Joint Systems in the 

Watchung Basalt Flows, 

New Jersey 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 864-B 

Joint Systems in the 

Watchung Basalt Flows, 

New Jersey 

By GEORGE T. FAUST 

STUDIES ON THE WATCHUNG BASALT FLOWS OF NEW JERSEY 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 864-B 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1978 
UNITED STATES DEPARTMENT OF THE INTERIOR 

CECIL D. ANDRUS, Secretary 

GEOLOGICAL SURVEY 

V. E. McKelvey, Director 

Library of Congress Cataloging in Publication Data 

Faust, George Tobias, 1908-

Joint systems in the Watchung Basalt flows, New Jersey. 

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

Bibliography: p. 

Includes index. 

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

l. Joints (Geology) 2. Basalt-New Jersey. I. Title. II. Series. III. Series: United States. Geological Survey. Professional paper; 864-B. 

QE605.F38 551.8'4 76-608178 

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

Washington, D.C. 20402 

Stock Number 024-001-03023-3 
Abstract 

Introduction ---------------------------------

Previous studies on jointing in the Watchung Basalt 

flows ------------------------------------ Sampling of the jointing patterns in Third Watchung 

Mountain ---------------------------------

Description of the joint systems --------------------

Cooling joints -----------------------------

Vesicular top --------------------------

Columnar zone -------------------------

B~ckyzone ---------------------------

Curvilinear zone ------------------------

Geometric character of the curvilinear 

jcin~ ---------------------------

Ve~cu~rba~ -------------------------

Occurrences of similar cooling joints in other 

basaltic provinces ----------------------

Tectonic joints ----------------------------

Vesicular top --------------------------

C~umnarzone -------------------------

Blocky zone -----------------:-----------

Curvilinear zone ------------------------

Pseudocolumnar joints (type 1) ___________ _ 

Pseudocolumnar JOmts (type 2)-platy-prismatic joints (fracture cleavage) _________ _ 

Basal platy joints ---------------------

Sheeting joints ----------------------------

Weathering joints and associated phenomena _______ _ 

Spheroidal joints ------------------------

CONTENTS 

Page 

Bl 

2 

3 

3 

4 

5 

7 

11 

12 

13 

15 

17 

19 

20 

20 

20 

21 

21 

21 

24 

25 

27 

27 

Description of the joint systems-Continued 

Weathering joints and associated 

phenomena-Continued 

Late stage, unloading "platy joints" 

Solifluction, a distorting agent of jointing pat-

~rns ------------------------------

A jointing miscellany ------------------------

Feather-fracture (plumose fracture) and other surface 

patterns on joints ----------------------

Width of joint openings -------------------

Quasi-geologic joints and nongeologic pseudojoints 

and fractures -------------------------

Frequency of cooling and tectonic joints in one of 

the least deformed parts of the border syncline 

Summary of the geometry of the cooling joint systems __ _ 

Summary of the geometry of the tectonic joint systems-with a contrast of the two types __________ _ 

A note on the paucity of zeolite deposits in the trap 

flows of Third Watchung Mountain ____________ _ 

Supplementary topics ------------------------

Glossary of terms and definitions -------------

Character of helicoidal surfaces --------------

Isothermal surfaces and lines ----------------

The phenomenological evidence for isothermal 

surfaces and the direction of heat flow ________ _ 

Acknowledgments -----------------------------

Literature cited ----·---------------------------

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

ILLUSTRATIONS 

FIGURE l. 

2. 

3. 

4. 

5. 

6. 

A photograph of the Millington quarry taken in 1952 --------------------------------------------

Skctchmapsofarea -----------------------------------------------------------------

Schematic diagram of the cooling joint systems in Third Watchung Mountain as observed in the quarry at Millington for the 

uppcrand~wcrflowun~s ------------------------------------------------------------

The pahoehoe surface between the lower flow unit and the upper flow unit. The curvilinear jointing system and the thin vesicular 

base of the upper flow unit rest atop the pahoehoe surface of the lower flow unit. South wall of the Millington quarry of 

Houdaille Industries at Millington, N.J ----------------------------------------------------

Exposure of the vesicular zone showing the rectangular (slabby) aspect of the top and the jointing systems in this zone. 

Locality: Liberty Corner Road between Mountain View Avenue (Dead River Road) and Mountain Road, near Liberty 

Corner ------------------------------------------------------------------------- A part of the zone of vesicular trap grading into the columnar zone below. Roadcut on the east side of Alps Road a short 

distance south of its intersection with Rockledge Terrace, northeast of Mountain View, on Packanack Mountain 

Page 

B28 

29 

30 

30 

32 

34 

36 

36 

38 

38 

38 

39 

39 

40 

41 

41 

42 

45 

Page 

B4 

7 

8 

10 

11 

ll 

Ill 
IV CONTENTS 

FIGVRE 7. Columnar joints, slightly curved and tapered, just below the vesicular top. Roadcut on the east side of Alps Road a short 

distance south of its intersection with Rockledge Terrace, northeast of Mountain View, on Packanack Mountain 

8. Remnants of the blasted and mechanically excavated trap in the roadcut at Lyons Station, Lyons, N.J., showing the 

mechanically disrupted columnar zone ----------------------------------------------------

9. Columnar joints in the upper flow unit of Second Watchung Mountain. Roadcut on U.S. Highway No. 287, near Liberty 

Corner -------------------------------------------------------------------------

10. Inverted fan structure formed of columnar basalt. In roadcut for U.S. Highway No. 280 near West Orange, N.J 

ll. The ball end of "ball and socket" joints in columnar basalt. Ferguson's quarry, near Little Falls, N.J --------------

12. The socket end of "ball and socket" joints in columnar basalt. Ferguson's quarry, near Little Falls, N.J ------------

13. Exposure at the top of the "east" wall of the Millington quarry. The blocky zone juts out. The geologist is pointing to the base of 

the blocky zone. At the lower right hand side of the picture, well-developed curvilinear joints may be seen. This wall forms the 

dumping ramp of a stock pile~ The ap'parent granular decoration on the top of the blocks and scattered over the faces is the 

remains of a former stock pile ----------------------------------------------------------

14. Detailed view of the blocky zone on the "east" wall of the Millington quarry. An enlargement of a portion of figure 13 

15. A hackled block from the blocky joint system which has fallen and tumbled from its position in the overhanging ledge to the 

floor of the Millington quarry. It was battered by a steel ball dropped from a crane boom. Such blocks are used as jetty stone. 

Other large blocks may be seen near the base of the wall -----------------------------------------

16. Weathered blocky jointed trap. Roadcut near Blackberry Lane and James Street, New Vernon trap sheet near Morristown, 

N.J ---------------------------------------------------------------------------

17. Glacial pavement developed on basalt of the blocky zone. This glacially polished outcrop is on the north side of Chapel Hill 

Road and Highland Street, Hook Mountain, near Lincoln Park, N.J ---------------------------------

18. Blocks of trap dislodged from their position at the top of the ridge. These were naturally quarried by alternate freezing and 

thawing which disrupted the jointed ledge to produce a jumble of blocks. When dislodged sufficiently or undermined, they 

tumble down the scarp slope. Northeast of the intersection of Pine Brook Road and Passaic A venue Road, Lincoln Park, 

N.J ---------------------------------------------------------------------------

19. Curvilinear joints in trap. "East" wall of the Millington quarry. Note thin layer of the closely jointed blocky zone (upper left hand 

20. 

21. 

22. 

23. 

24. 

25. 

26. 

27. 

28. 

29. 

corner) overlying the curvilinear zone and above this the irregular and hackly broken masses of the blocky zone -----

A close-up view of curvilinear joints in an old quarry wall. "South" wall Millington quarry. Note that the blocks that have 

dropped out from the wall are shield shaped and wedge shaped ------------------------------------

Excellently developed curvilinear joints in the trap. The roadcut is approximately perpendicular to the strike. The joints across 

the face of the curved planes are sheeting joints and are not cooling joints. Roadcut on Bloomfield Avenue near its 

intersection with Hook Mountain Road, Pine Brook, N.J ----------------------------------------

Curvilinear joints in relatively fresh basalt. This rock is very tough and required extra blasting to excavate it. The curvilinear 

joints are outlined by the shades and shadows. They are elongate approximately perpendicular to the floor of the excavation. 

Near the surface of the triangular area on the right some checking of the minor joints is apparent. This locality is an 

excavation at the intersection of U.S. Highway 46 and Hook Mountain Road, Pine Brook, N.J ---------------

A strongly blasted mass of curvilinear jointed trap preserving its characteristic morphology. The picture represents a portion of 

the "north wall" at the Millington quarry, Millington, N.J __ ..:_ ____________________________________ _ 

Weathered curvilinear joint masses having wedge shapes. This rock is similar to that in figure 22 except that it is from a strongly 

weathered zone. Excavation at the intersection of the U.S. Highway 46 and Hook Mountain Road, Pine Brook, N.J __ 

Curvilinear joints in the trap of Second Watchung Mountain. Geologist's hammer indicates the position of the trace of the 

helical path of the curvilinear joint. Gallo's quarry, Mt. Bethel, N.J ----------------------------------

Two right helicoids with parallel but displaced directrices (helicoidal axes), with generators of slightly different length, with 

equal pitches and out of phase by about 155° ------------------------------------------------

Portions of two steep right helicoids, moved parallel to one another graphically, until they intersect ---------------

Curvilinear jointed trap overlying the vesicular base of the upper flow unit in the Millington quarry. The hammer handle 

rests on the contact of the two zones. The quarry face in this photograph is nearly perpendicular to the quarry face shown in 

figure4 ------------------------------------------------------------------------

Outcrop of flow breccia on south side of Oakland Valley Road, approximately abreast the dam, Packanack Mountain, 

at Pompton, N.J. This relatively thin layer of flow breccia lies just under the curvilinear jointed lava at the base of the 

flow 

30. Curvilinear joints in the basaltic lava flow exposed on the Bay of Fundy at Canada Creek, near Black Rock Lighthouse, Nova 

Scotia -------------------------------------------------------------------------

31. Tension jointed base of the blocky zone (so-called seam), overlying the curvilinear joint system. Excavation on Northfield 

Avenue below Valley Road, West Orange, N.J -----------------------------------------------

32. Detailed view of the tension jointed base of the blocky zone overlying the curvilinear zone "East" wall of the Millington quarry 

33. Typical pseudocolumnar appearance in the curvilinear zone produced by the superimposition of tectonic planar vertical joints 

on the curvilinear system. Excavation on Northfield Avenue, below Valley Road, West Orange, N.J -------------

34. Pseudocolumnar joints produced by the superimposition of tectonic joints on the curvilinear jointing system in the north wall of 

the Millington quarry, Millington, N.J. The tectonic joints are very rare in the overhanging ledge of the blocky systems, in this 

photograph. This is the appearance of the pseudocolumns in a freshly blasted exposure ---------------------

35. Platy-prismatic joints (fracture cleavage) in Second Watchung Mountain. Alward's quarry at the intersection of Pill Hill Road 

and Meeker Road almost 2'4 miles west of Basking Ridge, N.J. These joints are close to the contact with the Triassic 

sedimentary rocks below -------------------------------------------------------------

Page 

Bl2 

12 

12 

13 

14 

15 

16 

17 

18 

18 

18 

19 

20 

21 

22 

23 

23 

23 

24 

24 

25 

25 

26 

26 

26 

27 

28 

28 

29 
CONTENTS 

FIGURE 36. A view of the zone of the platy-prismatic tectonic joints on Second Watchung Mountain. Musialowski's quarry on Washington Valley Road, northwest of Martinsville, N.J. Note the curvature of the sides, of the back joint face in profile. The 

fracture cleavage here shown in the walls of the quarry has its acute angle bisected by a line parallel to the axis of the major 

syncline ------------------------------------------------------------------------

37. The platy surface of the curved platy-prismatic joints (fracture cleavage) developed in or near to the axial plane ofthe tightly 

folded syncline in the New Germantown trap sheet, 1.2 miles southwest of Oldwick, N.J --------------------

38. Side view of the curved platy-prismatic joints (fracture cleavage). New Germantown frap sheet, 1.2 miles southwest of Oldwick, 

N.J ---------------------------------------------------------------------------

39. Top view, showing the prismatic cross section of the curved platy-prismatic joints (fracture cleavage). New Germantown trap 

sheet, 1.2 miles southwest of Oldwick, N.J --------------------------------------------------

40. Very abundant platy-prismatic joints on Second Mountain. The conjugate set of tectonic joints are so abundant that it is difficult 

to recognize the cooling joints. This section was formerly exposed in the cut for U.S. Highway No. 78 near Pluckemin, N.J. 

The outcrop is just above the contact with the underlying Brunswick Formation -------------------------

41. Basal platy joints at the base of the curvilinear zone, just above the contact with the hornfelsized Brunswick Formation. In cut, in 

Second Watchung Mountain, on U.S. Highway No. 280 at its intersection with Pleasant Valley Way, West Orange, 

N.J -------------------------------------------------------------~------------- 42. Sheeting joints in the transition zone between the blocky and the curvilinear zone of the basalt flow of Hook Mountain. This 

figure represents a view showing a section essentially at right angles to the strike. The roadcut, on Bloomfield Avenue in 

Pine Brook, is roughtly east-west -------------------------------------------------------

43. Sheeting joints in the blocky and curvilinear jointed trap of Hook Mountain. The step like aspect is clearly evident. Quarry near 

the northern end of Hook Mountain near Mountain View, N.J ------------------------------------

44. Spherical balls found in the deeply weathered columns of trap, near the surface. A ball3 inches (7.5 em) in diameter was cut and 

polished to show the "fresh" character of the minerals --------------------~---------------------

45. "Spherical jointing" in basalt produced by weathering. Quarry 2 112 miles south of Stirling, Second Mountain. Taken from 

Lewis (1908, pl. 38, fig. I) ------------------------------------------------------------

46. Late stage, unloading joints, probably developed in prestressed areas close to the surface of the earth. Their development 

may have been aided by weathering processes relieving stress, by man induced stresses inherent in blasting, excavating, and 

machine scraping or bumping operations. "North wall,'' Millington quarry and plant of the Houdaille Industries, 

Inc ---------------------------------------------------------------------------

47. Effects of solifluction are shown in the wall, which is essentially normal to the strike. This is shown in Tullo's quarry on Washington Valley Road, near Martinsville, N.J. The creep of the mantle down the slope has tilted the pseudocolumns, from their 

normal position shown at the base, to head downslope ------------------------------------------

48. Feather fracture developed on a curvilinear joint surface. Upper flow unit, Hook Mountain of Third Mountain, Pine Brook, 

N.J. The sharp end of the hammer is at the basal point of the feather ---------------------------------

49. Fracture pattern on a joint wedge broken out of the curvilinear zone at the Millington quarry (Houdaille Industries, Inc.), 

Millington, N.J. The scale is 10 em -------------------------------------------------------

50. A, A string model of Oblique Helicoid prepared by Olivier of Paris. "A helix and its axis as directrices; elements making an acute 

angle with the axis." B, A string model of Right Helicoid. "A helix and its axis as directrices; elements making a right angle 

with the axis." From Schumann (1946) (Published by permission of D. Van Nostrand Co., Inc.) ---------------

51. Two left-hand, right helicoids. The vertical distance 2 7rq is the pitch of one helicoid where q equals a constant and it represents 

the vertical distance traversed in one complete revolution (360°) of the generatrix. Scheffers ( 1902, v. 2, p. 60-61) ___ _ 

TABLE 

TABLE I. Joint frequencies in the Watchung Mountains along a line nearly normal to the strike and extending from Pine Brook on Third 

Watchung Mountain to near West Orange on First Watchung Mountain ------------------------------

ERRATUM 

On page A23 of Professional Paper 864-A, "A review and interpretation of the geologic 

setting of the Watchung Basalt flows, New Jersey," the following items in table 2, column I, 

were incorrectly cited: 

SrO 0.08 should be corrected to SrO 0.00 

C02 ---- should be corrected to C02 0.08 

v 

Page 

B29 

30 

30 

30 

31 

32 

33 

33 

33 

33 

34 

35 

35 

35 

40 

41 

Page 

B37 

STUDIES ON THE WATCHUNG BASALT FLOWS OF NEW JERSEY 

JOINT SYSTEMS IN THE WATCHUNG BASALT FLOWS OF NEW JERSEY 

By GEORGE T. FAUST 

"Die Kl~'fte" 

"Wir treten vor eine universelle Erscheinung. Kawn ein Vorgang, sei er vulkanischer oder tektonischer Natur, der 

nicht j(ihig wcire, Kl~fte zu erzeugen. "I 

ABSTRACT 

The Watchung Basalt flows of New Jersey were jointed by four different 

geologic processe~-the cooling of the lava flows, tectonic deformation of 

the graben, loading during glaciation, and weathering. After the lava flows 

were extruded to form sheets, they began to cool down, solidify, and joint. 

The developmental sequence of the joint systems was controlled by the character of the heat loss. The sequence, typical of the two flow units in Third 

Watchung Mountain, forms the basis of this study. The vesicular top 

formed first. It developed a system of joints which combined to form rectangular prisms with a slabby aspect. During the stage when the vesicular 

top was forming the base of the flow began to solidify, and for most of its 

length it formed a thin vesicular zone 6-8 inches thick ( 15-20 em). The central portion of the flow between the vesicular top and bottom cooled very 

slowly and eventually solidified and jointed. The sequence of the joint systems, arranged in descending order, which developed in the central portion 

is as follows: the vesicular top changes gradually or abruptly into the columnar zone, this in turn forms an abrupt boundary with the blocky zone, and 

the blocky zone changes abruptly into the underlying curvilinear zone, the 

latter zone passes abruptly or gradually into the vesicular base. 

The tectonic joints developed in the flows after graben development had 

ceased. These joints resulted from the deformation of the contents of the 

graben into a regional central arch with border synclines. In New Jersey 

weathering has removed all but the border syncline on the so-called "west 

wall of the graben." Tectonism produced transverse joints in the vesicular 

top, irregular or planar lateral joints in the columnar zone, a tension jointed 

base in the blocky zone, and three types of joints in the curvilinear zonepseudocolumnar, platy prismatic (fracture cleavage), and basal lateral 

joints. 

Sheeting, the third type of jointing, postdated all the other joint systems. 

It is best developed in the curvilinear zone north of the terminal moraine of 

the last glaciation. 

Weathering processes developed spherical joints. 

Observations made on jointing systems elsewhere in the United States 

and in Iceland, Great Britain, and Germany are compared with those 

observed in the Triassic basin. 

1 Cloos. Hans (1936, p. 214). "We are in the presence of a universal phenomenon. Scarcely an 

~vent. be it of volcanic or tectonic nature, that would not be capable of generating joints." 

