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THE

GEOLOGY OF B ABB ADOS

J. B. HARRISON, M.A., F.G.S.,

LA TV IRLAND PROF£RBOB OF CHBMI8TKT TN BARBADOS.

AND

A. J. JUKES-BROWNE, B.A., F.G.S.,

OF THE QE0LOO1CAL 6UBYBY OF GREAT BRITAIN.

BRING

AN EXPLANATION

OF THE GEOLOGICAL MAP OP BARBADOS PREPARED BY

THE SAME AUTHORS.

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••• •«■ •• •• tf»

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• • • • • . .

PUBLISHED BY AUTHORITY OP THE BARBADIAN LEaiSLATURE.

1890.

209354

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PREFACE.

In the following pages we have endeavoured to explain the
geological structure and surface features of Barbados in such a
manner that they may be understood by any educated person
without his having any previous knowledge of Geological Science.

Such technical terms as are necessarily used we have explained
in the first chapter.

The chapters which treat of the formation of the Gullies and of
the Physical History of the Island will doubtless have some interest
for all who are acquainted with Barbados ; and we hope that those
on Soils and Economic Products will have a practical value for all
who are commercially interested in the island.

We are indebted to several friends both in Barbados and England
for assistance and information. Due acknowledgment is given in
the text, but among them we may especially mention Mr. E.
Easton, C.E., F.G.S., Mr. G. F. Franks, Mr. E. C. Piggott,
Mr. J. W. Gregory, F.G.S., and Mr. W. Hill, F.G.S.

J. B. HARRISON,

A. J. JUKES-BROWNE.

.v2

* •

CHAPTER I.

General Description.

The island of Barbados has an extreme length of a little over 21
miles as measured from the South Point to the North Point and a
width of about tl miles between Bridgetown in the south-west to
Congor Rock on the eastern coast, but in the northern part of the
island the width is only half as much. Its total superficial area
is estimated at 166 square miles and its greatest elevation above
the sea level is 1104 feet.

In the southern portion of the island the land rises by a series
of slopes and terraces to a ridge which runs nearly due east and
west, and has a maximum elevation of 400 feet ; north of this
there is a broad depression or valley which nowhere rises above
150 feet. From this the land rises again to a central ridge which
describes a curve round the parishes of St. Joseph's and St.
Andrew's, and is for a length of several miles between 1000 and
1100 feet above the sea.

The district enclosed by the semicircular sweep of this ridge
differs in its soils and physical features from the rest of the island,
and is the only part which has a regular system of hills and
valleys. This area is known as the Scotland district, because its
comparatively bold and rugged scenery reminded some of the early
settlers of the Scottish Highlands at home. It is within this
district and its narrow continuation below Hackletons Cliff to
Conset Bay that the key to the geological structure of Barbados is
found.

The geology of Barbados is not so complicated as that of some
of the other West Indian islands, such as Trinidad and Jamaica,
which possess a much larger series of rock groups, but it is more
varied and interesting than some of the smiJler islands, which are
either wholly volcanic (like St. Vincent) or consist of volcanic rocks
partially covered by coral limestone (like Antigua and St. Eitt's).

There are no volcanic rocks in Barbados ; the idea that a core of
volcanic rock was exposed in the north-eastern part of the island is
a mistake ; fragments of volcanic rocks are not unfrcquently found

■J • •

V-..

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* « •
• • •

6 ./.*'• The Geology of Barbados.

irr.trhe surface soil, having been brought to the island in the guano
VJ<ich has been so largely used for agricultural purposes, and some
'• ^ of these were shown to a well-known American savant, who too
., / readily accepted the statement of his unscientific informant that
"^ * they were found " in situ.'' The still older idea that the ridge sur-
rounding the Scotland district is the rim of a partially destroyed
volcanic crater has no foundation in fact, and was merely suggested
by the semicircular sweep of the ridge and its steep inward slope.
Even Sir R. Schomburgk in his History of Barbados attributes the
gullies which radiate from this ridge to cracks initiated by volcanic
agency, but no modern geologist would entertain such an idea.
During our survey of the island we did not discover even so much
as a single dyke of volcanic rock nor any sign of surface volcanic
agency : the upheaval of the island may have been due to such
agency, but if so the subterranean force expended itself in the
uplift without producing any further manifestation at the surface.

Neither are there in Barbados any rocks belonging to the more
ancient formations, such as exist in Trinidad, San Domingo, and
Jamaica ; the rocks of which the island consists were all formed
during the later part of the Earth's history and belong to the era
which is known as the Tertiary. We recognise portions of three
distinct massive formations besides the more recent surface de-
posits and soils which have been found since the island became
dry land. The following are the names under which we shall
describe the several formations and the colours by which they are
distinguished on the map : —

The Scotland series coloured broivn.

The Oceanic series coloured blue.

The Coral limestones coloured yellow.

The Valley deposits and Blown Sand coloured green.
The Scotland Series is found to be the oldest of these rock-
groups because it always occupies an inferior position to the others,
that is to say, the upper surface of the Scotland group passes
underneath all the other formations, making it clear that the rocks
of this group must have been formed first and the others afterwards.
The fundamental principle of geological classification is simply
this, that the strata which emerge or crop out from beneath all the
others that occur in a district are the oldest, and each succeeding
bed or group of beds is newer than that which they overlie. It is
only in this way that the geological succession of a new country
can be established.

The Geology of Barbados. 7

The Scotland rocks consist chiefly of sandstones and dark sandy
clays ; they form the core and basis of the whole island, that is to
say of all that is above the sea level, and though they are only
exposed in the Scotland district and in a few other isolated spots,
yet they actually underlie the whole island and have been reached
in different places by some of the borings made for the Water
Supply Company.

The Oceanic Series comprises the white earths and chalks which
occur in so many places above the Scotland rocks, and with these
are included certain soft variegated clays (red, yellow and white)
which occur at several localities. These coloured clays must not
be confounded with the red clayey soil which lies on the higher
plateaux of the coral limestone. The red clays of the Oceanic
series pass under the coral rocks and have the appearance of marls
rather than clays, although they do not contain any carbonate of
lime. The Oceanic deposits do not cover very large exposed areas,
but they underlie much of the coral limestone at a greater or less
depth from the surface.

The Coral Liinestones, which cover about six-sevenths of the
whole area of the island, form a coating or mantle of greater or
less thickness over the surface of the older formations. Although
they occur up to a height of 1100 feet above the sea, the actual
thickness of the limestone at any one place does not seem to exceed
260 feet. As this rock was formed during the gradual upheaval of
the island the higher terraces and plateaux are of older date than
the lower levels. The terraces are in fact the remains of ancient
coral reefs, and each one marks a stage in the gradual elevation of
the land.

The recent detrital deposits consist chiefly of gravel, sand and
mud which have been washed down into the valleys of the Scotland
district during times of heavy rainfall. Along the eastern coast
there are long mounds of sand which have been blown up off the
shore by the wind.

The white lines which traverse the map in different directions
indicate planes of fracture and dislocation, that is to say they show
the places where the strata have been broken and where the rocks
on one side of the fracture have been moved upward or downward,
as the case may be. Such displacements are called Faults ; the
actual course of a fault is not always a straight line, and the lines
drawn on the map are only meant to indicate the general direction
in which each fracture runs. Neither must it be supposed that

8 The Geology of Barbados.

every line of fault is represented on the map, those shown are only
some of those which exist ; they probably inclade most of the
larger and more important dislocations, bnt there are donbtless
many smaller fractures the existence of which could only be
ascertained by a prolonged examination of the ground*

The faults which break the continuity of the Oceanic series,
bringing these white strata against the dark coloured clays and
sandstones of the Scotland series, are comparatiyely easy to trace
because of the sudden transition from one kind of soil to another,
but those which traverse the Scotland beds only are much more
difficult to discover and follow. It is quite evident, however, from
the faults which are shown on the map that the strata have cracked
in many places during the elevation of the island and that the
broken portions have slipped one against another, just as a solid
mass of masonry might do if it was supported at the sides but was
pushed upward by a force which bent its under surface into a curve.

Flexures and Contortions. — The lateral pressures to which the
older rocks have been subjected during the movements of sub-
sidence and elevation, have in many places bent the strata into
curves and contortions ; these being very frequent in the Scotland
series which are sometimes bent over till beds which were
originally horizontal now stand on end in a vertical position.
Both the older series are so tilted, bent and broken, that few parts
of them remain horizontal for. any great distance. The various
inclinations thus imparted to the strata are indicated on the map
by arrows, which point in the direction towards which the beds
slope at the spots where they are marked. The amount of
inclination (technically termed the dip) is measured by the angle
which the inclined stratum makes with a horizontal line ; thus we
may speak of beds dipping in any direction of the compass at any
angle from 1^ to 89^ ; 90 degrees being a right angle and the beds
being then vertical.

Conformity and Unconformity. — ^Besides the mere {act of the
superposition of one formation on the top of another it is always
important to ascertain whether the upper set of beds rests evenly
and regularly on the lower set, or whether there is a marked and
irregular plane of separation between them. In some cases one
formation succeeds another so regularly that its lowest bed always
rests on the same part of the lower group. This is called a con-
formable succession, and if the strata are inclined, the angle and
direction of dip will be the same in both groups. In other cases

♦ The Geology of Barbados. 9

the basement bed of the upper series does not always rest on the
same part of the lower series, the upper surface of the latter being
more or less irregular. This is an unconformable succession,
and the dip of the lower beds will always differ either in amount or
in direction from that of the upper series.

The one case proves that the newer set of beds was formed
immediately after the lower set without any sensible lapse of time ;
the second case proves that there was an interval between the
deposition of the two series and that some part of the older series
was destroyed and removed before the formation of the newer.
Such a break or gap is called an unconformity, and when we find
in the same locality beds belonging to one formation having a
certain dip and the beds of a newer formation having a different
dip, we suspect that there is an unconformity between them even
though we cannot see the actual plane of contact.

With the above explanations we think that the following descrip-
tions will be readily understood.

Contour Lines. — The irregular red lines on the map are the
contour lines for 200, 400, and 700 feet above the sea respectively.
In drawing these we availed ourselves of two sets of data, namely,
the heights given for numerous places on the large Admiralty map
of the island, and secondly, the heights obtained by the numerous
series of accurate levellings carried out by Mr. E. Easton, C.E.,
whom we have to thank for this and much other useful informa-
tion.

By combining these sources of information, so far as they were
available in 1889, and drawing lines to connect the points, we have
sketched in the contours shown on the map, which are sufficiently
accurate for all practical purposes on so small a scale, but do not
pretend to be absolutely accurate contour lines or to be on the same
identical level at every point along their course.

These lines are only drawn through the area of the coral rock
and are not continued through the Scotland district, where the
contours are much more irregular and where we had comparatively
few data to go upon.

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CHAPTER II.
The Scotland Rocks.

The name of Scotland Rocks was given by Sir R. Schomburgk to
the rocks which come to the surface in the Scotland district, and
owing probably to the numerous faults which break the continuity
of the strata and have let down tracts of the Oceanic Deposits
among the older rocks, he failed to realise that there were two
entirely distinct and separate formations in the district.

The recognition of the Oceanic earths as a separate series,
intermediate in position between the oil-bearing rocks and the coral
limestones, is one of the most important results of our Survey.
It became a question whether new names should not be given to
both the older series, but on completing the map we found that,
even after the separation of the Oceanic Deposits, the dark clays
and sandstones still occupied so large a portion of the Scotland
district that Schomburgk's name might reasonably be retained for
them, and we therefore employ it as a designation for all the strata
that are older than the Oceanic series.

The Scotland rocks consist of thick-bedded sandstones, coarse
grits, bituminous sandstones and shales, dark-grey and mottled
clays with nodules of ironstone. These beds are bent into so
many curves and flexures, and are broken by so many faults of
greater or less magnitude that it is difficult to form an estimate of
their thickness. There appear to be from 550 to 600 feet of them
exposed on the island, but as the base of the group is nowhere
exposed, and as they are succeeded unconformably by the Oceanic
Deposits, the full thickness of the whole series cannot be ascertained.

They bear a striking resemblance in their general characteristics
to the great series of sandstones and clays in Trinidad which
underlie the Naparima series, and which yield the material that
forms the well-known Pitch Lake of that island. We have reason
to believe that a similar series exists in Venezuela, and that these
isolated tracts of similar rocks are portions of a vast Tertiary
formation which once extended over a large part of the South
Caribbean region.

Next to the presence of petroleum^ the most striking feature

12 The Geology of Barbados,

of this set of rocks, as developed in Barbados, is the manner in
which the strata have been flexured and contorted. In certain
districts the beds are seen to be folded over and reversed, whilst in
others the beds are nearly vertical. These flexures are not shared
by the Oceanic series, and were evidently produced previous to
the deposition of the Oceanic series.

It will be most convenient in describing these beds to commence
at their northerly exposures which are inliers within the area
covered by the coral limestone. The most northerly of these
occurs at Grab Hill, and exhibits fine-grained sandstones of a light
brown colour. To the south-east of this, at and around Spring-
hall, is a much larger inlier in which similar fine-grained light
brown and yellowish sandstones are seen dipping at a low angle
to the north west. A little east of this, at Chancehall, there is
another small exposure of the same beds. Coming now to the
northern end of the Scotland district, wo find the beds cropping
out from beneath the Oceanic series in a little valley south of Pico
Teneriffe, from which point to the Gongor rocks in the south they
are continuously exposed. The beds in this valley are mottled clays
resting on sandstones which dip to the north. Near the southern
end of the valley these beds are cut off by a fault which strikes
from N.W. to S.E., and brings up lower beds on the south-west
side. Those seen near Boscobelle are finely laminated sandstones
with frequent bands of clay ironstone and occasional courses of
hard grit, all dipping at a very high angle to the north east. The
hard layers of iron stone and grit which stand out like walls or
dykes from the softer beds on the summits of the hills and the
sides of the many steep ravines cut by the tropical rains form a
striking feature. At Bredys there are brown sandstones and
mottled clays dipping to the north-west under the Oceanic Deposits,
and at Gockcrow Rock the latter rest on one of the sandstone beds.

Near St. Andrew's Church there are grey coloured micaceous
sandstones, remarkably contorted and twisted in various directions.
These we believe to be the oldest beds exposed in the Island, and
their base is nowhere seen. In this district between the two
great faults that run in a north-easterly direction the succession
and thickness of the beds can be best made out, and appears to
be as follows in ascending order : —

1. Micaceous sandstones.

2. Sandstones, forty to fifty feet.

3. Clays witli iroustone, ten to fifteen feet.

The Geology of Barbados. 13

4. Thin seam of calcareous sandBtone with broken shells, eighteen inches.

5. Sandstones of many colours and varying from finely-laminated sand

stones to somewhat coarse grits, about mty feet thick.

