8/11/2019 Sweeting, Marjorie m. the Karstlands of Jamaica
1/18
THE KARSTLANDS
OF
JAMAICA
M.
M. SWEETING
THE ROUGH AND uneven surface of the country . renders it qulte impassab1ej
high peaks, steep hills, ravines, gullies, sink holes, etc. present
so
many
obstacles that this portion of the parish has well earned the appellation of 'terra
incognita'.
0
This is part of Sawkins' description in 1869 of the cockpit distriCIS
of Jamaica (pp. 195-6), some of the most striking areas of tropical karstt landscape
to be seen anywhere in the world. This paper describes the most important
characteristics of the Jamaican karstlands, particularly those in the north and centre
of the island, including the area known
as
the Cockpit Country.
Jamaica is essentially a mountainous and hilly island. Two-thirds of its area is
made
up
of highly dissected limestone plateaus, varying in height from
Iooo-JOOO
feet above sea level.
The
White Limestone Series upon which these karst
areas
have developed are Upper Eocene-Lower Miocene in age with a total thickness, n
places, of the order of 2000 feet. The general structure of central and western
Fig. Ia. Section across north
central
Jamaica after
Zans,
I95I
Jamaica is anticlinal, with an axial trend from ESE.-WNW.; in the core of this
anticline rocks older than the White Limestones are exposed. The White Lime
stones dip generally both to the north and to the south off the flanks of this Central
Inlier (Fig. 1a).
The
lithology of the White Limestones is variable. By
far
the greater part of the
Series consists of fairly coarse, crystalline, well-jointed and highly fissured lime
stones.
The
drainage in these pure and hard limestones
is
rapid, vertical and free;
.' vertical e r o s i o n - ~ is predominant.
Certain
of
the
White Limestone Series are,
however, of a semi-permeable, chalky or marly facies and contain abundant
flint
nodules; these beds are known
as
the Montpelier Beds and they occur in par
ticular along the northern coastal zone, where they are normally separated from the
crystalline facies by the Duanvale Fault Zone (Fig. 1 .1 The Montpelier Beds
form a semi-pervious stratum in which water circulation occurs only along the major
ee
list
of
references at the end.
t
The tenn "karst1and" has now passed into general use both in European and American
geographical writing. t is used to denote a region
of
massive limestone or dolomite where
the evolution of the relief is dependant upon chemical erosion, i.e. solution, as the dominant
proceiS in land form development and where, as
a result,
surface drainage becomes diverted
into underground channela. The word Karst is the German form
of
the Slovene word
Kras, meaning a bleak, waterless place and is the name given to the country inland {rom
Trieste.
The
Montpelier Beds are usually considered to represent an offshore facies
of
the
crystalline White Limeatones.:l
8/11/2019 Sweeting, Marjorie m. the Karstlands of Jamaica
2/18
Black
River
Bay
Wolclestxm
;l t Somerset
~ j ~ t t i n o h o m
ile s
s r ~ w o r t own
DRY H RBOUR
/ J:icldy Pole
MOUNT INS
ut:l -flle f : . : ~ ; : : : : ~ PoftWhiu Umutofte
FoulcZon
White
lim stonft witlt
Montpelier
II IIIll Yellow LimatoM
===;
Pre Yellow LimutoM
flr rmont
Riwr ua
Fig. r Geological mop of north central Jamaica after llose nd V ersey, rgs6)
8/11/2019 Sweeting, Marjorie m. the Karstlands of Jamaica
3/18
186
THE
KARSTLANDS
OF
JAMAICA
fault lines; erosion is horizontal rather than vertical, and lateral planation by
flood waters is usual. The basal beds of the White Limestones (the Troy Lime
stones) are sometimes dolomitized; such dolomites are cut by great joints which
influence considerably their weathering and erosion.l
The
upper beds
of
the Yellow Limestone,
of
mid-Eocene age, lie immediately
below the White Limestones and form the essential karst basis to the Jamaican
karst areas (Fig.
.
The Yellow Limestone consists of an upper and a lower lime
stone series, separated
by
a group of beds containing clays and tuffs; along the top
of
these beds and within the upper beds of the Yellow Limestone, there is a large
circulation of underground water. Well-developed karst features also occur within
the upper Yellow Limestones.
Both the White and Yellow Limestones were affected by the Antillean
move-
ments
of
mid-Miocene age; these movements produced some slight folding, but
more especially extensive block faulting. Many of the faults cutting the White
Limestone plateaus are of Miocene age. The main trend of these fault lines is E.-W,
and N.-S. with important sub-diagonal trends running
NNE.-SSW.
and
NNW.