INTRODUCTION 

Joints are the record, imprinted in the rocks, of past geologic processes whose stress fields were of such a magnitude 

that they caused the brittle rocks to rupture. Joints are omnipresent in rocks. They can be formed by several physical 

processes-thermal and mechanical. The magnitude of the 

stress fields developed in a given region is not constant 

throughout time and may reach magnitudes sufficient to 

produce rupture at several widely separated times in the 

geologic history of the region. Commonly, the several geologic events which produced the stress fields that caused 

rupture were themselves unrelated. Each of the geologic 

events, if it is capable of rupturing the rocks, will produce its 

own characteristic set of joints. From a study of joints in the 

field it should be possible to determine: 

l. how many different joint systems are present, 

i the geometric morphology of each joint system, and 

3. the relation of each joint system to some past geologic 

event. 

Joints studied in this way may thus contribute in deciphering 

the geologic history of a region and provide an estimate of 

the minimum order of magnitude of some of the forces 

involved. 

Joints are commonly paths along which ground waters 

flow in traversing rock masses. The amount of water moving 

along joint planes is dependent upon the width of the joint 

openings, and the frequency of joints. It also depends on the 

degree of interconnection between the various joint systems, 

and between these systems and other structural planes or depositional surfaces. The zones of most intense fracture will 

be the zones of higher permeability. The relation of joint frequency in rocks and the yield of water in wells in these rocks 

may serve as a valuable aid in hydrologic studies. 

Joints may also be the paths along which mineralizing 

solutions flow, and they may themselves later become filled 

or coated with mineralized veins. By noting which ofthe sevBl 
82 STUDIES ON THEW ATCHUNG BASALT FLOWS OF NEW JERSEY 

eral joint systems are veined and which are not and by determining the paragenetic sequence characteristic of each type 

of veined joint system, the relative ages of the mineralization 

and the direction of flow of the mineralizing solutions may 

be obtained. Suc]l information can help in the search for ore 

deposits, or it may furnish diagnostic criteria in the interpretation of the petrologic history of igneous rocks. 

A detailed knowledge of the joints present in rock masses 

that are traversed by, or compressed by superimposed constructional loads, is very important to engineering geologists 

and civil engineers. Joints in rocks affect the stability of 

slopes, walls, tunnels, and other types of excavation and they 

may greatly influence the hydrologic regime within such 

rock masses. Under water-saturated conditions and high 

pore pressure, walls may become so unstable that they collapse. Quarry operators may also make use of information 

obtained in the study of joints in selecting the volumes of 

rock to be quarried. 

In order to answer some of the problems just posed to the 

reader, it is necessary to study joints in the field. The present 

study was undertaken to help in the interpretation of the geologic history of the region. This geologic history was needed 

as a background on which petrologic studies could be based. 

As a byproduct of this study, data were obtained and observations made on joints which may help scientists, engineers, 

and others working in the applied disciplines. 

The treatment of jointing presented in this paper is phenomenological. The theory of jointing and other interpretive 

discussions are reserved for another contribution. 

In the introductory paper of this series I described the 

circumstances which led to my study of the development of 

the joint systems in the basalts of the Watchung Mountains, 

Faust (1975, p. AI). About 1937 I had made very simplified 

calculations of the heat flow relations within a model sheet. 

By this means the probable direction of movement of the 

heat flow lines, within the model, was obtained. A geometrical method given by A wbery and Schofield ( 1929) and Schofield ( 1930, p. 495) showed that the heat flow lines could be 

taken as perpendicular to the isotherms at every point within 

a given body. In three dimensions, assemblies of adjacent 

heat flow lines will be normal to a common plane or to a portion of a common curved surface. It has been assumed, in 

petrologic studies, that at that temperature at which the 

joints form in a cooling igneous mass they form along surfaces perpendicular to the isothermal planes, Iddings ( 1909, v. 

1, p. 320-327). Tomkeieff ( 1940, p. 129) defined the "fracture 

isotherm" as that particular isotherm at which fracture takes 

place. Spry (1962) and Jaeger (1968) discussed the relations 

between isotherms and jointing in basalt. 

It was clearly recognized, at the outset of my studies, that 

this simplified model that I developed could only furnish 

ideas for a preliminary skirmish with such a formidable natural geometrical problem. Accordingly, I decided to compare the model with the natural system and I had the opportunity to test it while visiting a number of quarries and 

outcrops, in the company of Dr. Alfred C. Hawkins, Professor of Geology in Rutgers University. Although any real 

agreement between the model and the natural system had 

not been expected, the abundance of different sets of planar 

joints and the unique character of the curvilinear surfaces 

was totally unexpected. Moreover, the unequal frequency of 

occurrence of the joint surfaces for the different joint systems 

needs explanation. These observations led me to abandon 

theoretical studies and to examine the joint systems in the 

field. 

Subsequent studies of the field relations of the flows 

showed that there were at least two independent geologic 

processes which produced the joint systems. In Third 

Watchung Mountain the joints due to the cooling ofthe lava 

were found to be the most abundant. In Second Watchung 

Mountain the abundance of a new type of joints arising from 

a second geologic process, the tectonic deformation of the 

contents ofthe Newark graben varied with respect to the outcrop position in the synclinal basin. Once these distinctions 

were established the tectonic joints were readily differentiated from the cooling joints. A third type of jointing, 

sheeting, was observed in the northern portion of the 

synclinal structure north of the terminal moraine which 

extends from the vicinity of Morristown to the SummitShort Hills area. The jointing in First Watchung Mountain, 

in certain outcrops, as at and in the vicinity of the famous 

O'Rourke quarry at West Orange, described by Iddings 

(1886), showed a more complicated pattern with the greater 

development of the zone of columnar jointing, and this 

modified the magnitudes of the zones of the several joint systems. 

Certain aspects of this study are mentioned in Geological 

Survey Research 1961, 1972, and 1973 (U.S. Geol. Survey, 

1961, p. A97; 1972, p. A27; 1973, p. A36). 

A qualitative description is given herewith of the various 

jointing systems in the basalt flows, and of the interrelationships amongst them. Most of the examples will be chosen 

from outcrops in Third Watchung Mountain, but in addition examples of joint systems, well developed or more prevalent in Second Watchung Mountain and First Watchung 

Mountain, will be included. 

The several jointing systems are described first in an overall manner, showing the relationships between the several 

systems, and then in detail for each system. Emphasis is 

placed on describing as far as possible, the appearance of a 

particular joint system in a freshly exposed outcrop, a weathered outcrop, and in glacially abraded exposures. 

PREVIOUS STUDIES ON JOINTING IN THE 

WATCHUNG BASALT FLOWS 

In earlier geologic studies of the Newark basin, some of 

the geologists made observations on joints in selected parts 

of the Watchung Basalt flows. The columnar fan structures 

in the basalt of First Watchung Mountain at O'Rourke's 
JOINT SYSTEMS B3 

quarry just south of Llewellyn Park, West Orange, N.J., 

were made famous by the classical theoretical study of 

Iddings (1886, 1909). Fenner ( 1908) made observations on 

the character of the basal part of the lower flow unit of First 

Watchung Mountain. Lewis (1909, 1915) briefly described 

jointing patterns in the Watchungs and mentions columnar, 

platy, planar, irregular, and "sphenoidal or wedge-shaped" 

types of jointing. Bucher (in Bucher-Kerr, 1948) briefly described the jointing patterns in the lower flow unit of First 

Watchung Mountain and compared the section with that described by Tomkeieff (1940) at the Giant's Causeway, 

County Antrim, Ireland. Bucher's broad use of the term 

columnar makes difficult the comparison of his studies with 

those of other investigators. 

· Most of this early work consisted of observations made at 

one or a few outcrops. None of these geologists studied the 

distribution of joints in both the upper and lower flow units 

of any of the three sheets nor made any attempt to investigate 

the distribution of joint systems over the whole outcrop area. 

Sosman (1916) carefully evaluated the results of the 

experimental data obtained in the study of the formation of 

polygonal structures. He developed criteria for recognizing 

contraction and convection prisms and applied them to the 

interpretation of the data on the frequency of n-sided prisms 

(where n = 3, 4, 5, 6, 7) in columnar jointed basalts. 

SAMPLING OF THE JOINTING PATTERNS 

IN THIRD WATCHUNG MOUNTAIN 

The outcrop area of the several parts of Third Watchung 

Mountain is about 18 square miles along an outcrop scarp of 

approximately 41 miles length. In t'his area about 250 exposures were studied in detail. Four active and 16 inactive or 

abandoned quarries were studied. 

Fortunate for this investigation was the rather extensive 

building development which occurred during the course of 

this research. Attractive scenic views along the scarp slope of 

Long Hill, Hook, and Packanack Mountains caused this 

area to open up quickly for homes for the commuting suburbanites. Cellars excavated and occasionally blasted out of 

the trap rock offered excellent exposures. Ditches for the 

utilities, gas, water and electricity, permitted checking the 

continuity of. observations along the strike, and drilling for 

water wells, 'commonly through the basalt to the red shale 

below, permitted checks on the thickness and attitude of the 

flows. It should be emphasized that many of the outcrops described herein were open only during periods of excavation 

or building operations and cannot be seen today. The same is 

true for old and abandoned quarries which have had their 

floors leveled, and their walls graded, and have had apartments, dwellings, and factories built in them, or they have 

been converted into parking lots. For these some of the photographs included here are the only evidence. 

It is of course not possible to see all of the trap rock present 

in Third Watchung Mountain. On the basis of what is 

observable, it is possible to state that, the bottom of the 

lower flow unit most commonly rests directly on the red 

shale and sandstone, which were baked; less commonly it 

formed a flow breccia resting on the shale and sandstone. 

The description and the discussion of the minor zones of 

the flow units-agglomerate, pillow lavas, and tuff that 

occur locally- will be given in a subsequent part of this serIes. 

DESCRIPTION OF THE JOINT SYSTEMS 

The preliminary examination in 1936-37 showed that the 

jointing patterns were more distinct and apparently less 

complicated in the quarries and exposures in Third Mountain than in either Second Mountain or First Mountain. 

Further observations in 1946 showed that mineralization 

was chiefly confined to the joints and to a lesser extent to 

breccia zones as at the Millington quarry (then part of the 

North Jersey Quarry Co., now Houdaille Industries, Inc.). 

The large zones of "green rock," present in parts of First 

Mountain, were also absent from Third Mountain. Accordingly, it was decided to set up a standard section for study in 

the Millington quarry. The reasons for doing this were as follows: first, the jointing systems observed in Third Watchung 

Mountain appeared to be the least complex; second, the 

quarry at Millington was a very large excavation which 

exposed almost the entire section of the upper flow unit and 

a portion of the lower flow unit; and third, the possibility 

existed that the lower flow unit might be core drilled sometime in the future. Although the lower flow unit was exposed 

nearby in the weathered outcrops, the obvious advantage of 

obtaining fresher material from the core was also a decisive 

factor. In addition, in this quarry, the quarry faces had 

remained essentially dormant since large-scale quarrying 

operations temporarily closed down in 1930, and the jointed 

surfaces had acquired a reddish patina which stood out in 

striking contrast to the yellowish-brown color of the subsurface alteration of the uppermost portion of the flow. Most of 

the cooling joint patterns described herein were first 

observed and later delineated at this locality. An overall photograph of this quarry taken in 1952 is given as figure l. 

In order to relate the various outcrops, described herein, 

to their position in the synclinal basin which they in part 

form, a sketch map is given here, see figure 2A. An index to 

the U.S. Geological Survey topographical quadrangle maps, 

scale I :24,000, covering the exposure area of the Watchung 

Basalt flows is given in figure 2B. 

Joints are commonly defined as the cracks which divide 

rocks into separate volumes and along whose surfaces no significant movement has occurred. In the field, joints are 

observed to occur in sets which usually have a directional 

parallelism. The frequency of occurrence of a given joint set 

in the Watchungs may vary from a few inches to many tens of 

feet. The area of the different joint surf:,1ces is also quite variable, ranging from a few square inches to many tens of 
84 STUDIES ON THE WATCHUNG BASALT FLOWS OF NEW JERSEY 

FIGURE I. A photograph of the Millington quarry taken in 1952. The picture was taken looking in an easterly direction. Photograph courtesy of the Houdaille 

Industries, Inc ., and Mr. Thomas Stewart, formerly superintendent of the Millington operations. A-B is the blocky zone, Cis in the curvilinear zone, Dis a 

remnant of the curvilinear just under the closely jointed base of the blocky zone, E is the pond just above the vesicular base. 

square feet. The joint surfaces may be plane or curved surfaces. These characteristics define, in part, the geometrical 

relations of joints and joint surfaces, but by themselves they 

do not indicate the geologic process which produced the 

joints. 

The jointing developed in a given area may be the result of 

one or more geologic processes. When several geologic processes have each developed their own joint sets, the combined sets of joints are very complicated, and it is necessary 

to identify the joint sets arising from each process. It is sometimes possible to note that a combination of several joint sets 

produces a symmetrical pattern and that these individual 

joint sets appear to be related. Thus three mutually perpendicular joint sets may be combined to form a rectangular 

parallelepiped. Such a combination of genetically related 

joint sets which encloses space and forms a more 

symmetrical pattern is here referred to as a joint system. The 

recognition of joint systems leads to an understanding of 

their genesis. 

This usage of joint set and joint system is essentially the 

same as that described by Cloos (1936, p. 219) for use in the 

study of intrusive igneous, metamorphic, and sedimentary 

rocks. I have tried to avoid introducing new terminology, 

and I have followed Geike (1893, p. 529-530), in the use of 

transverse joints, those that "are oblique to the sides of the 

prism (referring to columnar joints)" and extended this term 

to cover joints that form as diagonal planes in an idealized 

orthogonal system. 

COOLING JOINTS 

The Watchung Basalt flows were formed by three volcanic 

episodes. Each volcanic episode poured out lava in two successive eruptive events. During each eruptive event, lava 

flowed out of the fissures and spread laterally until it reached 

the bounding "fault walls." Continuous discharge of lava 

built up accumulations from 100 feet (30.5 m) to perhaps 500 

or 600 feet (152.5 or 183m) thick. The flood oflava tended to 

attain a level surface. The upper surface of a flow cooled relatively rapidly and formed a vesicular top. This surface was 

gently undulating and relatively smooth in character, of the 

pahoehoe type. The bottom of the flow cooled much more 

slowly and formed, in general, a thin vesicular base. The central portion of the flow cooled very slowly. After the various 

parts of the central portion had cooled sufficiently, they too 

jointed. The resulting sequence of zones of joint systems owe 
JOINT SYSTEMS 65 

their origin solely to the cooling process which took place in 

the Ia va sheet. The sequence of zones of coolingjoint systems 

observed in both the upper and the lower flow units of Third 

Watchung Mountain are, in descending order, as follows: a 

vesicular top that changes gradually or abruptly to the 

columnar zone; this in turn forms an abrupt boundary with 

the underlying blocky zone; this in turn forms an abrupt 

boundary with the curvilinear zone, and the curvilinear zone 

passes abruptly or gradually into the vesicular base. 

A schematic diagram of the jointing relations in Third 

-·watchung Mountain as exposed in the quarry at Millington, 

see figure 2, is shown in figure 3. The vesicular top is overlain 

to the east by the Brunswick Formation ("Rb), and an outcrop of Brunswick appears on South Maple Avenue just 

above the Davis Bridge, Basking Ridge. When I first examined the quarry in 1946, the vesicular top and the columnar 

zone were only remnants left after scraping and bulldozing 

the upper surface. The upper flow unit rests directly on the 

lower flow unit, and there is no intertrappean layer of 

sediments exposed in the quarry nor in the many drill cores 

that penetrate this boundary. The boundary surface between 

the two flow units is a pahoehoe surface, figure 4, and it 

shows no evidence of any erosion, an indication that the two 

flow units were the results of two volcanic events not widely 

separated in time. 

The lower flow unit was only partially exposed as the 

vesicular top in the quarry, but it was well and more completely exposed as weathered outcrops and as fresher rock in 

roadcuts, nearby. I have also examined the fresher rock of 

the drill cores, and they show the vesicular base of the lower 

flow unit rests on a very thin hornfels zone which grades 

almost imperceptibly into the unmetamorphosed sedimentary layers below. 

A part of the sequence of the jointing systems and the 

interrelationships between them in the Millington quarry is 

shown in figure I. The arrow "A" indicates the position of 

the blocky layer which juts out as a ledge. Atop it, arrow "B," 

is the remnant of the columnar layer which has been badly 

shattered by quarrying operations. In the quarry face, 

marked "C," located in the picture between the stock pile and 

office building, the lower part of the section is exposed. Here 

the curvilinear layer is shown cracked by vertical tectonic 

joints. The promontory, at the top of this section, marked 

"D," was 15 feet higher than the roadway and contained the 

lower part of the blocky layer. At the edge of the pond, 

marked "E," the lower vesiculate zone of the upper flow unit 

and the upper vesiculate zone (top) of the lower flow unit 

were encountered in quarrying operations probably about 

1890-1900. More detailed views of the various boundary 

zones between the jointing systems are given in appropriate 

sections that follow. 

VESICULAR TOP 

Particularly fresh occurrences of the vesicular basalt are 

not very abundant on Third Watchung Mountain. The scarcity of such outcrop arises, in part, from the glacial erosion 

which removed much of this zone. It is still encountered in 

drilling wells for water; or in localities where it has been protected from erosion, it may appear in the top walls of quarries or in roadcuts. On Second Mountain at an exposure in a 

roadcut located on the east side of the Liberty Corner Road 

between Mountain View Avenue (Dead River Road) and 

Mountain Road, near Liberty Corner, a relatively fresh outcrop can be seen. The surface appears to be an original top; 

in places the gloss of the original surface has been dulled by 

weathering. The exposure probably lay beneath a red shale 

knoll, which has since been removed by erosion and excavation. Such red shale knolls in the Watchungs are not infrequent and usually offer good exposure. Some of them have 

been used as local quarries for brownstone and were apparently abandoned when the vesicular zone of the trap was 

encountered in quarry operations. 

The vesicular zone is characterized at the top by a rectangular aspect. Weathering along the joints produces 

rectangular slabs. With depth, this zone may show a jointing 

pattern that appears to be pseudocolumnar. 

The vesicular top, in the vicinity of the Millington quarry, 

has been largely removed in stripping operations, because it 

was much weathered and easily excavated. Nearby, at Davis 

Bridge, Basking Ridge excavations for the gas utility line 

starting in red shale penetrated through the contact with the 

vesicular trap and yielded relatively fresh samples of the latter. At some localities the vesicles are filled with minerals, 

chiefly calcite, but some prehnite and pectolite may be present. The rock is then part of an amygdaloidal top. 

The characteristic appearance of a good exposure in the 

vesicular zone is shown in figure 5, where the rectangular 

(slabby) aspect of the top of the zone can be seen. This exposure is approximately 30 feet long and 6 feet high. In addition 

to the rectangular joint system, two sets of transverse joints 

at about 45° to the principal joints are present. The rectangular joint system, which represents cooling joints, consists of 

the flat surface (the basal plane) and the rectangular prism. 

The transverse joints are interpreted as tectonic joints. This 

exposure represents the upper surface of the flow, and its 

change in character with depth cannot be followed here but 

elsewhere as at several exposures on Alps Road, northeast of 

Mountain View on Packanack Mountain, a part of Third 

Mountain, the lower portion of this vesicular zone may be 

observed. 