6. A bed of exceedingly coarse hard grit about forty feet thick, which

forms a marked feature in the valley below the road leading to Gregg
Farm.

7. Fine sandstones about thirty feet.

8. Clays containing large numbers of nodules of clay ironstone, seams of

finely-bedded sandstones, and other clays with ironstone, probably alto-
gether about forty feet.

9. Bituminous sandstones from eighteen to twenty feet thick. These con-

sist of coarse siliceous sands neld together by about 10 to 12 per cent-
of petroleum. They contain fossil shells, but not in good preservation.
These beds appear to be the principal source of the so-called Barbados
Tar.

10. Above these are about thirty feet of clays and shales of very varying

colours, with occasional sandstone seams, and which contain lenticular
masses of asphaltum, locally called " Man jack."

11. A very coarse grey -coloured grit bed about ten feet thick, containing

many fossil sheUs, many of which have a roUed and waterwom appear-
ance. These are succeeded by twenty or thirty feet of fine sandjstones
and mottled clays, grey, brown and yellow, with ironstone nodules.

12. Lastly comes a great thickness of blneish-grey clay containing small

quantities of petroleum.

This last group is better developed in the more southern parts of
the Scotland district, and is entirely absent in the northern part
beyond Swans and Bawdens. Where most fully developed, as near
Castle Grant, these beds appear to be about 300 feet thick.

The rough and hilly district which extends from Belle Hill
south-westward to Mount Hillaby, Turner's Hall, and Ghregg
Farm, consists almost entirely of the middle sandstones and clays,
bent into a series of flexures, and exhibiting in many places the
remarkable contortions which we have already mentioned. These
are particularly well seen along the road passing over the high ridge
between Mount Hillaby and Gregg Farm. Below Mount Hillaby,
however, a thin strip of the blue clay group comes in.

To the east of the great fault traversing the valley of St.
Andrew's the lower members of this series are not fully exposed,
but the hill sides along the coast from Chalky Mount to near
Bathsheba expose the beds numbered from 8 to 8, and these are
in many cases contorted and twisted to a remarkable degree. This
is especially well seen on the eastern slopes of Chalky Mount,
where in a very short distance the beds vary from a nearly hori-
zontal position to an angle that approaches the perpendicular. In
this district also the unconformity of the oceanic deposits to the
Scotland rocks is well illustrated ; at Chalky Mount the highly-

14 The Geology of Barbados,

contorted sandstones are capped by an outlier of Oceanic beds
dipping at a low angle to the north of north-east; the same
sandstones underlie the outliers near Cambridge and Hopewell,
but on the southern side of Bissex-hill and around Springfield the
Oceanic deposits rest on the upper bituminous clays.

The district which lies to the east of the great fault is cha-
racterised by a great development of the petroleum -bearing beds ;
an excellent section of them is seen at Cane Garden, and many
exposures of them occur near Springfield, and on the latter estate,
in a valley running towards the sea, are the wells from which the
** Barbados Tar*' is obtained. This substance is found floating
upon the surface of small springs all about this district. Asphalt um
also occurs in lenticular masses, but neither coal nor lignite has
been found. In the parish of St. Joseph's there is less contortion
and flexuring than elsewhere, and on either side of the Joes River
Valley there appears to be a regular succession from the middle
sandstones upward to the dark bituminous clays, the latter being
well developed below Castle Grant, and along the ridge from Castle
Grant to Chimborazo. The valley by Mellows and Frazers pro-
bably coincides with a broad anticlinal flexure, but the surface of
the Scotland series rises rapidly from the sea towards Chimborazo.

East of the Bathsheba fault the slopes are chiefly occupied by that
part of the series which lies below the bituminous beds ; this tract
is terminated by a fault which runs from Newcastle to Congor
Rock, but a small inlier is brought up by another fault north of
Quintynes.

Scotland beds are again exposed in Conset Bay, and for some
distance up the Codrington Valley, which has probably been
eroded along the axis of a low anticlinal flexure in the Oceanic
series, so that the surface of the Scotland beds has been brought
up above the sea-level. Dark clays and shales with thin beds
of sandstone, belonging to group 10, much contorted and fre-
quently dipping at high angles, ace seen on the shore of Consets
Bay ; and the same beds are exposed below the oceanic earths at
the south end of the railway siding to Codrington estate.

Still further south, within the coral area, there is an inlier of
Scotland beds, apparently part of a buried ridge which rises up
from beneath the Oceanic deposits, and has never been thickly
covered by coral rock. The beds seen here belong to a lower part
of the series, and consist of fine grained sandstones, while at
Whitehaven and Sheetes Bay there are clavs with ironstone nodules

The Geology of Barbados. 15

dipping to the north-west at angle^i of 20^ to 25°. These beds
probably belong to group 8, and the same clays are seen on the
shore opposite Culpepper Island.

On the coast at Ragged Point the most southerly exposure
occurs : the promontory itself consists of exceedingly coarse grit
(No. 6), dipping to the north-west, and weathered into slabs of
fantastic shapes, which have suggested the name given to the
Point. These grits are about 40 feet thick, and from beneath them
variegated sandstones crop out along the shore of Spring Bay
south of the Point.

Very few fossils have been obtained from the Scotland Rocks,
the majority of the beds being apparently unfossiliferous. A
thin seam of calcareous sandstone is found in places containing
many shells, but all fragmentary, those found in the bituminous
sandstones are also usually fragmentary ; the most fossiUferous
horizon is the bed of very coarse grit (No. 11) above the bitu-
minous clays. In two localities this bed has yielded fossils, one
of these is on the Spa estate, where Mr. Franks succeeded in
getting several fossils, but all in bad preservation, and the other is
near the top of the hill above Spring Vale Estate. In this locality
we have found a few large bivalve shells, none of which unfor-
tunately could be obtained entire from the matrix and many fish
teeth. All that can be said from the examination of these speci-
mens is that they have general resemblances to the fossils in those
deposits of Trinidad which are regarded as Miocene.

There are probably considerable tracts of Scotland Beds concealed
beneath the coral-rock area and it may some day become of
importance to ascertain the position of these tracts ; for if the
petroleum supply of the Scotland district is ever properly tested
and found to be in sufficient quantity to pay for raising, there is no
reason why a further supply of this material should not be found
nearer Bridgetown beneath the covering of coral-rock, which is
seldom more than 100 feet thick. Throughout the parish of St.
MichaeFs water is found in the lower part of the coral-rock and
generally at a less depth than 100 feet, even where the surface of
the ground is more than that height above the sea. It is probable
therefore that the coral is here generally underlain by impervious
clays, and so large an area of clay is most likely to be part of the

Scotland series.

The existence of Scotland rocks immediately below the coral-rock
has indeed been proved at Edgehill, on the south of the parish of

16 The Geology of Barbados.

St. Thomas ; a Bhaft made h^ for the Water Sapply Company was
examined by one of us, who found that the coral was about 100
feet thick and that it rested on a fine grained sandstone of which
only a few inches was seen ; below came a peculiar yellowish lime-
stone, and underneath this dark blue and brown clay, all these
beds dipping at an angle of about 25^ to the south-east. They
probably belong to the middle part of the series, either to group 8
or group 10, and are therefore either just above or just below the
group 9 which is richest in petroleum.

Again, in St. Philip, between Thicket and Palmers, there is
another concealed area of Scotland clays. It has been mentioned
(p. 14) that sandstones actually rise to the surface near Thicket,
and we are informed by Mr. Easton that a shaft, sunk for the
Water Supply Company in the gully about 600 yards south of
Palmers, passed through 77 feet of coral-rock into blue clay, which
seemed to dip to the S.W. Mr. Easton thinks that this clay
extends for some distance to the westward and that such an
extension may explain the fact of the curious uniformity of the
water levels at Mount Pleasant, Lightfoots, and Guinea, that of
Bowmanston being very little higher. It is not unlikely that there
is a broad tract of Scotland rocks beneath the coral between
Bowmanston and Thicket covered toward the south-west by a con-
siderable thickness of oceanic deposits, for these are found at
Lightfoots below about 108 feet of coral-rock though the water
level is 1*55 feet lower down.

Other tracts of Scotland rocks occur in the central, western, and
northern parts of the island, especially near Coles Cave, and along
a tract west of Farmers, Hillaby, and Greggs' Farm ; and probably
in the north of St. Peter*s parish, west of Mount Stepney and
Cherry-Tree Hill.

The tunnels and shafts made under the superintendence of Mr.
Easton have therefore an interest beyond the immediate result of
obtaining water and may serve as a basis of operations in the search
for another kind of liquid. It is therefore of importance that full
particulars of the strata met with in these openings should be
carefully recorded.

CHAPTER in.

The Oceanic Deposits.

This series comprises all the white earths which are generally
termed Chalk in Barbados. Some of these are highly calcareous,
and are really a kind of chalk, other beds are purely siliceous, but
the greater part contain both the calcareous and siliceous ingredients
in varying proportion. The chalky varieties contain from 60 to 80
per cent, of carbonate of lime, which, like the ooze that is now
accumulating on ocean floors, is in a very fine state of division.
The purer siliceous earths consist entirely of the skeletons of the
minute oceanic creatures known as Radiolaria and Diatomacece,
mixed with broken spicules which were originally part of the
framework of siliceous Sponges.

In the calcareous earths the shells of Foraminifera are common,
most of them belonging to species which are now found at
considerable depths, and on Bissex Hill there are lumps of hard
yellowish Umestone which are entirely composed of these calcareous
shells, the assemblage of species being such as might now be found
in Atlantic ooze at a depth of 1000 fathoms.* There can be no
doubt therefore that these chalky earths and limestones were formed
in the same manner and at the same depths as the chalky muds
which are now being formed in many parts of the Atlantic and
Pacific Oceans.

The siliceous Radiolarian earths indicate even a greater depth
than the calcareous deposits. Radiolarian ooze does not exist in
the Atlantic, but is found in the Pacific and Indian Oceans at
depths of from 2000 to 4000 fathoms. Its existence in Barbados
therefore suggests the idea that it was formed in a deep basin which
was open to the Pacific as well as to the Atlantic, and consequently
at a time when the Isthmus of Panama did not exist.

Even the red clays of modern ocean-beds find a counterpart
among the raised oceanic deposits of Barbados; for beds of a

* This statement is made on the authority of Dr. H. B. Brady, who has
examined specimens of the rock.

18 The Geology of Barbados,

peculiar soft clay occur at several places between Castle Grant and
Mount Hillaby. These are sometimes pink or red, sometimes pale
yellow or white, and more often variegated in pink and white.
Under the microscope they are almost structureless, but betray
their oceanic origin by the occasional presence of a Eadiolarian or
broken sponge spicule.

There are also at certain horizons layers of fine volcanic sand
consisting of small fragments of pumice and broken crystals of
felspar ; and on Mount Hillaby there is a tough grey earth which
seems to be a fine volcanic dust. These layers are evidently due to
the occurrence of showers of volcanic dust like that which fell on
Barbados and the surrounding sea in May, 1812, and is still so
well remembered in the island. They are the products of distant
volcanic eruptions, but we cannot say from what volcano they
proceeded.

It will be seen from the map that these Oceanic deposits (coloured
blue) are found in many places between the outcrop of the Scotland
rocks and the edge of the coral limestone. In the centre of the
island they occur at high elevations, but descend to lower levels
near the coast. Patches of them cap some of the Scotland hills,
and the beds are also exposed at several places within the area of
the coral -rock both to the north and south of that district. It must
not be supposed, however, that the deposits were originally laid
down in isolated patches and tracts ; it needs but little training in
the Science of Geology to see that all these tracts are portions of
one continuous sheet that was deposited over the whole area of the
Scotland rocks. This sheet was broken into sections by faults
during the elevation of the island, and these sections have been
separated from one another, partly by the erosive and destructive
action of the sea waves, and more effectually by the excavating
action of the rain and streams, which have carved out the whole
district into a system of ridges and valleys.

Although the base of the Oceanic series is seldom clearly
exposed, there is abundant evidence to show that this series rests
unconformably upon the Scotland Bocks. Where dips can be
found in both formations near one another they are generally in
different directions, and in some places, as at Gonset Bay, the white
marls have a steady dip in one direction, while the Scotland Rocks
below are tilted up at high and varying angles. Our survey of the
district has shown us that the principle flexures of the older series
were produced before the deposition of the Oceanic series, so that

The Oeology of Barbados, 19

the latter rest sometimes on the sandstone groups and sometimes
on the uppermost clay group.

The most complete sequence of these Oceanic deposits is to be
found on the flanks of Mount Hillaby, where their thickness cannot
be far short of 800 feet. The following is the succession which
appears along a trayerse from the southern to the northern part of
the hilly with the approximate thicknesses assignable to each sub-
division : —

Feci.
Grey earths and volcanic muds ... ... ... 25

Bed, pink and yellow clays ... ... ... ... 60

Calcareo-siliceous earths ... ... ... ... 20

Galcareo-siliceous earths with seams of volcanic sand 40

Siliceous Radiolarian earths .. . ... ... ... 100

Chalky calcareous earths ... ... ... ... 85

280

Taking Mount Hillaby as a convenient centre, we will briefly
describe the position of the Oceanic deposits on and near it, and
then indicate the tracts that occur to the south and south-east ;
afterwards those that exist to the north of it ; and lastly, the out-
lying patches in the Bissex district. The general arrangement of
the strata is shown in the sections Figs. 1 and 2.

Mount Hillaby is traversed obliquely by a fault, on the east of
which the beds dip to the east and north-east, while on the western
side, all down the valley which runs toward Farmers, there are steady
dips to N.N.W. This dip brings in the highest beds again near
Hillaby, but the whole series is then suddenly cut oflF by a fault
which runs nearly cast and west. This fault can be seen in the
road north-east of Hillaby Mill. It brings the dark Scotland clays
against the white earths, and must have a ''throw*' or displacement
of at least 200 feet.

The valleys near Hillaby and Farmers are cut down to the Scot-
land Beds, and at the base of the Oceanic series there is a thin
bed of hard white splintery limestone.

To the southward the Hillaby tract is bounded by another line of

fault, which runs from Farmer's Gully north-eastward between Airy

Cot and the School-house, the base of the series being about 100

feet lower under the School than it is near Airy Cot. Both these

faults have therefore * downthrows' on the south side.

From this line the oceanic beds occupy all the high ground

n 2

20 The Geology of Barbados.

that runs southward toward Mount Misery, Canefield and
Caledonia; along this tract the dip is always between N.E. and
N.N.E. On Canefield estate the lowest beds are highly calcareous
and chalky, the material being so exactly like English chalk that it
is used by the coopers on the estate for chalking the wood where
the hoops are put on the hogsheads. The full thickness of the
•Oceanic series is not found at Canefield, though traces of the red
clays exist ; the white siliceous earth may be seen all down the deep
foully that leads to Porey*s spring, and in the road cutting south of
this spring a few feet of mottled red and white clay come on above
the white earths, but are soon covered by coral-rock.

