murata, K. Jack --------------------- 1 

Murawski, Hans ---------------------- 30, 31 

N 

New Germantown trap sheet ---------- 3 

Newark basin, structure --------------- 27, 28 

subsidence of --------------------- 26 

tensional history ---------------- 31 

volcanism in -------------------- 26 

Newark Group, stratigraphy ----- 9, 10, 13, 14 

thickness ------------------------ 13, 14 

Nockolds, Stephen R ----------------- 23, 24 

Nomenclature, the Watchungs -------- 2 

trap ------------------------------ 2 

trap rock 2 

A41 
A42 

Obert, Leonard 

Opdyke, Neil D 

Owens, James P 

0 

p 

Page 

A29 

20 

7 

Peet, Charles E ----------------------- 8 

Petty, Arnold J ----------------------- 2 

Philbin, Philip W ------------------ 2 

Physiography ------------------------- 3 

Piburn, Michael D ------------------ 22 

Picard, M. Dane ---------------------- 9, 11 

Pillow lavas ----------------- 8, 21, 22, 23, 25 

Place, Frank Jr ---------------------- 2 

Pomperaug valley ----------------- 19, 26, 27 

Powell, John Wesley quoted ----------- 33 

R 

Raisz, Erwin J ---------------------- 3 

Ratcliffe, Nicholas M ---------------- 26 

Rayner, Dorothy H. quoted ----------- 14 

Reck, Hans -------------------------- 33 

Reeds, Chester A -------------------- 9 

Regional arch --------------------- 29, 30, 31 

Rinman, Sven -------~---------------- 2 

Rittmann, Alfred quoted -------------- 34 

cited ----------------------------- 35 

Rodgers, John ------------------------ 7 

Rose, Arthur W -------------------- 22 

Roy, Jean L. quoted ------------------ 31 

Russell, Israel C ------------- 7, 13, 20, 27, 34 

Russell, William L ------------------- 18 

s 

Sahasrabudhe, Y. S ------------------ 22 

Salisbury, Rollin D ------------------- 3, 8 

INDEX 

Page 

Sand Brook Ridge -------------------- A3 

Sanders, John E ----- 4, 6, 7, 13, 14, 22, 27, 28 

Sapper, Karl quoted --------------- 32, 34, 35 

Schafer, John P --------------------- 8 

Schaller, Waldemar T ----------------- 25 

Schneider, Karl ---------------------- 34 

Schottler, Wilhelm ------------------- 2 

Scrope, G. Poulett -------------------- 34 

Shaw, Herbert R. quoted ------------- 32 

Shepherd, Ernest S ------------------- 26 

Smith, Robert C. --------------------- 22 

Sollas, William J --------------------- 14 

Stearns, Harold T -------------------- 35 

Stratigraphy, Brunswick Formation ____ 8, 9 

local ----------------------------- 8 

Lockatong Formation ----------- 8, 9 

Palis!ldes Diabase ---------------- 8 

regional -------------------------- 18 

Stockton Formation -------------- 8, 9 

stratigraphic column ------------- 10, 11 

Watchung basalt flows ----------- 8 

Subramanian, Anantharama P -------- 22 

Surface tension ----------------------- 36 

Swanson, Donald A. quoted 32 

T 

Teall, Jothiro J. H 24 

Tectonic subsidence ------------------- 26 

Thorarinsson, Sigurdur quoted -------- 32 

Torrey, Raymond --------------------- 2 

Traverse, Alfred ---------------------- 9 

Troger, W. Ehrenreich --------------- 2 

Tyrrell, George W. quoted ------------ 33, 34 

cited ----------------------------- 20 

Tyson, Natalie S ---------------------- 2 

u 

Urry, William D ---------------------

U.S. Geological Survey --------------

v 

Page 

A16 

2 

Van Houten, Franklyn B ------ 7, 8, 9, 11, 13, 

14, 15, 16, 18 

Vesiculation, bubble formation -------- 95 

bubble movement ----------------- 35 

equilibrium process --------------- 35, 36 

in basaltic magma ---------------- 35 

rate processes -------------------- 35, 36 

Von Bubnoff, Serge ------------------- 29 

Von Engelhardt, Wolf ---------------- 19 

Von Knebel, Walther ----------------- 33 

Von Richthofen, Ferdinand Baron quoted 34 

cited --------------------------- 7, 32, 33 

Von Wolff, Ferdinand L -------------- 33 

w 

Wadia, Darashaw, "N ----------------- 2, 32 

Walker, Kenneth R ---------------- 9, 23, 24 

Washington, Henry S ----------- 2, 23, 24, 32 

Watchung Basalt flows, area extent ---- 21 

flow units --------------------- 7, 11, 13 

volume relations ------------------ 21 

Waters, Aaron C --------------------- 22, 23 

Wheeler, GiraTd ------------------4, 7, 19, 26 

White, Walter S., oral communication__ 22 

Widmer, Kemble E. quoted ------------ 28 

cited ---------------------- 3, 4, 8, 14, 28 

Widtmann, Julius quoted -------------- 36 

Williamson, Erskine D --------------- 1, 25 

Wilson, J. Tuzo ---------------------- 31 

Wilson, May ------------------------- 2 

Windes, Stephen L ------------------- 29 

Woodworth, Jay B ------------------- 27 

*U.S. GOVERNMENT PRINTING OFFICE: 1975 0-585-476/114