The vesicular layer as it appears in a roadcut on Alps Road 

just a short distance south of its intersection with Rockledge 

Terrace, northeast of Mountain View, is very instructive. 

Here one can see the change from the vesiculate layer (here 

amygdaloidal in part) into the columnar layer below, see figure 6. 

The weathering of the vesicular layer at some outcrops 

takes place so that the whole rock exposure has decomposed 

throughout to yield a soft product. At other outcrops it 

appears that the bridging rock between the vesicles, at the 
136 STUDIES ON TH E WATCHU NG BASALT FLOWS OF NEW JERSEY 

74 " 4 0' 

p£ 

New Germantown 

trap sheet 

lib 

74"30' 

p£ 

• Somenille 

p£ 

74 " 20' 

lib 

74"10' 

.orange 

West Orange 

0 5 10 MILES 

0 5 10 KILOMETE RS 

4 0 "30' L_ ____________ _L ____________________ ~ ____________________ L_ __________________ ~--~ 

EXPLANATION 

CllJ]D> Outcrop of basalt 

---Fault 

- ..:._- Anticl ine 

A 

-+- Syncline 

o40 Approximate location of 

figures with number 

M Location of M illington Quarry 
JOINT SYSTEMS 87 

75" 

NEW JERSEY 

41 ·oo· 

#' ~~ 

~ ~ 

~ ~ o+ ,.._o ~ ~ ~"' ~"' <.i ~ 

~ 0 ~~ ~ Bedminste ~ 

0~ 

Somerville 0 q) ~ 

# 0 

~ Boun ~ Brook 

75" 

0 10 

0 10 20 

H 

~+ ,.._o 

R o o4? 

~ 

Morris to 

#' 

~'t-"~ <.i 

~ 

~~ ~ q,~ 

20 

30 KILOMETERS 

0 

Oakland 

30 MILES 

41 ·oo· 

Jersey City 

FIGURE 2. A, Sketch map showing outline of the three Watchung Mountains and the New Germantown trap sheet (modified from Lewis, 1908, pl. 10). I, II, and III 

refer to First, Second , and Third Watchung Mountains. B, An index to the U.S . Geological Survey topographical maps, scale I :24,000, covering the exposure 

area of the Watchung Basalt flows. 

position of least volume, weathers more rapidly so that crude 

polyhedral volumes of less altered rock result. If the finer 

material of such a deposit is winnowed and washed away a 

coarse gravelly deposit having the appearance of weathered 

pyroclastic material forms. This type of alteration is made 

more obvious to the eye if the rock was an amygdaloid, for 

the light colored minerals stand out by contrast, and the 

more insoluble minerals such as quartz and prehnite are particularly conspicuous. 

COLUMNAR ZONE 

The columnar zone is characterized by columns, com-
B8 STUDIES ON THE WATCHUNG BASALT FLOWS OF NEW JERSEY 

0 

10 

t 

~,a'!-.-· _,.,. 

._.,,rtf 

- I..· 

~ I ) ~ 

F I 

.. 

UPPER FLOW UNIT 

Vesiculate zone 

Columns 

Blocky zone 

"Rw Watchung 

Basalt Formation 

Curvilinear zone 

Vesiculate zone 

FIGURE 3. Schematic diagram of the cooling joint systems in Third Watchung Mountain as observed in the quarry at Millington for the upper and lower flow units. 

The curvilinear joints are enclosed within the bounding surface of the convection cells. These cells are drawn as hexagonal prisms in torsion , see p.B 14. The 

amount of torsion has been exaggerated for purposes of illustration. Three patterns of curvilinear joints corresponding to figures 20, 21 , and 25 are 

schematicall y illustrated within the convection cells. The columnar and blocky zone of the lower flow unit were not exposed , but they are shown here. They do 

appear in other outcrops of the lower flow unit. 
JOI NT SYSTEM S B9 

LOWER FLOW UNIT 

monly six-sided but also five-sided, and best described as 

polygomil in outline to allow for the variations observed 

locally. Figure 6 shows the upper vesiculated surface with 

curved columns appearing with depth. The crude columns at 

first are curved and swirly in nature. Some appear to flare 

out from points in the upper rectangular joint system. The 

columnar joints are commonly nestled under the vesicular 

zone and if this zone is thin, then the columns will radiate, or 

fan out, under the undulating pahoehoe top. Vesicles appear 

to be common in the top of the curved columns. Weathering 

accentuates the curved columns. Well-developed columns 

are illustrated in figure 7. 

' 0 • 0 

• 0 ... 0 '0 .. 

o., () Q (> 

0 • 

0 0 ' 

liw Watchung Basalt 

Formation 

lib Burnswick Formation 

The columnar zone at the Millington quarry was well represented when the section was measured in 1949. lt stood out 

in marked contrast from the blocky zone on which it rested, 

for weathering had enlarged the space between the joints. 

The columns were polygonal, many were six and five sided, 

and a horizontal joint system formed the basal planes which 

closed the columns at both ends. In addition to the enlargemerh of the cooling joints, cross-joints are made more evident by weathering, or blasting. The columns at the Millington quarry were commonly 6 inches wide (15 em), but some 

ranged up to a foot (30 em) in width. Their height was about 

four feet (1.2 m) but some had been broken off and they 
HIO STUD IES ON THE WATCHUNG BASALT FLOWS OF NEW JERSEY 

FIGURE 4. The pahoehoe surface between the lower flow unit and the upper flow unit. The curvilinear jointing system and the thin vesicular base of the upper flow 

unit rest atop the pahoehoe surface of the lower flow unit. South wall of the Millington quarry of Houdaille Industries at Millington, N.J. Scale is shown by 

hammer. 

could have been in places up to 8 to 10 feet (2.4 to 3.1 m). 

Columnar cooling joints of the type described above are 

not commonly exposed on Third Watchung Mountain 

apparently because the advance of the North American ice 

sheet covered or beveled most of the outcrops. Nevertheless 

one may see the remains of eroded columnar coolingjoints at 

a number of outcrops. At Lyons station, blasted and 

mechanically broken out exposures of the columnar layer 

resting on the blocky layer could be seen near the top of the 

roadcut, see figure 8. 

Columnar joints in the upper flow unit of Second Mountain are better developed than in Third Mountain, and they 

are much larger, as much as 15 to 20 feet (4.6 to 6.1 m) long. 

They were better preserved from erosion so that they were 

excellently exposed during the excavations for U.S. Highway No. 287 in the vicinity of Far Hills and Liberty Corner, 

and on U.S. Highway 78 between Pluckemin and Mt. Bethel. 

A particularly fine exposure on U.S. No. 287 near Liberty 

Corner Road is shown in figure 9. The columns show the typical pinch and swell structure of Spry ( 1962). 

The columnar joints of the lower flow unit of First Watchung Mountain as exposed in the quarry near West Orange, 

N.J., and operated at the turn of the century by John 

O'Rourke, are world famous (Iddings, 1886, 1909). When 

the excavations of the cut for U.S. Highway No. 280 were 

made in the Oranges in the near vicinity of O'Rourke's 

quarry similar superb columnar structures were exposed. In 

mapping this cut it was found that the lower flow unit was 

cut by a dike. An example of an inverted fan structure, (in the 

terminology of Spry- 1962, p. 195), is shown in figure 10. 

The ball and socket type of jointing, in columnar basalt, 

made famous by its development in the Giants' Causeway, 

County Antrim, Ireland, Preston (1930), Tomkeieff (1940), 

is a relatively rare type of jointing in the Watchungs. In my 

fieldwork on Third and Second Watchung Mountain, I have 

only seen one good exposure of this type of jointing and that 

is present in the old Ferguson quarry, in Second Mountain 

near Little Falls, N.J., see figures II and 12. 
JOI NT SYSTEMS Bll 

F IGURE 5. Exposure of the vesicul ar zone , showi ng the rectangul ar (slabby) 

aspect of the top and the jointing systems in this zone . Locality: Liberty 

Corner Road between Mountain View Avenue (Dead River Road) and Mountain Road , near Liberty Corner. 

BLOCKY ZONE 

The blocky zone forms a distinct ledge in the north wall of 

the quarry at Millington, N.J., where it juts out noticeably 

from the wall itself, see figure I (arrow marked "A"). A typical exposure of the blocky zone at Millington shows a ledge 

broken by a series of parallel joints which extend from the 

top to the bottom of the ledge and subdivide it into a set of 

large blocks which have the shape of rectangular parallelepipeds. Some of these large blocks have uninterrupted faces 

of as much as several tens of feet long. The blocky joints are 

remarkable for their planar quality and their surface area. A 

view of a well developed exposure of blocky jointed trap 

cropping out on the "east" wall is given in the upper part of 

figure 13. The blocks had been badly battered by -the crane 

shovels -during removal of the overlying crushed rock. The 

typical system consists of a rectangular parallelepiped, faces 

of which are three sets of pairs of rectangles, each pair having 

a different area. The geologist is holding a hammer at the 

base of the blocky zone. A more detailed view of this system 

of joints is shown in figure 14, where the blocky aspect is 

clearly developed in an exposure of an old quarry wall from 

which the loose masses and fragments once part of it and the 

soil above it have been removed by the action of freezing and 

thawing, and rainfall over a number of years. 

In the quarry walls the blocky zone may be seen jutting out 

from the other jointing zones. It does so by virtue of the 

great strength, toughness, and resistance to excavation oft he 

basalt in this zone. Such overhanging ledges may remain for 

many years in unquarried walls. When active quarrying is 

resumed a succeeding blasting will tumble huge blocks 

almost unbroken to the quarry floor. The planar joint faces 

FIGU RE 6. A part of the zone of vesicular trap grading into the columnar zone 

below. Roadcut on the east side of Alps Road a short distance south of its 

intersection with Rock ledge Terrace, northeast of Mountain View, on Packanack Mountain . The hammer is near the boundary. 

of such blocks may be partly defaced in the falling and tumbling over the loose blasted rock. Such hackled surfaces 

reveal an internal structure within the blocks which suggests 

an assemblage of closely packed elongate polyhedra. The 

longest axes of these polyhedra are randomly oriented. This 

characteristic random orientation serves to differentiate 

defaced "blocks" from battered columnar joints in small outcrops. Such a hackled block is shown in figure 15. An exposure of weathered blocky trap in the New Vernon trap sheet 

near Morristown illustrates the significance of this criteria. 

In figure 16 the randomly oriented elongate polyhedra are 

easily identified. This outcrop was exposed many years ago 

by pickaxe and crowbar and was recently enlarged. Despite 

erosion a nd excavation it is still recognized as part of the 

blocky zone. 

In addition to defacing due to tumbling, the block in figure 

15 was also battered with a large steel ball in an attempt to 

break it down to a size the crushers could accept. Such tough 

large masses are called "jetty stone" and are shipped, as quarried, to the New Jersey seashore for use in jetties, groins, and 

seawalls. 
Hl2 STUDIES ON THE WATCHUNG BASALT FLOWS OF NEW JERSEY 

FIGURE 7. Columnar joints, slightly curved and tapered, just below the vesicular 

top. Roadcut on the cast side of Alps Road , a short distance south of its 

intersection with Rockledge Terrace, northeast of Mountain View, on Packanack Mountain. 

FIGURE 8. Remnants ot the blasted and mechanicall y excavated trap in the 

roadcut at Lyons Station , Lyons, N.J., showing the mechanically disrupted 

columnar zone. 

The outcrop of the basalt of Third Watchung Mountain 

appears as a ridge with a steep scarp slope and a gentle dip 

slope. During glaciation much of the scarp slope was parallel 

FIGURE 9. Columnar joints in the upper flow unit of Second Watchung Mountain. Roadc ut on U.S. Highway No. 287 , near Liberty Comer. 

to the direction of the oncoming ice of the North American 

ice sheet as it advanced. To the north of the terminal moraine 

and along the ridge the three units-the red shale above the 

flow, the vesicular zone, and the columnar zone, all of which 

are easily eroded by mechanical forces- were largely 

removed. The blocky jointed trap on the other hand was very 

resistant and was polished and in part striated and grooved 

by passage of the glacier. Surfaces of polished blocky basalt, 

the glacial pavement, are commonly observed as bosses on 

Hook Mountain, Rikers Hill, and Packanack Mountain, see 

figure 17. Salisbury (Salisbury and others, 1902, p. 540) gives 

data for striae measured on various exposures of glacial 

pavement. 

The resistant blocky zone is visible in many outcrops 

along the ridge of Third Mountain, but there are sections 

where it cannot be seen. At many such sections the former 

presence of the blocky zone can be confirmed by examining 

the loose massive blocks at the base of the scarp slope, see 

figure 18. These blocks tumbled down from the ridge top 

where they were formerly exposed. Alternate freezing and 

thawing, oft repeated, spread open the blocky joints and 

jostled the blocks loose so that when they were undermined, 

they fell. The tumbled blocks commonly have been defaced 

so that they show the randomly oriented elongate polyhedra. 

CURVILINEAR ZONE 

The joints in this zone are bounded by curved surfaces. 

The typical appearance of this type of jointing in an old 

quarry wall in relation to the overlying blocky layer is seen in 

figure 14, and a close-up view is given in figure 19. Here the 

curved surfaces clearly differentiate this jointing system 

from its congeners. A block of curvilinearly jointed trap 

breaks out rather commonly in the form of a massive escut-
JOINT SYSTEMS Bl3 

A 

8 

F IGURE 10. A, B, Inverted fan structure formed of columnar basalt. In roadcut 

for U.S. Highway No. 280 near West Orange , N.J. 

cheon similar to those hewn from rock and used in the stone 

work decorating buildings. A close-up view of the curved 

joints in an old quarry wall, figure 20, shows the wedge shape 

aspect of this type of jointing. When such wedge shaped 

masses weather out they produce shieldlike masses. 

The pitch of the curved surfaces, as measured along the 

vertical extension of these curvilinear joints, varies from one 

exposure to another and a comparison of a recently weathered surface of a blasted excavation, figure 21 , shows a different curvature from the surfaces shown in the preceding 

figures 19 and 20. In the outcrop shown in figure 22, a few of 

the shields were measured and found to average about 10 feet 

in height and 5 feet in breadth. 

The toughness of this rock and its ability to preserve its 

characteristic curvilinear appearance is well shown in a 

strongly blasted mass located on the "north wall" of the Millington quarry, figure 23. Here the vertical tectonic joints 

have been emphasized by blasting and yet the shieldlike 

curved surfaces of the curvilinear joints can still be easily recognized. 

The curvilinear joint system is the most commonly 

observed joint system on Third Mountain. It is usually very 

easily recognized. Weathering generally accentuates the 

joints producing wedge shaped masses of rock. That weathering has produced rather marked effects can be seen by 

comparing curvilinear joints in relatively unweathered and 

weathered zones, in a recently blasted excavation for a building. Those joints in the tough unweathered rock show clearly 

the curved surfaces with only a suggestion of the minor tectonic joints cutting normal to their vertical extension, figure 

22, whereas the weathered joints, belonging to the same original mass and approximately 15 feet (5 m) nearer to the outcrop surface in the weathered foreground, have separated 

into smaller parallel masses along the minor joints and produced wedges, figure 24. Each face is a curvilinear polygon. 

If a sufficient part of the joint system is preserved in a 

quarry wall, or other exposure, it may be possible to trace, 

with the eye, the curvature of the intersection of a curvilinear 

joint with its pseudocolumnar boundary and find that it follows a helical path. In figure 25 the geologist's hammer indicates the position of, and part of the path of, such a he lical 

curve. 

GEOMETRIC CHARACTER OF THE CURVILINEAR JOINTS 

Field observations, made in this study, on the curvilinear 

system of joints provides us with the following geometrical 

properties of their surfaces and their limiting bounda ries: 

I, the joint faces are all curved surfaces, see figure s 19, 20, 21 , 

22, 23, 24, 25. 

2, the overall vertical extension of the curvilinear joints suggests that they are bounded by a surface which is pseudocolumnar, having almost a cylindrical aspect, see 

figures 20, 21. 

3, the curvilinear joints seem to consist of a curved surface 

which has combined with it an element oftwist, see figures 19, 21 , 22 and 25, and photographs of curvilinear 

joints elsewhere in the text. 

4, where the curvilinear joints are viewed perpendicular to 

the principal axis of the joint, that is perpendicular to 

the direction of their pseudocolumnar aspect, the line 

of intersection of the curvilinear joints conveys the 

appearance of a helix, see figure 25. 

5, along the "helix" the curvilinear joints may show a repeat 

distance for a given point on the "helix." This distance, 

the pitch of the helix, may vary from outcrop to outcrop. It may be manifested in the steepness of the slope 

of the face of the joint. The pitch will be most easily recognized in right helicoids and much less so in oblique 

helicoids, see the section in supplementary topics on 

"character of helicoidal surfaces." 
Bl4 STUDIES ON THE WATCHUNG BASALT FLOWS OF NEW JERS EY 

FIGURE II. The ball end of "ball and socket" joints in columnar basalt. Ferguson's quarry, near Little Falls, N.J. 

6, the set of apparently parallel horizontal joints crossing the 

curvilinear joint system shown in figure 21 are not cooling joints but sheeting joints and have no genetic relation to the curvilinear joints. They do however suggest 

a ruled property to the curvilinear joint faces and that is 

a geometric property of helicoids. 

7, joints occur in groups and the closeness of the several 

parallel, subparallel, or otherwise geometrically 

related surfaces will be a measure of the spacing of a 

given joint system. For the curvilinear joint systems I 

have found that they are bounded by a pseudocolumnar surface and that these bounding surfaces will range 

from a few feet to about I5 feet (about 5 m) in lateral 

extent (diameter). 

In the list of observations on the helicoidal joints just 

given, reference is made to a boundary surface that contains 

the helicoidal joint surfaces (Nos. 2 and 7). Those bounding 

surfaces are a form of pseudocolumns and are so called here 

in contradistinction to the columnar joints described in the 

section "Columnar zone." The later joints are those normally 

called columns. I consider that these columnar joints have 

been produced by a conductive heat transfer process. When 

such columns are fractured they usually show a hackly surface. The pseudocolumns which enclose the helicoidal surfaces I consider, on the other hand, to have formed by a 

convective heat transfer process. When these pseudocolumns are broken they show helicoidal surfaces. The bounding surfaces are thus the former convection cells. The helicoidal character of the joints suggests that they reflect 

something of the nature of the former convective process. 

Detailed field and other studies will be given in a subsequent 

part of this series. 

These observed geometrical properties of the curvilinear 

surfaces are the criteria to be used in identifying and selecting 

analogous geometrical models. The combined criteria 

numbers 3, 4, and 5 eliminate identification with quadric surfaces, see supplementary topics the section on "Glossary of 

terms and definitions." They show that the surfaces to which 

they belong are the warped, or skewed, surfaces. Criterion 6 

suggests that these surfaces are also ruled surfaces. In particular the curvilinear joints are related to the class of surfaces 

known as helicoids (schraubenflache of the Germans, helicoide of the French). 
JOINT SYSTEMS BIS 

FiGU RE 12. The socket end of"ball and socket" joints in columnar hasalt. Ferguson's quarry, ncar Little Fa lls, N.J . 