Returning to Canefield we find the steady dip of the beds to the
north-west causes the lower boundary or base of the series to rise
to higher levels as it passes eastward, till near Caledonia there is
only a very narrow strip of white earth between the coral-rock and
the Scotland clays. A powerful fault then produces a sudden
change; this fault may be traced in the road 200 yards west of
Caledonia ; it throws the Oceanic series down on the east, at the
same time changing the dip to the S.E. By this fault a great
thickness of white earth is brought in, for these beds extend all the
way down the northern slope by Mallard's to Spring Vale, the base-
ment beds being found on the latter estate, and being, as usual,
calcareous.

A little further east we find a narrow strip of the Scotland clays
brought up between two nearly parallel faults and passing beneath
the coral-rock escarpment between Bloomsbury and Maynards Old
Mill. When the canes are off the ground this strip of dark clay
land shows up in striking contrast to the light coloured soils on
each side, and the course of the two faults can be easily traced
for some distance down the slopes to the north-east.

Another tract of oceanic deposits is found round Maynards and
Chimborazo, and a good section through nearly the whole of the
series is shown along the road up Melvins Hill. The basal beds,
white, chalky and heavy, can be seen resting on dark clay at the
junction of the roads below the School ; the higher beds consist of
whitish siliceous earth with yellowish stains in places, and near
the top of the hill there is a band of light grey volcanic sand con-
sisting of powdered pumice and broken crystals of felspar. In the
road cutting close to Chimborazo there are yellowish white earths
with a layer of tough brownish earth, the colour being probably
due to the presence of fine volcanic dust. On the knoll to the

The Geology of Barbados. 21

south of this cutting the heds are whiter and more calcareous, and
there are traces of the red clays at the top.

East of Chimhorazo the series is cut off by a fault which brings
the dark sandy clays of the Scotland gi-oup up to the top of the
ridge, and must have a throw of between 200 and 800 feet. The
exposure of the white earths is of course thrown back by this dis-
placement and forms only a narrow strip beneath the low cliflFs of
coral-rock that run from Chimhorazo to Nichols. The beds forming
this strip can hardly be more than 40 feet thick, and they belong
presumably to the lowest part of the series.

Below Nichols another fault with a downthrow to the south
brings in nearly the whole thickness of the Oceanic deposits again.
On the western part of Cnstle Grant estate there is a mass of
variegated red pink and yellow clays, apparently 40 or 50 feet
thick ; these pass beneath the coral-rock plateau on which Castle
Grant buildings stand ; and below the cliff on the northern part of
the same estate the lower part of the series is seen comprising in
ascending order above the spring (1) Calcareo-siliceous earths, base
not seen ; (2) Gritty silicious earths with a brown band and a bed
of grey volcanic ash ; (8) Siliceous earths with large lumps or con-
cretions of hard bluish grey chert. All these beds dip to the
south-east and pass below the red and yellow clays which occupy
the opening of the gully between Castle Grant and Little Island.
On the other side of Little Island a brown sandstone is found just
below the coral-cliff, whence we infer that the Oceanic deposits are
cut off by a transverse fault as shown on the map. White calcareo-
siliceous earths, however, emerge from beneath the escarpment
almost immediately and continue below Horse Hill, widening out
through Yaughans and Joes River estates to the slope above
Bathsheba Station. Along this tract the dip appears to be always
south-east, and as its width between Joes River and the cliff
below Binfield is nearly half a mile, and as the ground rises
through some 200 feet the thickness of the Oceanic deposits here
must be considerable. A careful search on the broken ground
below and north of Binfield would probably disclose the existence
of red and yellow clays like those of Castle Grant. The series is
abruptly cut off on the east by a powerful fault which runs between
Crab Hole and Little Diamond, striking obliquely from N.E. to
8.W.

From this fault to Newcastle the lower slopes consist of Scotland
Clays and the upper slopes of coral-rock, the Oceanic deposits

22 The Geology oj Barbculos.

being absent or concealed beneath the latter except along a narrow
strip beginning at Forster Hall Wood; from this a sample of
calcareo-siliceous earth was obtained for us through the kindness
of Mr. R. C. Pigott, of Castle Grant.

At Newcastle another powerful fault occurs striking nearly east
and west from the spring head toward Congor Bock. This brings in
a thick mass of the Oceanic earths which occupy the ground to the
south and south-east, and can be seen in many places along the
line of railway ; the beds are thrown into a series of curves or
undulations, and a hard brown gritty layer like that at Chimborazo
is conspicuous in several exposures.

One of the best sections is in a gully which opens into Conset
Bay where the beds are dipping at an angle of about 25^ to the
W.N.W. The succession is similar to that at Castle Grant, but
the lower beds are better exposed, and consist of hard calcareous
layers alternating with softer and more marly bands.

At Burnt Hill there appears to be a fault, along the plane of
which petroleum has made its way upward saturating and
blackening the white earths for a width of about 100 yards, and
lying in tarry-looking masses among the broken blocks of rock.
The tradition that this hill was once on fire receives confirmation
from the fact the beds at the top are in a red cindery and partially
vitrified condition. Near the fault there are high dips, but in the
eastern part of the cutting the beds dip to about 8° to the W.N.W.

The chalky basement beds are exposed in the cutting for the
railway siding to Codrington estate, and they form a great contrast
to the dark sandy Scotland clays on which they rest. The highest
beds are exposed in the garden below Codrington College, and
consist of white marls with traces of the red clays above. The
college itself stands on coral rock, by which the mass of the red
clays is either concealed or cut off.

Thence the white chalks and marls sweep round the head of the
valley by Sealy Hall, and pass beneath the ridge of coral-rock
on which St. Mark's Church is built. There is a good section
beneath the church showing nearly horizontal beds of coral-sand
resting unconformably on strata of white Badiolarien earth which
are inclined to the north east at an angle of about 80^. The deep
gully which runs northward is cut through the underlying siliceous
earth for at least 100 feet without exposing their base.

South of this area the Oceanic series is everywhere concealed by
the overspreading coral limestone, except in three localities. One

The Geology of Burhadoa.

of these is on the north side of Shcetes Bay,
whence it extends inland to Bayfield. South of
tbiB the coral covering is very thin for some
distance, and the white chalky earths are again I
exposed over a small tract by Three Houses and '
Wiltshire (see map). The third inlying exposure
is hetween Hopefield and Loamfield in Christ ,
Church pariuh. Here the lowest beds (hard and '■
calcareous) occur near Loamfield, and the dip I
being N.N.W. must bring in higher and higher ]
beds by Archers and Hopefield, but there arc
probably faults for the dips are rather high, and j
vary between west and N.N.W., and at Hopefield ;
there is a bed of grey pumiceous saud like that '
which occurs at many other pluceu below the
middle of the series. This is the most southerly
exposure in the islaud, and the manner iu which
the beds are probably concealed by the coral-
rock to the westward is shown iu Fig. 3.

Returning now to the centre of the islaud we
will describe the exposures which occur to the
north of Mount Hillaby. The ridge which rans
from the Hillaby fault northwards and then
westwards to Spring consists entirely of Scot- !
laud Beds. Belo^v Spring there Is a fault run- I
uiug north-east toward Bawdens ; and on the '
farther side of this the white siliceous earths
come in, dipping south-easterly. Their lower
bonndary runs round the hill above Swans and
thence northward by Sedge Pond, rising gru- .
dually to the steep slope below the coral-rock j
at Prospect ; the dip is everywhere iu a S.E. \
direction, but we do not think more than the
lower 140 feet of the Hillaby succeBsion is ex-
posed in this tract.

Below Prospect a fault striking east and west
throws the beds down on the north side and
brings in a much greater thickness, probably
200 feet ; the beds are well exposed along the
road up Cleland Hill. The base of the series is
seen near Cockcrow Rock resting on a fine- ;
grained sandstone belonging to the Scotland <

i 1
II

3"!
i&
Hi
SS'p

ill

lit

iii

24 The Oeology of Barbados.

group ; the first bed is a hard splintery white limestone succeeded
by about five feet of white chalky rock, passing up into isalcareo-
siliceous earth (20 or 80 feet). Then comes a thick mass of purely
siliceous earths as at Hillaby, passing up into more calcareous beds
and at the top just below the coral-rock of Farley Hill are ten feet
of some of the purest chalk in the island, containing over 80 per
cent, of carbonate of lime. The dip is throughout to the south-east.

The base line or lower boundary runs above Bredy*s and thence
runs to the N.N.E., rising gradually in level. On the road below
Cherry-Tree Hill the lower calcareous beds are visible with the
same dip, but a little beyond this they disappear beneath the coral-
rock. North-east of St. Philips they are brought in again by a
fault, and form a small tract which extends to Grant's Bay on the
coast. Here the beds have a low dip to the north and about 100
feet of them can be seen in the gully south of the bay. The lowest
beds are highly calcareous and the highest part is siliceous. At
Pico TeneriflFe about 50 feet are seen capped by the coral-rock,
which slopes northward toward Gay's Cove.

In the northern part of the island we have found five separate
exposures of the white earths. The first of these is on the coast
at and on either side of Laycock Bay, and stretching inland for a
little distance towards St. Clement's. Between this and Lowland
are two small inlying patches. A larger exposure extends from
River Bay on the coast to Spring Barn and Ishcot. Lastly, a
narrow tract of chalky earth, precisely like that of Grant's Bay,
stretches for about 600 yards along the coast north of Cluffs.

From the existence of these exposures we may infer that a
considerable tract of Oceanic beds underlies the whole of the lower
ground bordering the coast between Cluffs and Gay's Gove. It
must be remembered also that all the tracts which have been
described pass beneath the coral limestone, and that large areas of
the chalky and siliceous earths must exist beneath the coral-rock
which covers the western and southern parts of the island. (See
the sections Figs. 1, 2, and 8).

Outliers. — The largest and most important of these is that which
covers Bissex Hill, and a good section is afforded by the road
which is carried up the southern slope. The Oceanic beds come
in above the Scotland clays at the bend of the road near Cocoa
Grove, and the lower beds are similar to those seen near Cod-
rington and elsewhere, being calcareous at the base and siliceous
above. At about 140 feet from the base they become calcareous
again, and contain large blocks or concretions of hard, rough

The Geology of Barbados. 25

whitish rock ; this rock has been examined under the microscope
by our friend Mr. W. Hill, F.G.S., and is found to consist almost
entirely of the shells of Foraminifera set in a matrix of crystalline
calcite. At the summit of the hill there are a number of loose blocks
of very hard and compact bluish-grey limestone, which were pro-
bably originally embedded in chalky earth, for the limestone
contains both Radiolaria and Foraminifera as well as a scattering
of crystals derived from volcanic rocks. The earth in which these
blocks were embedded has been largely dissolved and washed away
by rain, but the blocks being too hard and too large to be so
disposed of have been left on the hill. The sharks' teeth which
are found in the soil around them appear to have lain in the same
beds, for Mr. Armstrong, of Little Island, possesses a specimen
which is partially embedded in a fragment of the grey limestone.

The beds dip steadily to the north, and the base line descends
to a much lower level on the northern spur of the hill. On the
south side the base is about 760 feet above the sea, below Bissex
Estate Mill it is about 500, and on the northern spur it is not
more than 360 feet above the sea level. Here, too, the basement
bed is compact blue limestone, quite different from the hard chalky
rock generally found in that position, and more nearly resembling
the limestone of the blocks by the Police Station, but bluer and
smoother : it appears to form a continuous bed some three or fom*
feet thick, and can be traced for some little distance. It would
form a good building stone, except that its hardness would make it
rather difficult to work. Possibly it could be utilised as a marble.

Of the outliers at Cambridge and Hopewell there is little to say ;
they have only been separated from the Bissex Hill tract by the
erosion and removal of the intervening tracts through the action of
rain and floods, and by the landslips which have taken place from
time to time.

The central peak of Chalky Mount, which has an elevation of
551 feet, is capped by beds of white chalky earth, dipping to the
N.N.E., and there are also smaller patches (not marked on the map)
on the two minor summits to the eastward. Their occurrence here
at such a much higher level than the nearest outlier to the south
is doubtless to be attributed to the existence of a fault in the
intervening ground.

The outliers near Springfield consist mainly of siUceous
Badiolarian earth of light specific gravity, and have been dug
extensively for the manufacture of boiler felting. At one spot the
earth contains small concretions of dull glassy silica.

26 The Geology of Barbados,

The fossils fouud iu the Oceanic series are chiefly Microzoa,
which can only be seen and studied under a microscope ; but there
are two localities in the island where other organic remains of
larger size have been found. One of these is the top of Bissex
Hill, where the lumps of rough whitish calcareous rock, mentioned
on p. 24, contain casts of a small turbinate or cup-shaped coral,
and the spines of a species of sea-urchin, probably a Cidaris, but
no portions of the test have yet been found. It was probably from
this rock that Sir R. Schomburgk obtained the Scalaria figured in
his History of Barbados, and named Sc, Ehrenhergii by Forbes.

The other locality is unfortunately not one that can be further
explored, though the single fossil found is of extreme interest.
This is an Echinoderm obtained by Mr. T. D. Hill from the
Radiolarian marl brought up out of a well at Haynesfield at a depth
of 166 feet. The specimen was presented to the British Museum
by Mr. G. E. Thomas, of Haynesfield, and was described by
Mr. J. W. Gregory, F.G.S., under the nsime of Cystechinm crasstis.
The following remarks are quoted from Mr. Gregory's paper in the
Quarterly Journal of the Geological Society of London: — *' The
discovery of a species of Cystechinus in these deposits is therefore
of interest as confirmatory of these opinions [that the white earths
are raised oceanio oozes] . Cystechinus is one of the most typical
of deep-sea Echinids : thus for example Neumayr quotes it with a
few other genera as never found above the 1000 fathom line.*'
Three species of this genus were found by the Challenger
Expedition, all of which came from great depths ; Cystechinus
WyviUei was dredged at depths varying from 1375 to 2160 fathoms.
C. vesica has been found to range firom 1675 fathoms in the Arctic
Ocean to 2225 fathoms in the Pacific near Juan Fernandez.
C clypeatus, the species which is probably the nearest ally of
C. crassus, has been found at depths of 1050 and 1900 fathoms.
We may therefore regard C. crassus as confirming the view that
the Badiolarian marl was accumulated on the ocean floor at a depth
of more than 1000 fathoms.

The fossil is also of importance in helping to. fix the age of the
Oceanic series of Barbados. Before its discovery no fossil form of
Cystechinm was known. The genus was only founded in 1879 by
Agassiz on the specimens obtained by the Challenger Expedition.
Consequently, as Mr. Gregory observes, its presence *' seems to
show chat the beds are of comparatively recent date, either Pliocene
or Pleistocene."

