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PAC: JUKES-BROWNE, B.A., ¥.G.S.,

m Jon's COLLEGE, CAMBRIDGE, AND H.M. GEOLOGICAL SURVEY.

_ CAMBRIDGE: DEIGHTON, BELL AND CO,
; LONDON : GEORGE BELL AND SONS.

Hibrary of the Museum
COMPARATIVE ZOOLOGY,

AT HARVARD COLLEGE, CAMBRIDGE, MASS.

Founded by private subscription, tn 1861.

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No *7 2; cay

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THE POST-TERTIARY DEPOSITS

OF

CAMBRIDGESHIRE,

BEING

Che Sedgwich Prize Cssay

FOR 1876.

BY

A. J. JUKES-BROWNE, BA, F.GS.,

OF ST JOHN’S COLLEGE, CAMBRIDGE, AND H.M, GEOLOGICAL SURVEY.

CAMBRIDGE: DEIGHTON, BELL AND CO.
LONDON: GEORGE BELL AND SONS.

T1878

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PREFACE.

THE subject proposed for the Sedgwick Essay in 1876 was
“The Post-tertiary deposits of Cambridgeshire and their relations
to deposits of the same period in the rest of East Anglia.”

Circumstances have prevented the earlier publication of this
Essay, to which the prize was awarded; but the delay has
enabled me to make a few additions to the original manuscript,
such supplemental matter being indicated by the use of square
brackets in the text. With the exception of this and of the
concluding remarks, the Essay is now printed in the same form
in which it was sent to the Adjudicators of the prize.

I am indebted to the Director of the Geological Survey
of England for permission to make use of the information
obtained during the survey of that part of Cambridgeshire
on which I was engaged at the time the Essay was written.
My thanks are also due to my colleagues, Mr W. H. Penning
and Mr S. B. J. Skertchly, for the notes relating to other
parts of the county which they placed at my disposal.

A. J. JUKES-BROWNE.

5 West Hini, HicHGATE,
July, 1878.

CONTENTS.

CHAPTER I,

Introductory

CHAPTER II.
Literature of the Subject .

CHAPTER III.

Physical Features of the County and Description of the Glacial

Deposits. : ‘ : : :

CHAPTER IV.
Description of the Hill-gravels

CHAPTER V.

Valley-gravels of the early river system

CHAPTER VI.

Valley-gravels of the present river system

CHAPTER VII.

Correlation of the Cambridgeshire Drifts with those of East Anglia.

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CHAPTER I.

INTRODUCTORY.

THE existence of a series of deposits and accumulations, inter-
vening between the vegetable soil and the older strata of the
earth’s crust, has long been known to Geologists; they rest in-
discriminately on formations of Tertiary, Secondary or Primary
age, and they form what farmers call the sub-soil over large
portions of those districts in the British Islands which have
been brought under cultivation. Notwithstanding, however,
their importance from an agricultural point of view, these
superficial deposits were little studied in the early days of
Geology, and the first endeavours to account for their occur-
rence were very crude and unsatisfactory; it is only indeed
within the last 20 or 25 years that they have received that
amount of attention which they merited, and only within the
last 10 or 12 that Geologists have been able to give anything
hke an adequate and comprehensive account of their distri-
bution and mode of formation.

By the Huttonians these deposits were all classed together,
and regarded as the result of atmospheric action and fluviatile
erosion on the surface of the continents during a long lapse of
ages. The possibility of separating them into two groups or
series, differing in their constitution and mode of occurrence,
was first indicated by Cuvier in the Preface to his work on
“Fossil Quadrupeds” at the close of the last century (1798).
In this preliminary essay, now known under the name of
“Cuvier’s Theory of the Earth,” ‘which was translated into
English in 1813) he speaks of the beds forming the Paris basin
as surmounted by various alluvial deposits. He notices that some

12

4

of these contain mammalian remains belonging to extinct species,
while “the bones of species apparently identical with those
now living are never found except in the very latest alluvia ;”
these deposits he describes as resulting from causes now in
operation, but believes this present state of affairs to have been
preceded by a great catastrophe or deluge.

Referring to this supposition in a paper read before the
Geological Society in the year 1819, Dr Buckland says—“ For
the purpose of impressing more strongly this distinction which
I have drawn between diluvian and post-diluvian gravels, it will
be convenient if Geologists will consent to restrict the term
diluvium to the superficial gravel-beds produced by the last
universal deluge; and designate by the term alluvium those
local accumulations that have been formed since that period,”
by the action of torrents and other causes in daily operation.

In 1823 Dr Buckland published his Reliquie Diluviane,
and developing more fully his hypothesis that the diluvial
deposits were produced by the waters of the Mosaic Deluge,
he gave a fresh importance and signification to the terms
Diluvium and Alluvium.

The nomenclature thus proposed by Por Buckland was for
many years accepted and made use of by Geologists, and it
required a long series of close and accurate observations com-
pletely to dispel the false ideas and analogies with which this
terminology had invested the subject. The principle of the
classification however was a sound one, and the original dis-
tinction between those formations which originated “in a
former and different order of things,” and those which have
resulted from causes still in operation, has in fact become
more clear and defined in the progress of Geological knowledge.

Thus we find Prof. Sedgwick contributing two papers “On
the Origin of Alluvial and Diluvial Formations” to the Annals
of Philosophy for 1835, in which he points out that the
Diluvial deposits occur with different characters and generally
at different elevations from the Alluvial, but that where both
are present the latter always rest on the former, and that
they belong therefore to distinct epochs.

The Diluvial formations he divides into two classes :—‘ The
first composed of coarse materials often lodged at considerable

+)

elevations and apparently drifted into their present position by
the first rush of waters; the second generally found at lower
elevations and apparently comminuted by the continued attri-
tion of the retiring waters.” As he refers to this latter class of
deposits the gravels which are found between Cambridge and
Lynn, and which are clearly river-gravels of Post-glacial date,
it is evident that the Diluvial and Alluvial formations did not
accurately correspond with what are now known as the Glacial
and Post-glacial deposits.

It is necessary to remember this while perusing the older
papers written on the subject; and we may perhaps correlate
the old and new nomenclature as follows :—

Diluvial (Older division = Glacial Deposits.

Detritus Wickes division = Older Valley-gravels.

Alluvial Detritus = Newer Valley-gravels
and Alluvium,

Post-glacial
Deposits.

It soon began to be felt, however, that the formation of the
deposits grouped under the head of Diluvial Detritus could not
be attributed to one and the same set of agencies, and in his
Anniversary Address to the Geological Society in 1831, Prof.
Sedgwick observes that “we ought to have paused before we
adopted the Diluvian theory and referred all our old superficial
gravels to the action of the Mosaic flood....Bearing upon this
difficult question there is I think one great negative conclusion
now incontestably,established—that the vast masses of diluvial
gravel scattered almost all over the surface of the earth do not
belong to one violent and transitory period.”

He apparently adopts the idea subsequently taken up by
De Beaumont, viz. that deluges were caused by the sudden
elevation of mountain-chains. De La Beche in 1834 takes the
same view, and accurately points out the probable northern
origin of the erratic blocks scattered over the north of Europe ;
he suggests that the elevation of the bed of the northern ocean
occasioned such a deluge, and adds—“such waves (elsewhere
called waves of translation) would necessarily tend to float
the northern glaciers with their usual burdens of blocks of
rock, lifting them to the southward’.”

i Researches in Theoretical Geology, pp. 388, 389.

6

In this curious theory therefore we find some perception of
the true explanation, but obscured and distorted by the cata-
clysmal ideas which had so long obtained possession of men’s
minds. The successive editions of Lyell’s Principles of Geology
contributed greatly to remove the old and deep-rooted belief
in cataclysms and rushing waters, and to show how most
geological phenomena may be explained by the continued
action of agencies which are now actuaily operating in different
parts of the globe.

The mistake of placing the older valley-gravels amongst the
Diluvial detritus began to be noticed. Lyell pointed out that
there might be Alluvia of various ages (see 4th Edition of
Principles, 1835, Vol. Iv. p. 209), and he appears to use the
same term for denoting all superficial accumulations, to the
entire exclusion of Diluvium.

The difficulty of distinguishing between the so-called
Diluvial and the older Alluvial detritus is commented upon
in Phillips’s Guide to Geology, 2nd edition, 1835.

In 1837 Dr Buckland withdrew his opinion regarding the
identity of the Diluvian epoch with the Noachian deluge,
though he retained the term Diluvium and the idea of great in-
undations of water. After this recantation, however, the name
was gradually dropped, and the deposits began to be spoken of as
Drift or Northern Drift’; the theory of ice-agency was resus-
citated and finally adopted; for the transporting power of
icebergs had been suggested long previously, and is mentioned
in Conybeare and Phillips’ Geology (1822) as an attempted
though improbable method of accounting for travelled boulders,

Our present knowledge of the Drift deposits has resulted
from a more careful examination of their distribution and
contents than had previously been undertaken ;—according to
Mr Trimmer’ it was Prof. Johnston about the year 1840 who
first called attention to the necessity for maps of the surface
geology, which should exhibit as he says “not only the limits
of the rocky formations, but also the nature and relative ex-
tent of the superficial deposits (Drifts) on which the soils so
often rest and from which they are not unfrequently derived.”

1 By Dr Mitchell for instance in 1838. P.G. 8. 1. p. 3.
2 Quart. Journ. Geol, Soc. Vol, vit. p. 37.

7

Mr Trimmer himself says, “That maps of the surface geology
of these Islands would be of great utility, must be obvious to
everyone who combines agricultural with geological knowledge,
and who is aware of the extent to which our country is covered
by the superficial deposits, whether we call them Drifts, Erratic
Tertiaries, or by any other name.” In consequence of the hint
given by Prof. Johnston, Mr Trimmer was induced to enter
upon the task of mapping the surface geology of Norfolk during
the years 1844—1846. The results of this survey were entered
on the ordnance-map, and the author contributed a paper on
the Distribution of Soils to the Journ. Roy. Agric. Soc. Vol. VL. ;
while the more purely geological details were embodied in a
memoir written for the Geological Survey but never published,
the main generalizations were however given in two papers
communicated to the Geological Society in 1851*. He regards
the distribution of the Drifts or Erratic Tertiaries of Norfolk to
be such as would have resulted from the action of shore-ice on
gradually sinking land, and classifies them under two heads:
(1) Boulder Clay, or Lower Erratics ; (2) Sands and Gravels, or
Upper Erratics ; believing this arrangement to hold good over
the whole of the Eastern Counties. (See Tabular View in
Q. J. G. S. Vol. rx. p. 295. 1853.)