When the probable relationship between the geometry of 

the curvilinear system of joints as deduced from field relations, and the geometry of the helicoidal surfaces was realized many of the outcrops were reexamined to verify the correspondence. Unfortunately it is not always possible to see 

the full developments of the helicoids in natural outcrops or 

in the walls of quarries and excavations. Outcrops that have 

been exposed long enough for weathering to remove the 

loose blocks and form long continuous surfaces usually yield 

sufficient surface to identify their geometry. It was also 

found at many outcrops that the various shieldlike surfaces 

of the curvilinear joints, in unrelated pseudocolumns, show 

surfaces suggesting a considerable variation in pitch. 

This reexamination and subsequent observations showed 

that some curvilinear joints appeared to be parts of the surface of a right helicoid, others appeared to correspond to 

oblique helicoids, still others appear to be more irregular and 

yet they still convey an indentity with helicoidal surfaces. 

These latter surfaces suggest an indentity with helicoids of 

varying pitch or varying length of the generatrix (sometimes 

referred to as the radius when the limiting surface is a 

cylinder). These geometric relations can be grasped from an 

inspection of the parametric equations of helicoids, see supplementary topics the section on "Character of helicoidal 

surfaces." Wellman (1948, p. 219) has discussed this type of 

helicoid as he observes that "helicoids of varying pitch and 

varying radius, although uncommon, are also feasible, and 

in such cases the angle between the generatrix and the axis is 

also variable.2 Screw propellers are frequently of variable 

pitch." It also became apparent that some of the joints could 

be represented in terms of the curves formed by the 

intersection of helicoids. 

My colleague, Howard T. Evans, Jr., carefully considered the correspondence between the field observations, as 

portrayed in the photographs, and my sketches, and the geometrical theory of helicoids and drew two relevant illustrations. Figure 26, shows the intersection of two right helicoids 

which have parallel but displaced directrices, generators of 

slightly different length, equal pitches, and are out of phase 

by 155° ( t ). The intersection edge is similar to some of those 

seen in some outcrops. Figure 27, shows parts of two steep 

right helicoids moved parallel to one another until they 

intersect. 

VESICULAR RASE 

The vesicular base of the flow units are of two kinds, the 

base of the upper flow unit overlying the vesicular top of the 
Rl6 STUDIES ON T HE WATCHUNG BASALT FLOWS OF NEW JERSEY 

FIGURE 13. Exposure at the top of the " east" wall of the Millington quarry. The blocky zone juts out. The geologist is pointing to the base of the blocky zone. At the 

lower right hand side of the picture, well-developed curvilinear joints may be seen. This wall fonm the dumping ramp of a stock pile. The apparent granular 

decoration on top of the blocks and scattered over the faces is the remains of a former stock pile. 

lower flow unit and the vesicular base of the lower flow unit 

overlying the sedimentary rocks of the Brunswick Formation (R b). 

The vesicular base of the upper flow unit overlying the 

vesicular top of a lower flow unit is a relatively thin layer, 

commonly 6 to 8 inches (15 to 20 em), and it is illustrated in 

figures 3 and 4. The base is uneven and conforms directly 

with the pahoehoe surface of the lower flow. The relations 

between the curvilinear zone and vesicular base are shown in 

figure 28. Here the passage between the two zones appears to 

be transitional. 

The character of the vesicular base overlying the sedimentary rocks in the Watchung Mountains is quite variable. This 

variability arose from a nonuniform distribution of water in 

the sedimentary floor. For most of the area the sediments 

were dry or slightly moist; parts of the areas, after storms, 

were moist, and scattered throughout the basin were playa 

lakes under which the sediments were saturated. Hot lava 

pouring out onto sediments with the above water contents 

would produce, respectively, breccias, thin layers of 

vesiculation, heavy layers of vesiculation, and pillow lavas. 

The thickness of the pillow lavas would depend on the depth 

of the playa lakes. Areas with braided drainage would produce alternate zones of pahoehoe toes (lobes) and pillow 

lavas. 

In Third Watchung Mountain the base is almost uniformly a thin zone with only a very rare development of a 

flow breccia as in the vicinity of Oakland, N.J. In contrast, 

Second and First Watchung Mountains have more variable 

vesicular bases. In part they have the thin vesicular zone 

above a hornfelsized zone and in part they show the development of pillow lavas and (or) pahoehoe toes (lobes). 

The most common type of bottom of the basalt flows of 

Third Mountain, where they rest conformably on the Triassic sedimentary rocks, is a vesiculated base. 

Flow breccia is present as a very thin zone at the bottom of 

the lowest flow unit at the upper end of Packanack Mountain at Pompton, figure 29. The mass consists of fragments 

of basalt and of a lesser amount of sedimentary material, 

that were picked up as the lava flow rolled forward, and it is 

held together by interstitial lava to form a firm unit. This 

breccia is of limited areal extent. 

Geologists making field studies in the Triassic Lowland in 

an earlier time when the sandstone was quarried for dimen-
JOINT SYSTEMS BI7 

FIGURE 14 . Detailed view oft he blocky zone on the ' ' east" wall of the Millington quarry. An enlargement of a portion offigure 13 showi ng the blocky joint system. 

sion stone and the more easily quarried vesicular basalt was 

used as riprap to prevent erosion and as road metal for paving, had unusually good opportunities to study the physiographic conditions of the floor prevailing at the time of the 

eruption of the basalts in New Jersey, Connecticut, and Massachusetts. Fenner (1908, p. 310-311, 326) has made a 

detailed study of these relations in New Jersey, and Krynine 

(1950, p. 169, 195-196) has similarly examined the broader 

relations of the environment and landscape of the Newark 

epoch in Connecticut. 

These studies both agree that the intermontane valley onto 

which the Triassic lavas flowed was essentially flat land. In 

New Jersey my study of the scarp of Third Mountain, exposing the bottom of the flow for so great a distance, affords 

additional field evidence. 

Excavations of the vesicular base of the lower flow unit of 

the basalt were also more easily studied, and the unique 

observation of Lewis (1908, p. 152-153) is pertinent. Lewis 

had the opportunity to examine the dumps made during the 

tunneling operations through Hook Mountain, north of 

Pine Brook, and he found a very small amount of tuff. He 

was uncertain of the stratigraphic position of this tuff in the 

base of the flow. This is the only evidence for basalt tuff in 

Third Mountain. 

OCCURRENCES OF SIMILAR COOLING JOINTS 

IN OTHER BASAL TIC PROVINCES 

My field studies of jointing systems in basalt have been 

confined to the Watchung Basalt flows of New Jersey. As 

time and occasion have permitted I have examined the 

various cooling joint patterns in other basaltic provinces to 

see if the same kind of cooling joint systems are present. Visits to these provinces have been brief, and extended study of 

the jointing systems at any one outcrop was not possible, so 

that my observations were cursory in nature. In the fissure 

type eruptions of the Triassic of Connecticut, Massachusetts, and the Bay of Fundy area ofN ova Scotia, as would be 

expected, I have seen jointing patterns identical with those in 

New Jersey. The curvilinear joint system because it is the 

thickest zone is the most frequently observed. In the vicinity 

of Canada Creek, near Black Rock Lighthouse, Bay of 

Fundy, Nova Scotia, several of the joint systems were 

observed. In figure 30 two joints systems are to be seen. 
Bl8 STUDIES ON THE WATCHU G BASALT FLOWS OF NEW JERSEY 

,_ 

. ~{,i'~~~':j:<::".;:<J•·~~~'::~~,:~- ,·- .~ ,_ 

FIGURE 15. A hackled block from the blocky joint system which has fallen and 

tumbled from its position in the overhanging ledge to the floor of the Millington quarry. It was battered by a steel ball dropped from a crane boom. 

Such blocks arc used as jetty stone. Other large blocks may be seen near the 

base of the wall. 

FIGURE 16. Weathered blocky jointed trap. Roadcut near Blackberry Lane and 

James Street, New Vernon trap sheet near Morristown. 

The geologist is standing on the columnar zone of the 

lower flow unit; behind him the base of the curvilinear zone 

of the upper flow unit can be seen. The columns of the lower 

flow unit have a larger diameter (25 inches l ) than the 

FIGURE 17. Glacial pavement developed on basalt of the blocky zone. This 

glacially polished outcrop is on the north side of Chapel Hill Road and 

Highland Street, Hook Mountain , near Lincoln Park , N.J. 

columns occurring under the pahoehoe tops of the upper 

flow units in Third Watchung Mountain. The vesicular base 

of the upper flow unit and the top of lower flow unit are 

covered. At a locality nearby the base of the curvilinear zone 

and the vesicular base of the upper flow unit could be seen. 

Evidence of the blocky and columnar zones of the upper flow 

unit were observed as blocks and columns lying at the foot of 

the cliff. 

Columnar jointing in the vast fissure eruptions of the 

Columbia River Basalt Group is a well-known phenomenon. The abundance, size, and arrangement of the joints in 

tiers has been described by Mackin ( 1961 ), Bond ( 1963), and 

Bingham and Grolier ( 1966 ). My visit to the Columbia River 

Basalt Group was limited to a very small area in the vicinity 

of the Grand Coulee, Wash., and there I saw, in addition to 

the excellent columns, areas where blocky and curvilinear 

joints were well developed. 

At the Hoher Meissner, in Nordhessen, Germany, the 

basalt plateau overlies brown coal beds. Here a thick zone of 

very well developed curvilinear joints occurs above a thin 

vesicular base which in turn overlies a baked brown coal 

layer. In the very large central type volcano, the Vogelsberg, 

in West Germany I have observed some very large helicoidal 

surfaces. Some of these surfaces appeared to be oblique helicoids. 

In Iceland I have seen many examples, in the tops of flows, 

of the type of columnar jointing observed in the Watchungs, 

short columns 4 to I 0 feet ( 1.2-3.1 m) long and 0.5 to I foot 

( 15-30 em) wide. These columns lie beneath a thin vesicular 

top, and their attitude is determined by the curvature of the 

tumuli surface. Curvilinear joints were observed at Detti-
.JOINT SYSTEMS Bl9 

FIGURE 18. Blocks of trap dislodged from their position at the top of the ridge. These were naturally quarried by alternate free zing and thawing which d isrupted the 

jointed ledge and produced a jumble of blocks. When dislodged sufficiently or undermined, they tumble down the scarp slope. Northeast of the intersection of 

Pine Brook Road and Passaic Avenue Road, Lincoln Park , N.J. 

foss, MyYatn, Thingvellir, and elsewhere. Observations in 

Iceland suggest that if the flow units are thin the blocky zone 

is absent and the sequence becomes- thin vesicular zone, 

vesicular grading into the columnar zone, curvilinear zone, 

and vesicular base. 

These observations were made at widely separated outcrops in other basaltic provinces. The identity of the cooling 

joint systems in the flows of fissure eruptions, wherever 

observed, with those in the Watchung Basalt flows is significant. It supports my opinion that more detailed studies in 

these areas will reveal similar patterns and sequences with 

those in the Watchungs. 

TECTONIC JOINTS 

In order to ascribe the cause of the joints produced in the 

lava flows by tectonism it is necessary to review briefly that 

portion of the geologic history of the Newark graben that 

involved them, Faust ( 1975), and to evaluate the capacity of 

the several tectonic processes to produce joints. The 

Watchung lava flows appeared in the Newark graben after 

the basin was largely filled with sediments. If it is assumed 

that the Newark Group in New Jersey is II ,800 feet (3,600 m) 

thick, then the basin would have been nearly 80 percent 

filled; if the greater thickness of 25,000 feet (7 ,620 m) is 

assumed, then the basin would have been about 90 percent 

filled . Over this floor the first eruption from fissures took 

place. After the completion of the volcanic episode that produced the first Watchung Basalt flow, the two flow units 

cooled down to earth temperatures, and subsequently they 

were buried by about 600 feet (183m) of sedimentary materials. 

Faust (1975) observed at Oakland, N.J., a fanglomerate 

bed that underlies the base of the second Watchung Basalt 

flow. Although the contact relations could not be observed, 

the fanglomerate at the most is about 50 feet (15m) below the 

contact, and it could be much closer. Barrell (1915, p. 29) 

pointed out that the occurrence of the fanglomerate (conglomerate) beds "indicated a re-growth of the mountains" that 

supplied the sediments to the basin and that this uplift necessitated a boundary consisting of a fault wall along which 

renewed movement took place. The presence of the fanglomerate at Oakland, N.J., indicates that faulting, a tectonic 

process, that could have produced joints in that part of the 

underlying basalt of First Mountain close to the fault wall. 

Similarly, after the extrusion of about 750 feet (229m) of the 

second Watchung Basalt flow and its solidification and burial by 1,500 feet (457 m) of sediment, another fanglomerate 
B20 ST UDIES ON TH E WATCH UNG BASALT FLOWS OF EW JERSEY 

- r ·· -

/ ,, I_,.., I ' 

--

F IGU RE 19. Curvilinearjoints in trap . " East" wall of the Milli ngton quarry. Note thi n layer of the closely jointed blocky zone (upper left hand corner) overlying the 

curvilinear zone and above this the irregul ar and hackly broken masses of the blocky zone. 

appeared and is evidence of another tectonic event. The sequence was again repeated after 300 feet (91 m) of the Third 

Watchung Basalt flow was extruded, cooled, buried under at 

least 300 feet (91 m) of sediments and followed by a fanglomerate. These three tectonic events, signalized by the presence of the fanglomerates, were small-scale events and could 

have produced jointing locally near the walls in these buried 

flows but for the flows as a whole they were of minor importance. 

The deformation of the Newark graben by the tensional 

forces associated with the drifting apart of the North American plate from the adjoining parts of Pangaea resulted in · 

downfaulting of the graben block. This crustal movement 

created a space problem and the contents of the graben were 

folded into a regional arch with border synclines in accord 

with the model developed by Murawski ( 1968). This tectonic 

event was a major process which resulted in extensive jointing in parts of the syncline. 

The tectonic joints are best developed in Second Mountain, less so in First Mountain, and they are not very prominent in Third Mountain. In the weathering of the basalt of 

the Watchung Mountains the tectonic joints are emphasized 

and their extended planar boundaries tend to overshadow 

cooling joint boundaries. As a result of this emphasis the 

eyes of the observer a re distracted from other structures in 

the rocks which are also of a first order of importance. 

The tectonic joints in the various zones are described in the 

following sections. 

VESICULAR TOP 

The transverse joints in the vesicular zone are tectonic 

joints. They may occur in conjugate pairs, and they make an 

angle of about 45° with one another. 

COLUMNAR ZONE 

The tectonic joints in the columns are not always clearly 

developed. In some columns they consist of irregular breaks 

that cut across the columns. In other columns planar basal 

joints were formed. 

BLOCKY ZONE 

Tectonic joints in the blocky zone are essentially perpendicular to the surface oft he flow. In some blocks an apparent 
JOINT SYSTEMS 82 1 

F IGURE 20. A close- up view of curvi li near joints in an old quarry wa ll. "South " 

wall Mill ington quarry. Note that the blocks that have dropped out from the 

wall are shield shaped and wedge shaped. 

single joint may consist of a series of discontinuous parts 

which form an interrupted linear trace. 

At the base of the blocky zone appears what is termed a 

seam or a layer by the quarrymen, figure 31. It has a thickness of approximately 2 feet and serves as a marker in the 

Millington quarry. From a distance it has the appearance of 

a fissile shale and has been thought by some to be a shaly 

interbed, see figure 32. A careful examination of the bottom 

of the blocky zone shows clearly the origin of this subunit, 

for fine hairlike joints at the base can be traced into the separated joint platelets. The presence of this shear zone is an 

indication of thrust faulting, and in the Millington quarry 

the blocky zone jointed at its base as it moved over the curvilinear jointed basalt below it. A similar type of jointing is 

called a Deckensohle by Cloos (1936, p. 245). 

CU RVILI NEAR ZONE 

Three types of tectonic joints are observed in the curvilinear zone-the first, and most prominent, are the pseudocolumnar joints which may extend from the top to the bottom 

of the zone and are essentially normal to the surface of t he 

flow; the second type are the platy-prismatic joints which are 

found near the base of the Second Mountain flow, and their 

abundance is related to the geometry of the syncline; and the 

third type- the basal platy joints- form very close to the 

base of the flow ,just above the vesicular base and the contact 

with the Brunswick Formation. 

PSEUDOCOLUMNAR JOINTS (TYPE I) 

When one looks at the curvilinear joints from certain 

directions, they have a distinct columnar aspect. As a result 

this vertical system of tectonic joints has conveyed to most 

geologists the impression of a columnar type of jointing. 

Consequently it has caused confusion in the identification of 

the cooling joints and has led to the misinterpretation of the 

jointing. Because of its columnar aspect it is termed here 

pseudocolumnar jointing. This aspect is produced by a 

combination of one of the cooling joint systems and a set of 

parallel planar vertical tectonic joints. These joints have 

appeared on some of the previous figures, but an attempt 

was made to select photographs taken to deemphasize this 

aspect. A photograph typical of the pseudocolumnar joints 

as seen in older quarries, roadcuts, and power-shovel 

bumped exposures is shown in figure 33. In contrast the 

appearance in a freshly blasted exposure is shown in figure 

34. Compare fig ure 34 with figure 22. 

PSEUDOCOLUMNAR J OI NTS (TYPE 2)-

PLATY-PRISMATIC JOINTS (FRACTU RE CLEAVAGE) 

Pseudocolumnar joints of a second type were observed by 

early workers in the Watchungs, who included them in the 

general classification of columnar joints. These joints are 

here designated platy-prismatic joints, and their close spacing shows that they are; in fact, a fracture cleavage. Joints of 

this type have not been observed on Third Mountain proper, 

but they have been observed in the axis of the syncline composing the New Germantown trap sheet, and they are quite 

abundant on the scarp slope side of Second Watchung 

Mountain. 