CHAPTER IV.
The Coral-rock or Reef Limestones.

Six-sevenths of the surface area of Barbados, that is 1*14 out of
166 square miles, have a subsoil of coral-rock or limestone con-
structed from the broken debris of corals and of the shells and
other organisms which live on coral-reefs.

This rock may be regarded as a sheet or mantle spread over the
surface of the older rocks ; the Oceanic Deposits and the Scotland
rocks may be viewed as forming a broad and low dome-shaped
mass or basis, on which the coral-formation has been gradually
built up. This limestone, however, cannot be regarded as an
even and continuous sheet, for both its lower and its upper surfaces
are extremely irregular ; it really consists of a number of separate
stages or platforms built up one around another as the island
slowly rose from the level of the sea.

Each of these platforms was once a fringing coral reef hke that
which now surrounds the greater part of the island, and they now
present a succession of steps or terraces, of varying width, rising
one above another from the sea level to a height of nearly 1100
feet in the centre of the island ; each step in this ascent being of
older date than the one below it.

The first noticeable feature is that these terraces are not all
subsidiary to one centre. The principal system of terraces con-
forms to the central ridge of high elevation which curves round
the highest part of the Scotland district between Mount Hillaby
and Castle Grant. This system descends by a series of slopes
and plateaux from a height of over 1000 to a level of about 180
feet on the southern side, and to the sea level on the western and
northern sides.

The southern part of the island has a smaller independent
system of terraces which form what is known as the Christchnrch
ridge. No part of this is more than 400 feet above the sea, and
all of it that lies above 800 feet is broken up into a series of
irregular east and west ridges, the form of which is probably due

28 Thp Geologj/ of Barbados.

partly to original conformation, and partly to the subsequent
action of rain ; these ridges are concentrically surrounded by a
series of lower terraces, those between 100 and 180 feet on the
north side meeting the terraces of the central system in the broad

valley or depression which traverses the island east of Bridgetown.

Hence it is clear that when the sea-level coincided with the con-
tour of 200 feet (see contour line engraved on the map) Barbados
consisted of two islands instead of one ; these islands being
separated by a shallow sea or strait lying over the broad transverse
valley above mentioned. As time went on reefs gradually formed
in this strait and were by subsequent elevations brought up to the
surface, so that the two islands were eventually united into one.

The surfaces of all these raised coral reefs have of course been
considerably altered and modified during the elevation of the
island, by the action of the rain water which has coursed over
their surface. And similarly the internal structure of the higher
and older reefs has been greatly altered by the action of the
rain water which has soaked and percolated through its substance.
The surface action of the rain in running off the island has
excavated the numerous gullies and channels which now furrow
its surface, and has also caused the formation of basin-shaped
depressions and hollows at spots where the water has tended to
accumulate and sink into the ground. The subterranean action
of the rain water has also formed subterranean water-courses
and caverns by dissolving portions of the rock ; while in other
places the carbonate of lime dissolved by the passage of water
through the highest layers of rock has been re-deposited in the
form of a calcareous cement which has bound together the loose
particles and filled up all the small cavities and empty spaces, con-
verting portions of the rock into a hard white compact limestone.
This hard variety of rock is found at various levels, but is more
prevalent at higher than at the lower levels, and it is this kind of
rock which is used for road-metal.

As might be surmised from the above remarks, the coral-rock
varies considerably in structure and hardness, even on the same
level or terrace, but its usual character at levels below 800 feet is
that of a rather rough coarse-grained limestone, which is generally
sufficiently consolidated to stand in road cuttings with a vertical
face. In some places, however, it is so loose and soft, beneath the
surface crust, that it can be dug out with a spade ; these portions
are locally termed inarl ; very frequently it is soft enough to be cut

The Oeology of Barbados. 29

with a saw, thongh coherent enough to remain in solid blocks which
harden in the atmosphere and form a useful building-stone. This
is generally termed sawstone, and its only detrimental quality as a
building-stone is its porosity, some varieties being so porous that
they are scooped out into large pitchers or cup-shaped basins which
serve as filters ; this kind of stone is locally known as ** dripstone.**
Both the sawstone and the dripstone are what we should call
freestones in England, since they cut in any direction and do not
split along planes of bedding. Here and there, however, floors of
hard compact rock occur, the material requiring a strong blow of
the hammer to break it, and being consequently fit for use as road
metal.

The structure and composition of the coral-rock is most clearly
displayed in the freestone varieties, and in these it is seen to
consist of the broken fragments of corals, shells (both bivalve and
univalve) and nullipores (or calcareous seaweeds). The smaller
particles of these substances form a kind of ^ sandy paste or matrix,
in which are scattered larger lumps and branches of coral, perfect
shells of mollusca, and occasionally large blocks or masses of coral
in position of growth, but the number of coral pieces more than
two inches long is seldom large enough to make up half the bulk
of the rock. It must also be remembered that the proportion of
the various constituents varies considerably in different places,
sometimes the corals predominating and sometimes the mollusca ;
and sometimes the mass consists chiefly of small particles more or
less coated with earthy carbonate of lime.

Between the levels of 800 and 400 feet the rock generally shows
certain peculiarities and differences from that at lower levels. The
mass of the rock is harder and more compacted, but it is traversed
by numerous small holes and cavities which are apparently spaces
left by the solution and removal of certain kinds of branch-coral.
The corals which are left are also partially dissolved, the original
hollows and spaces in them being filled with crystalline carbonate
of lime, so that they have a different appearance from those in the
softer rock and "marl.'* These characters become still more
marked at higher levels, and in many places between 700 and 1000
feet the rock has been converted into a hard white compact lime-
stone perforated in all directions by branching holes and con-
taining fossil corals, or rather the casts of such corals, in crystalline
calcite, which show a glistening crystalline fracture when they are
broken.

30 The Oeology of Barbados.

We are informed by those who have been concerned in sinking
wells in the higher parts of the island that this hard limestone does
not often extend to any great depth, and that the lower parts of the
rock are generally looser and more easily worked than the higher
part, sometimes resembling a mass of loose rubble.

As far as we coald learn large coral blocks or growths of coral
are most abundant on the outer slopes of the terraces and on
their upper surfaces, being seldom found in the lower part of deep
wells.

Wherever we have been able to see and examine the actual base
of the old coral reefs we have found the lowest bed to consist of
loose rubbly rock or of semi-consolidated coral sand or marl. Thus
in Coles' Cave, where the base of the rock can be followed for some
distance resting on a surface of a dark clay (Scotland beds), the
base of it is loose and rubbly, and in a distance of half a mile
underground only one lump of coral was seen in it. In Harrison's
Cave, which opens into a higher part of the same gully, all the rock
seen is calcareous sandstone, like that which may be seen in some
places on the shore, and has been formed by the cementation of
beach sand; it here rests on a surface of oceanic Radiolarian
earth.

In a cave recently discovered by the Water Supply Company,
between Coles' and Harrison's Caves, the same calcareous rock rests
on a curious soft deposit, consisting partly of coral sand and partly
of siliceous earth washed out of the Oceanic deposits, and con-
taining many broken and waterworn fragments of corals. This
deposit was evidently a submarine sand bank, which the upheaval
of the area gradually brought up to within the limit of depth at
which reef corals can grow, and it then became the basis for a new
coral reef, the thickness of the limestone above the cave being now
about 200 feet.

A more convenient place for examining the base of one of the
raised reefs is below St. Mark's Church, in the parish of St. John's.
The surface of the rock at the church is 290 feet above the sea, and
it terminates in an escarpment from 15 to 20 feet high, the erosion
of rain and springs having cut back the coral and exposed the
underlying beds between St. Mark's and Codrington. The base of
the coral here consists of a soft whitish marl resembling a friable
earthy chalk; this passes up into a soft marly rock containing
many coral fragments, and this rock gradually changes upward into
a hard limestone. An analysis of this marl shows that it consists

The Geology of Barbados, 81

mainly of carbonate of lime (97*5 per cent.) with 2*54 per cent, of
clay and siliceous matter.

The thickness of the coral limestone, as might be expected from
the manner of its formation, varies greatly in different places. The
tendency of coral growth being to fill np the hollows of the
underlying surface and to build up a platform that is limited by the
sea-level of the time, it is clear that some parts of the reef must be
deeper and thicker than others. It is not therefore surprising to
find that the thickness of the raised reefs along one shelf or terrace
varies considerably.

In some places the coral-rock is so thin that it only forms a
superficial crust, and in a few localities this has been worn off and
washed away over a certain area so as to expose the underlying
strata, as near Loamfield, Three Houses, and other places.

So far as we have been able to ascertain there are few places
where the thickness of the coral-rock exceeds 200 feet. The only
place where a greater thickness has actually been proved is Bow-
manston ; the shaft of the well there is 260 feet to the bottom of
the cavern in which the water flows and which is presumably
excavated along the bottom of the coral-rock. We are informed by
Mr. E. Easton, C.E., that several of the borings recently made for
the Water Supply Company have proved a thickness of more than
100 feet of coral beneath the floors of gullies, which are themselves
over 100 feet below the country on either side. Thus the gully
near Lightfoots is about 130 feet below the surface of the ground
at the mill, and a boring at the bottom of this gully passed through
108 feet of coral before reaching the underlying beds, which were
first red clay and then* Radiolarian earth. There would seem
therefore to be 288 feet of coral-rock below Lightfoots.

The case is similar at Byde Mill, but at lower levels toward
Bridgetown there is seldom more than 100 feet of coral-rock. At
Coles' Cave the watercourse is 110 feet below the floor of the gully,
and this is about 70 feet below the surface at the top of the gully.
Hence the rock here is about 180 feet thick. At Easy Hall the
well is 164 feet deep in coral-rock with blue clay at the bottom.

The coral-rock covers all the southern, western, and northern
portions of the island, but terminates inland along the abrupt
descent or escarpment which follows a sinuous course through
the parishes of St. John, St. Joseph, and St. Andrew, and forms
the principal physical feature of the island. The escarpment com-
n^ences near St. Mark's Church, where it is of no great height.

The Geology of Barbados,

and cnnring roand the head of the Codrington Valley by Sealy Hall
rans into the 800 foot terrace below a slope that rises to about 570
feet above the sea. Thence it trends to the north-west, rising to
higher and higher levels ; the upper part of the slope is very steep,
and near St. John's Church it becomes a line of nearly vertical
cliffs which are continued by Edgecliff, Hackletons Cliff, Binfield,
and Horse Hill, and terminate a little west of Castle Orant.

The vertical descent of this cliff is in many places 60 or 70 feet,
and below it is a broken and uneven slope covered with large
masses of rock that have fallen from the cliff above. Most of the
cliff face is covered with small shrubs, ferns, and climbing plants,
while the slopes below are clothed with trees and underwood, so
that Hackletons Cliff as viewed from the railway looks like a
ruined rampart nearly concealed by foliage. The summit of these
cliffs is about 1000 feet above the sea, and the base of the coral-
rock near Mount Dacres is only 500 feet, but it must not be
inferred from this that there is 500 feet of coral-rock below the
summit ridge. We have good reason to think that the lower parts
of the coral-covered ^lope are continuations of the terraces which
occur to the southward between 500 and 700 feet, and that they
are banked against a slope of Scotland and Oceanic strata (see
Fig. 4). In other words we believe that the cliffs were formed
when the coast-line coincided with a line that is now about 700
feet above the sea, and preseuted a line of cliffs resting on a steep
slope of Oceanic earths, as now occurs at Pico Teneriffe, this slope
being subsequently covered by coral growth as the island was
lifted higher and higher out of the sea.

5l-

Fio. 4.— Skction 7AOM Edgbcliff to thn Sba.
a Scotland Beds. 6 Oceanic Deposita. c Coral Bock.

It has been said that the cliffs terminate on Castle Grant estate,
for it is here that what may be termed the central ridge of the
island emerges from beneath the coral-rock and runs by Chimborazo,

The Qeohgy of Barbados. 88

Maynards, and thence north of Canefield to Mount Hillaby and
Spring, where it again passes beneath the coral-rock. Outside this
ridge, however, that is to the west and south of it, there is
everywhere a low escarpment of coral-rock, generally from 20 to 80
feet high ; this is the border of the highest terrace or plateau of
coral-limestone, and the escarpment is its weathered edge, which
has been cut back by the action of rain and streams ; from its
original boundary line, which lay along the ridge above indicated
and thinned off on the western slopes of Mount Hillaby, it has
receded to its present position.

On Spring Estate and below Spring Head there is again a more
precipitous slope and a greater thickness of the coral-rock. Thence
the escarpment runs northward to Prospect and Farley Hill, beyond
which it trends to the north-east, sinking to lower and lower levels
by Cherry Tree Hill and Mount Stepney down to the sea at Pico
Teneriffe, the conformation of its northern extremity presenting
similar features to that of its southern end near St. Mark's.

Within the area of the Scotland district there is very little coral-
rock ; isolated reefs appear to have been formed from time to time
on the slopes and ridges of this area, but probably they were always
of small extent, and as the detritive action of rain and running
water has been greater in this district than in any other part of the
island, only small portions of them have escaped destruction. The
largest patch caps the end of the ridge on which Bawdens is situate
at a level of 389 feet, and there is a little patch (too small to be
shown on the map) on the same ridge to the southward by Lower
Turners Hall at a height of 4G2 feet ; these are the highest outliers
we discovered, but isolated blocks as big as cottages are not
unfrequent at intervals along the slopes of the valleys in the parish
of St. Andrew's, about the level of 800 feet. Boscobelle, in the
north of the same parish, stands on a small outlier of coral-rock,
forming a little circular plateau at a height of about 200 feet above
the sea. The tract of coral-rock that borders the sea to the north
of Boscobelle is in reality an outlier, having been cut off from the
Pico Teneriffe mass by the valley which ends in Grants Bay.

A small isolated tract of coral-rock also occurs by the railway
north-west of Bath Station, and part of it had to be blown up in
making the line.

Fossils. — The fossils which afford the best evidence for deter-
mining the geological age of the reefs are the corals and the shells
of mollusca. The corals which we were able to obtain came chiefly

84 The Geology of Barbados,

from Ceres and from Castle Grant, with a few from near Grove,
and one fine specimen of Astrea crassilamellata from Ellis Castle
well, obtained for us by Mr. R. C. Piggott, of Castle Grant. The
collection has been examined by Mr. J. W. Gregory, F.G.S., of the
British Museum, who reports that half of them can be identified
with living West Indian species, and that most of the rest are
forms which are known to occur in the coral-rocks of Antigua and
Barbuda. Several of the living species occur at Castle Grant, and
he therefore infers that the whole of the reefs, from the highest to
the lowest, are of comparatively modern date, and do not reach
beyond the Pleistocene age, which is the last and newest member
of the Tertiary series.