In 1857 (just before his decease) Mr Trimmer became
aware of the existence in the Gorleston cliffs of an Upper and
Lower Boulder Clay separated by a thick mass of sand. In his
former papers he had thought that there was only one Boulder
Clay, for having traced the Upper Clay (characterised by an
abundance of Oolitic detritus) over the south of Norfolk, and
believing the Cromer Till (containing blocks of Scandinavian
origin) to be confined to the north of the ccunty, he had sup-
posed the two clays met on the same level. The sands under-
lying both he referred to the Crag series, but he finally accepted
the results of Mr Gunn’s observations as establishing the fact
that the Upper Boulder Clay overlaps the Lower “with a mass
of sand interposed’”’ In 1864 Mr S. V. Wood junr. read a
paper before the Geological Society “On the Drift of the East
of England and its Divisions.” He demonstrated more fully the

1 Quart. Journ. Geol. Soc. Vol. vu. p. 19 and 38. 2 Ibid, Vol. xiv. p. 171.

8

succession which was hinted at in Mr Trimmer’s last paper, and
indicated the distribution of the several divisions over the whole
of East Anglia; he maintained that the main mass of the
Boulder Clay overlaid the Sands and Gravels which cap the,
cliffs along the Cromer coast, and that these therefore must be
distinct from the Gravels overlying the Boulder Clay in the
centre of Norfolk. Mr Wood however still continued to divide
the series into two groups, an Upper Drift and a Lower Drift,
the latter being again divided into an Upper and Lower series’.
The above-mentioned paper was withdrawn from the Geological
Society and privately published in 1865, when he saw the
desirability of a more simple terminology, and proposed the
following :

1. Upper Drift (= Upper Drift, 1864).
2. Middle Drift (= Upper series of Lower Drift, 1864).
3. Lower Drift (= Lower series of Lower Drift, 1864).

Mr Wood’s more recent views on the Glacial Series are pub-
lished in the preface to his father’s Supplement on the Crag
Mollusca, which includes “An Outline of the Geology of the
Upper Tertiaries of East Anglia:” he here adopts the name of
Glacial beds in preference to that of Drift, and the various
divisions of the series are described in some detail according to
the ascending order given in the following classification.

‘

1. Pebble beds ..

OE SO romier: Ualaeke2:V caer crasesaet: = Lower Glacial.
3. Contorted Drift

4. Sands and Gravels ...............= Middle Glacial.
5. Great chalky Boulder Clay .... = Upper Glacial.
G6. ‘Plateau Gravely occ secessia'es- :

7. Estuarine and Valley ane Seas aw

In 1863 Sir Roderick Murchison,then Director General of the
Geological Survey, decided, “that as the superficial drift deposits
attain a thickness so considerable in many parts of England
that they conceal the solid geological formations,” it would
be desirable to publish special maps of these districts showing
the superficial deposits, and to re-survey certain areas in order

1 Quart. Journ. Geol, Soc. Vol. xx. p. 141, and Ann. Mag. Nat. Hist. 1864,

9

to insert these Drifts and Gravels. This work has been in
progress ever since, and has been completed over most parts of
the South-eastern counties. The only maps yet published,
however, are sheets 1, 2, 7, 48, S.E. and 64 of the Ordnance
Survey and the excellent map of London and its environs.
Two descriptive Memoirs have also been published, one by Mr
Whitaker, entitled “A Guide to the Geology of London,” the
other, on the Fenland, by Mr S. B. J. Skertchly. Memoirs on
the other sheets are likewise in course of preparation.

Having thus indicated the history of opinion regarding the
Post Tertiary beds, I will proceed to the consideration of such
portions of these deposits as are found in the county of Cam-
bridge, and form the subject of this essay.

CHAPTER | LT.
LITERATURE OF THE SUBJECT.

THE occurrence of various drift deposits and superficial gravels
in the county of Cambridge has been noticed by many geolo-
gical writers since the beginning of this century. Some of
these authors have described important local sections, others
have given a general account of the distribution and relations: _
of the several beds, and most of them have discussed at more or
less length the questions connected with their origin and mode
of formation. Before, however, we can hope to ascertain the
complete and correct history of the deposits under consideration,
it is necessary that their distribution and mode of occurrence
should be much more accurately known than they hitherto
have been; it is therefore the object of the present essay to
add more facts to our stock of information on these points, and
to present as complete an account as possible of the accumula-
tions which are met with in the Cambridgeshire district; but
before entering on such detailed descriptions, it will certainly
be desirable to review what has previously been written on the
subject. With this view I have prepared brief abstracts of the
various papers and memoirs treating of the Cambridgeshire
drifts, arranging them in the order of their publication ; in doing
this I have endeavoured to avoid the description of sections
which would be subsequently repeated, mentioning chiefly the
localities described and the conclusions arrived at by the
several authors.

The earliest notice I have been able to discover which refers
specially to the drifts of this county is from the pen of the

11

Rev. Prof. Hailstone, sixth occupant of the Woodwardian chair
at Cambridge; this is entitled—* Outlines of the Geology of
Cambridgeshire,” read before the Geological Society in 1816,
and published in the Trans. Geol. Soc., Vol. 11. p. 243.

Herein he observes that “upon some of the highest hills
near Cambridge a deposit of gravel and loose stones in horizon-
tal layers has been found resting immediately upon the chalk.”
He notices that it contains many pebbles derived from strata
lying to the North and N.W., and remarks upon the difficulty
of conceiving how the more tender fragments can have been
transported without having been entirely destroyed, (the
agency of ice did not apparently suggest itself to his mind).
“The gravel,” he says, “contains numerous fragments of strata
belonging to the Oolitic series, which occur in the neighbouring
counties of Northampton and Rutland..., but the prevailing
material is the pale blue or light grey variety of flint with traces
of alcyonium &c., which is chiefly to be found in Lincolnshire
and Yorkshire, according to my observation.”

From the great difference in character as well as in level
between this gravel and that dispersed over the plain below, he
rightly concludes that they belong to different epochs. The
two localities he mentions for this gravel are the summit of the
Gog Magogs and a hill near Harston about 5 miles 8. W. of the
former; the latter spot was visited by Mr Warburton, whose
observations upon it are given in the paper, together with a
list of the derived rocks and fossils found there.

1818. Ina paper “On the Strata of the Northern Division
of Cambridgeshire,” Zrans. Geol. Soc. Vv. p. 114, Mr Lunn
treats mainly of the Lower Greensand and Gault, but he
evidently confused the Boulder Clay with the latter formation,
since he speaks of it as overlying the ferruginous sand at
Gamlingay, and describes the villages of Hatley, Great and
Little Gransden, and Caxton as situated on the Gault; since
however these all stand on Boulder Clay, we may take his
description as chiefly applying to this formation. He mentions
that in the parish of Long Stow are many beautiful septariz,
together with rounded flints embedded in the clay, and that the
fossil cornu-ammonis is also abundant.

1825. Next we come to the papers previously mentioned

12

as communicated by Prof. Sedgwick to the Annals of Philo-
sophy, Ser. 2, Vols. 1X. and x. (See p. 4.)

In the first of these he takes the fenlands of Cambridgeshire
as a typical example of the alluvial deposits, and briefly de-
scribes some of their physical features, characterising them gene-
rally as exhibiting several levels of distinct fenny regions,
interrupted here and there by extensive protuberances of dilu-
vial gravel.

Under the head of diluvial formations he remarks that “the
true relations of the diluvial detritus are beautifully exemplified
on the flanks of the Chalk Hills which skirt the south-east side
of the marsh-lands above described”’...... “it is constantly seen
to rise out from beneath all the alluvial lands, and sometimes
to lie in scattered masses on the very top of the Chalk Downs.”

The Diluvium he mentions more particularly in the second
communication, where, as we have already seen, he divides the
deposits into two classes; among the Gog-Magog gravels he
speaks of finding rolled masses of granite and porphyry pebbles
resembling those in the New Red Sandstone, masses of trap and
mountain-limestone, and a fine series derived from the Oolitic
formations.

1836. Dr Fitton, in his well-known memoir on the Strata
between the Chalk and the Oxford Oolite, makes some mention
of the Cambridge Drifts at p. 303, of Zrans. Geol. Soc. Ser. 2.
Vol. Iv. He says, “Another general circumstance which charac-
terises the north-east of Cambridgeshire is the great extent and
varied composition of the transported masses with which the
strata are often invested. This superficial deposit imceludes...
rounded pebbles of chalk in such abundance as to form a very
large proportion of the entire mass. With these are certain
fossils...Belemnites and Gryphites, portions of skeletons of
Elephants, Rhinoceros, Hippopotamus, Deer, Gigantic Oxen
and Horse. The mass thus composed forms many of the hills
on the borders of Cambridge and Essex, and occupies a great
part of the platform which runs along the confines of the former
county and Huntingdonshire; a brown variety of it obscures the
junction of Gault and Lower Greensand, W. of Cambridge,
forming an upland which extends from Bourne by Toft and
Hardwick to Dry Drayton, where it declines into the plain.”

13

He notices that these masses of Drift closely resemble those he
had already mentioned in the counties of Bucks and Bedford ;
but it is evident that the older river-gravels containing Mam-
malian remains are here still confounded with the true Diluvial
or Glacial deposits.

1837. In a paper on the Geology of Suffolk by Mr W. B.
Clarke, Geol. Trans. 2nd Ser. Vol. v. p. 365, the Diluvium is
divided imto three classes—(1) Clay, (2) Gravel, (3) Erratic
blocks, Under the head of Diluvial Clay he says, ‘‘This deposi-
tion covers a great portion of the county, and extends into
Norfolk, Cambridgeshire and Essex; a large portion of the clay
is of a yellowish hue, but the greater part is blue.” He describes
its general distribution, and notices that its western extension is
limited by a line drawn through Haverhill and Newmarket ;
The gravel he regards as less generally diffused than the clay,
sometimes lying underneath it, but often mixed up with it; and
he considers the river valleys to have been excavated through
both clay and gravel.