A typical example of this variety of pseudocolumnar habit 

can be observed in Alward's quarry at the intersection of Pill 

Hill road and Meeker road about 2V4 miles west of Basking 

Ridge, see figure 35. An examination of these 

pseudocolumns shows that they are made up of a fracture 

cleavage superimposed on the preexisting cooling joints of 

the curvilinear zone. Well-developed curvilinear joints may 

be seen about 10 feet above the top of the pseudocolumns 

shown in this photograph. According to Hartmann's Law 

(see Nevin, 1931 , p. 23-24), the acute angle of the fracture 
FIG U RE 21 . Excellent ly developed curvilinear joints in the trap. The roadcut is approximately per pcndicula r to the strike. The joints across the face of the curved planes are sheetingjoints and are 

not cooling joi nts. Roadcut on Bloomfield Avenue near its intersection with Hook Mountain Road , Pine Brook, N.J. 

o:l 

N 

N 

(/] 

-1 

c: 

0 

rn 

(/] 

0 

z 

-1 

:c 

rn 

:E 

> -1 

() 

::t:: 

c: 

2 

0 

o:l 

> 

(/] 

> 

r 

-1 

.,., 

r 

0 

:E 

(/] 

0 

.,., 

2 

rn 

:E 

'-

rn 

;::l 

(/] 

rn 

-< 
JOINT SYSTEMS B23 

FIGURE 22. Curvilinear joints in relatively fre sh basalt. This rock is very tough 

and required extra blasting to excavate it. The curvilinear joints are outlined 

by the shades and shadows. They arc elongate approximately perpendicular to 

the floor of the excavation. Ncar the surface of the triangular area on the right 

some check ing of the minor joints is apparent. This locality is an excavation at 

the intersection of U.S. Highway 46 and Hook Mountain Road , Pine Brook, 

N.J. 

cleavage is bisected by the axis of maximum stress, and at 

Alward's quarry this direction is essentially parallel to the 

southwest limb of the syncline. A top view of the platyprismatic joints, just described, is identical with the 

prismatic cross section shown in figure 36. In the walls of the 

quarry these platy-prismatic joints exhibit an eminent cleavage and show little evidence of the curvilinear joints arising 

from the cooling of the sheets. A careful study of the talus 

pile reveals the curved surfaces on the longer broken prisms, 

see figure 36. The loose prism shown in this picture was photographed so as to emphasize the curvature of the joints on 

the sides. 

A type of platy-prismatic jointing, a fracture cleavage, 

similar to the aforementioned jointing, except that the 

prisms are curved plates, is found in or near the axial plane of 

a tightly folded syncline which constitutes the New Germantown trap sheet. These joints were exposed by quarrying. 

FIG URE 23. A strongly blasted mass of curvilinear jointed trap preserving its 

characteristic morphology. The picture represents a portion of the " north 

wall " at the Millington quarry, Millington , N.J. 

FIG URE 24. Weathered curvilinear joint masses having wedge shapes. This rock 

is similar to that in fi gure 22 except that it is from a strongly weathered zone. 

Excavation at the intersection ofU .S. Highway46 and Hook Mountain Road , 

Pine Brook, N.J. 
824 STU DI ES ON T HE WATCHUNG BASALT FLOWS OF NEW JERSEY 

FIGURE 25. Curvilinear joints in the trap of Second Watchung Mountain. 

Geologists' hammer indicates the position of the trace of the he lical path of the 

curvilinear joint. Gallo's quarry , Mt. Bethel, N.J. 

They have an eminent cleavage and are very smooth; in fact, 

they appear at a short distance from the outcrop to be polished. A view of the platy surface is seen in figure 37; the side 

view, emphasizing the curvature, is shown in figure 38; and a 

top view showing the typical prismatic cross section is shown 

in figure 39. 

The frequency of tectonic joints increases in relation to the 

geometry of the syncline. Along the limbs the tectonic joints 

are abundant, but their frequency is greatest in the vicinity of 

the nose of the syncline, figure 40. 

BASAL PLATY JOINTS 

On the limbs of the syncline, away from the nose, basal 

platy joints are commonly developed just above the contact 

with the underlying Brunswick Formation. They may occur 

\ 

FIGURE 26. Two ri ght helicoids with parallel but displaced directrices (helicoidal axes), with generators of slightly different length , with equal pitches and 

out of phase by about 155° . The dotted line is the intersection edge . Such 

edges are simil ar to those seen in some outcrops. 

in a zone of about 10 feet (3 m) in height above the base, see · 

figure 41. They are generally spaced about 10 to 12 inches (25 

to 30 em). They may extend for many tens of feet (many m). 

It is suggested here that they formed concurrently with the 

syncline. The interpretation, proposed here, is that the base 

of the flow and the hornfelsized zone welded to it attempted 

to behave elastically as a single unit. These joints are developed at the base of Second Mountain. 
JOI NT SYSTEMS 825 

FIG URE 27. Portions of two steep right helicoids, moved parallel to one another 

graphically, until they intersect. 

SHEETING .JOINTS 

Sheeting joints are a set of parallel, generally closely 

spaced joints which divide the rock into layers called sheets. 

These sheets are developed in essential conformity with the 

topography and where the ground surface is flat or nearly so 

they are horizontal. Sheeting joints generally form as a result 

of physical weathering which removes the superimposed 

load from the rock it exposes, Oilier ( 1969, p. 5-9). This removal of overburden permits the rock to dissipate its stored 

strain energy chiefly in the formation of cracks oriented 

parallel to the ground surface. In this discussion sheeting 

joints are classified separately from weathering phenomena 

solely to differentiate these joints from other types of horizontal joints. 

At a late stage in the geologic history of the Newark basin 

the North American ice sheet covered its northern part and 

FIGURE 28. Curvilinear jointed trap overlying the vesicular base of the upper 

flow unit in the Millington quarry. The hammer handle rests on the contact of 

the two zones. The quarry face in this photograph is nearly perpendicular to 

the quarry face shown in figure 4. 

loaded the rocks below it with ice. Retreat of this glacier 

unloaded the rocks but left them strained. Strain relief was 

accomplished by sheet jointing. In the area north of the 

terminal moraine, which extends from Summit to Morristown, sheeting has been developed in the basalt. This sheeting conforms to the topography. 

Two fine examples of sheet jointing on Hook Mountain 

are shown in figures 42 and 43. The outcrop shown in figure 

42 is at the southern end of Hook Mountain at Pine Brook. 

The wall is approximately west-east, and it is a section 

normal to the strike and cutting through the dip slope. The 

quarry shown in figure 43 is at the northern end of Hook 

Mountain near Mountain View. The quarry was opened and 

excavated in the dip slope, and the photograph is taken in a 

nearly east-west direction. 

The flat, steplike surfaces of the trap in the zone of sheet 
l:l26 STUDIES ON THE WATCHUNG BASALT FLOWS OF NEW JERSEY 

FIGURE 29 . Outcrop of tlow breccia on south side of Oakland Valley Road , 

approximately abreast the dam , Packanack Mountain, at Pompton , N.J. This 

relatively thin layer of flow breccia lies just under the curvilinear jointed lava 

at the base of the flow. 

FIGURE 31. Tension jointed base of the blocky zone (so-called seam) , overlying 

the curvi linear joint system. Excavation on Northfield Avenue below Valley 

Road , West Orange, N.J. 

FIGURE 30. Curvilinear joints in the basaltic lava flow exposed on the Bay of Fundy at Canada Creek , near Black Rock Lighthouse , Nova Scotia . The geologist is 

standing on the columnar top of the lower flow unit. 
JOINT SYSTEMS B27 

FIGURE 32. Detailed view of the tension jointed base of the blocky layer overlying the curvilinear zone . "East" wall , of the Millington quarry. 

joints is well shown in figure 43, which is a photograph that 

was taken looking down on the upper surface of the sheet 

joints. A similar stairlike morphology, developed by erosion 

on rocks in Sweden gave rise to the name trap from the 

Swedish "Trappar" (= steps) (Rosenbusch, 1923, p. 440; 

Kemp, 1929, p. 286). 

Curvilinear joints in the quarry at Millington, which is 

south of the terminal moraine, do not show these planar 

joints cutting across the curvilinear surfaces. (See figs. 20 

and 28.) 

WEATHERING JOINTS AND ASSOCIATED PHENOMENA 

S PH ERO IDAL JOINTS 

In the upper portion of the columnar zone, in places where 

weathering has been thorough, a "spheroidal jointing" is 

commonly observed. I have found zones of spheroidal 

weathering only below the surface. The symmetry of the 

weathering pattern, one in which the edges and corners of the 

columns have been completely destroyed leaving a sequence 

of concentric shells in successive stages of disintegration surrounding a hard central core, strongly suggests that the alteration process is not surficial but takes place below the surface . I have also observed spheroidal weathering in 

weathered shear zones made up of jointed blocks a foot or so 

wide and a foot or two long and weathering at a depth of 20 

feet(±) below the surface. This observation suggests that the 

symmetry of the joint block may exert a control on the rate 

of disintegration. 

In unworked sections of a quarry where spheroidal weathering can be seen exposed in the walls, "exfoliation boulders," the firmest remnants, may be observed in the talus 

pile. These consist of the concentric spheroidal layers about 

a central core. Such "exfoliation boulders" are also observed 

in shallow excavations. Eventually these concentric layers 

peel off leaving a spheroidal corestone. These residual 

spheroids range in size from 2 to 6 inches in diameter. 

Locally, they have mistakenly been considered by some 

people to be spent cannon balls from the Revolutionary 

War. Such remanants of weathering may be relatively fresh 

on the inside, see figure 44. 

Sosman ( 1916, p. 229) does not believe that spheroidal 

weathering is due solely to the rounding off of joint blocks 

but that some original structure within the columns is also 
1328 STUDIES ON THE WATCHUNG BASA LT FLOWS OF NEW J ERSEY 

FIGURE 33. Typical pseudocolumnar appearance in the curvi linear zone produced by the superimposition of tectonic planar verti cal joints on the curvilinear system. 

Excavation on Northfield Avenue , below Valley Road , West Orange, N.J. 

exerting an influence in determining the shape. This opinion 

is probably based on the observations of the shells which 

make up the so-called "spherical joints" described by Lewis 

(1909) fr9m an occurrence in a quarry, at Stirling, in Second 

Mountain, shown in figure 45. 

LAT E STAGE, UNLOADING "PLATY JOI TS" 

A second set of "platy" joints, approximately horizontal, 

oriented parallel to the present surface are noticed throughout the Watchung flows. These joints are commonly barely 

visible, and only become so as weathering proceeds, or excavating and quarrying are done. In relatively fresh outcrops 

many of these joints are probably blind.J In some excavated 

roadcuts and quarries they are, however, well developed 

near the surface. This system of joints is of a lower order of 

magnitude than the previously described basal platy joints of 

tectonic origin occurring near the base of the flow. They are 

' They <H C discontinuous and stop abruptly. 

FIG URE 34. Pseudocolumnar joints produced by the superimposition of tectonic 

joints on the curvilinear jointing system in the north wall of the Millington 

quarry, Millington ,N.J. The tectonic joints arc very rare in the overhanging 

ledge of the blocky systems, in this photograph . This is the appearance of the 

pseudocolumns in a fresh ly blasted exposure. 
JOINT SYSTEMS 829 

FIGURE 35. Platy-prismatic joints (fracture cleavage) in Second Watchung 

Mountain. Alward's quarry at the intersection of Pill Hill Road and Meeker 

Road about 2\4 miles west of Basking Ridge, N.J. These joints are close to the 

contact with the Triassic sedimentary rocks below. 

characteristically short in length, very thin, and some may be 

slightly curved. Generally they are not as well developed as 

the typical tectonic joints. Observations, made over a period 

of years, suggest that many of these approximately horizontal joints were incipient joints. That is they represented 

areas which had long been in a state of stress. Some of these 

stresses could have originated totally, or in part, as a result of 

the local faulting which took place along the walls of the 

horst at the time the border syncline was formed. When the 

basalt was exposed by weathering the areas in a state of stress 

altered more rapidly than the unstressed areas, and this disequilibrium permitted the rocks to separate along planar 

surfaces to relieve the accumulated stress. 

In quarries or in zones of excavation, the removal of the 

overburden involving much scraping, by power shovels, bulldozers, and other heavy machinery may add additional 

stress to the already stressed areas near the surface and thus 

may aid in the formation of these approximately horizontal 

joints. Blasting and bumping of the quarry walls by the 

power shovels may also be significant contributory factors in 

producing or emphasizing these joints. On the "north wall" 

of the quarry at Millington, N.J., near the surface there are 

some approximately horizontal joints of this type, figure46. 

Their short length is apparent. 

SOLIFLUCTION , A DISTORTING AGENT 

OF JOINTING PATTERNS 

Early in this study of jointing it was noticed that a distortion of the joint systems was sometimes observed on the 

scarp slope of Third Mountain. Close inspection showed, 

however, that a supposed change in attitude of the joint 

prisms on these slopes was unreal and arose from the creep of 

FIGURE 36. A view of the zone of the platy-prismatic tectonic joints on Second 

Watchung Mountain. Musialowski 's quarry on Washington Valley Road, 

northwest of Martinsville, N.J. Note the curvature of the sides, of the back 

joint face, in profile. The fracture cleavage here shown in the walls of the 

quarry has its acute angle bisected by a line parallel to the axis of the major 

syncline. 

the mantle down the steep slope. Such a gradual movement 

was accomplished by (1) alternate freezing and thawing, (2) 

alternate wetting and drying, and (3) by a slow movement of 

the whole system, of joint "blocks," interstitial mud, and 

water behaving more or less as a unit, down the slope. This 

type of movement, called solifluction or hill-wash, contrasts 

with that sometimes observed in quarries along the steep 

faces especially in areas recently artificially disturbed at the 

top. Here (I) the rainfall and drainage wash out much ofthe 

finer materials in the disturbed top (2) drying conditions 

remove most of the water and dry out the remaining mud 

and loose materials which served as an adhesive between the 

joint "blocks," and (3) the whole loose mass suddenly collapses and tumbles to form a conical pile at the quarry bottom. 

In some roadcuts or excavations where small faults, of 
B30 STUDIES ON THE WATCHUNG BASALT FLOWS OF NEW JERSEY 

FIGURE 37. The platy surface of the curved platy-prismatic joints (fracture 

cleavage) developed in or ncar to the axial plane of the tightly folded syncline 

in the New Germantown trap sheet, I .2 miles southwest of Oldwick , N.J. 

postglacial age, appear in the unconsolidated sediments on 

the scarp slopes which overlie the separated joint blocks, the 

smaller joint "blocks" were observed to have moved out of 

their primary alinement. All of these occurrences were easily 

recognized by close inspection at the outcrop to be distortions of the true relationships. 

Solifluction probably was enhanced on Third Mountain 

at the close of the glacial period when the North American 

ice sheet began to melt and Lake Passaic formed. At this time 

the waters began to spill over the sides of the scarp slope. 

To determine whether the joints on the scarp slope of 

FIGURE 38. Side view of the curved platy-prismatic joints (fracture cleavage). 

New Getmantown trap sheet, 1.2 miles southwest of Oldwick, N.J. 

FIGURE 39. Top view, showing the prismatic cross section of the curved, 

platy-prismatic joints (fracture cleavage). New Germantown trap sheet, 1.2 

miles southwest of Oldwick , N.J. 

Second Mountain are disturbed is a more subtle and perplexing problem to the observer. These joints can be misleading, they look very natural in exposures on a slope in 

which only a few feet in depth are seen, and they resemble 

closely certain aspects of true radial columnar joints as those 

shown in figures 9 and 10. Close examination of the 

exposures on the scarp slope, which are limited in depth, 

discloses a much wider separation of the joint prism than is 

normally observed, and the presence of finer material in the 

openings. These criteria suggest movement. The best evidence of movement is seen in an undisturbed wall of a 

quarry, pit, or excavation, essentially normal to the strike, 

where the tilting of the columns and their movement "en 

masse" down the slope is clearly apparent; such a slope is 

shown in figure 47. 

A JOINTING MISCELLANY 

FEATHER-FRACTURE (PLUMOSE FRACTURE) AND 

OTHER SURFACE PATTERNS ON JOINTS 

Feather-fracture, so-named because of its barb like or plumose structure, was amongst the earliest type of surface feature of joints described in the rocks of Eastern North America. Woodworth (1896, p. 178) in an excellent paper on joint 

surfaces, particularly their macroscopic features, describes 

in detail feather-fracture occurring on the joints in the trap of 

the Somerville quarry at Somerville, Mass. Woodworth 

(1896, p. 165) defined these fractures as follows: The granulations of the surface of a joint-plane when organized take on 

the form which I have been accustomed in fieldwork to call 

"feather-fractures" [he states further] Feather-fracture is not 

limited to true joint-planes, but is traceable on the surfaces of 

other divisional planes as I shall show below. On the typical 
JOINT SYSTEMS 831 

FIGURE 40. Very abundant platy-prismatic joints on Second Mountain. The conjugate set of tectonic joints are so abundant that it is difficult to recognize the cooling 

joints. This section was formerly exposed in the cut for U.S. Highway No. 78 near Pluckemin , N.J. The outcrop is just above the contact with the underlying 

Brunswick Formation. 

joint-planes of the Mystic quarry district,4 feather-fracture is 

a delicate tracery of feathery lines diverging from a roughly 

outlined axis which traverses the face of the joint-block in a 

plane parallel with the stratification. When the axis of the 

feather-fracture departs from this plane, it becomes sinuous. 

In the massive rocks, it is characteristically sinuous. Woodworth also described discoidal joints and percussion rays 

appearing on specimens of argillite. 

Sosman (1916, p. 230) noted the presence of feather patterns on some basalt prisms and suggested that they might be 

due to contraction. Feather fracture and other surface patterns have recently aroused interest amongst students of rock 

jointing, and papers by Roberts(1961)and Hodgson(1961) 

have modified and developed the approach of Woodworth 

(1896). Price (1966, p. 120-126) and Bankwitz (1965, 1966) 

give further data and interpretation. 

I have seen excellently developed feather fractures in the 

curvilinear layer of the upper flow unit of Third Mountain at 

l Cambrian slates. 

Pine Brook, N.J. , and in both the upper and lower flow units 

of Second Mountain at many localities. The fractures are 

commonly 2 square feet or more in area. A fine example is 

shown in figure 48. Here the axis of the fracture was oriented 

vertically. 

Other types of surface patterns are occasionally observed, 

but most were too incomplete to describe. A particularly 

well-developed surface pattern on a curvilinear surface was 

found on a joint wedge at the floor of the Millington quarry 

after a wall had been blasted down. It is shown in figure 49. 

This specimen was part of a larger joint surface, and it was 

not possible to trace its former position in the quarry wall, so 

that there is no knowledge of its orientation and location 

except that it came from the zone of curvilinear joints. A description of this rather large individual is given here because 

of the unusual clarity of its details. The fracture surface occupies an area of 17 x 25 em. It is a warped surface, best described as billowy. The surface itself is contained in a volume, roughly a parallelepiped of 17 x 25 x 2 em. Its whorls 
l:l32 STUDIES ON THE WATC HUNG l:lASAL T FLOWS OF NEW .JERS EY 

FIGURE 41. Basal platy joints at the base of the curvilinear layer, just above the contact with the hornfe lsized Brunswick Fonnation. In cut, in Second Watchung 

Mountain , on U .S. Highway No. 280 at its intersection with Pleasant Valley Way, West Orange , N.J. 

widen counterclockwise so that its direction of obliquity is 

sinistral. The widest whorl increases from a few millimeters 

on the left to nearly 2 em on the right. If the lowermost portion of the specimen, where there is a decided change in 

slope, is taken as the shoulder, then the b-planes (borderplanes) of Woodworth and the c-planes (cross fractures) of 

Woodworth (1896) can be seen at the lower left-hand side of 

figure 49. The b-planes (called F-joints by Hodgson, 1961) 

make an angle of about 5° with the shoulder. The whole surface pattern has a general conchoidal appearance. Woodworth in discussing discoidal joints describes a surface that 

resembles this one as "The warped surface thus formed may 

in some specimens be likened to the rim of a soft hat curled 

up behind and pulled down in front." The whole surface is 

covered with a brownish patina showing that it represents a 

former part of an old quarry wall. 