The fossil shells, so far as they are known, confirm this conclu-
sion. A collection made from the reef-rock near Ceres has been
examined by Mr. E. A. Smith, of the British Museum, who finds
all of them to be recent West Indian species. We have seen many
of the same species at various places up to 400 feet above the sea.
In the higher reefs the shells have been dissolved, leaving only
casts which are not easy to identify, but they all belong to genera
which are common on the modern reefs, and there is no reason to
suppose that any of them are extinct forms.

CHAPTEE V.

Physical History op the Island.

Having in the previous chapters given some account of the
geological structure of the island and of the lithological characters
of the rocks that enter into this structure, and having also de-
scribed the physical conditions under which each of the three great
rock-groups were formed, we are in a position to give an outline of
the physical history of the area since the time when the oldest of
these rocks were deposited.

A consecutive series of strata may be likened to a book composed
of so many pages, or to a pile of written records, and if we can
read the language in which these records are written, we may glean
from their contents a history of the manner in which the strata
have been formed, and of the changes which took place from time
to time in the geography of the region.

Moreover, each great series or system of strata may be regarded
as a separate volume treating of a separate epoch in the history of
the region, but unfortunately it seldom happens that any of the
volumes are complete ; consequently we rarely possess materials
for a full and complete history, and can only recount the events
which happened during certain episodes which were separated from
one another by greater or less intervals of time.

The History of Barbados starts with a period when the sand-
stones of the Scotland series were being accumulated. Since many
of these beds consist of coarse sand they cannot have been depo-
sited vei7 far from a shore nor in very deep water ; rocks of this
kind are in fact almost always formed in shallow water within 20
miles of laud. It is clear, therefore, that the geography of the
Caribbean region must at this early period have had a very different
form from that which it now presents. There must have been a
land area of some size in the immediate neighbourhood of Bar-
bados to furnish the materials of which these sandstones are com-
posed. Whether it was continental land or only a large island we
cannot say ; but it must have had mountain ranges consisting of

hard rocks like those which form the mountains in the north of

36 The Geology of Barbados.

Trinidad, or those in the central ranges of Jamaica and San
Domingo.

It is quite possible that the northern part of Trinidad formed a
portion of this land, for there is mach resemblance between the
Scotland rocks of Barbados and the Newer Tertiary (Caroni-Moruga)
series of Trinidad. Other parallel ranges may have existed in the
intervening space, but as yet we know nothing about the geology of
Tobago and Grenada, so that this is a mere speculation. It is quite
certain that none of this ancient land is now left above the sea
within 100 miles of Barbados. We can be sure, however, that it
had strong and rapid rivers capable of carrying large quantities
of sand and mud down to the sea in which the Scotland strata were
being formed. It is also probable that at the time when these
strata were being accumulated the land was slowly sinking beneath
the sea ; this we infer partly from the great total thickness of the
Scotland series and of the similar series in Trinidad, and partly
from the fact that the highest beds are clays with nodules of iron-
stone, and are likely to have been deposited in rather deeper water
than the sandstones.

This, however, is all we can say of the first episode in the
geological history of Barbados, and it may be stated in one sen-
tence — that the Scotland series is a comparatively shallow water
formation, owing its origin to the detritus carried down by the
rivers running off a land that was composed of quartz-bearing
rocks.

Between this episode and the next there is a gap in the record,
certain leaves are missing, and it is impossible to say how long a
period of time elapsed between the formation of the highest
Scotland clay and that of the lowest Oceanic deposit.

From the nature of the newer deposits we can safely infer that
this intervening period closed with a great and profound sub-
sidence, which carried the previously formed strata down to the
depths of an ocean, a subsidence which probably submerged the
whole of the ancient Caribbean land above mentioned, or at any
rate reduced it to a few scattered groups of islands like those which
rise out of the Pacific Ocean.

As stated on p. 17 the calcareous and siliceous earths which form
the Oceanic series are similar to the calcareous and siliceous muds
or oozes which are being accumulated on the floors of the great
oceans at the present time, and are especially like those which
prevail in the Pacific and Indian Oceans. What is now the island

The Geology of Barbados. 87

of Barbados was then buried beneath a depth of ocean-water that
amoanted to at least 1000 fathoms, and probably varied between
that and 2000 fathoms.

The variety of the deposits which compose this Oceanic forma-
tion is one of the most remarkable points about it, and is at the
same time a puzzling character, because at the present day the
several kinds of ooze which are represented in the series occupy
distinct areas on the ocean floor, and the formation of each separate
kind seems to be dependent on a certain association of conditions,
among which depth of water and the temperature of the surface are
the most important.

The Foraminifera which occur in the Barbadian Rocks appear to
indicate a depth of 500 to 1000 fathoms. The fossil Echinoderm
(see p. 26) found at Haynesfield seems to indicate a depth of more
than 1000 fathoms.

Pure red clays without any trace of carbonate of lime like those
of Barbados seldom occur at a less depth than 2500 fathoms ; and
pure Radiolariau ooze is only found from the same depth down to
4000 fathoms and more. Moreover, Professor Haeckel remarks
that the fossil Radiolaria of the Barbadian earth are most nearly
uUied to those which occur in the deepest parts of the modern
oceans.*

Whether the variations in the nature of the material composing
the Oceanic series indicate corresponding changes in the depth of
the ocean in which they were formed is uncertain, but there can be
little doubt that the depth of the water was often about 2000
fathoms, which is 12,000 feet.

The layers of volcanic sand which are interstratified with these
deposits demonstrate the existence of active volcanoes somewhere
in the Caribbean region during the period of their accumulation.
Some of this sand is so very fine that it appears like silt or mud,
and this may have been carried by the wind for many hundred
miles before it dropped into the ocean ; but the larger particles of
felspar and pumice in the light grey sands suggest that the volcanic
vent was within 200 or 800 miles of Barbados, and they may have
come from some of the volcanoes which still exist to the westward.

To the period of Oceanic depression and quiet deposition of
sediment on the ocean floor there succeeded a period of disturbance
and upheaval. Although there are no truly volcanic rooks in

* Challenger Reports, vol. xviii., pt. ] , p. clxxv.

88 The Geology of Barbados,

Barbados, nor any sign of an active volcano in its immediate
vicinity, yet it is significant that the highest beds on Mount
Hillaby are largely composed of fine volcanic silt or mud. There
can be little doubt that the upheaval of the island was due to
volcanic agency, and that it took place at a time when volcanic
eruptions occurred in some of the other Caribbean Islands.

It is not improbable that a local uplift was caused by the uprise
of a mass of lava into the underlying rocks forcing a portion of
these upward without leading to the establishment of a volcanic
vent. We know that a rising column of lava has sometimes found
it easier to lift a mass of rock bodily than to rend its way through
it ; in such cases the lava has flowed laterally along the plane of
separation and occupies a space below the strata which it has lifted.
Such a cake or solidified cistern of lava is called a LaccolitCy and
there may be a laccolite of volcanic rock deep down beneath
Barbados.

The supposition of such a subterraneous intruded mass of rock
would indeed explain the arched position which the Oceanic deposits
now occupy, for, ignoring the faults which break their continuity,
they form portions of a thick sheet covering a dome-shaped surface
of the older rocks, this surface descending from the central part of
the island in every direction toward the sea level.

But the special and local uplift was certainly accompanied or
followed by a general elevation of the whole Caribbean region, as
testified by the occurrence of Oceanic deposits in other islands,
and by the raised coral reefs which occur from one end of the
Antilles to the other. The upheaval of the area from the ocean
depths to within a certain distance of the sea level may have been
comparatively rapid, and though the coral limestone is naturally
unconformable to the Oceanic series, the interval of time between
the uplift of the latter and the commencement of coral-growth may
not have been a very long one. The subsequent elevation of the
island during the formation of the coral platforms seems to have
been slow and regular, and to have acted evenly over the whole area.

The first part of the island to emerge above the level of the sea
was of course that which is now at the greatest height above it.
The original Barbados was a small island, which included the
heights now known as Mount Hillaby and Chimborazo, but lying
rather to the eastward of a line drawn from one to the other. The
greater part of this original island has indeed been destroyed and
carried away by subsequent erosion and denudation, but part of the

The Geology of Barbados. 39

coral reef which encircled its leeward side still remains in the low
escarpment of coral-rock which extends from Greggs Farm and
Hillaby to Castle Grant ; the northern and southern boundaries of
the island in this early stage of its existence being defined by the
sudden and rapid slope of the base of the coral-rock on the
Hillaby and Castle Grant estates. At Hillaby, to the north-east of
the mill, layers of coral-rock can be seen sloping to the W.N.W. ;
and at Castle Grant 60 or 70 feet of coral-rock come in on a slope
that is inclined to the east and south-east. West of Castle Grant
the rock thins oS on a surface of red clay at a level of about 1050
feet, while above St. Joseph's, only a mile to the east, its base is
not more than 800 feet above the sea.

It is not unlikely that Bissex Hill formed part of the nascent
island, for the conformation of the ground makes it certain that
this outlier was originally joined to the main mass at Chimborazo,
the Oceanic deposits then covering the whole of the ridge which
now joins the bases of the two hills. Bissex Hill rises to 966 feet,
and yet no remnant of coral-rock occurs on it, whereas if it had
lain outside the slope of the original island it would probably have
been deeply buried in coral, like the ground of a similar altitude
below Little Island and Horse Hill, and a cap of coral would have
remained on its summit. The entire absence of coral on or around
Bissex Hill shows that this district has been exposed to the action
of detritive atmospheric agencies for a long time, and favours the
view above suggested. We believe then that when Barbados first
established itself as a coral-girt oceanic island it had a somewhat
kidney-shaped outline, its southern shore extending from Mount
Misery to Castle Grant, while on the north there was a bight or bay
over the site of the great valley which lies between Mount Hillaby
and Bissex Hill.

Whether this island was completely encased in coral or consisted
of a mass of Oceanic earth fringed by coral-reefs we cannot say ;
it would depend greatly on the rapidity of the final elevation which
lifted the island nucleus above the sea. It seems however to have
remained nearly stationary for some time after this elevation, for
we cannot otherwise account for the great thickness of coral which
still exists to the south of it by Welchman Hall, Industry, and
Blackmans. During this period of rest or slow upheaval the higher
parts of the island were naturally exposed to the disintegrating and
erosive influences of the atmosphere, the encasing coral (if such
existed) was broken up and the older rocks would be fully exposed.

40 'The Geology of Barhiidos.

There can be no doubt that a much larger area of the Oceanic
earths and clays existed at this time than is now to be found above
the 1000 feet contour, and that this tract dominated the surround-
ing coral reefs just as Mount Hillaby now dominates the escarp-
ment of coral-rock to the west of it.

After a time the movement of upheaval continued at a more
rapid rate, as indicated by the steep slopes which prevail between
800 and 750 feet. At this time the Golden Bidge bank began to
be formed, probably as a barrier-reef situate at a little distance
from the southern shore of the island, which then ran by Indian
Pond, Belmont, and Hothersall ; and the barrier-reef seems to have
been connected with the inner reefs by a tract which now forms
the high ground by St. John's Church and Clifton Hall.

All this time the main drainage system of the island was
directed chiefly into the bay on the northern coast, but partly into
a bay on the eastern side over what is now the Frazers and Joes
River valley. At this time there was probably a considerable
amount of coral growth on the northern and eastern shores just
as there is now on the windward side of most of the other Carib-
bean islands, but as the protecting mantle of Oceanic earths and
chalks was gradually worn off the Scotland district, and the streams
began to cut down into the underlying clays and sandstones,
muddy water would be frequently discharged into the sea, and
would prevent the growth of coral opposite the mouths of the
principal valleys, for it is well known that corals are killed by
mud much more rapidly than by pure fresh water. When there-
fore deep valleys were once established the reefs on that side of
the island would cease to be continuous, and the action of the
waves would come into play in many places, and would cut back
the softer and looser portions of the older rocks. It is owing to
those causes that the slopes between Bissex and the sea are so
steep and short, and that the patches of coral rock in the Scotland
district are so few and so small ; for in consequence of these con-
ditions the area of the island increased less rapidly towards the
north and east than in any other direction, and in spite of the
continued upheavals which have carried the contour of 800 feet
far inland from the western and southern coasts, on Bissex Hill it
is still within a mile of the shore.

Successive elevations of the region carried the island up through
the levels of 600, 500 and 400 feet; fringing reefs continually
forming on the submarine slopes, as fast as these were brought up

The Geology of Barbados, 41

within the limit of coral growth, all round the northern, western
and southern sides of the island, and also along that part of the
eastern coast where there was still some thickness of Oceanic earths
below Hackletons Cli£fs and St. John's Church.

When the upheaval had proceeded till the sea-level coincided
with the contour of 400 feet, the Christchurch ridge began to
appear above the waves, and formed a long line of reef which lay
about three miles off the southern coast of the island at that time.
The formation of this reef seems to have been due to the growth
of coral on a separate bank of Oceanic earth (see Section Fig. 8),
and the intervening channel seems at the same time to have been
deepened by the action of the currents flowing through it, for there
is reason to think that along the low ground where the railway runs
the coral-rock lies for the most part on the Scotland rocks, the
Oceanic beds having been washed off the surface of the older rocks
before the coral-reefs began to grow at that level.

The Christchurch ridge, as stated on p. 28, must have remained
for a long time as a separate island with a strait or channel to the
north of it, both it and the main island being encircled by fringing
coral reefs. As time went on and the uplifts continued the channel
grew narrower and shallower, and coral grew over its floor till at
length only a tract of flat coral reef, interrupted by shallow lagoons,
lay between the two islands. Such was the geography of Barbados
at the time when the shore-line coincided with a contour which is
now about 160 feet above the sea, and if the island were now to
sink till the sea reached the same contour-line the same conditions
would be reproduced.

After the union of the two islands was accomplished Barbados
quickly assumed the shape it now possesses ; the shallow water at
each end of the transverse channel would be rapidly filled with
growing coral, so that partly by coral growth and partly by the slow
upheaval which was still in progress, all the low-lying land behind
Bridgetown and in the eastern part of St. Philip's would soon be
added to the island. It is probable that by this time the elevatoiy
movement was dying out and acted but very slowly, so that the
upward growth of coral was the chief agent in the formation of
these undulating plains ; still they could not have risen to their
present height above the sea without an uplifting movement, and
it cannot have been very long ago (geologically speaking) since this
movement finally ceased. If the human history of Barbados had
extended back as far as that of England, some human records of
the final elevations would doubtless have existed.

CHAPTER VI.

Explanation of the Surface and Subterranean Watercourses

OF THE Island.

