Kellys_Berks_Bucks&Oxon_1915_0463.jpg

d ir ec to r y

.]

BU C K IN G H A M SH IR E.

15

with the G a u lt below, which have determined the sites of a Beaconsfield and Rickm answorth, we find sands and clays
■whole string of villages. The G au lt and the Upper Green- of an age altogether distinct from , and later than, those
sand are closely related, and are now often grouped together rocks of which we have hitherto been speaking.
Reading B eds. — These extend eastw ardly from Woburn by
as one formation, under the nam e of Selbornian.
(3.) The W hite C h a lk.— This well-known rock (a soft Burnham , Beaconsfield, Hedgerley, Chalfont St. P eter’s and
Denham
; they consist of variegated plastic clays with lightearthy and alm ost pure lim estone! constitutes a large por­
tion of the south of the county, rising in the Chiltern Hills coloured and green sands, altogether about 80 feet in th ick ­
ness
;
they
are exposed n brick-yards a t Hedsor, Burnham ,
to a height of about goo feet above the sea level.
&c. There are several outliers of the Reading Beds seen
(a) The Lower Chalk.— The lowest beds are of soft whitish upon the Chalk, as at Penn, Pollard Wood, &c. No fossils
chalk marl, about 80 feet thick, and form rising ground have been found in them here.
between Bledlow,Risborough and the reservoirs near MarsThe London Clay. — This stratum (about 200 feet thick)
worth.
The characteristic fossil of the Chalk Marl is rests on the Reading Beds round F’ulm er, at Stoke Common,
Ammonites varians. The top of this division is formed by Iver, Red Hill, &c. ; it is a stiff brownish clay, often con­
the hard Totternhoe Stone, a rather brownish sandy chalk taining large nodules called septaria, which are rounded
with dark grains ; it is well seen in a sm all quarry near lumps of im pure limestone, traversed by fissures filled with
' ‘ Tring W h arf,” and in several road cuttings along the line carbonate of lime.
just mentioned.
E c o n o m ic G e o l o g y . — Th e minerals of Buckingham shire
(b) The M iddle Chalk.— This division is about 160 feet m ay be said to be “ conspicuous by their absence.” In
thick and has but few flints ; it forms the north-west slope the south of the county the brick-earth at Langley is largely
of the great chalk escarpm ent, and is exposed along the worked for brick-m aking ; the Portland stone is quarried
sides of the valleys which cut that escarpm ent back ; the a t H artsh ill; and there are other stone quarries in the G reat
top is m arked b y a thin but very constant bed of Chalk rock Oolite ; coprolites (phosphatic nodules) were form erly dug
hard and pinkish, which is really the base or bottom layer a t Towersey and at Brickhill. The following figures for
of the Upper Chalk ; we see this layer in a large chalk-pit the year 1909, are taken from M ines and Quarries :—
one mile north of Henley-on-Thames (the town itself is in
Chalk, 530 tons ; value ,£28.
Berkshire), and in various chalk-pits between the latter
C lay, 71,567 tons ; value .£2,331.
town and Marlow, also near High W ycombe, Chesham, &c.
G ravel and Sand, 5,300 tons : value £7,70.
Well-sinkers call it “ rock,” and have to blast it on account
Lim estone, n o tons, value X45.
of its hardness.
Sandstone, 545 tons, value ¿¿693.
Persons em ployed— (a) Under-ground or inside quarries,
(c) The U-pper Chalk with F lin ts.— This rem arkable mass
of soft white limestone is some 450 feet thick and form s the 73 ; ( b) Above-ground or outside quarries, 26 : total, 99.
F or 1912 statistics see p. 2.
eastern slope of the Chiltern Hills ; it m ay be distinguished
T h e D r i f t .— In attem pting to trace the beds of regu­
from the lower beds not only by the presence of countless
la
rly
stratified and more or less continuous rocks of which
nodules and layers of flint, but by the character of the
fossils. W e find in it m any species of sea-urchins, sponges, we have been speaking, the geologist finds th at they are
largely
covered over and obscured by irregular, often thick
&c., whilst in the Lower Chalk whorled and spiral univalve
surface masses of clay full of pebbles, or by m ore or less
shells more com m only occur.
Beech trees grow largely over this tract of chalk, and their extensive patches of sand or gravel. These irregular surface
wood is used for chair-m aking. Th e chalk itself is much deposits are relics of the g lacial period ; the stony clays
burnt for lim e ; it is go t in large pits from 50 to 150 feet were probably pushed out from and before the end of a great
deep ; the men w ork at the top of the pits with crowbars glacier which travelled down from the north into B ucking­
dislodging great masses, which break to pieces in their f a l l; hamshire and the adjoining counties, although the ice pro­
fortunately the chalk is traversed by fissures or joints, for bably never reached quite to the River Thames. The
were it one homogeneous mass it would be scarcely possible northern side of the Ouse valley between B rackley and