SSE. Such lines of tectonic weakness are of fundamental importance in guiding the
directions of both surface erosion and the underground water flow.
8/11/2019 Sweeting, Marjorie m. the Karstlands of Jamaica
4/18
. .
. .
Miles
Coekplt
\ o r ~ t
f'":""'":l
1. ..:.. .J
~ g r o d ~
Cnc lcpt Kor st
~ j j
Tower
Korst
De9raded Tower
l orst
Fig.
2
Karst land frmns JWTth tentral Jammca
0
P ~ y ~ l l o w l m ~ a t o n e
U lntt:riOf ' vollt') S Ot'
polj
Rocks mtWt' r
thc n
whiU llrttntoM'
D
Dolint'KOI ltt
N
t
8/11/2019 Sweeting, Marjorie m. the Karstlands of Jamaica
5/18
188
THE
KARSTLANDS OF JAMAICA
Both these types occur in Jamaica, though their development is confined to the
areas of the hard crystalline White Limestone and to the areas of high rainfall.
In the areas where the White Limestone beds are more marly, or where the
rainfall is low, a doline karst develops with land forma resembling those found in
temperate latitudes.
oljes
(interior valleys) are normally associated with the
marly
limestones, since
polje
formation is closely connected with extensive flooding and
lateral planation.
The cockpit
karst
This type of karst landscape is the most widespread in Jamaica and is particularly
well developed in the north and centre (Figs. 2 and 3). Cockpit karst consists
essentially of a success;on of cone-like hills with alternating enclosed conical depres
sions or cockpits. A striking feature is the uniformity, both in area and in
height range,
of these depressions and the intervening hills. Thi s is clearly seen in
the sections (Figs. 3a and 3b), and in the photograph, plate
1 .
The
Cockpit Country proper in the parishes of Trelawny and St. James, forma a
region of continuous cockpit karst (Fig. 2). In this area the average depth of the
cockpits is between 300 feet and 400 feet, and some are as deep as 500 feet. A good
idea of their dimensions is given by the aneroid traverse across the area shown in
Figure 3; it will be seen that although the bases of some of the cockpits
may
be
about
4
mile across, there is little levelland in the true Cockpit Country. The bases
of the cockpits consist frequently of a puddled muddy area, containing yellow or
r o w n i s h ~ clay; in wet seasons, this area may contain a pond fomting a
small perched water-table. The slopes of the cockpits are usually between 30 to 40
and are made up of chemically weathered and honeycombed blocks and scree;
where the White Limestones are exposed, the sides are steeper and can be cliff-like.
Most of these slopes are covered with dense forest, though the bottoms of some of
the larger cockpits have been cleared for banana and yam cultivation.
The
cockpits and the cone-like hills are conspicuously arranged in lines following
the trend of the joint and fault patterns in the White Limestones, plate 1. This
rectilinear alignment has been .referred to by many workers in Tropical karst land
scapes and is often called gerkhteter ( directed ) karst. Individual cockpits are
extended by growth along lines of jointing and faulting, and two or more may
coalesce and enlarge along a well-defined tectonic line. This has happened at
Barbecue Bottom, a depression more than mile long and 400 feet deep, and
situated along a
N N E . ~ S S W . t r e n d i n g
fault line in the north-east part of the
Cockpit Country. Such elongated and enlarged cockpita are called glades and
are the equivalent of uvalas.l
Nonnally the cockpita and conical hills are more or less symmetrical, but some
times the slopes on one side of a cockpit are steeper than those on the other. This
asymmetry seems to occur
as
a
result
of two circumstances First
n areas
where
the dip of the White Limestones becomes greater than a few degrees, the slopes of
the cockpita are more gentle along the dip slopes and steeper on the
up-dip
side;
this is illustrated in the south-west part of the Cockpit Country near Retirement.
Secondly, asymmetry is common in cockpit karst near the north coast, where the
slopes are steeper on the south and south-west sides and less steep on the north
side; this suggesta that in this part of Jamaica, at least, solution and weathering of
the limestones is greater on the northern slopes which face the incoming trade
winds
1
So
c.alled for their resemblance to the arenas for cockfighting.
8/11/2019 Sweeting, Marjorie m. the Karstlands of Jamaica
6/18
.c . ...r_
i
~ r w
-:> -
..