A SPECIAL peculiarity of Barbados is that its surface is without
any permanent rivers or streams, except in the Scotland district,
where some of the valleys contain small rivulets fed by permanent
springs. Watercourses or gullies, as they arc called in Barbados,
are indeed frequent over the whole coral -rock area, but water never
runs down them except after unusually heavy rain, and then only
for a few hours' time.

The explanation of this absence of surface streams is very simple ;
the coral-rock is so porous that the rain which falls upon it is
quickly absorbed, and, percolating downward through the rock,
flows outward through the lower parts of the rock or through the
equally porous Oceanic earths which so frequently underlie it.

The rain is in fact carried ofif by a subterranean system of
drainage, instead of by a surface system of brooks and rivers ;
most of these underground streams run into the sea below the level
of its surface, and it is a well-known fact that springs of fresh
water issue beneath the sea at many points round the coast, and
that at one place in Bridgetown Harbour good fresh water can be
obtained by letting down a bucket through the surface salt water to
the freshwater stream that runs underneath. There are, however,
a few streams which have a short daylight course just before
reaching the sea ; thus, Indian River, about a mile north of
Bridgetown, has a course of about 200 yards, rising suddenly out
of the coral-rock and having a permanent flow of about a million
gallons of water daily. Near Brighton is another stream, with a
less volume of water, but having a longer course, about 400 yards,
and at Spring Garden are others which form ponds of considerable
size. Other similar short rivers occur at Holetown, Speightstown
and Six Men's Bay, all of them suddenly issuing to the surface in
the same way.

The main watershed of the island is the long line of escarpment
of coral-rock, except for a space between Canefield and Springs

The Geology of Barbados, 48

where the ridges to the north and south of Mount Hillaby form
the watershed. Nearly all the water falling on the coral-rock area
makes its way either to the south or west from the watershed, but
a small quantity issues in the form of springs below the escarp-
ment and flows into the valleys of the Scotland district.

The existence of a subterranean system of drainage has led to
the production of two sets of phenomena which are always found
in elevated limestone districts ; these are surface swallow holes and
subterranean caves or caverns. The absorption of the rainfall does
not take place equally over the whole surface, the rain makes its
way towards a depression or a place where a crack occurs below the
soil and then sinks into the ground, forming a ''swallow*' or
" sink-hole," which is gradually deepened and enlarged by the
solution of the rock below and the sinking in of the surface. Such
basins and holes are a characteristic feature of the coral limestone
district of Barbados : they are sometimes diy, but more often
enclose a pool of water. Most of the ponds which occur in the
island lie in such hollows, and we believe they are all of the nature
of swallow holes.

They are found at all levels, but are perhaps most numerous on
the middle platforms between 800 and 700 feet. They sometimes
occur in curious positions near the edge of steep slopes and away
from any surface line of drainage. Thus there is one at ClifF
Cottage, at a height of 650 feet, and within 100 yards of the clifF-
like escarpment of the limestone.

Another at Castle Grant is within 150 yards of the cliff and
about 1050 feet above the sea and is known as the Devil's Punch-
bowl. It lies on a slope, the ground to the north being higher
than its rim, and that to the south sloping away from it. Esti-
mated by the height of a palm which grows from the bottom its
depth is between 40 and 50 feet, and the circumference of the rim
is about 250 yards. There is generally a little water at the
bottom, and we were informed that after heavy rains water burst
out from the cli£f due north of the hole through a crack or fissure
in the coral-rock. This indicates the existence of an underground
channel of drainage with which the swallow hole is doubtless
connected.

Open hollows of this kind are not common at such a high level,
but we are informed by Mr. R. C. Piggott, of Castle Grant, that
hollows filled with the red earth or loam which forms the soil on
these heights are frequently found, and that he knew of several

The Geology of Barbados.

wells sunk in these places for 40 or 50 feet without reaching the
bottom of the red earth, and in one place near Castle Grant for 90
feet in red earth. It would seem, therefore, that at these levels
the swallow holes have mostly been filled up with rain wash.

Fia. 5.— Diagram Section thbouoh a filled up Swallow-hole.
cc Coral Bock, s Soil, w Water forming a Pond.

At Haynesfield (700 feet) there are three ponds, probably occu-
pying swallow holes, and the people still draw their water supply
from them, for the present well, sunk in 1882 — 83 through the
coral-rock and siliceous earth does not yield water.

Indian Pond is another such hole, at a height of 800 feet, and
near the edge of a very steep slope.

On the Sweet Vale estate, just below 700 feet, there is a large
shallow hollow about 200 yards across, which receives the drainage
of the surrounding slopes, and has a large pond in the middle, but
no visible outlet.

At Woodland, in St. George's, there is a curious dry hole irre-
gularly pear-shaped and very deep ; its southern edge is only about
60 yards from the border of a deep gully. The following levels
here are furnished by Mr. E. Easton : — On its eastern edge 607*76
feet, at the bottom 465*75 feet, so that its depth is just 42 feet.

There are dozens of other ponds and holes in other parts of
the island, some of which may be larger than those we have
mentioned.

Most of these swallow holes probably open downwards into
subterranean caverns, for these caverns owe their existence to the
solution of the limestone by underground streams, and it is evident
that every swallow hole must be the starting point or the feeder of
an underground stream. Some of the caverns have an external
entrance by which they can be entered and explored, such are the
caves known as Cole's Cave and Harrison's Hole ; but there mast

The Geology of Barbados. 45

be a much larger number which have no such external entrance
and their course is quite unknown, except where the sinking of a
well has accidentally discovered their existence as in the case of the
Bowmanston Cave.

It is not unlikely that some of the subterranean passages are
quite dry, haying been formed when the island was less elevated and
when the inland water-levels were much higher than they are now,
for it must be remembered that the continued upheaval of land
always tends to lower the water levels of a country.

One of the most striking and peculiar physical features of
Barbados is the frequency of the deep, narrow, and dry valleys
which are locally called gullies. They pursue very tortuous courses,
and a glance at the map will show that they radiate from the main
watershed of the island ; they are, in fact, regular watercourses,
and no geologist who saw them would doubt for a moment that
they had been excavated by the action of running water ; but it is
open to argument whether they have all been formed by water
flowing over the surface, or whether some at any rate may not have
been caverns which were gradually enlarged till their roofs fell in
and the rock above sank on to the floor of the cavern.

Those who advocate the latter mode of origin point to the fact
that long caverns or subterranean passages traversed by permanent
streams are common throughout the limestone districts, while the
occupation of the surface channels by running water is a rare and
temporary occurrence. It is also remarked that the walls of the
gullies are in many places nearly vertical, and that they are often
coated with stalagmitic incrustations like those which always occur
in limestone caverns, and also that blocks of rock with pendant
stalactites are sometimes found on the gully floors.

When these points are examined, however, none of them are
found to be very convincing arguments. A coating of stalagmite
is often found on cliif faces, as, for instance, on the coast cliffs near
Crane and on the front of the coral-rock escarpment at Castle Grant
and Hackletons Cliff. The vertical walls are due to the falling
away of the rock along vertical planes of jointing, and all valleys
which are cut through hard limestones present similar features.
Small caves and recesses often occur in the walls with pendant
stalactites, and it is from such places that the fallen blocks have
come.

With regard to the conversion of a subterranean channel into a
BUi'face one by the falling in of the roof, it is conceivable that this

46 The Geology of Barbados,

might happen in the case of a wide and lofty cavern, the roof of
which was in some places at no great depth below the surface of
the ground, but it is very unlikely to occur in the case of a deep-
seated cavern. Now the gully floors are in many places from 80 to
100 feet below the surface of the ground on each side, and the
modern caverns are often 150 or 200 feet below the general surface ;
we do not think caverns formed at such depths would be likely
to fall in completely and entirely along the whole of their course so
as to form continuous open gullies.

It is true that in some parts of the existing caverns blocks are
frequently falling from the roof and are piled up on the floor
below, and that where this occurs the roof is always at a con-
siderable height above the general surface of the floor. It is
conceivable that such falls might continue till a hole was formed
at the surface of the ground, and possibly this does sometimes
happen, and may be the explanation of the existence of swallow
holes near to cliffs and steep slopes. But such falling in is not
likely to occur along the whole course of the cavern, and as a
matter of fact it is not found to be the case in the present caverns,
where for long distances the roof is low and coated with
stalactitic mRterial, and appears to be in a fairly stable condition ;
in other parts, and especially in the dry caverns the roof is often
50 or 60 feet from the floor. It will probably be found that where
the roof of a cavern is now falling, as at Bowmanston, it is
where there is a downward soakage or drainage, either from an
older cavern at a higher level or from the surface. The great
variation in the height of the roof above the floor is a well-known
feature of all limestone caverns, aad it is clear that the roofs of
such caves could not fall in completely for any great distance at
one time, small portions only would break down leaving tunnels
and natural bridges between the open sections. Now, if the
Barbadian gullies had been formed in this manner by a process
which would have continued to the present time they would surely
exhibit all stages in the process of formation, and we should find
many which were incomplete, and were partly in the state of
caverns and partly open gullies. Nothing of the kind is known,
and so far as we are aware no such natural bridge or tunnel exists
in any part of the island.

We do not think therefore that this theory is the true explanation
of the formation of the gullies. We believe that they have been
formed as ordinary surface watercourses, and that the caverns have

The Geology of Barbados. 47

been formed subsequently, bpth being produced while the island
was being gradually elevated to its present position, and as the
water-levels of the interior were being gradually lowered. We
think that both the gullies and the caves were formed in sections,
and were extended from one reef-mass to another as each was
gradually raised ; that the highest part of each gully was formed
first, and the channel thus started was prolonged through each
lower plateau as it was brought above the sea-level.

In order to understand how this took place, we must remember
that the area of the island, when it first appeared, was very much
smaller than it is now, and, as mentioned in Chapter V., it con-
tained a central ridge of impervious rocks which threw off the rain
water falling upon it. Moreover, it is probable that the annual
rainfall previous to the colonization of the island was always much
greater than it is now, because it was then covered with a dense
forest, and the effect of forests on the rainfall of a country is well
known.

The greater extension of the dominant ridge of older rocks above
the altitude of the highest coral-reef when the island first rose above
the sea has been mentioned in the previous chapter. As soon as
the first-formed coral-reef was raised above the sea-level the streams
flowing off the interior of the island would commence to cut
channels through it, and these channels were the commencements
of those gullies which now pass through the coral-rock escarpment
in the centre of the island.

The lower parts of the first raised reef would still be below the
level of the sea, and would consequently be water-logged, but as
upheaval continued the inland water levels would be lowered, and
at the same time the streams would be able to deepen their
channels, while a shallow extension of each watercourse would be
formed over the surface of the next raised reef. Thus every
succeeding increase of elevation would increase the length of the
watercourses, and would lead to the deepening of the higher parts
of their channels.

Meantime subsidiary watersheds would be formed within the
area of the raised reefs, and other watercourses would be started
on this area, though they might only be continuously occupied by
running streams during the rainy season. It is well known,
however, that intermittent streams resulting from occasional floods
accomplish more erosion in a few hours than a constantly flowing
stream does in the same number of vears.

48 The Geology of Barbados.

Let us next oonsider what changes woald be caused during a
period of more rapid upheaval such as appears to have occurred
during the formation of the steep slopes between 850 and 750 feet.
The first eflfect would be to lower the subterranean wat^r levels in
the coral-rock plateaux above 850 feet so rapidly that the ordinary
rainfall would soon be absorbed and carried ofiT by subterranean
channels, leaving the surface channels in the state of dry gullies
as we now find them. Much, however, of the water thus absorbed
would be thrown out again at lower levels in the form of springs,
so that the lower portions of the gully channels would still be
occupied by running streams, and these portions would be gradually
deepened by the action of the running water as the upheaval went
on and allowed the streams to cut down to lower and lower levels.
The elevation of land always has this efiect, and in technical
language it is said to enable rivers to cut down to a lower base-level
of erosion.

We have said that much of the water would be thrown out in
the form of springs ; this would happen because the downward
percolation of the water is everywhere arrested by the clays which
occur in the underlying strata, and because the slope of the surface
of these strata does not correspond with that of the external surface
of the ground. In many places the former is much loss steep than
the latter, and consequently the subterranean surface over which
the water is flowing is much nearer the external surface in some
places than in others, and where the water is thus brought very
near the surface springs are likely to break out. It is at such a
place that Poreys Spring now issues at an elevation of 700 feet
above the sea ; the existence of this spring is probably due either
to a fault or a flexure by which the clays of the Scotland series are
brought up below the coral-rock at that point, so that the water
which has percolated through the tracts of coral-rock and Radio-
larian earth which lie to the eastward is forced to rise along the
surface of the impervious clays.

The water issuing from Poreys Spring does not now flow for
more than about 100 yards along the gully below, its volume
becoming less and less till the whole of the water has sunk below
the surface of the ground : but when the sea-level stood at about
650 feet it probably had a continuous course down to the sea,
forming a short river like Indian River and the other streams men-
tioned on p. 42. Such short rivers indeed must always Iiave existed
near the coast line at every stage in the upheaval of the island.

The Geology of Barbados,

To sum ap therefore we believe that all the gullies owe their
origin to the ordinary erosiye action of running water, and that in
every gnlly each part has been at some time occupied by a surface
stream, though probably the whole length of the gully has never
been so occupied at one and the same time by a constantly flowing
stream.

There is however one other fact in connection with this subject
which requires mention and explanation ; this is the absence of
any well-marked gullies on the slopes of the Christchurch ridge
in the southern part of the island. As some parts of this ridge
are nearly 400 feet above the sea, and its central line is in some
parts 8^ miles from the coast, the absence of gullies is rather
curious. It is probably due to the fact that the higher part of
this ridge is broken up into a set of irregular east and west ridges
with broad depressions between them. There is no central ridge
of less pervious rock to gather the rainfall and direct it over the
coral area, and the rain which falls on this district is soon absorbed
in the hollows between the ridges ; finally the rainfall itself is
decidedly less than in the other parts of the island. (See
Appendix.)

The following analyses of stream waters may be useful : —

ANALYSIS OF STREAM WATERS IN THE ISLAND.
Showing amoant of Mineral Matter in gprains per gallon.

BowmanstOD.

Town

Water

Belle PlaU

Supply

■tream in

Stream

Roof

from

Valley

St.

Water.

Newoastle.

Eitete.

Andrew's.

SUica

•81

•66

•60

•80

1-00

Peroxide of iron

• ■ •

•03

traces

• • •

Calcium carbonate

9-87

10-23

1087

1217

21-40

Calcinm sulphate

•54

•58

•76

-44

47-84

Calcium nitrate

•38

•09

•77

• • «

1-29

Magnesium nitrate

1-59

1-77

164

213

• • •

Magrnesium chloride
So£um chloride

• • •

•85

1-16

-02

3-28

3-87

3-26

121-60

Potassium chloride

■ • •

• • •

• • ■

• • »

2-90

16-47

16-61

19-39

19-96

196-05

The first four of these are waters derived from the coral-rock,
the last is a water largely supplied by springs rising in the Scot-
land district, and containing a large amount of saline matter.