1838. “On the Drift from the Chalk and the Strata below
the Chalk in the counties of Norfolk, Suffolk, Essex, Cambridge,
&c,”—is the title of a paper by Dr J. Mitchell in the Proc. Geol.
Soc. Vol. ll. p. 3; but only an abstract is there given. He
apparently described the Drift deposits, noticing the prevalence
of Boulder Clay, which he says is sometimes overlaid by sand
and gravel, and sometimes contains or rests on such deposits.
_ In Cambridgeshire he mentions Ely and the country between
Caxton and Arrington, noticing the enclosed transported rocks,
and concluding that the materials came from a point East of
North, derived in part from Scandinavia and in part from the
destruction of strata which once occupied the site of the
German Ocean.

1844. A notice of the occurrence of Land and Freshwater
shells with Bones of extinct animals in the Gravel near Cam-
bridge, by Rev. P. B. Brodie, occurs in the Trans. Camb. Phil.
Soc. Vill. p. 138. He describes the section then exposed in the
Barnwell gravel-pit as exhibiting alternating layers of fine white
sand and pebbly gravel, resting upon a thin bed of brown clay,
the whole thickness amounting to about 20 feet. He says,
“The stratum in which most of the shells occur is composed of

14

a thin bed of shelly gravel abounding in many perfect specimens
and comminuted fragments of the same fossils; to this succeeds
an equally thin bed of fine white loam, containing shells far
more perfect but less numerous.” He had reason to think the
sand and the loam contained a somewhat different collection of
molluscs. He gives a list of 18 species.

Prof. Sedgwick adds a note to Mr Brodie’s paper, commenting
on the different kinds of Diluvial deposits near Cambridge ;
these he now groups into three divisions.

(1) The great brown clay, forming the table-land between
Cambridge and Bedfordshire.

(2) The coarse gravel, occupying the crests of the Gog-
Magog and Harston Hills, and containing fragments from most
of the older formations in England.

(3) The fine flint-gravel of the plains, covered by the bog
earth and alluvium.

He mentions bones of Mammoth and Rhinoceros as having
been found in the Brown clay(!), and cites the following mam-
mals as represented by bones from the Barnwell gravel: Mam-
moth (common), Equus (common), Rhinoceros (common), Bos
(very abundant), Hippopotamus teeth (rare), Cervus (several sp.),
Trish Elk (horns of).

1845. At the British Association in 1845 Prof. Sedgwick
read a paper “On the Geology of the neighbourhood of Cam-
bridge’,” wherein he gives some description of the Brown Clay,
noticing its contents, irregular thickness and distribution ; he
believes that 99 parts out of 100 of the whole mass are derived
from the country of the Great Fen Clay (lyimg to the north).
With regard to its origin he says that “Icebergs may during tlie
period (of submergence) have transported boulders to a great
distance and dropped them among the superficial deposits of
the country ; but no conceivable action of icebergs could have
scooped out the great hollow of the Fens and spread the
materials far and wide over all the higher lands on the south-
east side of the Great Level.” He further remarks that in the
neighbourhood of Cambridge there are no old local freshwater
deposits above the Brown Clay, like those found on the coast of
Norfolk. The expectation implied in this remark is accounted

1 Rep. Brit. Assoc. Trans. of sections, p. 44.

15

for by the fact that the Cambridge Boulder Clay and the
Cromer Till were at this time thought to be one and the same
deposit.

1847. An Essay on the “Farming of Cambridgeshire” is to
be found in the Journ. Roy. Agric. Soc. Vol. vu. p. 35, by
S. Jonas Esq. A brief outline of the Geology of the county is
here given, and illustrated by two rough diagrammatic sections,
one from Gamlingay to Madingley, the other from St Ives to
Swaffham. He remarks that the southern and central portion
of the county is light land, consisting of chalk covered in places
with diluvial sands and gravels; but that the eastern part
adjoining Suffolk and Essex has a heavy clay-soil which requires
draining. The western side of the county is also much covered
by a tough tenacious clay-soil, though the lower lands afford a
good deep staple. Lastly he mentions the Isle of Ely and the
Fen lands in the northern part of the county.

1861. Inasupplement to a lecture “On the Strata near
Cambridge and the Fens of the Bedford Level,’ published in
1861, Prof. Sedgwick gives a much fuller account of the Drift
deposits. The evidence for a recent glacial period had then
been more fully developed, and the Professor assumes the sub-
mergence of the British Isles and the transport of Drift by
means of ice-floes and icebergs. For the resulting accumulations
he adopts the name of Diluvial Drift, but still groups with them
the higher and older portions of the Cam Gravels. The term
Boulder Clay is now used instead of Brown Clay, by which
name he had formerly designated it, and he notices that “In all
places, where it is seen near Cambridge, it contains many rolled
fragments of Chalk; and the abraded Chalk is sometimes so
abundant as to give to the Clay a tinge of light grey,” he briefly
indicates the distribution of this Boulder Clay over the Eastern
Counties, referrmg to Mr Barrett’s map (published in 1859) for
its disposition near Cambridge.

He next describes the coarse Gravels found on the Harston,
Stapleford, and Gog-Magog Hills,—he observes that specimens
of many of the great rock formations of England may be
obtained from these deposits, and instances some found by him-
self....“None of the rock specimens,’ he says, “are perfectly
angular. They have been partially rounded, and a few of

16

them are grooved and scratched, but with much irregularity.
The grooved specimens do not generally look like rocks that
had been grooved by the glaciers of an alpine valley; but
rather like rocks which, having been mechanically acted on by
the drifting ice of a glacial shore, had then been borne away on
ice-rafts, and stranded on the hills where we now find them. No
shells, or other organic remains, have been found in these
deposits of coarse Gravel.”

I have quoted the above passage in full, in consequence of
the accurate observations and acute deductions it contains,
which partially anticipate the conclusions arrived at in a sub-
sequent part of this essay. Prof. Sedgwick proceeds to notice
the flint-gravel covering the plains bordering on the Cam, and
he still refers the formation of these gravels to the “long con-
tinued action of the waters of the sea, as it was gradually
falling to its present level, near the end of the glacial period,”
although he observes that the stones are more angular and less
waterworn than in most marine gravels. As regards the rela-
tive ages of these deposits, he knew of no evidence to show
whether the Boulder Clay is older or younger than the coarse
Gravel. But he mentions the fact of flint Gravel overlying the
Boulder Clay near Ely, and also on the St Neots road, a few
miles from Cambridge.

Lastly, the marine Gravels at March are referred to, and the
indications of their dipping under the Boulder Clay are spoken
of as doubtful. The large clay-pit near Ely, called Roslyn or
Rosswell Hole, is referred to at p. 28 of Prof. Sedgwick’s paper
just mentioned, and a diagrammatic section is given of the beds
therein exposed.

1864—5. This pit is the subject of subsequent papers by
Mr Seeley, entitled “On a Section of the Lower Chalk at Ely,”
Geol. Mag. 1. p. 150, and “On a section discovering the Creta-
ceous beds at Ely,’ Geol. Mag. 11. p. 529. In the former
Mr Seeley gives a description of the appearance which the beds
presented before the year 1862, and adopts the explanation of
their relative position which had previously been suggested by
Prof. Sedgwick, viz. that Chalk and Boulder Clay had been
faulted down together against the Kimmeridge Clay. In the
latter he gives a sketch of the section as seen in 1865, and he

Ly

describes the Boulder Clay as extending from top to bottom of
the pit, and being full of all sorts of rocks; “at one place,” he
says, “the upper part is devoid of pebbles or boulders, and at the
north end there are rough courses of nodules making a kind of
curved stratification...The Clay is capped by about 15 ft. of
Gravel, in part interstratified with it.”

In 1865 Mr Searles V. Wood, Junr. published a map of the
Upper Tertiaries in the Counties of Norfolk, Suffolk, Essex,
Middlesex, Hertford and Cambridge, with remarks and sections
(privately printed). In this he establishes the divisions of the
Upper, Middle and Lower Drift, describing their general posi-
tion and the relation of the latter to the underlying crag. He
looks upon the Cromer Till as a Marine Drift but considers its
inland chalky representative to have resulted from the action of
local glaciers ; the Middle Drift he speaks of as a marine though
littoral formation, accumulated in channels and straits between
islands which he believes to have been submerged at the
incidence of the Upper Drift or true Boulder Clay; this, he says,
“bears evidence of being the deposit of an open sea burdened
with floe-ice, drifting from shores of Cretaceous and Jurassic
strata.” At p. 13, he remarks upon the position of the Upper
Drift near Sandy and Gamlingay and states that it is here
bedded round the Lower Cretaceous sand “which rises like an
island from its midst.” His explanation of this is not very
clear, but if I understand him rightly he believes it to have been
an island in the sea of the Middle Drift, and that the Boulder’
Clay was dropped first round it and then on it as the area sank
beneath the waters of the Upper Drift sea; and that subsequent
denudation has removed nearly all the Boulder Clay from the
top of the sands. The map, of which these remarks are in
explanation, purports to show the distribution of the Crags and
of the three divisions of the Drift in the counties mentioned ;
among the sections are several through parts of Bedford, Cam-
bridge and Huntingdon, illustrating the relation of the Boulder
Clay to the Middle Drift and Neocomian Sands.

1866. Ina paper on the Warp and Trail’, the Rev. O. Fisher
illustrates his views by a section in an old gravelpit, Victoria
Road, Cambridge; the succession here seen was as follows :—

1 Quart. Journ. Geol. Soc. xx. p. 561,
2

a

18

a. Warp (of Mr Trimmer) forming pockets or channels.

b. White sandy brick-earth (much contorted).

c. Yellowish sandy earth.

d. Fine sandy gravel.

e. Yellowish brick-earth.

f. Fine gravel, more contorted than the contiguous layers.

g. Sand.

The sands contain Bithinia, Xe.