- - ~ ..... H H
, .............. Jlf
/ , / /At
~ , ; I
:
e
,a.., /
I c......-
1 l ,; ' rAIIM I '
.,...,_...7_
t
'
'
0
'
;
CO'UNTRY
/ :
\
DRY HARBOUR
: p
t Jl:::;i>
, /
,' \ /
- . /J ' I \ XA.Ift'....,..,. _...;, & '
---.._AH.,.. ~
,'
\MOUNTA INS .,. '
MQNCAGUC , /
-
X 1 .IJ \ Xl . . . : ,_n ,
\
' \ ' - ~ '
~ d o .
I - I A
- - . . - -
- \
~ - . . . . - , ~ - - - . . . ~ j
. .0 \
OISTRICT
'
r .
.
\ > ' - \ ~
' 1 I " I J \ _ I ' '
\ lll 1 1
\tl
.,. ~
' .. - \ ', ,
\ ~ t + ' _ ,
X
~ c ; . , . . \ '
~
\ ,_ ___________ -------? ) \. >
\
~
. . . _
I / / ST.TH.j _
-
Mttj- .,.," P
e ltlue holft
0
Mojor
3WOtfow holu (slnb}
a
Mojor cow
__ .Proboth UnH of
undcr - d -ur-n
- -
Moin tenhed of'
lslond
_A ,Kim4PU liM
af
. . . . .o;d
~ { H e f i ~ .
JbJ
~ ~ ~ ~ -
10
Fig. J.
Main
features of
the hydrology
north central
Jamaica
8/11/2019 Sweeting, Marjorie m. the Karstlands of Jamaica
7/18
'90
THB KARSTLANDS
OF
JAMAICA
In the Cockpit Country the summits of the conical hills tend to reach to an even
summit-level at a height which varies from
1000
feet to
2000
feet; this summit
level is in part a structural surface, but may also be part of a more extensive pene
plain (Figs. 3a and 3b).s
The
skyline of this summit surface shows two types of
dissection-a shallow dissection up to so-70 feet by cockpits which may be regarded
as one-cycle land forms, and a deeper dissection by the larger and more successful
cockpits, which may be multicycle land forms (Figs. 3a and 3b).
True cockpit karst occurs only in areas where the hard crystalline White Lime
stones outcrop.
In
these areas rainwater sinks immediately into fissures in the rock
and it is doubtful if normal fluvial erosion has ever taken place. Rivers rising on the
more impermeable and less fissured beds below the White Limestones sink into
holes very shortly after crossing on to the crystalline White Limestones. This is
well seen along the south-eastern side of the Cockpit Country, where every river
flowing off the rocks of the Central Inlier ends in a blind valley. Some of the
rivers sink into a series of muddy and stony holes in the line of the river's bed, as in
the Hector's river; more frequently, the rivers disappear into a slightly inclined
bedding-plane cave, as in the One Eye River at Wallingford Sink (Fig. 3). The
blind \'alleys are often terminated on the downstream side by limestone cliffs, vary
ing in height from 5o-2oo feet.
water-table in the accepted sense
is
not present in the crystalline White
Limestone areas, though a rest-level of variable height may be recognized. Deepen
ing and enlargement of cockpits takes place by solution caused by acidulated
\Vater
from the dense vegetation and from temporary ponded water, acting along the lines
of fissure. The nature of the cockpit karst changes when the bases of the cockpits
extend down to a level where they are frequently flooded.
In
normal cockpit karst,
the
subterranean circulation of water in conduits and caves is well below the base
of the deepest cockpits.S
It
is of interest to record the Geological Survey's original explanation of the for
mation of the cockpit depressions. Sawkins wrote in 186g, The waters sinking
through the cavernous structure of
the
limestones, forced their way through and
removed the subjacent beds of shale and sand, thus forming cavities below the
limestone which being unsupported gave way and originated the 'Cockpit' depres
sions (p. 24 2
1
. a n e ~
was
the first worker to adopt the hypothesis that these
depressions originated predominantly by solution of the limestones along joints and
fissures; he assumed that local collapse of caverns would also help to enlarge the
hoUows. Modern workhas taken the solution ideas f Dane for granted; how
ever, it should be noted that Meyerhoff writing in 1933 of the Sumideros (similar
land forms to cockpits) of the Lares area in Puerto
Rico
regarded these depressions
as being almost entirely unroofed caverns. From the regular distribution and
linear arrangement of the cockpits in Jamaica and their dissociation from the sub
terranean circulation of water, it would seem that they are formed largely by
solution and subsequent enlargement by collapse along fissures; it is difficult to
believe that such a regular pattern would be brought about entirely by collapse of
cavern roofs, unless such collapse was very systematic.