to work it. The Chiltern Hills command an extensive pros­ O lney is tolerably free from D rift, but south of this line and
pect and rise sharply from the Oolitic plain which lies be­ spreading over the plain formed by the Oolitic Clays we find
thick and varied Drift deposits ; clean gravel beds occur
yond them to the north-west.
Zones o f the Chalk.— A t first sight nothing m igh t seem round H ardwick, between Finm ere and Buckingham , and
more hopeless than to attem pt to divide the great mass of round Stowe and A keley. In the gravel-pit at Tingewick
the English Chalk— whose total thickness is not much we see false-bedded coarse gravels with beds of soft clean
under 1,500 feet— into distinct beds, bands or “ zones.” sand. Near Buckingham there are several exam ples in
Yet by the labours of the distinguished French geologist,Dr. gravel-pits of the m anner in which these beds are sometimes
C. Barrois, continued by the work of the officers of our own contorted and bent into curves ; this is supposed to be due to
Geological Survey, and in quite recant years completed by the pressure exerted by the ice form ing the G reat Northern
the painstaking and accurate studies of Dr. A. W. Rowe, G lacier ; sim ilar cases occur at Foxcott and Maids Moreton.
even this great task has been so far completed that only the Th e stiff clay drift is well shown round Leckham pstead,
details now remain to be worked out. To p ut the matter where it contains striated boulders of carboniferous lim e­
into a few words, it has been proved th at, commencing stone, &c. There is also a connecting link between the
with the lowest beds of the Chalk and passing upwards, we “ drift clays ” and the “ drift sands ” in the shape of clayey
find that in practically every locality in England where the d irty gravels which are w idely distributed.
Over the chalk hills there is m uch “ clay with flints,”
sequence is complete, we can separate this thick mass of
white soft earthy limestone into about a dozen beds or probably a result of the decomposition of the chalk during
long
ages.
zones, each zone characterised by the presence of a distinct
The Ouse river-gravels cover much ground ; they abound
group of fossils. Of these fossils the m ost characteristic
in
derived
oolitic fossils, especially belemnites, which are
and least widely diffused (vertically) is chosen to give a name
sometimes collected by the villagers, who consider them,
to the zone.
when pounded, an excellent cure for rheum atism 1
The highest beds of the Chalk in Buckingham shire are
B o r in g s in B u c k s . -— H ardly any deep borings in search
probably those exposed in a deep quarry near Taplow, and of coal, w ater, etc. have been m ade in this county. We
may belong to the Marsupites zone; the rock here includes m ay, however, mention the successful boring for w ater at
two beds of brown phosphatic chalk, and is without flints.
the Stone A sylum (near A ylesbury), which attained a depth
of 570 fe e t; passing through Portland Beds, 25 ft., Kim eZ ones o f t h e C h a l k .
Max. thick- ridge, Corallian, and Oxford C lays, 515 ft. ; and G reat
Cliaracter of the Rock.
Zone Fossil.
ness in feet. Oolite to 30 ft.
A t Bletchley, in 1887, a boring for w ater put down by
A ctinocamax quadratus \
§ « ( White Chalk, with
the L. & N.W . Railway Co. term inated in a rather rem ark­
£ ^ -< numerous Flints Marsupites testtcdinarius j 100
able
manner. The strata passed through were “ Oxfordian
M ia %
aster cor-anguinum ... 300
Clays and Lim estones ” for 378 feet, at which depth the
vC b alk Rock ....... HolaMer planus ................ 50
borer entered a rock described by Prof. Bonney as “ a rock
3 2 f White Chalk with ) rn , . , •
closely allied to granite ” — possibly a variety of the igneous
few Flints
| Terebratuhna .................... 100
rock called quartz-felsite. This granitoid rock was pierced
o ^Melbourn R ock
Rhynchonella cuvieri ....... 60
for nearly 30 feet, when the boring was abandoned. It has
been supposed that this bottom rock was m erely a boulder,
* » f G rey, Marly Cha\k... A ctinocamax pletius
6
or erratic, contained, perhaps, in the Kellaw ays Rock (base
of
Oxford C lay), but its thickness and the absence of sim i­
o 3 j H W 'hitichaikand j H olaster sul-globosils ....... 80
lar boulders in the same stratum elsewhere tell against this
^ v Chalk Marl
A mmonites varianns
80
supposition ; and it seems to us to be m ore likely for the
T e r t i a r y B e d s — E o c e n e F o r m a t io n . — A t the top of quartz-felsite to be in situ, and to be part of a peak of the
the Chalk there is another great break, or interval of time, old land-surface which form s Charnwood F orest in Leices­
during which no strata now existing in B ritain were de­ tershire, and which is known to extend underground in a
posited. O ccupying a large triangle between Colnbrook, south-easterly direcTon.