The irregularities observable between a and b, which Mr Fisher
describes as similar to the tenons in the framework of a dis-
sected puzzle, are considered to be the sections of channels of
drainage. In the Cambridge gravel pits, he says, “the percola-
tion and consequent erosion seem to have taken place in the
layer beneath the ductile Clay, which is folded into such
remarkable forms.”

He remarks with truth that these contortions must in some
way or other have resulted from sub-acrial causes and cannot
be due to any kind of ice-action.

1866. In “A Sketch of the Gravels and Drift of Fenland’,”
Mr Seeley describes the Drifts in this part of Cambridgeshire.
Following Prof. Sedgwick’s triple Classification and commencing
with the Boulder Clay, he notices its colour, thickness, contents
and extent over the high ground immediately West and N.W.
of Cambridge. He gives a section of the Fossiliferous Gravel
at March, from which this marine deposit would appear to be

-intercalated between two sheets of Boulder Clay. “Tracing
this Gravel south to Wimblingdon, near the railway station, the
deposit, quite at the surface and only a foot or two thick, rests
on one of the thin stonebands so common between the Oxford
and Kimmeridge Clays. It is a fine sandy gravel with the
usual shells; but the argillaceous limestone rock was drilled
with the burrows of Pholades, the shells being still in the holes.”

He proceeds to say that the gravels are somewhat con-
tinuously spread southwards by Chatteris, Somersham, Earith,
St Ives and Willingham to Swavesey, and that he had found
marine shells in gravel taken from old pits near Drayton Gate
House. From the gravel at March he cites 20 species of
Mollusca.

1 Quart. Journ. Geol. Soc, Vol. xx. p. 470.

19

The fine flint-gravel in the vicinity of Cambridge is next
treated of, and its extent to the North and East of that town
briefly noticed ; Mr Seeley records the occurrence of shells at
the Observatory, at Barnwell, Chesterton and Oakington, and
teeth of Rhinoceros tichorhinus from a patch near Comberton.
He minutely describes the character and contents of the Barnwell
Gravel, giving a list of the Mammalian remains and of the Land
and Freshwater shells.

Lastly he refers to the Coarse Gravel on the Gog-Magog
Hills, from which he had collected boulders of the Palaeozoic
rocks of North England, fragments of the Yorkshire Oolites
and of the Red-rock of Hunstanton; he remarks that the
flints are often unbroken and that there is a rough stratification ;
he states also that descending on the east side towards Fulbourn
“it becomes Boulder Clay,’ by which expression Mr Seeley
probably intends to refer to a stiff sandy loam, like re-arranged
Boulder Clay, now seen to overlie part of the gravel on this
side. The remainder of the paper is occupied with theoretical
considerations, which only appear in abstract.

These were subsequently printed in the Geol. Mag. Vol. 11.
p. 495, under the title of “Theoretical Remarks on the Gravel
and Drifts of the Fenlands.” These only demand a brief notice,
as some of his conclusions have already been shown to be
without foundation, and others are disproved by the observa-
tions recorded in future portions of this Essay.

(1) In the Boulder Clay of Ely, he states that he has found
old and thick specimens of Tellina like those in the Lower
Boulder Clay of Norfolk ; from this and the [supposed] fact that
it rests on beds which have since been removed by denudation
from the country, he concludes that it is the oldest Drift in the
Cambridge district, and correlates it with the Brown Clay or
Till of Cromer.

(2) Coarse Gravel; he mentions three cases of such gravel
overlying Boulder Clay, viz. in the Ely pit; on the Hogs-back
going to St Neots, and on the Gog-Magogs. His observations
on these coarse gravels agree in the main with my own, and
his facts quite warrant him in concluding that their materials
were derived from the destruction of the glacial Clay, which
was at that time more widely spread. In his own words: “They

9.9

iA

20

seem to be masses of re-constructed Boulder Clay, washed of its
mud and converted into gravel.’ When however he ventures
to correlate both the Hill-Gravels and the blue Boulder Clay
with the contorted Drift, he is in entire opposition to the facts
and conclusions, published by Mr 8. V. Wood, Junr., in the
previous year.

(3) Concerning the so-called “Fine Gravel of the plains,”
Mr Seeley imagines that the physical geography of the district
demonstrates all these beds to have been of marine or estuarine
origin, and comes to the extraordinary conclusion that they
correspond to the Upper Boulder Clay and coarse Gravel of
Norfolk. At Overton and Whittlesea he says they contain land
and estuarine shells; at Mareh, marine; at Doddington and
Drayton, marine; while the Barnwell stratum he would refer to
an intercalated freshwater band.

I shall have oceasion to show in the sequel that several
different series of gravels have here been confounded and treated
together under the name of “fine gravel of the plains.”

1867. A detailed paper on the Post-glacial structure of the
South-East of England by Mr 8. V. Wood, Junr. appeared in the
Quart. Journ. Geol. Soc. Vol. Xxui1. p. 394,

In this he argues that “the entire valley system of the East
of England originated in centres of arc-lke or curvilinear disturb-
ance, which immediately preceded the elevation of the bed of
the sea from which was deposited the wide-spread deposit of
Boulder Clay forming the latest ef the Glacial beds of the South
of England.”

He illustrates this opinion by sections through some of
these post-glacial upheavals, one of which is across the Cam
valley from Eversden on the N. to the Chalk Hills above
Royston on the S. and shows the Boulder Clay overlapping the
Mid Drift towards the N.W. He does not seem to see however
that the disposition of the Drifts in the three sections on p. 402
is just as easily explained by the supposition of the pre-glacial
existence of the chalk escarpment, as by its subsequent post-
glacial upheaval. The facts cellected for this essay have led me
to take the former view, and I cannot but think that the
whole theory of curvilinear elevations rests upon a very slight
foundation of evidence.

21

1868. The Roslyn or Rosswell Hill Clay-pit is the subject
of a communication from the Rev. O. Fisher, Camb. Phil. Soc.
and Geol. Mag. Vol. v. p. 407, in which he dissents from
Mr Seeley’s mode of accounting for the presence of the Creta-
ceous beds, and considers them to form a Boulder-like mass in
the Glacial Clay, similar to those in the cliffs near Cromer. He
gives a ground plan of the pit and notices that at the western
end, the chalk thins out and the Boulder Clay passes beneath
it. He believes the hollow to be a trough ploughed out of the
Kimmeridge Clay and the mass now occupying it to have been
dropped by an iceberg. The slickenside surfaces “only occur in
recent slips of the Boulder Clay and not along the junction
between the two clays;” he therefore concludes that the evidence
in the pit is against any theory of faulting, though he acutely
observes that if the country were mapped and a fault affecting
other strata traced through the pit this would settle the ques-
tion in its favour. In the same volume of the Geological
Magazine these views of Mr Fisher are criticised by Mr Seeley
and the “Boulder hypothesis” is scornfully rejected. Mr Seeley
conceives the facts to prove (1) that there is a sequence from
Chalk to Kimmeridge Clay, (2) that the sands under the Gault
may be connected with those outside, above the pit, (3) that
indubitable slickenside occurred in the junction between the
Boulder Clay and the Cretaceous beds figured in Geol. Mag. U.
p. 532. He adheres to his previous statements and conclusions
regarding the faulting of the strata.

1871. In a paper “On Phenomena connected with Denuda-
tion, observed in the Coprolite pits near Haslingfield’,’ Mr
Fisher describes the sections then observable; in these the
upper portion exhibited a variable thickness of soil containing
land shells, to which he gives Mr Trimmer’s name of “ Warp.”

Below this is found the disturbed soil which Mr Fisher has
elsewhere denominated by the name of “Trail” (see Q. J. GS.
Vol. xxir. p. 553): this he describes as sometimes little else
than disturbed clunch with occasional pebbles and boulders,
but at other times containing patches of clayey gravel and
sand. In accounting for the presence of this “Trail,” he rejects
as inapplicable the agency of rivers, admits that it may possibly

1 Geological Magazine, Vol. vii. p. 65.

22

be due to rainwash, but finds some difficulties in the way of
this explanation. Amongst these he adduces two instances of
lateral thrust, causing a reduplication of the coprolite bed, one
of which he accounts for by supposing the upper bed to be a
travelled mass in the trail. Finally from these and other con-
siderations he concludes that the irregularities in the surface
of the Gault near its outcrop are probably due to the action
of land ice, and that the gravelly “trail” above is the remnant
of the moraine profonde which was pushed forward beneath it.

1872. “An Outline of the Geology of the Upper Tertiaries
of East Anglia,” by Messrs 8. V. Wood Junr. and F. W. Harmer,
appeared as a preface to the volume issued as a supplement
to Mr S. Wood’s Monograph on the Crag Mollusca (Pal. Soc.).
The final classification of the Glacial series proposed herein has
already been given in the introductory chapter. No special
mention is made of these beds in Cambridgeshire, but among
the Post-glacial deposits the March Gravel receives some notice.
This is said to occur in the midst of the Cambridgeshire fens
and to form small islands rising out of the great level, “so that
there are no means of geologically testing its position’,”

The fauna they find to be rich in Mollusca and to resemble
that of Kelsea and Hunstanton in consisting entirely of recent
species, which with two exceptions are now living in British seas;
Ostrea edulis is abundant at all three localities, and they think
there can be little doubt that the beds belong to the earlier or
Cyrena fluminalis part of the Post-glacial period.

In 1872 Rev. T. G. Bonney published some “Notes on the
Ely Clay-pit®,” and these are reprinted in the form of an ap-
pendix to his “ Cambridgeshire Geology ” (1875).

After referring to the previous papers on the subject, he
states his adoption of Mr Fisher’s view, in opposition to that of
Mr Seeley, and minutely describes the disposition of the strata
as seen between the years 1868 and 1872. Four sections are
drawn across the pit and a ground plan is also given; by this
means he shows that, if the “fault hypothesis” be assumed,
no less than four faults are necessary to bring the beds into

1 From this remark it is evident that Mr Wood does not believe in the sup-
posed intercalation of the gravels between two Boulder Clays at March,
2 Geological Magazine, Vol. 1x. p. 403.