0
lu tower k rst
Tower (or Turm karst, like the cockpit karat, occurs only on the crystalline
White Limestones but s much less widespread; its distribution is shown in
Local
co iapse of cavern roofs is of course important, one of
the best examplea being
Dunn s Hole, 1 cliff-bounded chasm over 400 deep, south
of
Stewart Town,
8/11/2019 Sweeting, Marjorie m. the Karstlands of Jamaica
8/18
w.
u' -,.s,n S' r_,.
1 r
/ .
1000
10;?0
O 0 2 3 4 6 7
I
8 I )
II 12 1)
M 1G
l ' f tl
IJI 20
:1 01
O
-
OO(I
fOliO
s
ln.g/od.
tolll t t
L
' ~ ' '
l
F1g.3o. Section west
to
east:
across
t:he
Cockpit
Country
Based on
D.O.$.
map
r
Jamaica, on
t:so,ooo
Bounth 'Y ktwt t:,.
L1mds
St>ldit:> lt
Lond
Bf'(XI(/It:of'
MNI'tt:l
r id$lt
l ,NdJ
c,., l .
s.. Jl
' 'f '
s TJ
Boundary betwtmrr
lewJs
I I D b i , . , ~ . , ;
Ptro nt
:
P
8/11/2019 Sweeting, Marjorie m. the Karstlands of Jamaica
9/18
THE KARSTLANDS OF JAMAICA
Figure
2.
Tower
karst
is made up of steeppsided, forest-covered hills
or
mogotes
whose slopes vary between 6o
and go
Each hill or group of hills is separated
by a more or less flat alluvial plain which is often inundated. he height of the hills
above the plain is usually about
3 feet,
but may be
as
much
as
soo feet. The
bases of the hills are frequently the sites of springs and are honeycombed with
caves (Fig. 3 .
Tower karst develops where the bases of the cockpits extend
to
the underlying
rest-level of the water, when solution and sapping along the base and sides of the
cockpit takes place. Hence, geological and physiographical circumstances which
tend to produce a water-table or a spring-line
are
favourable for the development
of
tower
karst.
Erosion, particularly corrosion, by springs and flood waters
at the
base
of
the cockpits gives rise to the steeper, sometimes overhanging, sides, and
also to the flatter alluvial floors, both of which are characteristic of tower karst.
he slipping of the limestone blocks along joint-planes assists the widening of the
base of the cockpits and
also
the parallel retreat of the steep-sided hill-slopes. Each
successive flooding of the floor of the cockpit adds further
to
the deposit of alluvium.
The
development
of
tower
karst
is usually associated with large-scale lateral move
ments of water and explains why the bases of these steep-sided hills are the sites of
both large springs and caves.
Conditions favouring the development of large springs and lateral planation by
flood waters occur near and at the base
of
the \Vhite Limestones at their junction
with the Yellow Limestone and also
in
those areas where the crystalline facies of
the \Vhite Limestone
are
in close association with the marly vlontpelier facies.
Tower
karst formation at the base of the \'llhite Limestones is well illustrated in the
Maroon Town
area
along the east
and
west sides
of
the Cockpit Country, where
steep tower-like masses of the White Limestone (plates
2
and 3 rest upon a
stripped surface of Yellow Limestone. Further, in those areas, as in the Cave River
Valley, where the basal beds of the White Limestone are dolomitized, the strongly
marked vertical jointing characteristic
of
those beds is
an
important factor in tower
karst
development. Tower karst also occurs
in
the neighbourhood of the Duanvale
Faul t Zone, along the northern margin of the Cockpit Country. Here the crystal
line hite Limestones give way to the l\1ontpelier Beds; the semi-permeable
and tightly-jointed nature
of
the l\1ontpelier Beds encourages a more horizontal
or lateral circulation
of
underground water with the formation
of
large springs.
Relatively rapid spring-head recession is frequently associated with tower karst
particularly when. the springs are cutting back along a fault-line,
as at
Windsor
(Fig. 3). Such recession
gives
rise to flat-floored, steep-sided and steep-headed
pocket valleys" which
are
a normal accompaniment to tower karst development;
the northern margin of the Cockpit Country is much indented with pocket
valleys."
A slackening of the karst (solutional) processes can cause both cockpit and
tower
karst
to become degraded, In degraded cockpit karst, effective deepening of
the cockpitsceases, the sides slump
in
and
the slopes become more gentle, about
20
to
30 The
cockpits
are
consequently shallower, and the relief becomes more
subdued and rolling. There is also
an
even greater dissociation between the surface
water
in
the cockpits and the ground water circulation
at
depth. Considerable
areas
of
degraded karst occur
in
northern and central Jamaica, particularly
in
the Dry
Harbour Mountains where it is associated with large deposits of bauxite (Fig. 2 .