Despite the size of this surface, there is not a sufficient 

amount of critical detail, particularly the presence or absence of a bulb of percussion, to decide whether this represents ( 1) a type of discoidal joint or (2) a percussion figure developed in the older method of quarrying using bars and 

sledges, or by blasting. From observations of similar surfaces on the old walls of quarries the evidence given here suggests that this surface may be a part of a percussion ray. 

WIDTH OF JOI NT OPEN INGS 

The width of joint openings is of interest to geologists 

studying the fracture characteristics of rocks. Such measurements are most significant when the effects of a single process such as the cooling of a lava flow or the effects of a single 

tectonic event can be evaluated. The width of openings of 

cooling joints is best made on recent lava flows. The Watchung Basalt flows are of Late Triassic age and have been 

subjected to some metamorphism-at least to the zeolite 

facies and possibly to the green schist facies. The cooling 

joint openings were disturbed by the tectonic deformation of 

the graben. Some cooling joints were reactivated as tectonic 
JOINT SYSTEMS B33 

FtGURE 42. Sheeting joints in the transition zone between the blocky and the 

curvilinear zone of the basalt flow of Hook Mountain. This figure represents a 

vi ew showi ng a section essentiall y at right angles to the strike. The roadcut , 

on Bloomfield Aven ue in Pine Brook, is roughl y east-west. 

joints. As a result the present-day width of the coolingjoints 

bears little relation to their original width. 

To gain some idea of the order of magnitude of cooling 

joint widths in a relatively recent lava flow (8,000 years ±) 

measurements were made, in 1971, on the fault wall of the 

flow at Thingvellir, Iceland.s A mechanics gage with a 

~ Agt da ta- Written communication from Dr. Gudmundur Sigvaldason, Feb. 22. 1974. 

FIGURE 43 . Sheeting joints in the blocky and curvilinear jointed trap of Hook 

Mountain. The steplike aspect is clearly evident. Quarry near the northern end 

of Hook Mountain near Mountain View, N.J. 

FIGURE 44. Spherical balls found in the deeply weathered columns of trap, near 

the surface. A ba113 inches, 7.5 em, in diameter was cut and polished to show 

the "fresh" character of the minerals. 

minimum thickness of 0.0015 inch (0.0381 mm) was used to 

make the measurements. Good quality joints, I II in all, were 

measured. A group of 54 joints were found that were smaller 

than the smallest element of the mechanics gage-0.00 15 

inches (0.0381 mm). These joints ranged from those just 

thinner than 0.0015 inch (0.0381 mm) down to those very 

thin joints that were closed by a thin film of altered material. 

A total of 57 joints were found to be in the range of(+) 0.0015 

inch (0.0381 mm) up to those having a width of 0.0240 inch 

(0.61 0 mm). If we assume that the distribution of joints less 

than 0.0015 but greater than zero is similar to the distribution of the joints between 0.0015 and 0.0240 (0 .61 0 mm), 

then an inspection of these data suggests that the joint 

openings yield a flat symmetrical curve with a nearly perfect 

assortment of joint widths. This distribution curve was 

unexpected. The sample may be too small and the inclusion 

FIGURE 45. "Spherical jointing" in basalt produced by weathering. Quarry 2'/z 

miles south of Stirling, Second Mountain. Taken from Lewis ( 1908, pl. 38, 

fig. 1). 
B34 STUDIES ON THE WATCHUNG BASALT FLOWS OF NEW JERSEY 

FIGURE 46. Late stage, unloading joints, probably developed in prestressed areas close to the surface of the earth. Their development may have been aided by 

weathering processes relieving stress, by man induced stresses inherent in blasting , excavating, and machine scraping or bumping operations. "North wall ," 

Millington quarry and plant of the Houda ille Industries, Inc . 

of the weathered closed joints may have biased the interpretation. Nevertheless, these data do suggest the order of 

magnitude of the pristine joint widths. 

The measurements of the cooling joints at the Thingvellir 

in Iceland suggest the probable order· of magnitude of the 

openings of the cooling joints in the Watchungs. In the Watchungs many of these joints which now appear tight were 

actually once open but water percolating along them has 

altered them and closed them. It is commonly possible to see 

some evidence of alteration indicated by a border zone of a 

different color and frequently a bleached appearance. 

The width of opening of the tectonic joints reached larger 

values up to one-half inch (1.2 em). Good evidence of the 

width of opening of tectonic joints is to be observed in the 

widths of the mineralized veins that fill them. Detailed measurements on these veins have been made in all three of the 

Watchung basalt flows. 

The width of opening of weathering joints is generally 

much larger than that of the other types of joints. In weathering zones alternate freezing and thawing in the winter season 

and heating and cooling in the summer season spring apart 

the joint blocks producing ever wider gaps. 

Geologists, hydrologists, geological engineers, and civil 

engineers are interested in the width of joint openings as they 

exist at the time of the "joint survey." Such measurements 

may give valuable information on the permeability of a rock 

and on the stability of rock slopes. 

QUASI-GEOLOGIC JOINTS AND NONGEOLOGIC 

PSEUDOJOI NTS AND FRACTURES 

The rocks close to the surface of the earth are commonly in 

some state of stress, Hast (1967), Voight (1966, 1969a, b). 

Hooker and Johnson (1967) measured the "in situ" stress in 

several distant parts of the Newark graben particularly in the 

Triassic diabase at Nyack, N.Y., St. Peters, Pa., and Rapidan, Va., at depths of0.5 feet (15 em) to 4.9 feet (1.5 m) and 
JOINT SYSTEMS 835 

FIGURE 47. Effects of soliOuction are shown in the wall , wh ich is essentia ll y 

normal to the strike. This is shown in Tullo's quarry on Washington Valley 

Road , near Martinsville, N .1 . The creep of the mantle down the slope has 

tilted the pseudocolumns, from their normal position shown at the base, to 

head downslope . 

found secondary stresses that are compressive with values of 

173 psi (12.2 kgf/ cm2) to I ,660 psi ( 117 kgf/ cm2). The existence of stress in the Triassic sandstones of Connecticut was 

dramatically demonstrated in the early development of the 

""" •' . _' --:: - ' l. 

FIGURE 48. Feather fracture developed on a curv il inear joi nt surface. Upper flow 

unit , Hook Mountain of Third Mountain , Pine Brook , N.J. The sharp end of 

the hammer is at the basal point of the feather. 

Fracture pattern on a joint wedge broken out of the curvilinear zone 

at the Millington quarry (Houdaille Industries, Inc .), Millington, N.J. The 

scale is I 0 em long. 

"Brownstone" quarrying operations in Portland. Johnston 

( 1854, p. 285, 286) describes the instantaneous release of the 

stress as follows: 

The first instance observed occurred some two or three years ago, and 

occasio ned some alarm among the workmen. The excavation had then 

reached the depth perha ps of one hundred and twenty feet from the original 

surface of the ground ; and a beginning was to be made in the stratum then 

constituting the bottom of the cavity that had been formed. For this purpose 

the workmen were directed to cut with their picks a channel or groove, a 

foot or more wide, quite through the stratum, and some fifty or eighty feet in 

length. To facilitate the operation, the work was begun by the side of one of 

the natural joints or seams that occur at intervals, crossing the strata nearly 

at right angles; and as several workmen commenced upon it at the same 

time, all along the li ne it was made to sink with about the same rapidity, the 

loose fragments being thrown out as they were separated by the instrument. 

The stratum was found to be about six or seven feet in thickness, and it happened that the channel or groove was cut in an east and west direction. 

When the channel ;lad been sunk to within about nine or twelve inches of the 

bottom of the stratum, suddenly the remaining stone at the bottom was 

crushed to fragments with a loud report by a n enormous lateral pressure, 

and the men in alarm leaped from the excavation they had made. By examination it was found that the walls of the groove or canal just made had 

approached each other about three fourths of an inch, the stratum through 

which they had cut having on one side slidden this distance in its ancient 

bed! 

These observations in the rocks of the Triassic basins indicate that the rocks are in a state of stress above that to be 

expected from the lateral component of stress associated 

with gravitational loading. The magnitude of this stress is, by 

itself, incapable of producing joints but it may produce 

regions of incipience. 

The application of stress by various engineering operations may provide the small amount of energy necessary to 

climb over an energy barrier and thus open up the incipient 

joints in these rocks. These joints may be very difficult to recognize in very shallow cuts but in somewhat deeper cuts 

these joints may be-visible, and it may be possible to observe 

a reduction in the frequency with an increase in depth in the 
H36 STUDIES ON THE WATCHUNG BASALT FLOWS OF NEW JERSEY 

section, and this observation may permit an evaluation of 

the effect. I have observed such differences in quarries. 

In making frequency counts it is necessary to discriminate 

between joints arising from geologic processes and those 

caused by the works of man. Incipient joints opened up by 

the works of man I classify as quasi-geologic joints.6 Since 

some of these joints develop in a large volume of rock and are 

not limited to the surface of the outcrop they must be formed 

as a result of the application of a significant stress acting 

throughout a large volume. Such a stress could be generated 

in blasting operations. 

Nongeologic pseudojoints and fractures are produced, in 

response to stresses developed generally from sudden shock, 

in the course of engineering, mining, quarrying, and 

construction operations. They may be produced by the 

action of percussion machinery- pneumatic drills and 

hammers, or the accidental dropping of the buckets of power 

shovels, etc. They may also be produced by the crushing and 

abrasion occasioned by the movement of heavy excavating 

equipment over the exposed rock or by its brushing against 

the walls. These pseudojoints and fractures are commonly 

short in length, a few inches (a few centimeters), and they 

may fade out into hairline cracks. They may radiate out from 

a burred area where the concentrated force was applied. A 

grouping of several fractures may produce a local hackly 

appearance. These pseudojoints and fractures are all confined to a thin surface layer, and in this respect they differ 

completely from the quasi-geologic joints. They should be 

tallied separately from the other joints in a joint survey. 

Piteau ( 1973) has presented methods of characterizing joints 

for joint surveys in engineering practice and discusses errors 

in measurement and gives an extensive interpretation of the 

data. 

FREQUENCY OF COOLING AND TECTONIC JOINTS 

IN ONE OF TI-lE LEAST DEFORMED PARTS OF THE 

BORDER SYNCLINE 

The roadcut for U.S. Highway No. 80 at Pine Brook 

passes through the lower end of Hook Mountain, a part of 

Third Watchung Mountain. The roadcut for U.S. Highway 

No. 280 passes through the Second Watchung Mountain in 

the vicinity of Livingston, and through First Watchung 

Mountain at West Orange. These three cuts lie on a line that 

is nearly perpendicular to the strike of the Watchungs and at 

a position that is near the center of the syncline and nearly 

parallel to its minor axis (see figure 2, note line extends from 

Pine Brook to West Orange). 

The joint frequencies measured along the walls of the 

roadcuts, for 50 feet intervals, are contained in table I. Most 

of the values are averages. All of the joints recorded are the 

result of geologic processes. The frequencies of the cooling 

r. In !he disci pline of Rock Mechanics stresses deve loped as a result of geologic processes an: 

referred to as .. virgin stresses," whereas those developed as a result of engineering operations a rc 

n:krn:d to as ''induced stre sses·• (Oliveira. 1971). 

joints are not significantly different for the several joint systems within the three Watchung Mountains. The tectonic 

joints on the other hand show that the frequency of the tectonic joints in Second Mountain is a different order of magnitude from the frequency values in Third and First Mountains. 

These data give a quantitative estimate of the frequencies 

of cooling and tectonic jointing. They are only a part of a 

more complete collection of data obtained on Third and 

Second Mountains and of a more limited set on First 

Mountain. When the study of First Mountain is completed, 

these data will be used in interpreting the structural relations 

in the border syncline. 

It should further be noted that the frequency of the cooling 

joints in the curvilinear zone of the lower flow unit of Second 

Mountain is relatively constant except close to the base of 

the flow, near the contact, where incipient curvilinear joints 

were emphasized by the tectonic deformation. 

SUMMARY OF THE GEOMETRY OF THE COOLING JOINT 

SYSTEMS 

The cooling joint system of the vesicular zone consists of 

widely spaced basal joints and short rectangular prisms. This 

combination gives rise to a platy or tabular aspect. The prism 

joints are commonly a foot (0.3 m) apart, and the basal 

joints, in the longest direction, are of 4 to 10 times, or more, 

the spacing of the prismatic joints. The basal surfaces tend to 

be rectangular and not square. 

The cooling joint system of the columnar zone, in Third 

Watchung Mountain, consists of a set of prismatic joints, 

commonly six or five sided together with capping basal 

joints which terminate the prisms. Many of the joints resemble hexagonal and pentagonal right prisms, but some are 

tapered and then seem almost pyramidal in aspect. The 

dimensions of the columns are variable, but they range from 

8 to I 0 feet (2.4 to 3.0 m) high and 6 inches to 1 foot ( 15 to 30 

em) wide. 

The blocky joints are so-called because of their shape as 

rectangular parallelepipeds. In size they tend to be greater 

than 4 x 5 x 10 feet (1.2 x 1.5 x 3.0 m). In some exposures 

they were as large as I 0 x I 0 x several tens of feet long (3.0 x 

3.0 x many tens of meters). 

The curvilinear joints are quite variable in shape, but they 

all have curved faces. These curved faces are warped surfaces. They are here interpreted as helicoidal surfaces. When 

the large helicoidal surfaces are broken, they break up into 

shieldlike, wedge-shaped, and sphenoidal volumes, whose 

faces are curvilinear polygons. These curvilinear surfaces 

may vary from a few feet(± meter) to 20 or more feet (6.1 m) 

in height and 5 feet ( 1.5 m) in breadth. 

In making joint frequency counts it is necessary to be able 

to rapidly identify the type of joints being counted. One of 

the complicating problems arises in excavated cuts for highways, and it is important to point out these modifications 

introduced by the works of man. The columnar zone 
TABLE I.-Joint frequencies in the Watchung Mountains along a line nearly normal to the strike and extending from Pine Brook on Third 

Watchung Mountain to near West Orange on First Watchung Mountain 

Flow unit 

Upper 

Lower __________ _ 

Lower -----------

Lower 

Blocky zone 

Curvilinear zone ___ top to middle -------------

--- do ------ middle to base ---------------

Ve~cu~rba~ ---------------------------

Vesicular top ----------------------------

Columnar zone 

Curvilinear zone ___ top 

___ do------ middle --------------------

--- do ______ near the base ----------------

--- do ______ zone of basal platy 

___ do------ joints ---------------------

Shale and sandstone of the Brunswick 

Formation below Second Mountain. 

"Blocky zone" ( Massive)2 

Columnar zone -----· 

Curvilinear zone ___ top to middle 

___ do ______ middle to bottom -------------

Vesicular base ---------------------------

Cooling joints 

Third Mountain 

6 joints in 50 feet (6/15 m) 

72 joints in 50 feet (72/15 m) 

56 joints in 50 feet (56/15 m) 

a few indistinct joints 

a few indistinct joints 

20 columns in 19 feet (20/5.8 m) 

Second Mountain 

45 joints in 50 feet (45/15 m) 

25 joints in 50 feet (25/15 m) 

73 joints in 50 feet (73/15 m) 

First Mountain 

3 joints in 100 feet (3/30 m) 

62 columns in 50 feet (62/15 m) ___ _ 

57 joints in 50 feet (57/15m) 

72 joints in 50 feet (72/15 m) 

a few indistinct joints 

1

The>e are cut by joints nearly normal to them, and this normal set is about 18-20 inches apart. 

ketonic joints 

9 joints in 50 feet (9/15 m) _______ 

16 joints in 50 feet (16/15 m) ----- 3 joints in 50 feet (3/15 m) -------

a few indistinct joints ----------

14 joints in 50 feet (14/15 m) ----- 91 joints in 50 feet (91/15 m) ----- 150 joints in 50 feet (150/15 m) ____ 

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

lOjointsin 12feet(l0/3.7m)l _____ 

7 to 10 joints in 50 feet (7-10/15 m) _ 

lOjoints in 50 feet (10/15 m) 

(3) 

2 joints in 50 feet (2/15 m) 

5 joints in 50 feet (5/15 m) 

'This zone was much disturbed. It contained in addition 125 sigmoidal shears in 260 feet (125/79 m), equivalent to 24 per 50 feet (24/15 m). 

'Slipping along columns probably took place during the period of tectonic deformation. 

L~ngth of traverse 

Feet Meters 

213 

175 

60 

21 

19 

400 

~00 

450 

12 

100 

260 

1091 

780 

365 

65 

53 

18 

6+ 

6 

122 

244 

137 

37 

30.5 

79 

333 

238 

Ill 

'-

0 

z 

-1 

r:/l 

.....:: 

r:/l 

-1 

m 

s: 

r:/l 

co 

w 

-..1 
838 STUDIES ON THE WATCHUNG BASALT FLOWS OF NEW JERSEY 

although infrequently observed is almost always easy to 

identify. The chief difficulty arises in the distinction between 

the blocky and curvilinear zones. 

The recognition of the blocky zone is usually an easy task, 

but its identification may be complicated by weathering, by 

glacial processes, by tectonic deformation, or by quarrying 

and excavation. Weathering may remove the sharp edges 

and give rise to some rounding of edges, and it may accentuate the joints; but the general rectangular pattern, the presence of few curved joints, and the presence of well-defined 

parallel joints usually leave no doubt as to zonal identity. It 

tends to preserve its massive character to a remarkable 

degree. When blocky joints are bumped and gouged by 

heavy buckets of power shovels, they usually develop a pseudocolumnar structure, for this operation tends to emphasize 

the tectonic joints, many of which are incipient in character. 

The blocky zone is, however, very hard to excavate, and it 

tends to jut out beyond the curvilinear zone below it. 

Further, the fact that the internal structure of the blocks 

resembles an assemblage of closely packed elongate 

polyhedra is a very helpful criterion in making a decision. 

These estimated sizes for the joints are only average values 

and in some areas they may be larger and smaller. In Second 

Mountain huge curvilinear joints as much as 15 x20feet(4.6 

to 6.1 m) were observed. 

SUMMARY OF THE GEOMETRY OF THE TECTONIC JOINT 

SYSTEMSWITH A CONTRAST OF THE TWO TYPES 

The tectonic joints consist principally of (1) systems of 

parallel joints occurring in bands from a few inches (few centimeters) to 10 or more feet (3m or more) apart and usually 

oriented normal to the surface of the flow, (2) sigmoidal 

joints (S-shaped) 7 which may be quite long and oriented normally or transversely to the surface of the flow, (3) a conjugate set of closely spaced joints which appear near the base of 

the flow and are oriented normally or nearly so, and (4) a set 

of basal platy joints which are developed as a zone 10 to 12 

feet (3-4m) thick, parallel to and at the base of the flow just 

above the vesicular zone. These basal platy joints may be difficult to see in weathered exposures where slumping has 

occurred. 