23

the positions they now occupy, viz. two simple downthrow
faults and two reversed upthrow faults, both hading in differ-
ent directions from each other! and yet the Kimmeridge Clay
on each side the pit is undisturbed and nearly horizontal.
He naturally concludes that so extraordinary an arrangement
renders the fault theory in the highest degree improbable ; and
there remain only two possible hypotheses, viz. either there
has been a land-slip from a Chalk cliff overhanging a valley in
the Kimmeridge Clay, and the Chalk once on Roslyn Hill has
since been denuded away, or, the mass is an included Boulder,
and has been brought to its present position onan ice-raft. He
points out that Mr Seeley’s section at the south end of the pit
(G. M. v. p. 348) is certainly wrong, that the Brown Sand
which with superjacent Gault is there shown between the
Kimmeridge Clay and Boulder Clay, is not in situ, but consists
only of numerous blocks of Neocomian Sandstone included in
the latter Clay. Mr Bonney says, “I can only explain the mode
in which these blocks occur by supposing that, before and
during the accumulation of the Boulder Clay there was, nearly
along the line of the south side of the pit, a cliff or bank of
Kimmeridge Clay, capped by Neocomian Rock, from which
fragments slipped and fell.”

He does not think however that any such slip will explain
the position of the Gault and Chalk; he fails to see any
conformity between the Gault and Neocomian Sands in any
part of the pit, and considering that the Gault (with presumably
the Chalk and Greensand) rests now on Boulder Clay, now on
Kimmeridge Clay, and now on disturbed Neocomian Sand, he
concludes that the idea of these Cretaceous beds being a huge
fragment or transported mass in the Boulder Clay is more
in accordance with the observed facts, and that it presents far
less difficulty than either of the other theories. He only
differs from Mr Fisher in thinking that the valley existed
before the Boulder was dropped.

“1875. In his “Cambridgeshire Geology,’ Mr Bonney
describes the Post-pliocene deposits at p. 49 and quotes largely
from Mr Seeley’s papers on the subject, which have been already
reviewed.

Under the head of Boulder Clay Mr Bonney refers to a fresh

24

section in the coprolite pits near Whitwell, and mentions most
of the kinds of rock-fragments found in the Boulder Clay and
Hill Gravels, especially noting the occurrence of nodules from
the Cambridge Greensand. He is inclined to think the Barn-
well Gravel older than that of Chesterton, and notices the
extent of the former towards the Railway Station. The account
of the Barnwell Gravel pit is mainly quoted from that of
Mr Seeley, some information about the evidences of Paleolithic
man being added.

Finally he notices the absence of the Lower and Mid-glacial
series in Cambridgeshire, and correctly states the relative age of
the Blue Boulder Clay, Hill Gravels and River Gravels.

1876. In December 1875 Mr W. H. Penning read some
“Notes on the Physical Geology of East Anglia during the
Glacial Period,” which were published in the Quart. Journ. Geol.
Soc. Vol. Xxx1I. p. 191. Mr Penning gives an explanation of
the behaviour of the Middle Glacial beds which he had been led
to adopt after personally surveying large parts of Cambridge,
Suffolk and Essex. He observes, as Mr Searles Wood had
done, that these Gravels and Sands are overlapped by the Upper
Boulder Clay which caps the Chalk escarpment and then
plunges down into the Cambridge valley. He regards this
valley as of pre-glacial origin, and as having formed a land-
locked inlet during the period of Middle Drift, whence gravel-
bearing currents were consequently excluded.

He mentions three kinds of gravels as occurring within the
brow of the escarpment: (1) Recent valley gravels, (2) Some
patches of doubtful age but at high level, (3) An elongated
series of gravels and loams ata height of 20 to 60 feet above
the present river Cam, and in some parts distant from its
present course; as these contain here and there recent land
shells, he concludes that they indicate an ancient course of the
Cam. His general conclusions may be stated as follows :

(1) That we have evidence of but one glacial submergence
followed by a corresponding movement of elevation.

(2) That there are no Middle Glacial deposits whatever
within the area of the Cam valley.

(3) That the surface of the Boulder Clay was eroded and
covered by gravel on emergence.

25

In the supplementary notes further details are given of the
Post-glacial Gravels, the higher series having been found to
run down the escarpment and to overlie the Boulder Clay at
several points. He is inclined to consider all of them as having
resulted from the action of rivers on the newly emerged land,
but the series described as indicating the ancient course of the
Cam he regards as representing the latest stage of all, previous
to the present system of drainage. He points out that in many
cases the gravels occupy hollows along the top of ridges, the
gravel deposited in the old channel having preserved the clay or
chalk immediately beneath, and that many of these ridges run
up into coomb-like valleys among the hills.

[1877. A Memoir on the Geology of the Fenland, by Mr
S. B. J. Skertchly, was published in this year by the Geological
Survey ; the greater part of this book is occupied by an account
of the newer Post-glacial beds, but the Gravels and the Boulder
Clay are also described.

Mr Skertchly classes the Fenland Gravels under three heads:
(1) Ancient Valley Gravels. (2) Marine Gravels, forming beaches.
(3) “ Flood-Gravels,” which run down from the hills into the
Beach-Gravels. In describing these deposits, however, he treats
them geographically, and not according to their age or mode of
formation. In Cambridgeshire he notices the Fossiliferous
Gravels occurring near Peterborough, Whittlesey and March,
and gives a list of the shells which they contain.

The sections described under the head of Boulder Clay are
mostly in Lincolnshire, but a full account is given of the well-
known pit near Ely, which will be referred to again in the
sequel. |

CHAPTER. III.

GENERAL PHYSICAL FEATURES OF THE COUNTY AND
DESCRIPTION OF THE GLACIAL DEPOSITS.

CAMBRIDGESHIRE is divisible into four natural regions or
districts, which are separated by the valleys of the principal
rivers that traverse the county; each district having a different
geological structure and consequently presenting different physi-
cal features.

The first of these regions is that comprised between the two
tributary streams of the river Cam, called respectively the Rhee
and the Bourn or Linton river, the one taking its rise in Hert-
fordshire and the other in Essex ; such portions of these counties
therefore as form part of the same valley system are included in
the area hereafter described. Through the centre of this district
runs the river which may be considered the main stream of the
Cam'; it rises near Quendon in Essex, and running due North
by Newport, Wenden, Littlebury, Chesterford, Hinxton, Duxford
and Whittlesford, is jomed by the Linton brook at Shelford,
whence the united streams flow to meet the Rhee about a mile
below Hauxton Bridge,

The second region lies to the N.E. of the Linton stream and
to the S.E. of the Cam or Granta as the river used to be called
below its junction with the Rhee; it includes the high ground
formed by the Gog-Magog and Balsham Hills and the hilly

1] think this branch has stronger claims to be taken as the main stream
than that which is called the Rhee, for it has more important towns on its banks,
its course is rather longer, and I believe the valley in which it flows to be much
older than that of the Rhee.

27

country near Newmarket, whence the land slopes northward
and north-westward down to the broad level of the South Fens.
The river Lark and the hills between Newmarket and Bury
may be considered as forming the north-east boundary of this
district.

The valleys of the Rhee and Granta run almost directly
parallel to the strike of the Chalk escarpment, following indeed
very closely the main outcrop of the Chalk Marl; so that roughly
speaking we may say that Chalk forms the foundation of all the
south-eastern portion of the county above described, and is only
covered by drift deposits where it rises into high ground in the
extreme South and East.

The third district comprises the south-western part of
Cambridgeshire, with the adjacent portions of Bedfordshire and
Huntingdon, between the valleys of the Rhee and Granta on the
one hand and those of the Ivel and Ouse on the other; the
intermediate high ground constitutes a kind of table-land, and
the whole district is a country of clays, the Cretaceous and
Jurassic Clays are only separated by a thin strip of Neocomian
Sand, while covering all and concealing them from sight over a
considerable area lies a thick sheet of stiff Boulder Clay; this
latter sends out long spurs to the North and East, such as those
of Haslingfield, Madingley and Drayton, from which excellent
views are obtained over the broad and low lying valley of the
Cam. Northward the country slopes down through Histon,
Oakington, Long Stanton, Rampton and Cottenham to the fens
bordering the old west branch of the Ouse which receives
the waters of the Cam near Thetford, about three miles south
of Ely.

The old course of the river Ouse therefore separates the
above mentioned southern districts from the rest of the county
on the North, and the Cambridgeshire Fenland thus forms the
fourth and last of the natural regions into which the county may
be divided. This great plain of the fens is interrupted only bya
few low islands which rise from amidst its wide expanse, and by
the somewhat bolder outlines of the old Isle of Ely, which
forms an irregular patch of elevated ground from Haddenham
and Sutton through Stretham and Witchford to Ely and thence
in a northerly spur to Chetisham and Downham.

28

The formation underlying the greater portion of the fen-
country is the Oxford Clay; the Isle of Ely is formed of Kim-
meridge Clay capped by outliers of Lower Greensand and
Boulder Clay ; and the other low islands are caused by banks of
the older estuarine Gravels.

Having thus given an outline of the general physical and
geological features of the country, I will proceed to describe in
greater detail the Post-tertiary or Pleistocene deposits, treating
first of the Glacial beds exhibited in each of the above named
districts, and secondly considermg the Post-glacial Gravels
which for the most part oecupy the intermediate valleys and low
grounds,

Tue GLACIAL BEDs.

§a. The Southern District. This area presents an undu-
lating surface of Lower Chalk covered here and there by a
patch of Boulder Clay or early River-Gravel. It is bounded on
the south and south-west by the escarpment of the Upper
Chalk, which extends from Hitchin and Baldock by the hills
south of Royston to Saffron Walden and Linton, and is capped
with the Drift deposits which extend thence south-westward
over Essex.

The boundary of the Upper Boulder Clay may be traced
along the summit of the hills by Tharfield, Newsells Bury,
Chishall, Heydon, Elmdon, stretching out in a spur to Strethall
and Littlebury Green, but trending south-westwards from
Christhall and Rockell’s Farm to Arkesden and Wenden.