CHAPTER VII.

Soils and Surface Deposits.

In an island so entirely devoted to agriculture as Barbados the
manner in which the surface soils have originated, and the reasons
why they differ from one another, must be an interesting subject to
the planters and other inhabitants.

The basis of every soil is the subsoil or rock-formation which
underlies it ; that is to say, the slow disintegration (or breaking up)
of the underlying rock-material by the various surface agencies to
which it is exposed gives rise to the loose earth which we call soil.
It does not follow, however, that the same subsoil is everywhere
covered by exactly the same kind of soil, because there are several
circumstances which cause mixtures and varieties of soils. Thus
on every slope there is a tendency for the soil to move down the
slope, and wherever there is a depression or valley there soil will
accumulate and vegetation will thrive. Consequently, soils often
contain ingredients derived &om subsoils which occur at higher
levels, and the amount of organic matter in them is always a
varying quantity.

Where, however, the area occupied by a rock-formation is not
dominated by tracts of a different rock, there is always a great
uniformity in the character of its soil ; though the quantity of that
soil necessarily varies with the conformation of the ground and
with the amount of the annual rainfall.

These general principles are well illustrated in Barbados. The
soils of the island naturally divide themselves into two classes,
(1) those of the Coral-rock area, and (2) those of the Scotland
District, and in each of these there is more than one variety of soil.
Barbadian soils may be thus classified : —

1. Soils of the Corsl Area { JJ^ J^J^^^^J^"* '°*'"«-

/ The clay and sand soils.

2. Soils of the Scotland District } The white earth soil.

( The valley alluvium.

In the coral area the most remarkable soil is certainly the red
clay or loam which occurs on all the higher parts of the area. This
is thickest on the very highest plateau above 900 feet, below 80O

The Geohfiy of Barbados.

feet it is much thinner, and it does not reach below 500 feet;
indeed, between 500 and 700 feet it becomes rather a yellow clay,
and is in many places covered and concealed by dark carbonaceous
earth, the so-called ^' black soil," which is black or brownish black.

Where best developed, the red clay appears as an unctuous
loamy clay of a deep red colour, or more often variegated red
yellow and brown, and it bears a great resemblance to the red and
mottled clays which are so frequently found on the chalk districts of
southern England. The average thickness of this soil on the high
ground is from 2 to 8 feet, but the surface of the coral-rock is so
very uneven that the depth of soil varies in every few yards — it
fills up the hollows and is *' piped" into the holes by which this
rock is honey-combed. Deop deposits of it are frequently found,
and wells have been sunk 40, 50, and even in one case near Castle
Grant 90 feet, without reaching the bottom of such clay-filled
holes. (See Fig. 5.)

Where there is any thickness of the clay the lower part is gene-
rally stiff and moist, but it varies somewhat in character, being
looser and more loamy in some places than in others. The fol-
lowing analyses show, in fact, that there is considerable variation in
the amount of pure silicate of alumina, but that they are fairly rich
in organic matter, phosphates, alkalis and nitrogen.

TABLE I. — Analysis of Soils on the Coral Rock.

Red Soils.

Black Soils.

Moistnre

12117

11-947

10-681

10-849

11-988

12-843

Combined water . . .

9-612

10-266

9-370

9-669

6059

7-890

Organic matter

3-740

2-518

2-173

1-714

2809

1-660

Silica as silicates

(clay, Ac.)

24160

31178

40-561

51609

35-747

} 47-623

Quartz sand

17-418

14-375

14-478

7033

16-856

Silica soluble in acid

•696

•570

•635

1-360

•445

•525

Phosphoric anhydride

•196

•194

•258

-079

-198

•080

Sulphuric anhydride

-137

•146

•051

trace

•120

-153

Nitric anhydride . . .

•022

trace

•018

•007

-003

trace

Chlorine

-004

•005

•007

•022

•014

-047

Ferric oxide

8-920

9-680

8-480

5-393

6-480

3-864

FerrouB oxide

•720

•648

•576

•278

•216

-065

Alumina

16784

15-356

8332

6-369

9-782

19-434

Manganic oxide

•550

•700

1190

•771

-580

•150

Calcium carbonate. . .

3-295

1-891

1250

•725

4-432

-919

Calcium oxide

619

-313

1-344

2142

2-978

2-899

Mi^esium oxide . . .

•602

-306

•450

•955

•810

1-405

Po&sh and soda . . .

422

-190

•299

-822

-482

443

100-000

100-283

100153

99-807

99-979

100-000

>ritrogen

•226

-163

•163

•101

•098

62 The Geology of Barbados.

The principal differences between the two classes of soils are
that the red soils on the upper terraces contain far more iron than
the black soils, whilst the latter contain the silicates of calciam
and magnesium in larger quantities. The red soils also contain
a larger proportion of organic matter, humus and root residues,
but when the proportions of humus present in the soils were
determined, it was found that the red soils contained on an
average 0*295 per cent., against 0*520 per cent, in the black
soils.

With regard to the origin of the red soil we have no doubt
that it has been produced by the gradual disintegration and
solution of the coral-rock itself. At first sight it seems hardly
possible that the decay of a nearly pure white limestone should
result in the formation of a red clay, for the coral-rock is almost
entirely composed of carbonate of lime, with generally less than
2 per cent, of silica and silicates, and only a minute quantity of
oxide of iron ; while the red soil contains about 60 per cent, of
silica and silicates with 9 or 10 per cent, of iron oxide, and only
some 2 per cent, of carbonate of lime.

It is, however, a fact that wherever a limestone is exposed to
the slow solvent action of rain water a similar red soil is produced,
and Barbadians need go no farther than San Domingo to find a
case where this admits of proof, for along the western part of the
south coast of that island there are raised coral reefs covered by a
similar red soil, and this soil is absolutely confined to the coral
areas. Again in Jamaica a red soil occurs everywhere over the
surface of the white limestone which forms such a large part of
that island.

These red soils represent the residue of a great thickness of the
limestone rock; that is to say they indicate the removal of a
great thickness of the rock, the pure carbonate of lime having
been dissolved by the rain water which has fallen upon the surface
and has then run off or percolated through to lower levels, while
the small proportion of insoluble matter has been left on the
surface or swept into its hollows. This mode of origin explains
the fact of the red soil being thickest on the highest levels, for it
is these parts which have been the longest above the level of the
sea, and which have therefore been exposed for the longest time
to the action of the rain and the weather.

Basing a calculation on the average amount of insoluble matter
in the coral-rock, we find that from 50 to 60 cubic feet of such

The Geology of Barbados. 68

rock must have been destroyed in order to produce one cubic foot
of the red clay, and if we could ascertain the rate at which the
destruction of the rock took place under natural conditions we
should have a basis for calculating how long it is since Barbados
first rose above the waves.

The black earth soil is only found on the lower parts of the coral-
rock area from about 500 feet downward. It partakes more of the
nature of an alluvial soil, and the fact of its overlying a reddish or
yellowish clay in many places proves that much of its material has
been brought from higher levels, and it is probable that the red
clay is actually in process of formation beneath it, though this
process must now be going on much more slowly than it did
formerly when the natural vegetation died and decayed on the
ground.

The occupation of an island by man, which ultimately results in
the deforestation of the land and the more complete draining of the
soil, alters the conditions of things and greatly diminishes the
rapidity of many natural processes. When Barbados was first
colonised it was covered by a continuous forest, and the ravines
were occupied by a dense mass of tangled vegetation with frequent
pools and marshy places. Under these circumstances a certain
depth of dark coloured vegetable soil must everywhere have been
formed, while the natural decay of the vegetation must have
supplied the rain water with a far greater amount of Carbonic and
Humic Acids than it ever now holds in solution. Now, it is the
acids dissolved in the rain water which are its active principle, and
it was during this time that all the operations of which we see the
results in the swallow holes, the caves and caverns and the deep
red soils, were accomplished.

Little is being done now, for, as shown by analysis, see p. 49,
the underground waters are rather soft than hard, and do not
contain on an average more than 10 or 12 grains per gallon of
carbonate of lime. Clearly there is now so little Carbonic Acid
set free in the soil that the rain water passing through it and
through the rock below cannot dissolve much lime and conse-
quently all the processes depending on this action are progressing
very slowly indeed.

In the Scotland district there is a much greater variety in the
soil| but most of the soils are less productive. Moreover, on some
of the steeper slopes where the subsoil consists of clay or
disintegrated sandstone there is very little soil at all, for it is

54 The Geolofiy oj Burf^affnA.

BO loose and incoherent that everv hearr rain washes some of it
down the slopes into the Yallejs.

The soils derived from the Oceanic series of deposits differ con-
siderably in character according to the beds from which they have
been derived. Those from the npper clays and rolcanic ash beds
are aa would be expected somewhat heavy, red-colonied, soapy clay
soils, consisting chiefly of pure silicate of alamina coloured by
peroxide of iron. These soils require careful tieatment, and in
consequence of their deficiency in phosphates and potash are
peculiarly liable to injury by heavy and repeated dressings of purely
nitrogenous manures. They occur principally on Castle Grant,
Chimborazo, Bloomsbury, Highland, and Canefield estates and on
the upper part of Mount Hillaby.

The lower beds of the Oceanic series generally give rise to light-
coloured, cold, calcareous soils, such as those at Bath and at
Cleland estates, but from the hilly nature of the ground are seldom
of any great extent, and from the same reason it is difficult to
distinguish those arising from the purely siliceous strata and from
the calcareous ; the overlyiuff soils being as a rule derived in part
from both. The analysis given in the fifth column of Table U.
well represents the usual composition of this class of soil, and is of
one from the lower slopes of Hillaby. The silica present is chiefly
of organic origin, and is soluble in alkaline solutions ; the alkalies
in it are doubtless derived from the decomposition of certain of the
beds of volcanic ash which occur throughout the Oceanic forma-
tion. The analysis in the last coliunn is derived partly from the
lower Oceanic earths and partly from the blue Scotland clay.

The Scotland beds give rise to many varieties of soils, which
may be classed generally as heavy argillaceous and light sandy
soils, with all degrees between the two extremes.

All soils belonging to this group are deficient in lime, and in
consequence the most fertile fields are those where the soil is
derived in part from the sands or clays of the Scotland series and
in part from the marls of the Oceanic series (as in that of column
six, Table II.) The clay soils are heavy, dark coloured, very
tenacious soils, rich in phosphoric anhydride, sulphuric anhydride,
and potash, and if dressed with lime or marl would be the most
fertile soils in the island. The sandy soils are deficient in phos-
phoric anhydride and in potash as well as in lime, and it is
remarkable that the planters are at all able to raise crops of any
value upon some of tibem.

The (leology of Barbados.

TABLE n. — Soils op the ScotlaiId Dibteict.

Sand Stoitbs.

Clatb.

Moisture

Organic matter and
combined water . . .
Claj <& colloid silica
Quartz sand
Silica soluble in acid
Phosphoric anhydride
Sulphuric anhydride
Chlorine
I^erric oxide
Ferrous oxide
Alumina
Man^nic oxide
Calcium carbonate . .
Calcium oxide
Magnesium oxide . . .

Potash

Soda

100-183

3099

5081

14-349

70-t504

•310

•073

•085

•023

4-24^

•1-27

•587

none

•644

•504

•126

•159

Whitk Eabtbb.

99919

3-6o9

4425

5-740

6122

78-062

76222

•880

•135

•270

•281

•446

•OOi

•Oil

18i0

1040

•864

1080

5-230

6379

none

•193

•659

1012

1059

1-189

1-315

•3S8

•466

•177

-aso

99-954

99-990

Pure.

8-796

63188

1-264
•149
•248

trace

3077
-226

1338

337

12-732

•488

1239
•306
•740

99849

Mixed.

11-810

6-999

63422

•055
•254
•154
-016

1-240
•468

8-686
-200

3-977
•845
•973
•359
•337

99-795

There remain for consideration the soils in the valleys of the
Scotland district ; these soils consist of the detritus which has been
washed down the slopes during heavy rain, with a considerable
depth of coarse detritus (gravel and boulders) covered in the lower
reaches with silt and alluvial soil. This boulder gravel consists of
rounded blocks of the harder members of the Scotland rocks, and
occasionally of blue limestone derived from the lowest beds of the
Oceanic series. The detritus is not like that of an ordinary river
gravel which has been brought down by the upper tributaries of the
stream; it is rather what may be termed a ''flood wash/' and
consists of the soil and stones carried down the slopes along the
whole length of the valley during heavy rains. The action of the
stream at the bottom of the valley seems to have been mainly
employed in washing out the finer silt and soil from the stones
and in transporting the former to lower levels, where it is spread
out over tracts of some width.

It is a curious fact that in many places isolated blocks of coral-
limestone are found apparently in situ upon this alluvial deposit,
but it is so very unlikely that the valleys in their present form were
ever inlets of the sea that we think the position of these coral
masses is deceptive, and that they have slid down with the soil from
their original positions on the slopes above.

56 Th^ Geology of Barbn/io9,

Id tome pkees, sod espeeudlj near the eoast in St. Joseph's
\, the allinrud deporits consist of re-arranged deposits of the
earths. The most striking instance of this is to be fonnd
at Joes BiTer, where this re-deposited BadiohuiAn earth has a great
thickness (probably 50 feet), and corers an area of sereral acres.
This rain-wash from the Oceanic deposits freqnentlj contains Und
and freshwater shells, which attest its manner of accnmnlation.

These ralley and allnTial deposits coyer all the lowest lerels in
the Scotland district, and have been coloured on the map, because
they are limited to these areas. The green colonr includes, how-
erer, two small tracts of sand which has been blown up by the
trade winds off the sea shore ; these form low ridges or dunes, one
of them extending for about a mile to the north-west of Long
Pond in the parish of St. Andrew^s, and the other forming sereral
low ridges to the west of the Pond between it and the river, by
8t« Andrew's Station.

Wind-blown sands also occur in some places along the western
coast, but differ from the abore in being entirely calcareous,
consisting of minute fragments of shells and corals. If plentifully
supplied with water, these tracts can be cultiTated with success,
but the siliceous blown sands of St. Andrew*s are quite unfertile.

CHAPTER VIII.

Economic Products and Water Sui^ply.

We propose in this chapter to indicate some of the mineral
products which are of economic and commercial importance to
the people of Barbados, and the practical importance of a
knowledge of geology in the matter of water supply.

i. Mineral Products.