The occurrence of cooling joint systems and tectonic joint 

systems differ in the following ways: 

1. cooling joints are always present whereas the occurrence of tectonic joints varies in any particular outcrop from 

very rare to extremely abundant; 

2. the cooling joints are limited to certain zones in the flow 

and appear in a definite sequence; 

3. the frequency of cooling joints does not change as the 

structure of the sheet changes, except for the quasi-geologic 

joints, whereas the abundance of the tectonic joints is 

directly related to the stress trajectories; see table 1; 

7 For a discussion of the use of the term sigmoidal jointing, particularly applied to sedimentary 

rocks, see Engels (1956). 

4. some of the tectonic joint systems., having been produced by the deformation of the graben during arching when 

the border synclines were formed, are characterized by a 

pronounced conjugate relationship, (as for example the 

pseudocolumnar joints (type 2)); 

5. some of the tectonic joint systems consist of planes 

extending without interruption from the top to the base of a 

zone and having a uniform attitude, (as for example the 

pseudocolumnar joints (type 1)). 

A NOTE ON THE PAUCITY OF ZEOLITE DEPOSITS 

IN THE TRAP FLOWS OF THIRD WATCHUNG MOUNTAIN 

The field study of Third Mountain has shown that the 

occurrence of zeolites and other minerals of the same or similar paragenesis is rather local in areal extent and relatively 

small in quantity. It is observed chiefly in the following 

modes of deposition: 

1. mineralized veins 

2. mineralized joint surfaces 

3. breccia zones 

4. cavities-generally located near the top of the flow (these 

cavities were formerly occupied by gases). 

This field study has not disclosed any pillow lavas in Third 

Mountain and this confirms the earlier findings of Lewis 

(1915). The normal vesiculated bottom is only rarely mineralized and the chief mineral species appears to be calcite. The 

vesiculated base of Third Mountain thus does not show the 

great mineralization observed in First Mountain. These 

observations support Fenner's (1908) theory for the relationship of the large zeolite zones with extrusion of lava flows 

into shallow bodies of water, chiefly playa lakes, forming pillow lavas in which the mineralization took place. 

Schaller (1932, p. 8, 9) also contrasted the behavior of the 

lavas flows that poured over ordinary sediments with those 

that flowed over lake beds and commented on the condition 

and appearance of a "lava flow that came to rest quietly over 

dry sediments and crystallized to a normal compact basalt" 

with that of a lava that "flowed into water and acquired a 

spheroidal or boulder like structure." (Pillow lava). His 

study of the crystal cavities of the zeolite region in First W atchung Mountain showed that "the crystal cavities appear 

only in the lower spheroidal phase." (That is the pillow 

lavas). 

Joints in the basalt were of minor importance compared to 

pillow lavas as sites for deposition of the zeolite mineral 

association. 

SUPPLEMENTARY TOPICS 

Implied in some of the descriptions of joint systems are 

some geometric concepts that may not be familiar to all readers of this paper, and they have been added here for those 

who wish to read them. In order that the usage given or 

implied herein will be clear a section entitled "Glossary of 

terms and definitions," and a section on "The character of 
JOINT SYSTEMS B39 

helicoidal surfaces" have been subjoined. In addition Preston's ( 1904) classic description of "Isothermal surfaces and 

lines," and a section on "The phenomenological evidence for 

isothermal surfaces and the direction of heat flow" have been 

included. 

GLOSSARY OF TERMS AND DEFINITIONS 

A system is anything which we wish to isolate for purposes 

of study. 

A bounded system is a system which is closed by a single 

surface, such as a sphere, or by the intersection of several surfaces such as a parallelepiped. All points in a bounded system are described by the restrictions on the analytical expressions of the surfaces. Thus, for a sphere every point xyz, on 

or within it is described by the family of equations x2 + y 2 + z2 

= a2 and for a bounded system a2 < r2, where r is the radius of 

the sphere. 

A closed form encloses space and examples are a sphere, a 

cube, or a parallelepiped. 

Open forms cannot by themselves enclose space since they 

extend to infinity. Examples of open forms are the cylinder, 

a prism, or a cone. Open forms may be terminated by other 

open forms. Thus, a cylinder may be terminated by basal 

planes. 

A surface may be defined as a boundary, real or imagined, 

that separates two contiguous volumes. A single equation 

such as F(x, y, z) = 0 represents a surface. 

A plane is defined as a surface which meets the requirement that any straight line joining any two points in it lies 

entirely in the surface. 

A curved surface fails to meet the above relation and 

therefore no part of it is a planar surface. Familiar examples 

of curvilinear surfaces, i.e. those that consist of curved lines, 

are the cylinder, cone and sphere. 

Curvilinear polygons are polygons whose sides are curved 

lines and whose surfaces are curved. Note this definition 

excludes planar surfaces with curved sides. 

A quadric surface is any surface defined by an equation of 

the second degree in x, y, z, Osgood and Graustein (1921, p. 

548). 

The sphere and the quadric cylinders, cones, and surfaces 

of revolution are special types of quadric surfaces, Osgood 

and Graustein (1921, p. 548). 

General types of quadric surfaces are ellipsoids, hyperboloids, and paraboloids. 

Ruled surfaces are those on which straight lines may be 

drawn. "There are three classes of ruled surfaces: I, Planes; 

II, Single curved surfaces; III, Warped surfaces" Schumann 

(1946, p. 223). 

"A warped surface is one generated by a straight line moving so that no two consecutive positions lie in the same 

plane," Schumann ( 1946, p. 264). 

Warped surfaces are not developable surfaces, because 

they cannot be unrolled into a plane. I 

CHARACTER OF HELICOIDAL SURFACES 

Helicoids are geometric surfaces that are rarely described 

in modern texts on analytical geometry and so are not too 

well known. For this reason several definitions are given 

here, and references to the pertinent literature have been 

added. Helicoids are defined in slightly different ways by 

mathematicians (differential geometers) and engineers (descriptive geometers), but their operations generate identical 

surfaces. The mathematician is interested in an analytical 

treatment of the surfaces; the descriptive geometer is concerned with the accurate graphical representation of 

geometric objects and with the solution of problems relating 

to the shape of objects and their disposition in space. The 

mathematician Frost (1886, p. 218) defines a helicoid as follows: 

The helicoid is a scroll generated by the motion of a straight line which 

intersects at right angles a fixed axis, about which it twists with an angular 

velocity which varies as the velocity of the point of intersection with the axis. 

Schumann ( 1946, p. 223, 282-289) gives an especially clear 

presentation of the approach to these surfaces from descriptive geometry. The following definitions are taken from his 

text: 

A surface is generated by the continuous motion of a line (straight or 

curved) called the generatrix, having a relationship to a fixed line called the 

directrix. The consecutive positions of the generatrix are elements of the 

surface. A surface is not a solid but is a boundary of a solid. 

The helicoid is a warped surface generated by a straight line moving so that 

it constantly touches a helix and its axis and makes a constant angle with 

that axis. 

When the generatrix makes an angle of90° with the axis the helicoid is right. 

This surface is also a surface of two nappes. 

When the generatrix makes an angle with the axis other than 90°, the 

helicoid is oblique. It' consists of two nappes*** [See figure 50A.] 

A nappe is a surface, or a portion of a surface, forming a continuous sheet. 

[See figure 50B.] 

The general analytical expression for a helix and a helicoid 

provide a means of grasping the significance of their properties. The following discussion is based on the treatment of 

Eisenhart (1909) and Graustein (1935). The parametric 

equations defining a helix are: x = uCosv, y = uSinv and z = av 

where z is the axis of a right cylinder, x andy the coordinate 

axes, vis the angle between the radius of the right cylinder to 

a point P and the positive x axis, and a is a constant. The 

pitch of the helix, h, is equal to 2 ·7T' a, and the tangent of the . 

helical angle is tan(]'= _h_ . The tangent relation shows 

2 7TU 

that as the angle of the helix increases the pitch, h, increases. 

The parametric equations for the helicoid are commonly 

referred to the orientation with z as the axis of rotation and 

the meridians defined as the planes through the z axis, then 

the equation of the helicoidal surface is: 

x = uCosv, y = uSinv, and z = cp (u) + av 
840 STUDIES ON THE WATCHUNG BASALT FLOWS OF NEW JERSEY 

FIGURE 50. A, A string model of Oblique Helicoid prepared by Olivier of Paris. ''A helix and its axis as directrices; elements making an acute angle with the axis.'' 

B, A string model of Right Helicoid. "A helix and its axis as directrices; elements making a right angle with the axis." From Schumann (1946) (Published by 

permission of D. Van Nostrand Co., Inc.) 

where 

z = cp (u) is the generating curve; 

u =the perpendicular distance of a point from the z 

axis; 

v = the angle of the meridian plane through the point 

to the ZX plane; 

a = constant, the parameter of helicoidal motion; and 

2-rra = the pitch of the helicoidal motion. 

In these equations it can be noted that: 

l. if cp (u) =constant, then the curves v =constant are straight 

lines (rulings) perpendicular to z and the surface is a right 

helicoid. 

2. if a= 0, then the equations define a surface of revolution. 

3. from the method of construction it follows that the curves 

v = constant are the rulings and curves u =constant are 

circular helicies on the helicoids. 

4. if the pitch, h, is variable or the length of the generatrix is 

variable more general types of helicoids are generated. 

Wellman (1948, p. 219) points out that in such cases "the 

angle between the generatrix and the axis is also variable." 

From these definitions we may further observe that helicoids can be right-handed or left-handed depending on 

whether they twist to the right or to the left, see figures 50 and 

51. A right-handed helicoid advances away from the end of 

the helical directrix in a clockwise direction and a lefthanded helicoid advances in a counterclockwise direction. 

Helicoids are warped surfaces because successive positions 

of the generatrix do not lie in the same plane and if the surface is unrolled onto a plane it will not lie flat but will have a 

warp in it. Helicoids have also been called screw surfaces 

because of their obvious relations to these objects. 

For an analytic treatment of helicoids the reader is 

referred to the works of Eisenhart (1909), Frost (1886), 

Graustein (1935), Hilbert and Cohn-Vossen (1932), and 

Scheffers (190 1, 1902). For a descriptive geometric approach 

reference is made to the treatments of Schumann ( 1946), 

Von Sanden (1960), Watts and Rule (1946), and Wellman 

(1948). 

ISOTHERMAL SURFACES AND LINES 

According to Preston (1904, p. 663), 

In the general case the temperature at any point of a body will be a function 
JOINT SYSTEMS 841 

z Directrix (axis) 

A 

: 

FIGURE 51. Two left-hand, right helicoids. The vertical distance 27rq is the pitch 

of one helicoid where q equals a constant and it represents the vertical distance 

traversed in one complete revolution (360°) of the generatrix. Scheffers 

(1902, v. 2, p. 60-61). 

of the co-ordinates, x, y, z, of the point and of the time t, so that the general 

expression for 0 at any point will be of the form 

0= f(x,y,z,t). 

Hence, if we write 

f(x,y,z,t) =a, 

where a is a constant, we obtain the locus of all the points at which the 

temperature has the same value a at the time t. These points lie on a surface, 

determined by the function/, and named an isothermal surface because it is 

one of equal temperature. When the flow has become steady the temperature at any point remains steady, and therefore does not involve the time. In 

this case, then, the isothermal surfaces are fixed in shape and position, each 

separating those parts of the body which are hotter than a certain temperature from those which are colder. In the variable state, on the other hand, 

the shape and position of an isothermal surface corresponding to a definite 

temperature will in general vary with the time. 

If a system of such surfaces be supposed drawn within the body, the 

temperature of each differing, by 1 o suppose, from that which immediately 

precedes or follows it, the whole body will then be divided into a system of 

layers or shells such that the temperature of one face of each layer exceeds 

that of the other by 1 o, and a flow of heat will proceed through the shell from 

the hotter face to the colder. The direction of the flow at each face will also 

be perpendicular to the surface, for since the temperature is constant all over 

each isothermal, it follows that there can be no flow along such a surface. 

It follows then that the direction of the resultant flow at any point of a 

body is along the normal to the isothermal surface passing through that 

point, so that if a line be drawn cutting the whole system of surfaces orthogonally, the direction of the flow at every point of this line will be along the 

line. For this reason a line drawn so as to cut each of the system of surfaces at 

right angles is termed a line of flow. 

The whole body may thus be imagined to be divided into a system of infinitely thin shells by a system of isothermal surfaces, and the infinite system 

of lines which can be drawn cutting these shells orthogonally are the lines of 

flow. 

One property of these systems is that no two isothermal surfaces, or no 

two lines of flow, can intersect each other, for no point can possess two different temperatures at the same time, nor can the flow at any point be at 

once in two different directions. 

THE PHENOMENOLOGICAL EVIDENCE FOR ISOTHERMAL 

SURFACES AND THE DIRECTION OF HEAT FLOW 

Geologists established long ago the relation of the columnar joint systems in lava flows and dikes and observed that in 

vertical dikes the columnar joints were horizontal whereas in 

flat-lying lava flows the joints were vertical. They further 

observed that in curved contacts with the country rock that 

the joints tilted to conform to a normal position to the contact. They also noted that in pahoehoe tops and other curved 

surfaces in lava tops that the joints tilted in conformity with 

the surface. From this they concluded that the isothermal 

surfaces were parallel to the tops of flows and the walls of 

dikes and that the direction of heat flow was normal to the 

isothermal surfaces. Their conclusion was reinforced by the 

observations in the furnace practices of their day. 

Iddings (1886; 1909, v. 1, p. 320-322) studied the columnar 

jointing in the famous O'Rourke quarry at West Orange, 

N.J. He made a theoretical study of the heat flow relations 

and jointing in which he assumed that the joints formed in 

the cooling lava along surfaces perpendicular to the isothermal planes. Tomkeieff (1940, p. 121-135) worked out the 

cooling relations and formation of joints for his study of 

basalt of the Giant's Causeway district of Northern Ireland. 

He defined (p. 129) the fracture isotherm as that particular 

isotherm at which fracture takes place and suggested "that 

the rate of advance of the fracture isotherm will determine 

the nature of the jointing, while, the amount of accumulated 

stress will determine its magnitude." 

These model studies of heat transfer relations, by conduction, to the geometry ofthe jointing produced in a solidifying 

lava sheet have been calculated for only very simple cases. 

The calculation of the heat conduction relations, including 

the corner and edge corrections of Langmuir, Adams, and 

Meikle (1913) can only be made for simple solids. For more 

complex shapes the mathematical solutions become formidable, and a graphical method, based on geometrical 

principles was developed by Awbery and Schofield (1929) 

and Schofield (1930). It has been found very useful by Ingersoll, Zobel, and Ingersoll (1954, p. 200-203) in analyzing 

"steady-state heat conduction in two dimensions, involving 

the construction of an isotherm and flow-line diagram." 

Numerical methods used in conjunction with a computer 

may yield solutions for yet even more general problems, 

Myers (1971). 

ACKNOWLEDGMENTS 

Richard C. Erd, U.S. Geological Survey, worked closely 

with me in the mapping of much ofThird Watchung Mountain, and I am indebted to him in many ways in the testing of 

the ideas regarding the jointing patterns in the trap flows. 

The late Theodore Woodward, John R. Houston, and the 

late Charles Minard, former members ofthe U.S. Geological 
B42 STUDIES ON THE WATCHUNG BASALT FLOWS OF NEW JERSEY 

Survey, served as assistants in the field studies on Third Watchung Mountain. Many of the photographs were specially 

taken for this study by John P. Marble, Jr., formerly of the 

U.S. Geological Survey and Dr. Gudmunder E. Sigvaldason, then of the Dept. of Industrial Testing and Research, 

Reykjavik, Iceland, who from 1959 to 1961 was a visiting 

research scientist at the U. S. Geological Survey under sponsorship of the National Academy of Sciences. I am also 

indebted to the many property owners, quarry companies, 

and quarry managers in the area. The standard reference 

section for Third Watchung Mountain was set up in the Millington quarry and accordingly, I am particularly grateful to 

the late Thomas J. Stewart, former superintendent, of the 

Millington Plant of Houdaille Industries, who aided me in 

many ways and who constantly encouraged me. 

The names given to the abandoned quarries were obtained 

in part from former owners and in part from local residents. 

The late Clyde L. Wolfe of Bernardsville was knowledgeable and helpful on this subject. 

In order to gain a knowledge of jointing in other basaltic 

provinces and to make comparisons, brief field excursions 

were made to them with geologists familiar with the areas. 

This provided the opportunity to study the possible influence of the nature of the underlying rocks on the character of 

the jointing in the basalt flows above them. I wish to thank 

the following colleagues who are members of the U.S. Geological Survey for showing me jointing phenomena in the 

basaltic rocks of the areas of study-Henry R. Cornwall and 

Walter S. White in the Michigan copper district, Albert E. 

Weissenborn in the flows of the Columbia River Basalt 

Group south of Spokane, Wash., and John K. Adams in the 

Table Mountain basalt near Golden, Colo. In Europe I was 

shown jointing in the basalt flows of Iceland at Thingvellir 

and elsewhere by the late Professor Tomas Tryggvason of 

the University Research Institute of Reykjavik, in the 

Vogelsberg Mountains in Hesse, Germany, by Professor 

Hans Hentschel of the Hessische Landesamt fur Bodenforschung in Wiesbaden, Germany. Professor K. Hans Wedepohl of Gottingen University, showed me the basaltic plugs 

in the vicinity of the University and Professor Sigmund 

Koritnig took me to the "Bhiue Kuppe"' bei Eschwege and to 

the Roher Meissner. The later flow was famous in the controversy of the Neptunists and the Vulcanists, Johannsen 

(1937, p. 264). The late Professor Sergei I. Tomkeieff of 

King's College, University of Durham, showed me the Whin 

Sill and discussed his jointing studies on the Giant's Causeway district, Northern Ireland. Niels Oskarsson, of the University of Iceland assisted me in the measurement of joint 

widths at the fault wall at Thingvellir and for which help I 

thank him. 

My colleague Howard T. Evans very kindly prepared the 

complex illustrations of the geometrical models of the various helicoidal surfaces. Dallas L. Peck and Thomas L. 

Wright discussed related problems in the lavas of Hawaii 

and the Columbia River flows. 

An early version of this manuscript was critic~lly reviewed 

by my colleagues Gudmunder E. Sigvaldason, Harry W. 

Smedes, and Robert L. Smith, and this version by Rosalind 

L. Helz, Ray E. Wilcox, and David R. Wones, all of the U.S. 

Geological Survey. 

LITERATURE CITED 

Awbery, James H. and Schofield, Francis H., 1929, Effect of shape on heatloss through insulation: Congress on Refrigeration, 5th Internat. 

Proc., 1928, pt. 3, p. 591-596. 

Bankwitz, Peter, 1965, Uber Kliifte-1. Beobachtungen im Thiiringischen 

Schiefergebirge: Geologie, Zeitschr. fiir das Gesamtgebiet der Geologischen Wissenschaften, Jahrg. 14, p. 241-253. 