There are two remarkable points about the lie of this clay:
first that it everywhere rests directly on the chalk, without the
intervention of sand or gravel; secondly that it not only runs up
to the very crown and brow of the hills above mentioned (about
500 feet high), but it appears to have also run down the northern
slope of the scarp, and outlying patches occur at lower levels
beyond the limits just indicated. Near Newsells Bury, for
instance, a tongue runs down into the valley; near Royston there
are one or two small outliers that must be at least 150 feet lower
than the top of the scarp; a larger outlier caps the high ground

29

between Duxford Grange and Ickleton, which is not more than
200 feet above sea-level, while the scarp two miles to the south-
ward must be nearly 450 feet high. The spur which runs east-
-ward by Littlebury Green descends considerably towards the
valley of the Cam, and farther south the Boulder Clay runs
down quite into the valley by Wenden and Newport. It is thus
shown that the chalk escarpment and the Cam valley were
both in existence before the deposition of the Upper Glacial
Clay.

The river Cam, rising among the drift-covered slopes
between Quendon and Thaxted, runs at first south-westward,
but turning northward by the former village, has cut for itself a
valley of some depth through the hills by Newport and Wenden;
in this valley several good sections of the Glacial beds may
be seen.

Gravel and Sand underlying Boulder Clay and consequently
taken to be Middle Drift, may be seen in a pit just South of
London Wood opposite Quendon, and that village itself is pro-
bably built upon deposits of the same age.

A section about three quarters of a mile E. of Newport
showed 16 feet of gravel and sand overlaid by 18 feet of Boulder
Clay, the latter rolling over the gravel towards the valley.

At Wicken Bonnett, 1} miles W. of Newport and situated
in a tributary valley, there is a large pit near the Church; this
exhibits about 30 feet of coarse gravel with occasional inter-
bedded seams of fine sand and loam, The gravel is almost
entirely composed of flints, mostly unworn, some of them
being large nodular lumps as perfect as those in a chalk pit,
only stained brown with iron; large lumps of Hertfordshire con-
glomerate also appeared to be common, and the material would
seem to have been almost entirely derived from the destruction
of Chalk and Tertiaries. The hill above is capped with Boulder
Clay which rests on chalk both eastward and westward of the
village, so that the gravel is only a lenticular mass at the bottom
of the clay, and exposed in the valley.

The gravels which flank the river near Newport and Wenden
are probably river deposits, though being to a large extent
derived from the Glacial Gravels, they greatly simulate them in
appearance: there is nothing in this neighbourhood which can

30

be considered as unquestionable Middle Drift ; in many places
the Boulder Clay can be proved to rest directly upon the Chalk,
though there are occasionally patches of gravel and sand at or
near its base.

At Audley End Station, the railway cutting on the North
side of the bridge exhibits a succession of clays and loams lying
in a hollow scooped out of the chalk and all inclined to the 8. at
an angle of about 25°, The lowest is a grey Boulder Clay full of
chalk stones, and contains a thin inter-bedded band of loam ;
next succeeds a yellow laminated loam, and then the section
becomes obscure, but there are traces of more Boulder Clay, while
at the bridge yellowish brown loam is shown on one side the
cutting, and gravel on the other.

Eastward of the station, and barely a mile distant, a good
section has been exposed in the railway-cutting on the Saffron
Walden branch; this exhibits an outlying mass of Drift, lying
within the general depression of the valley and occupying a
hollow in the side of the chalk slope against which the more
recent valley beds rest at a lower level. Below the bridge over
this cutting the following section is shown:

1. Boulder Clay, capping the hill............... about 14 feet.
2. False-bedded sands and loams with a 10
hard calcareous band at the bottom } 7 aes
3. Boulder Clay, similar to that above........ 35° One
4. Chalk rising rapidly to the east............. spon Shem

The calcareous band is about six inches thick near the
bridge, and the loamy sand above 1s also similarly hardened ;
this infiltration has probably resulted from the presence of
the impervious Boulder Clay below, which has stopped the
passage of the downward percolating water and allowed the cal-
careous material in solution to be deposited. Beyond the bridge
the sand and loam are seen to thin out wedge-wise between the
two similar Boulder Clays, they can hardly therefore be called
Middle Drift, and the whole series, as also that at Audley End,
probably belongs to the Upper Glacial beds of Mr Searles
Wood, They appear to increase in thickness towards the
valley, and at the west end of the cutting the sands pass by
contorted and laminated loams into the Boulder Clay above ; but

31

this portion of the section is now rendered obscure by the over-
growth of vegetation,

From the hills north of Saffron Walden the irregular boun-
dary of the Upper Boulder Clay is traceable through Great
Chesterford Common and Park, round by Abington Park and
Hildersham Wood to Hadstock ; it then runs down northward
and skirts the 8.W. side of the valley by Linton and Bartlow.
This valley here divides into two branches, and the tributary
brooks occupying these have cut back the Boulder Clay as far
as Ashdon Street and Castle Camps respectively; from this
point the boundary turns finally northward, and may be followed
over the country a little west of Shudy Camps and Horseheath,

Throughout all this country the Boulder Clay almost always
rests directly upon the Chalk, and it is only in one or two
localities that any intermediate gravels have been found. One
of these is near Littlebury, where the road-cutting just above
the words North End on the Ordnance Map appears to show an
upper and a lower clay with an intercalated patch of gravel.

No more such gravel is seen till we reach the slopes above
Linton, where it appears to underlie the Boulder Clay rather
more extensively, and may be seen in several pits about
Hadstock, In the railway-cutting near Newnham Hall Mr W. H,
Penning informs me that a lenticular patch of gravel and loam
occurs in the mass of the Boulder Clay, near a knob of Chalk
which rises up from beneath, (See Geological Survey Memoir
on Sheet 47.) At Ashdon a small pit near the Church exhibits
a few feet of rough chalky gravel, but its relation to the Boulder
Clay is not seen,

§ 6. Eastern District. Eastward of Ashdon the Boulder
Clay appears to stretch uninterruptedly through Castle Camps
and Shudy Camps to Helion Bumpstead and the neighbourhood
of Haverhill. This high ground forms the watershed between the
valley systems of the Cam on the one hand and the Stour on the
other; hence the small brooks and streams which form the
tributaries of these two rivers run off the Boulder Clay slopes
northward, eastward and westward, The lower formations are
entirely veiled by the clay, nor is anything else seen till the
vicinity of Haverhill is reached; where several sections show
gravelly beds underlying the clay. One of these occurs about

32

24 miles S.S.E. of the Church in a pit of some size disclosing
the following series:

Boulder ‘Clay. s.dspssegdaiess- Seabee eo ht. eae ee 10 feet.
Lenticular, patchraf brown sand! Woa03. 2 i<si20 Gey ade tee Ogg
Grey and variegated loam (with flint pebbles) probably

due to the reconstruction of Reading Beds ............ © sy

In a gravel pit half a mile 8.W. of Haverhill the thin edge
of the Boulder Clay is seen overlying six feet of coarse gravel with
large boulders, being in fact part of a boss of gravel which here
protrudes through the surrounding Boulder Clay.

North-west of Haverhill there is gravel and sand in the
valley, but these are probably river deposits, as the clay is found
to come close down to the stream in many places.

Following the line of railway, Boulder Clay is seen near
Withersfield Station, and the long cutting near Horseheath
Green exposes about forty-five feet of grey clay enclosing some
large boulders of Chalk and other rocks, A well made here by
the contractors showed its total thickness to be 120 feet. This
clay covers all the country northward round MHorseheath,
Withersfield and West Wickham, but the highest hills of this
district are not more than 340 to 360 feet high. The boundary
of the clay is continued from the point where we left it, near
Horseheath along the S.E. flank of the open valley, which here
runs up into the hills and m which the Chalk is exposed for a
considerable distance. Crossing this hollow however and ascend-
ing the high ground upon which Balsham Wood is situate, we
again find Boulder Clay covering the surface, and extending as
an irregular patch in every direction round the village of
Balsham, which thus occupies a central position at a height of
about 370 feet above the sea.

Walking southwards we find the high ground covered by
Boulder Clay through Yole Farm, Borley Wood and Short
Wood; here it would appear to be rather thin, but Barrington
Hill on the West again brings in a great thickness of it, and
thence it runs westward down the slope towards Hildersham,
where its level must be at least 200 feet lower than that of the
Balsham and Barrington Hills; before the deposition of the

33

Glacial Clay therefore this part of the Chalk scarp existed in
nearly its present position,

At Barrington Hill a thin bed of intercalated loam appears
in the road-cutting about three-parts of the way up from the
Linton side. Another remarkable feature of this hill is that its
summit is capped with a patch of later gravel, which forms one
of a series of outliers extending along the spur of hilly ground
to the N.W., toward the Gog-Magog Hills. These deposits how-
ever, inasmuch as they are superior to the Upper Glacial beds,
T will leave for future consideration, __

Returning now to our central position at Balsham, we find
there are smaller spurs and outliers of Boulder Clay westward
and northward of that place. One of these caps the hills near
Gunners Hall, and a smaller patch within the brow of the long
valley to the east is covered by later gravels and loams.

A long spur runs out across Balsham Ditch to the Trigono-
metrical Station near Congers Well, the height given here
being 346 feet. Returning along the northern edge of this
spur, which is bounded by a long, deep, and dry valley running
northwards from the hill slopes between Balsham and West
Wratting, we find the Boulder Clay traceable through the latter
village and thence skirting the high ground by Weston Colville,
Brinkley and Westley Waterless. At all these places it rests
directly upon the Chalk without any intervention of gravels,
sands or loams. From Westley Waterless it appears to trend
eastward, south of Dullingham, Stetchworth, Wood Ditton and
Saxon Street, and the level of its boundary seems to be at the
same time declining northwards, as indeed it has been along the
whole line we have been following. I have not been able to
obtain much information about this part of the county, but
Boulder Clay occurs again on Warren Hill east of Newmarket,
and may be seen ina large pit near the road, where about 20 feet
of buff-coloured chalky clay is exposed. It does not cap the top
of the hill, which is 267 feet high, and where the bare chalk is
covered only by about four feet of sandy soil, so that the clay
would not appear to rise above 250 feet. From this point we
look northward over the lower plateau between Icklingham and

Brandon, where the Boulder Clay sinks under newer gravels and
sands,

os

34

Sc. Western District. The greater portion of the third
district, lying to the west of the Cam Valley, is likewise over-
spread with a broad and often thick coverimg of Boulder Clay,
which has filled up the pre-existing hollows and now forms an
elevated plateau or upland; there is however hardly any gravel
either above or below this clay, and there are few sections that
merit description. I will therefore simply poimt out the limits
and the ‘behaviour’ of the Glacial Clay.