Building Materials. — One of the most important of such
questions is the material of which Barbadian houses are built.
This has hitherto been almost without exception the coral-rock
which covers so large a part of the island, and the beds which
have been usually chosen for this purpose are the soft oolitic
freestones which are locally known as sawstone. Now it is from
the very same beds, only from their more porous portions, that
the large stone filters so largely used in the island, and commonly
called '' dripstones" are constructed : consequently it is clear that
the rock is too soft, porous, and unconsolidated to be a good
building stone. It is true that after exposure to the air the blocks
assume a considerable degree of hardness, probably in consequence
of a process of solution and redeposition of the material which
is due to the alternate wetting and drying of the stone. This
hardening, however, does not entirely destroy though it doubtless
reduces the porosity of the rock, and it has consequently been
found necessary to coat the outside of all buildings with plaster
or cement. Even this, however, does not entirely prevent the
rain from soaking into the stone and making the wi^s more
or less damp. The plaster moreover has a monotonous and
unsightly appearance.

Now the fine sandy clays which occur in the Scotland series, and
are of considerable thickness would make excellent bricks, as
indeed Mr; Brocklehurst demonstrated some years ago. Some of
them also are quite fit for making fine tiles which could be used
instead of the wooden shingles now employed for roofing. We
would urge upon Barbadians the desirability of developing this

68 The Geology of Barhadoa.

indastry, and of establishing brick and tile fields in the Scotland
district without loss of time.*

Buildings constructed of the bricks which could be made in the
island would be found to be drier than those made of coral-rock,
and should not require any external plastering, so that they would
possess a much more pleasing colour and appearance.

From the chemical composition of the coloured clays which occur
at the top of the Oceanic series in the central part of the island, we
believe that good fire-bricks might be made, if prepared and com-
pressed by suitable machinery, the small percentage of lime and
alkalis present in them making them peculiarly suitable for such
purpose. Some of the sandstones and gritstones which occur in
the Scotland district would furnish valuable material, especially
suitable for the lining of furnaces.

Lime-making, — In certain parts of the coral-rock Barbados
possesses excellent material for burning into lime, and as there is a
great demand for lime throughout the West Indies a good export
trade ought to be developed. The most suitable beds for making
lime are the harder portions of the rock which are now quarried in
so many places for road metal. These beds contain from 96 to 98
per cent, of carbonate of lime, and the lime which is made from
them is quite equal in quality to the best Bristol lime, which is at
present the lime most favoured by West Indian planters.

Siliceous Earths. — In the middle portion of the Oceanic series
beds of white Radiolarian earth occur which are of exceedingly
light specific gravity, and are almost purely siliceous. Such beds
occur at Springfield, on Joes River Estate, on Melvin's Hill, at
Mount Hillaby, and below the Spring Estate. The use of these
earths as lagging or non-conducting surfaces has been pointed out
in Ure's Dictionary, (last edition, 1879, vol. 4, under the head of
Tripolite), and the subject was brought to the notice of Mr. G.
Brocklehurst by one of the authors in 1884. That gentleman took
it up with characteristic energy, and has rapidly converted the
previously unused product into a valuable material. It is now in
use as a boiler-covering or felting through the British West Indies
and in the most important works of British Guiana. No time
should be lost in placing this Barbadian product before a wider

* We are pleased to learn that quite recently and since both of us quitted
Barbados, a company has been formed to develop this industry, and that works
have been opened on the Greenland estate in St. Andrew's, where they have
found a variety of fine-grained clays, suitable not only for making the best
bricks, but also for the manufacture of ornamental tiles and pottery. .

The Geology of Barbados. 59

market, especially as the writers are aware of the existence of
extensive deposits of similar material elsewhere in the West Indies.

Another use for these siliceous earths is as a substitute for
kiesel-guhr in the manufacture of dynamite, and the characters of
some of the Barbadian samples appear to be admirably suited for
this purpose. A third use to which these light siliceous earths can
be put is the preparation of polishing powders, and their freedom
from all gritty matter makes them peculiarly suitable for this
purpose.

They might also be used in the manufacture of sodium silicate,
on account of the easy solubility of the silica they contain. Lastly,
they have been used with considerable advantage for accelerating
the filtration of saccharine liquids in filter presses.

Cement Making. — The lowest chalky beds of the Oceanic series
possess a value which is derived partly from their chemical com-
position and partly from the fact of their lying, in the southern
part of the Scotland district, immediately upon the dark clays of
the highest Scotland group. In these two deposits we have the
materials for .the manufacture of cement in juxtaposition. This
ought to form the basis of an important industry, and should
enable Barbados to furnish the West Indies with a good and cheap
cement at a moderate cost. We believe that cement-making will
be, if the suggestion is followed up with energy, one of the most
promising of the minor industries of the island. We may mention
that there are other beds of chalky earth at a higher horizon in the
series which would be equally suitable for the manufacture of
cement, as on Cleland Hill ; and, further, that there are beds of
dark grey earth on Mount Hillaby, consisting partly of chalky
earth and partly of fine mud, which have a chemical composition
that seems to indicate their suitability for making cement without
any admixture of clay.

There are also near Chalky Mount and elsewhere large nodules
or septarian concretions, often called cement stopes, and as they
occur in some quantity, they would also provide raw material for
cement.

Petroleum and Asphalt. — We have already alluded (p. 14) to
the occurrence of large quantities of petroleum in the clays and
sandstones of the Scotland District. At present the industry of
collecting and refining this substance is in a languishing condition,
and it is chiefly employed as a lubricant and as a constituent in
certain quack medicines. But we believe that it might become of

60 Tk-e Geology of Barbados,

great importance to the planters as a fuel for nse in the sugar
works. It might be tried in the present furnaces by steeping the
cane trash in the petroleum, but to obtain the full advantage of its
use special furnaces would probably have to be constructed. As a
matter of supply, we think that larger quantities would be obtained
if wells were sunk to the north-west of Springfield, and especially
in the tract of country between Bissex Hill and the great fault
which traverses the St. Andrew's Valley.

In the same strata there are small deposits of asphaltum or pitch
glance, a substance which is known locally by the name of manjack,
and has often been mistaken for coal. It differs from coal in being
fusible by heat, and in being soluble in alcohol, turpentine, &c.

.Unfortunately very large quantities of this substance occur in
Trinidad and elsewhere, and consequently it is not likely that the
Barbadian deposits will ever have much commercial value. It is
the basis of black varnishes such as '' Brunswick Black,'' and
excellent black varnishes and paints can easily be prepared from it
by dissolving it in spirits of turpentine, and adding to the solution
a small quantity of linseed oil to reduce its brittleness when dried.

It might be used with considerable advantage for making gas,
but on account of its fusibility special arrangements would be
required in order to carbonize it.

Phosphates, — These do not occur in sufficient quantity to be of
much commercial value, but the existence of guano and phos-
phatised limestone in some of the caves which open on to the
cliffs and slopes in the western part of the island may be pointed
out. The guanos contain from 6 to 20 per cent, of phosphate of
lime, and the phosphatic rock has from 60 to 80 per cent. These
deposits are apparently due to the caves having been in former
times the homes of large numbers of birds, and not, as is usually
assumed, to the accumulated excrements of the bats which now
inhabit them.

Ochres, — It is just worthy of mention that the clays at the top
of the Oceanic series, from their diversity of colour and peculiar
composition, are suitable for use as ochres, and are in fact so used
by the inhabitants of that part of the island in which they occur.

2, Water Supply.

In early days the water supply of the island was entirely
derived from the ponds which existed on the -surface, and which
were formerly much more numerous than they now are. As the

The Geology of Barbados, 61

population became larger wells were sunk and water was generally
found at depths varying from 50 to 200 feet, either at the bottom
of the coral-rock or in the beds of Oceanic earth where these
happened to lie below.

In 1857 the Bridgetown Waterworks Company was formed,
and obtained their supply from the Newcastle Springs, which
issue from the Oceanic earths in the valley west of Newcastle
at a height of about 300 feet on the line of fault which is marked
on the map. These springs have a minimum discharge of 880,480
gallons a day, and the water is conveyed to Bridgetown in pipes,
the distance being about 18 miles. The supply, however, is only
sufiBcient for that town, and could not be extended even to the
suburbs or other settlements in the same parish, so that the rest
of the island had still to depend on local ponds and wells.

Another Compan}' was therefore formed in 1886 under the name
of the Barbados Water Supply Company, which undertook to find
a supply for the greater part of the island. Under the able
management of Mr. Edward Easton, C.E., F.G.S., the works of
this company are now in progress and a supply of good water is
being gradually extended over the island. This result has been
attained by a skilful interception of the underground watercourses
mentioned in Chapter VI.

Mr. Easton, after making a hydrographic survey of the island,
saw that it was not necessary for the supply to be taken from the
springs which happen to issue here and there at the surface, but
that water could be found at many places and at various levels, and
could be brought to the surface without being raised by pumping
machinery.

A considerable amount of labour and expense would have been
saved to the Company if the island had been geologically surveyed
before Mr. Easton began his operations. He was, in fact, obliged
to obtain some knowledge of the geological structure of the island
before he could realise the exact conditions of the subterranean
water system, and this was not obtained without the expenditure of
time and labour. A simple hydrographic survey did not, in fact,
tell him all he wanted to know, but having eventually made himself
acquainted with the general structure of the island he was able to
plan the system which is now in operation and to indicate with
greater certainty the places where water might be intercepted and
utilised. But we think he will be perfectly ready to admit that the
more he knows about the geology of the island the more he will be

62 J'he Geology of Barbados.

able to dispense with trial borings in search of the strongest local
aappUes of water.

The plan he adopts is to intercept the streams which are flowing
underground from the higher parts of the island and by means of
tunnels to bring the water to the surface at various points, whence
it can be distributed through pipes to all places in the neighbour-
hood which are at lower levels than the spot where the water is
intercepted. It is, in fact, a system of gravitation supply, and it
has the gi*eat advantage of avoiding all necessity for erecting
reservoirs or expensive pumping apparatus.

Mr. Easton^s name is a suiGcient guarantee for the soundness
of the scheme, but we may be allowed to say that if we had been
consulted in the capacity of geological experts we should have
recommended the same principle of supply. It naturally com-
mends itself to anyone who is acquainted with the geological
structure of the island.

APPENDIX.

The Rainfall of Barbados.

The mean annual rainfall of Barbados is a little over 60 inches,
but as might be anticipated from a knowledge of the physical
features of the island, this rainfall is unequally distributed. Not
only do the higher levels get more rain than the lower ground, but
the lowlands on the north-eastern side of the island have a greater
rainfall than those on the south and south-west.

The loUowing tables have been compiled from the records kept
by Dr. Bowie Walcott, who has obtained and recorded observations
on the rainfall ever since 1847. We have however chosen the 15
years between 1872 and 1886 as having been taken at a greater
number of stations than in earlier years. These tables show that
in the south of the island the mean rainfall is about 52 inches,
while that on the high lands of St. Joseph, St. Thomas, and St.
James, in the centre of the island, amounts to 72^ inches.

TABLES SHOWING THE MEAN MONTHLY RAINFALL IN BARBADOS

BETWEEN THE YEARS 1872 AND 1886.

I. — Rainfall on the Highlands (i.e., above 400 feet).

January . .

February . .

March

April

May

June

July

August

September

October . .

November

December

1.— St.

2.-8t.

3.-8t.

4.-St.

5. -St.

6.— St.

7.— St.

Oeorge.

PhUip.

John.

Thomas.

James.

Peter.

Joseph.

4-33

3-76

3-85

4-64

4-37

4-07

5-67

2-35

2-10

212

2-52

2-67

2-30

2-52

2-35

1-70

210

2-36

2-42

2-70

2-66

2-53

2-45

2-75

2-63

2-65

2-15

3-30

305

2-60

3-20

3-43

3-71

3-54

3-52

5-54

4-71

5-35

5-98

5-93

5-84

5-98

6-31

5-23

602

6-79

5-96

6-38

6-50

7-81

7-22

7-35

8-81

919

8-52

8-54

9-64

8-33

8-89

10-35

10-36

9-60

10-26

7-83

710

8-57

9-35

9-79

8-80

1000

8-78

7-75

8-92

9*57

8-85

8-42

9-92

4-71

3-76

4-52

5-42

5-57

4-57

5-12

65-23 .

56-71

63-64

71-85*

71-67

66-89

73-99

8.— St.
Andrew.

3-71
2-33
215
1-73
3-23
5-22
5-45
7-78
9-60
8-45
10-51
4-30

64*46

Mean Animal Rainfall on the Highlands = 66*80 inches,

* Obtained hy combininf;^ average of whole parish.

The Oeology of Barbados.

n. — Rainfall on thb Lowlands (t.«., thb countby lying below

400 feet).

l.-8t

2-Chri8t

8.— St.

4.— St.

6.-8t.

6.— St.

7.— St.

8.—St.

9.—8t.

10.— St.

Michael.

Gharoh.

George

Philip.

John.

Jame».

Peter.

Lncj.

Joseph

Andrew.

Janaar}' . . .

303

314

3-81

3-16

323

3-55

3-61

306

3-68

3-63

February

1-50

1-68

1-94

1-66

1-46

2-34

2-20

1-80

1-88

1-94

March ...

1-48

1-73

1-91

1-59

1-65

1-79

1-28

1-70

1-87

2-20

April

1-47

1-45

2-22

1-89

219

1-79

1-93

2-42

2-66

2-42

May

2-29

2-30

2-74

2-35

2-72

2-38

2-77

2-68

2-95

2-96

June

4-64

4-57

5-08

4-29

4-68

5-97

5-38

503

4-71

4-84

Jnly ...

5-59

5-33

5-97

503

5-35

5-43

5-72

5-78

5-30

5-76

August ...

6-91

604

7-02

6-47

6-57

8-31

7-92

6-78

7-85

7-46

September

810

6-60

8-54

7-56

7-86

9-59

8-82

812

9-02

912

October ...

6-71

703

7-26

6-69

7-84

8-18

8-47

7-52

8-95

8-59

November

8-07

7-91

8-45

9-11

8-53

7-42

8-36

7-47

801

900

December

3-55,

3-60

442

3-37

3-58

4-51

4-27

3-89

4-02

409

53-34

51-38

59-36

53-17

55-65

61-25

60-73 156-25

60-90

62-01

Mean Annual Rainfall on the Lowlands = 57*40 inches.

It will also be seen from these tables that the year is divisible into
a dry and a rainy season, the former coinciding with the winter and
spring months, the latter coinciding with the summer and autumn
months. The driest months are February, March, and April,
during which there is on the average only about two inches of rain
per month. The wettest months are August, September, October,
and November, during which there are frequent heavy rain-storms,
often accompanied by thunder, and the average rainfall varies from
7 to 10 inches in different parts of the island. Half the total
annual amount of rain in fact falls during these four wet months,
the other half being distributed over the remaining eight months
of the year.

Bvunett BiotUer«. PriDter^ Journal Offia«, Saliibar/.

\Cy