__ 1966, Uber Kliifte-11. Die Bildung der Kluftflache und seine Systematik ihrer strukturen: Geologie Zeitschr. fur das Gesamtgebiet der 

Geologischen Wissenschaften, Jahrg. 15, p. 896-941. 

Barrell, Joseph, 1915, Central Connecticut in the geologic past: Connecticut Geol. and Nat. History Survey Bull. 23, 44 p. 

Bingham, James W., and Grolier, Maurice J., 1966, The Yakima Basalt and 

Ellensburg Formation of south-central Washington: U.S. Geol. 

Survey Bull. 1224-G, p. G1-Gl5. 

Bond, John G., 1963, Geology of the Clearwater embayment: Idaho Bur. 

Mines and Geology Pamph. No. 128, 83 p. 

Bucher, Walter H., and Kerr, Paul F., 1948, Excursion to the First Watchung Basalt at Paterson, New Jersey: Geol. Soc. America Guidebook 

of Excursions, 6lst Ann. Mtg., New York, N.Y., 1948, p. 109-119. 

Cloos, Hans, 1936, Einfiihrung in die Geologie: Lehrbuch der inneren 

Dynamik: Berlin, Verlag Gebriider Borntraeger, p. XII+ 515. 

Eisenhart, Luther P., 1909, A treatise on the differential geometry of curves 

and surfaces: New York, Ginn and Company, p. xiv + 474. Reprinted 

by Dover Publications, Inc., N.Y., 1960. 

Engels, Bruno, 1956, Zur Deutung der Querplattung (Sigmoidalkliiftung): 

Hamburg geol. Staatsinst. Mitt. Heft 25, p. 5-25. 

Faust, George T., 1975, A review and interpretation of the geologic setting 

of the Watchung Basalt flows, New Jersey: U.S. Geol. Survey 

Professional Paper 864-A, 42 p. 

Fenner, Clarence N., 1908, Features indicative ofphysiographicconditions 

prevailing at the time of the trap extrusions in New Jersey: Jour. Geology, 16,p. 299-327. 

Frost, Percival, 1886, Solid geometry: London, Macmillan and Company, 

3d edition, p. xxiv + 408. 

Geike, Archibald, 1893, Textbook of geology: London, Macmillan and Co., 

3d ed., rev., p. xvi + 1147. 

Graustein, William C., 1935, Differential geometry: New York, Macmillan 

and Company, p. xi + 230. 

Hast, Nils, 1967, The state of stress in the upper part of the earth's crust: 

Eng. Geology, v. 2, no. 1, p. 1-17. 

Hilbert, David, and Cohn-Vossen, Stephen, 1932, Anschauliche Geometrie: Berlin, Julius Springer, 254 p. Translated by Nemenyi, P., 1952, 

Geometry and the Imagination, New York, Chelsea Pub. Co., p. ix + 

357. 

Hodgson, Robert A., 1961, Classification of structures on joint surfaces: 

Am. Jour. Sci., v. 259, p. 493-502. 

Hooker, Verne E., and Johnson, Charles F., 1967, In situ stresses along the 

Appalachian Piedmont: Proc. 4th Rock Mechanics Symposium, 

Ottawa, p. 137-154. 

Iddings, Joseph P., 1886, The columnar structure in the igneous rocks of 

Orange Mountain, New Jersey: Am. Jour. Sci., ser. 3, 31, p. 321-331. 

__ 1909, Igneous Rocks: New York, N.Y.,John Wiley and Sons, v.1,p. 

xi+ 464. 

Ingersoll, Leonard R., Zobel, Otto J., and Ingersoll, Alfred C., 1954, Heat 

conduction with engineering, geological and other applications: Madison, Wisconsin, Univ. Wisconsin Press, p. xiii + 325. 
JOINT SYSTEMS B43 

Jaeger, John C., 1968, Cooling and solidification of igneous rocks: in Hess, 

Harry H., and Poldervaart, Arie, Basalts-The Poldervaart Treatise on 

rocks of basaltic composition: New York, N.Y., Interscience, v. 2, p. 

503-536. 

Johannsen, Albert, 1937, A descriptive petrography of the igneous rocks: 

Chicago, The University of Chicago Press, v. Ill, p. xiv + 360. 

Johnston, John, 1854(1855), Notice on some spontaneous movements occasionally observed in the sandstone strata in one of the quarries at Portland, Connecticut: Amer. Assoc. Adv. Sci. Proc., v. 8, p. 283-286. 

Kemp, James F., 1929, A handbook of rocks: New York, N.Y., D. VanNostrand Co., Inc., p. xi + 300. 

Krynine, Paul D., 1950, Petrology, stratigraphy, and origin of the Triassic 

sedimentary rocks of Connecticut: Connecticut Geol. and Nat. History 

Survey Bull. 73, 239 p. 

Langmuir, Irving, Adams, Elliot Q., and Meikle, GeorgeS., 1913, Flow of 

heat through furnace walls: The shape factor: Am. Electrochem. Soc. 

Trans., v. 24, p. 53-84. 

Lewis, J. Volney, 1908, Petrography of the Newark igneous rocks of New 

Jersey: Geol. Survey New Jersey, Ann. Rept. State Geologist for 1907, 

p. 99-167. 

___ 1909, Building stones of New Jersey: New Jersey Geol. Survey Ann. 

Rept. for 1908, p. 53-124. 

___ 1915, The pillow lavas of the Watchung Mountains: New Jersey 

Geol. Survey Bull. 16, Ann. Adm. Rept. State Geologist of N.J. for 

1914, p. 51-56. 

Mackin, J. Hoover, 1961, A stratigraphic section in the Yakima Basalt and 

the Ellensburg Formation in south-central Washington: Washington 

Div. Mines and Geol. Rept. Inv. no. 19, 45 p. 

Murawski, Hans, 1968, Tektonik, a chapter in "Yom Erdkern bis zur Magnetosphere": Frankfurt am Main, Germany, Umschau Verlag, p. 67-

83. 

Myers, Glen E., 1971, Analytical methods in conduction and heat transfer: 

New York, McGraw Hill Book Co., p. xvii + 508. 

Nevin, Charles M., 1931, Principles of structural geology: New York, John 

Wiley and Sons, Inc., p. xii + 303. 

Oliveira, R. A.M., 1971, Nature of stresses: Internat. Symposium on the 

detm. of stresses in rock masses, Lisbon, 1969, Proc. vol., p. 34-36. 

Oilier, Clifford D., 1969, Weathering: New York, American Elsevier Pub. 

Company, Inc., p. vii+ 304. 

Osgood, William F., and Graustein, William C., 1921, Plane and solid analytic geometry: New York, The Macmillan Company, p. xvii + 614. 

Piteau, Douglas R., 1973, Characterizing and extrapolating rock joint 

properties in engineering practice: Rock Mechanics, Supplementum 2, 

p. 5-31. 

Preston, Frank W ., 1930, Ball and socket jointing in basalt· prisms: Royal 

Soc. London, Proc. pt. b, v. 106, p. 87-93. 

Preston, Thomas, 1904, The Theory of Heat [2d ed., revised by J. Rogerson 

Cotter]: London, Macmillan and Co., Ltd., p. xix + 838. 

Price, Neville J., 1966, Fault and joint development in brittle and semibrittle rock: Oxford, England, Pergamon Press, p. x + 176. 

Roberts, John C., 1961, Feather fracture, and the mechanics of rock 

jointing: Am. Jour. Sci., v. 259, p. 481-492. 

Rosen busch, Harry, 1923, Elemente der Gesteinslehre: Stuttgart, Germany, 

E. Schweizerbart'sche Verlag, p. x + 779. 

Salisbury, Rollin D., Kummel, Henry B., Peet, Charles E., and Knapp, 

George N., 1902, The glacial geology of New Jersey: Final Rept. State 

Geologist, 5, p. xxvii + 802. 

Schaller, Waldemar T., 1932, The crystal cavities of the New Jersey zeolite 

region: U.S. Geol. Survey Bull. 823, p. vii+ 90. 

Scheffers, Georg, 1901, Einfiihrung in die Theorie der Curven in der Ebene 

und in Raume: Leipzig, Verlag von Veit and Company, v. 1, p. x + 360: 

1902, Einfiihrung in die Theorie der Flachen: v. 2, p. x + 518. 

Schofield, Francis H., 1930, The heat-loss from a plate embedded in an 

insulating wall: Phil. Mag., ser. 7, v. 10, p. 480-500. 

Schumann, Charles H., Jr., 1946, Descriptive geometry: New York, D. Van 

Nostrand Company, Inc., 4th ed., p. xi+ 338. 

Sosman, Robert B., 1916, Types of prismatic structure in igneous rocks: 

Jour. Geology, v. 24, p. 215-234. 

Spry, Alan, 1962, The origin of columnar jointing, particularly in basalt 

flows: Geol. Soc. Australia Jour., v. 8, pt. 2, p. 191-216. 

Tomkeieff, Sergi 1., 1940, The basalt lavas of the Giant's Causeway district 

of Northern Ireland: Bulletin Volcano!., ser. II, Tome VI, p. 89-143. 

U.S. Geological Survey, 1961, Geological Survey Research 1961-Synopsis 

of geologic and hydrologic results: U.S. Geol. Survey Prof. Paper424-

A, p. A77-Al94. 

___ 1972, Geological Survey Research 1972: U.S. Geol. Survey Prof. 

Paper 800-A, p. A27. 

___ 1973, Geological Survey Research 1973: U.S. Geol. Survey Prof. 

Paper 850, p. 36. 

Voight, Barry, 1966, Interpretation of in situ stress measurements: Internat. 

Soc. Rock Mechanics, Proc. Int. Cong., v. 3, p. 332-348. 

___ l969a, A discussion-The state of stresses in the upper parts of the 

earth's crust: Eng. Geology, v. 3, p. 335-339. 

___ l969b, Evolution of North Atlantic Ocean: Relevance of rockpressure measurements: Amer. Assoc. Petroleum Geologists Mem. 12, 

p. 955-962. 

Von Sanden, Horst, 1960, Darstellende Geometrie: Stuttgart, B. G. 

Teubner Verlag, p. 115 + 42 Abbildungen. 

Watts, Earle F., and Rule, John T., 1946, Descriptive Geometry: New York, 

Prentice-Hall, Inc., p. viii+ 501. 

Wellman, B. Leighton, 1948, Technical descriptive geometry: New York, 

McGraw Hill Book Company, Inc., 1st ed., p. xii + 508. 

Woodworth, Jay B., 1896, On the fracture system of joints with remarks on 

certain great fractures: Boston Soc. Nat. History, Proc. v. 27, p. 163-

183. 

A 

Abstract ------------------------------- B I 

Acknowledgments------------------------- 41 

/\dams, Elliot Q -------------------------- 41 

Adams, John K -------------------------- 42 

Alward's quarry -------------------------- 23 

Amydaloidal minerals ----------------------- 5 

·\wbery, James H ________________________ 2, 41 

B 

' Ball and socket jointing --------------------- 10 

Bankwitz, Peter -------------------------- 31 

Barrell, Joseph. quoted --------------------- 19 

Bingham, James W ------------------------ 18 

Bond. John G --------------------------- 18 

Brownstone ------------------------------ 5 

Brunswick Formation ------------------ 5, 16, 21 

Bu-:her, Walter H. quoted--------------------- 3 

c 

Cloos, Hans, cited------------------------- 21 

quokd ------------------------------4 

Cohn-Vossen, Stephen---------------------- 40 

Columbia River Group ___________________ 18, 42 

Cooling joints, blocky zone ------------------- 11 

columnar zone _______________________ 9, 14 

curvilinear zone ----------------------- U 

in other basaltic provinces----------------- 17 

rectangular joint systems ------------------ 5 

Cnnnecticut Triassic Basin -----------------~- 17 

Cornwall, Henry R ------------------------ 42 

D 

Oeckcnsohle ---------------------------- 21 

Dimt:nsion stone-------------------------- 16 

E 

Eisenhart. Luther P ----------------------39, 40 

Engels. Bruno --------------------------- 38 

England: 

Whin Sill --------------------------- 42 

Erd, Richard C --------------------------- 41 

Evans. Howard T ----------------------- 15,42 

F 

Falls\, George T _________________________ 2, 19 

feather fracture ------------------------ 30, 31 

Fenner, Clarence N ____________________ 3, 17, 38 

Flow. breccias --------------------------- 16 

Fracture isotherm ________________________ 2, 41 

Frost, Percival, cited ----------------------- 40 

quoted ----------------------------- 39 

G 

Geike. Archibald, quoted --------------------- 4 

Geometry, cooling joint systems ---------------- 36 

tectonic joint systems-------------------- 38 

Germany: 

Blaue Kuppe ------------------------- 42 

Gottingen --------------------------- 42 

Hoher Meissner _____________________ 18, 42 

Vogelsberg ------------------------ 18,42 

Glacial pavement ------------------------- 12 

Glossary of terms ------------------------- 39 

Graustein, William C. cited ------------------- 40 

quoted ----------------------------- 39 

Grolier, Maurice J ------------------------ 18 

INDEX 

[Italic page numbers indicate major references] 

H 

Hast, Nils ----------------------------- B34 

Hawkins, Alfred C -------------------------2 

Helicoidal surfaces ------------------------ 39 

Hdicoide ------------------------------ 14 

Hcl7. Rosalind --------------------------- 42 

Hentschel, Hans -------------------------- 42 

Hilbert, David --------------------------- 40 

Hodgson, Robert A---------------------- 31, 32 

Hooker, Verne E ------------------------- 34 

Hornfels zone _____________ 5, 24 

Houston. John R 41 

Iceland: 

Dettifoss -------------------------- 18. 42 

Myvatn -------------------------- 19, 42 

Thingvellir ------------------- 19, 33, 34, 42 

Iddings, Joseph P ____________________ 2, 3, 10, 41 

Ingersoll, Alfred C ------------------------ 41 

Ingersoll, Leonard R ----------------------- 41 

lntertrappean layer -------------------------5 

Introduction ----------------------------- 1 

Isothermal surfaces ------------------------ 40 

Jaeger, John C ---------------------------- 2 

Johannsen. Albert------------------------- 42 

Johnson, Charles F ------------------------ 34 

J,)hnston, John, quoted --------------------- 35 

Joints, cooling __________________________ 4, 36 

miscellany --------------------------- 30 

sheeting ---------------------------- :!5 

tectonic -------------------------- 19, 38 

weathering -------------------------- :!7 

K 

Kemp, James F -------------------------- 27 

KIT~Pa~F ---------------------------~-3 

Knapp, George N ------------------------- 12 

Koritnig, Sigmund ------------------------ 42 

Krynine, Paul D -------------------------- 17 

Kummel, Henry B ------------------------- 12 

L 

Langmuir, Irving ------------------------- 41 

I ava flow unit zones, blocky zone -------------- 11 

columnar zone ------------------------- 7 

curvilinear zone ----------------------- 1:! 

vesicular base------------------------- 15 

vesicular top -------------------------- 5 

Lewis, J. Volney-------------------- 3, 17, 28, 38 

Literature cited--------------------------- 41 

M 

Mackin, J. Hoover ------------------------ 18 

Marble, John P -------------------------- 42 

Meikle, GeorgeS ------------------------- 41 

\·lillington quarry -------------------------- 3 

Minard, Charles-------------------------- 41 

Murawski, Hans-------------------------- 20 

Myers, Glen E --------------------------- 41 

N 

Nevin, Charles M ------------------------- 21 

:-.lew Germantown trap sheet ------------ 7, 21, 23,24 

:-.le\~ark graben, geologic history---------------- 19 

:'-Jewark Group. thickness -------------------- 19 

:\ova Scotia-Bay of Fundy ----------------- 17, 18 

0 

Oliveira, R. A. M., quoted ------------------ B36 

Oilier, Clifford D ------------------------- 25 

O'Rourke quarry -------------------------- 2 

Osgood, William F., quoted ------------------ 39 

Oskarsson, Niels-------------------------- 42 

p 

Pahoehoe 5urface ------------------ 4, 5, 9, 16, 41 

Peck. Dallas ---------------------------- 42 

Peet, Charles E --------------------------- 12 

Pillow lavas------------------------- 3, 16, 38 

Pitcau, Douglas R _________________________ 36 

Preston. Frank W ------------------------- 10 

Preston. Thomas. quoted -------------------- 39 

Previous studies ---------------------------_2 

Price, :'-Jeville, J -------------------------- 31 

R 

R iprap -------------------------------- 17 

Road metal ----------------------------- 17 

Roberts, John C -------------------------- 31 

Rosenbusch, Harry ------------------------ 27 

Rule, .John T ---------------------------- 40 

s 

Salisbury, Rollin D ------------------------ 12 

Schaller, Waldemar T ---------------------- 38 

Scheffers, Georg -------------------------- 40 

Schofield, Francis H ______________________ 2, 41 

Schraubenflache -------------------------- 14 

Schumann, Charles H., cited ------------------ 40 

quokd ----------------------------- 39 

Sheeting joints ------------------------- 14, 25 

Sig\aldason, Gudmunder -------------------- 42 

Smcdes, Harry W ------------------------- 42 

Smith, Robert L -------------------------- 42 Sosman, Robert B _____________________ 3, 27,31 

Spry, Alan ____________________________ 2, 10 

Stewart. Thomas J _______________________ 4, 42 

T 

r ectonic joints, basal platy 

joints. vesicular base -------------------- 24 

perpendicular joints, blocky zone ------------ 20 

planar basal joints, 

columnar zone ------------------ ____ 20 

pseudocolumnar joints, curvilinear 

zone ------------------------- 5, 14, 21 

shear wne, blocky zone ------------------ 21 

transverse joints, vesicular 

~P-----------------------------~20 

T omkeieff, Sergi ! _________________ 2, 3, 10, 41, 42 

Tryggvason, Tomas------------------------ 42 

U, V,Z, W 

li.S. Geological Survey ----------------------2 

Voight, Barry---------------------------- 34 

VonSande~Hor~------------------------40 

w 

Watchung Basalt flows, sequence of 

?ones in each unit ----------------------- 5 

Watts, Earle F --------------------------- 40 

Weathering joints. late stage, 

unloading "platy joints" ------------------ 28 

solifluction, a distorting agent 

of jointing patterns-------------------- :!9 

845 
B46 

Weathering joints~Con. 

spheroidal joints---------------------- B27 

Wedepohl. K. Hans------------------------ 42 

Weissenborn, Albert E ---------------------- 42 

Wellman, B. Leighton ____________________ IS, 40 

White, WalterS -------------------------- 42 

INDEX 

, Wilcox, Ray E --------------------------- 42 1 Width of joint openings -------------------- 833 

Wolfe, Clyde L --------------------------- 42 

Wones, David R -------------------------- 42 

Woodward, Theodore ---------------------- 41 

Woodworth. Jay B ____________________ 29, 31, 32 

Wright, Thomas L ------------------------ 42 

z Zeolite deposits in the trap 

flows of Third mountain----------------- 838 

Zobel, Otto J ---------------------------- 41 

i:I U.S. Government Printing Office: 1977-261·221/146