The hills above Haslingfield, Harlton and Orwell are capped
with it everywhere above a height of 200 or 220 feet, but as
they nowhere rise above 250 feet, a long narrow ridge of Boulder
Clay is the result, probably not more than 30 feet thick at any
spot; it stretches from Haslingfield chalk-pit to Orwell may-
pole, and thence to Cobb’s Pound and Eversden Wood, a dis-
tance of four miles, and may be seen in many of the quarries
between the above places; it is shown to be a stiff grey clay,
full of chalk fragments, but only containing a sprinkling of other
rocks, such as Red Chalk, quartzites, and nodules from the
Cambridge Greensand.

It spreads out westward and descends to a lower level,
closely following the outcrop of the chalk about Wimpole and
Arrington ; indeed the position of this outcrop and the general
features of the country have clearly been determined by the
presence of the Boulder Clay, and its power of resisting denuda-
tion has no doubt been the means of preserving this outlying
area of chalk marl, with the underlying coprolite bed, from the
destruction to which they must otherwise have been exposed.

Its former extension 1s indicated by the occurrence of stones
and boulders over the fields far beyond its present limit; a very
large boulder stands in Lord Hardwicke’s grounds at Wimpole.

From Arrington the Boulder Clay continues to cap the high
ground bounding the north side of the Rhee Valley by Croydon
to Tadlow and Wrestlingworth, overlapping the Chalk Marl on
to the Gault; its boundary passes eastward of Sutton and Potton,
to the neighbourhood of Gamlingay. There is a small outlier
capping Sutton Hill, and another on the hill just 8. of Potton
Church. From Gamlingay Wood the boundary is continued by
Waresley and Gransden to Eltisley and Croxton, the numerous
little streams which flow off the neighbouring high ground having

35 +

cut back its edge into a deeply indented line, and the whole of
the valley from Little Gransden by Abbotsley to St Neots
having evidently been excavated through the Drift by similar
fluviatile action.

The Boulder Clay continues to cap the hills bounding the
north side of this valley until this opens out into the main
valley by St Neots.

These drift-covered hills stretch northward into Huntingdon-
shire, but on the eastward slopes the action of rain and streams
has cut back the Boulder Clay, causing its boundary to re-enter
Cambridgeshire by Graveley, Yelling and Papworth St Everard.
The most noticeable feature to be observed along the northern
edge of this great spread of clay is the way in which it runs out
along the projecting spurs and hills separating the valleys by
which it is here indented; the bounding line may thus be traced
eastward from Elsworth, retreating up the hollows and curving
round the hills by Knapwell, Boxworth, Lolworth, Drayton and
Madingley to the high ground above Coton, the summit of which
is registered at 175 feet above the sea.

South of this it is eut back by the valley of the little brook
which rises near Hardwick, but running out again on the other
side along the broad spur of Barton Field, it returns finally
along the southern slope of these hills and bends south-west-
ward to Toft and Caldecote ; thence it descends into the valley
of the Bourn, and crossing over by Kingston runs nearly up to
Eversden Wood and into the long spur which was first described.

Mr H. H. Howell, who has surveyed a great part of the area
(of which the circumscribing limits have been traced in the pre-
ceding paragraphs), informs me that it is covered almost
entirely by grey or greyish-brown unstratified clay, its colour
and contents varying somewhat according to the locality and
the particular formation which happens to underlie it, but
fragments of chalk and chalk flints are found everywhere in
more or less abundance ; Oolitic rocks of the immediate neigh-
bourhood are likewise present in great quantity; ice-scratched
fragments of the older formations, chiefly from the New Red
Sandstone, Coal-measures and Carboniferous limestone, are
found, but much less frequently ; pebbles and blocks of Basalt
and other igneous rocks also occur occasionally,

bo

* 36

From the frequency of the words “gravel pit” on the
Ordnance Map between Great Gransden and Eltisley, it might
be supposed that there was here an extensive area of Glacial
gravel; this however is not the case, Boulder Clay ean be seen
in the immediate neighbourhood, and the pits themselves
appear to have been dug in small hollows or pot-holes of denu-
dational gravel resting on the Clay.

It may be mentioned that in the valley at Caxton End near
Bourne the Neocomian Sands come up to the surface, probably
forming a ridge against which the Boulder Clay thins out, for it
is found filling up the valley lower down. Mr 8S. V. Wood,
Junr. notices a similar disposition of the Boulder Clay near
Gamlingay (see ante p. 17), speaking of this deposit as bedded
round the Lower Cretaceous Sand, the two sections however
which he gives across this district are inaccurate in several
particulars. In the first place he ignores the existence of the
Gault upon which the Boulder Clay rests about Wrestlingworth
and Tadlow, and which crops out in the valley east of Potton ;
it is evident moreover from the lie of the formations that it also
rests upon Gault at the Old North Road Station, and that the
latter must have formed a great part (at least 60 ft.) of the
mass pierced by the well and called Boulder Clay by Mr 8. V.
Wood. The Glacial Clay merely appears to have filled up a
pre-existent valley, and there is no evidence of any great scoop-
ing out of the Gault as Mr Wood supposes ; there can I think
be little doubt that the water was obtained from the Neocomian
Sands, for there is no evidence of any Middle Drift in the neigh-
bourhood ; the gravel near Moggerhanger also is probably of
later date than the Boulder Clay. I would therefore correct
the section given by Mr Wood as follows; the minor details of
the geology being of course omitted on so small a scale.

Fig. 1. Diagram Section from Old North Road to the Ouse Valley.
Moggerhanger Sandy Gamlingay Mills Old N. Road.

Horizontal scale 4 miles to an inch; vertical, one inch =300 feet.
a=Jurassic Clay. c=Gault. «= Post-glacial Gravel.
b =Neocomian Sands. 1=Boulder Clay.

37.

The large outlying mass of Boulder Clay which has just been
descfibed as forming the upland between the valleys of the
Ouse and Cam must be looked upon as having once been con-
tinuous with that which rested against the chalk escarpment ;
the surface on which it lies forms an inclined plane, the base of
the clay being 220 feet high on the south and only 125 feet at
Lolworth, so that there is a fall of 100 feet in a northerly direc-
tion. It has nowhere to my knowledge been proved to be more
than 100 ft. thick, and its average thickness is probably much
less, except where it happens to fill up a pre-existing hollow.

Thus at Scotland Farm, north of Hardwick, the well is said
to be 144 feet deep, but at least 50 of this must be Gault, for
that is the depth of the wells (through Gault) in the valley at
Dry Drayton.

The same is probably the case at Old North Road Station ;
the well here is said to be 160 feet deep, but it is very impro-
bable that the whole of this is Boulder Clay, because in the valley
at Caldecote, only two miles to the N.E., about 60 feet of Gault
was pierced ; it would be safer therefore to assume that there is
a similar amount in the former well below the Boulder Clay,
especially as at Bourn, 1 mile N.N.E,, in a well recently made,
only 60 feet of Boulder Clay was found above the Neocomian.

[Mr Tomlison, C.E., of Cambridge, has since informed me of
a well at Hatley St George, which is said to have pierced the
following beds :—

feet
Cau (Boulder Clay) 31.00 lA ia se. 120
ere, GIES YI GA. NAIR BO as 28
xault (probably true Gault).................006 22
Sands (Lower Greensand)........0.0...c.seeneee 30
200

This is interesting as showing gravel beneath a great thick-
ness of Boulder Clay, but it is probably a local phenomenon, and
cannot be taken as indicating the existence of a Middle Drift,
or as giving the normal thickness of Boulder Clay.

The Rev. O. Fisher informs me that water was obtained at
Comberton vicarage by piercing the Boulder Clay, a supply

38

being found in a dark lead-coloured sand with chalk pebbles
underlying about 20 feet of clay; this sandy gravel is probably
a similar bed to that which forms the base of the Boulder Clay
near Hadstock and other places, see p. 31, the materials being
exactly the same as those in the Boulder Clay, but without the
compact clayey matrix. |

§d. The Isle of Ely. We have already found that as we
proceeded northward the Boulder Clay descended to lower and
lower levels; its edge at Lolworth and Boxworth is about 120
feet above ordnance datum, and near Ely its base is about 60
feet lower.

The low ridges or hills which stand out of the surrounding
fens, and constitute what was of old the Isle of Ely, are capped
by the Chalky Boulder Clay except where they rise higher than
70 or 80 feet above the sea-level, as at Haddenham and south-
ward towards Aldreth. Possibly the Glacial Clay was originally
banked round the outliers of Gault and Neocomian here, as it
was round the latter at Potton and Sandy.

Ely Cathedral and most of the city is situated upon the
Neocomian Sand, which is underlaid by the Kimmeridge Clay
(here however of no great thickness). Boulder Clay first comes
on near the Union House and stretches southward till it spreads
out over the high ground between Witchford and Thetford. It
caps the long ridge which extends westward from Witchford by
Wentworth to Sutton; it covers Sutton Field, but Mr Skertchly
informs me that the town itself stands on a patch of gravel which
appears to be intercalated in the Glacial Clay and that the
materials. composing this gravel are the same as those found in
the neighbouring Boulder Clay; so that as sometimes we have
Boulder Clay without the boulders, we have here Boulder Clay
without the clay.

North of Ely, Boulder Clay is found at Little London and
Roslyn Hill, whence it runs down in the form of a long tongue
through the clay-pit called Roslyn or Roswell Hole. Here it
lies in a long hollow which has been scooped out of the Kim-
meridge Clay, and contains at the particular place where the pit
was first opened a large boulder of gault and chalk; this has
been brought by the agency of ice from some point to the east-

39

ward and tumbled over the south bank of the hollow, squeezing
down at the same time underneath it portions of the Neocomian
Sands which then covered the surface of the Kimmeridge Clay.

Mr Bonney has sufficiently described the pit in his Cam-
bridgeshire Geology, and I will only mention that the section
has been further cut back since the time when his description
was written, so as to expose the Kimmeridge Clay as well as
the Boulder Clay on each side of the great Boulder.

[Mr Skertchly in his “Geology of the Fenland” has given a
detailed description of Roslyn Hole, with a plan and illustrations ;
the limits of the long Boulder are here indicated and its several
relations to the Neocomian Sands, the Boulder Clay and the
Kimmeridge Clay, are shown. The fault theory is examined and
dismissed : “I am confident,” he says, “that such faults do not
exist, or they would be traceable across the country by inter-
fering with the strike of the Neocomian Sands.”

After describing the positions of the beds in the several
parts of the pit, he states that the great Boulder of Gault and
Chalk does not extend into what he calls the lower pit, but that
a narrow band of Boulder Clay reaches down to the river. “In
thus working round the pit it is seen that everywhere Boulder
Clay is interposed between the great Boulder and the undis-
turbed Kimeridge Clay; that the Boulder Clay is always
found below the great boulder whenever its base can be seen ;
that the limits of the. Boulder lie within the pits, so that it is
bedded in Boulder Clay; and lastly that the Boulder Clay fills
a small valley in the Kimeridge Clay.” He speaks of a similar
old valley filled with Boulder Clay as intersected by the highway
a mile east of Witchford. Again, “Large masses of chalk are
not peculiar to Roslyn Hole, for one occurs in the Boulder Clay
in Witcham Fields five miles west of Ely, but is of minor
importance.” |

From Roslyn Hill the Boulder Clay stretches northward
and westward, capping the high ground by Little Street, Chetis-
ham and High-flyers Hall.

CHAPTER IV.

THE HILL GRAVELS’.

Tue Gravels overlying the Boulder Clay on Barrington Hill,
north of the village of Linton, have already been mentioned, and
their connection with those so long known as existing on the
summits of the Gog-Magog Hills has been pointed out. I will
now proceed to describe the position, extension and character of
these deposits, which have long been known by the name of the
Coarse Gravel of the Hills.

The height of Barrington Hill may be taken as about 350
feet above the sea, and 250 above the stream below. As before
mentioned, it is capped with coarse flint gravel, which was
exposed in a small pit by the roadside just north of the letter R;
this was open in 1874, but has since been filled up; it showed
about six feet of gravel, mainly consisting of large-sized flints
with pebbles and blocks of other rocks. Down the slope to the
N.W. Boulder Clay is found; but in a road-cutting beyond and
about a mile due E. from Hildersham, sandy gravel is again
seen overlying the Clay. The same road crosses another patch
to the S.W., and this was formerly worked near the word Sand-
pit on the map; these patches are at a level of about 200 feet
above the sea.

Westward of these another larger patch of gravel and sand
extends above Hildersham and descends as far as the old sand-
pit N. of the Church, having apparently overlapped the Boulder
Clay so as to rest on bare Chalk at a height of not more than
140 feet above the sea, and within 40 feet of the alluvium level.

North-west of this sand-pit, at the corner of the roads, is a

1 These gravels are fully described in a Memoir written for the Geological
Survey, now in the press.

4}

small cutting in stiff grey Boulder Clay, enclosing a lenticular
patch of sandy loam, like that on the slope by “The Rivey.” A
pocket of sandy gravel is also visible, the remnant of a mass
which has shrunk to a mere capping on the hill above.

Westward the clay appears to pass under thick beds of
gravel, which cover the country to the north of Clay-pit Planta-
tion, and which both northward and westward overlap the
Boulder Clay on to the Chalk. There is a small pit in these
gravels on the hill summit above the Plantation, exposing 8 feet
of compact angular flint gravel stained by iron to a dark brown
colour and containing an intercalated band of brown sand; the
materials appear to have been sorted by the action of water, and
no large stones were visible at the time of my visit.

In the road-cutting on the hill-flank midway between this
spot and Little Abington Grange, quite a different kind of
gravel is exhibited, though it is clearly continuous with the
other. A confused mass of chalky gravel and sand with scattered
flints and chalk-stones is here seen, looking as if it had resulted
from the destruction of Boulder Clay and Chalk in situ ; it is
probably hereabouts that the Gravel has cut out the Boulder
Clay, and impinged on the Chalk, and westward from this point
it is always chalky and often intensely so.

This particular outlier ends at Little Abington Grange, but
in the Chalk hollow to the N.W. another mass of Gravel occurs,
which hardly makes any feature, but clings apparently to the
base of the hill; an excavation in it exposes about 10 feet of
coarse gravel, consisting mainly of large flints and chalk pebbles
confusedly heaped together without any appearance of bedding ;
fragments of quartzite, Septaria from the Jurassic Clays, as well
as pieces of Red Chalk and Cambridge Coprolites, are not un-
common. The Gravel indeed presents a very similar appearance
to that of the Middle Drift in the neighbourhood of Sudbury
and Clare, a facies which I take to be a proof of its resulting
directly from the destruction of Boulder Clay and Chalk.

The hill beyond‘this pit appears to be thinly capped with
Boulder Clay, which is seen in the road-cutting by the 50th
milestone of the London and Newmarket road, and where the
upper two or three feet is rearranged into a reddish loamy soil,
containing stones of various sizes.

42

Similar material is seen in the old railway cutting to the
S.S.E., where numerous boulders, many of which are of large
size, lie scattered about ; this may however be formed from the
loamy and gravelly base of the Boulder Clay, as seen near
Babraham. The higher ground of Signal Hill is capped with
gravelly soil, but no exposure is visible.

The gravel pits near Worsted Lodge are dug in another
outlier forming an elongated patch and lying at much the same
level as that on Signal Hill; the Gravel here is very chalky,
consisting at one part entirely of chalk stones, stained yellowish
and packed close together. Another small recent excavation in
the pit showed the following succession :

Trregularly bedded sand and fine gravel —........s00e 3 feet.
Very chalky gravel .............00ecnsenseocerenesnescess 5 ke
Clean grey sand (bottom not seen) — ......eeeee eee eee 1 foot.

Gravel has also been obtained from a small hole farther east,
where it contained more flints. Passing across the chalk combe
in which Fulbourn Valley Farm is situated and climbing the
hill towards Fulbourn Lodge we again find gravel at a similar
level, apparently occupying a hollow on the northern side of the
hill summit; it may be seen in the old chalk- and gravel-pits at
the western end, where 6 or 7 feet of brown sand and chalky
gravel are visible passing southwards into 2 or 3 feet of mere
sandy clay and chalk rubble overlying the bedded chalk.

Copley Hill again is capped by gravel, as are also the Gog-
Magog Hills north of Wandlebury, but no sections were exposed
at the time of my visit, although the hollows of several old pits
were visible.

The gravel pits which have been noticed by so many writers
on Cambridge Geology (see pp. 15, 28, 36, 37) are to be found on
the north side of the Old Roman way called Worsted Street,
which appears to have been made hereabouts with the gravel
obtained from the above-mentioned pits and holes. These are
seldom dug now, and though I visited this locality many times
between 1872 and 1875, I could only confirm the observations
of previous describers as far as the meagre section then exposed
allowed of; this was at the east end of the pit and exhibited
stiff yellowish sandy clay showing slight lamination and contain-

43

ing stones of various sizes and inclined at various angles; the
chalk pebbles were rounded, and the others angular or sub-
angular, though few showed any traces of glacial strie; the
thickness shown was about six feet, but I was told that four
feet of coarse rubbly gravel lay between this and the Chalk
below.

The sandy clay I take to be the Boulder Clay spoken of
by Prof. Seeley (see p. 36), to which material it certainly bears
some resemblance; it appears more likely however to be a
lenticular bed of re-arranged Boulder Clay forming part of the
gravel mass,

The rock fragments to be found in this loam are—

Chalk, which formed about 50 per cent. of the pebbles.

Flints, of which there were about 30 per cent., leaving about
20 per cent. of other fragments consisting of the following rocks:

Red Chalk, more like that of Lincolnshire than the red rock of
Hunstanton.

Hard cream-coloured Chalk. % Chalk-rock.

Crinoidal Limestone. of Carboniferous series.

Oolitic and shelly Limestones, from Northampton or Lincolnshire.

White micaceous Grit. % from Coal-measures.

Brown Quartzite, possibly from the New Red series.

Septaria, from the Kimmeridge and Oxford Clays.

Coprolites from the Cambridge Greensand (not rare).

Gryphea incurva (Lias) and G. dilatata (Oxford Clay).

Besides these Prof. Sedgwick mentions :—
Pieces of Basalt and part of a basaltic column.
Rolled masses of Granite and Porphyry.
Pebbles resembling those in the New Red Sandstone (probably
the brown quartzites above mentioned.)

All the above rocks have evidently been derived from the
Boulder Clay, which contains an exactly similar collection, even
Coprolites having occasionally been found in it; these nodules
however appear to be more frequent in the gravels, although
this comparative abundance may be deceptive and may be due
to the sifting and collecting of the stones into narrower compass
than they originally occupied in the Boulder Clay. Under any
circumstances, however, it is not easy to account for the presence

44

of these Cambridge Coprolites more than 200 feet above the
level of their outcrop on the north and north-west.

Prof. Sedgwick in 1861 mentioned similar gravel on the
“Stapleford Hills’—by this he probably meant the height
called Little Trees Hill to the south of the main road; only
about a foot of gravelly soil however is now to be seen at the
top of the chalk-pit. Pipes filled with stones and gravel are
shown in the Shelford clunch pits on Steeple Hill.

Again, on Missleton Hill to the N.W. of the Gog-Magogs
there are hollows from which similar gravel has been obtained ;
flints and other stones are to be seen impacted into the upper
few feet of the rock in the chalk-pit on this hill.

Besides the series of outliers just described, I am not aware
of any other gravels in Cambridgeshire which occupy a similar
position; they appear to form a group by themselves, capping
all the hills in the vicinity which rise above the limits of a
certain inclined plane. This plane slopes from a height of 330
feet on Barrington Hill to a level of about 240 on the Gog-
Magogs, and where the gravels descend below this plain or fill
up hollows, as near Abington, we may suppose that these
existed previously, as irregularities of the surface, or that they
were excavated out of the Boulder Clay during the period when
the gravels were formed. The latter is probably the more correct
view, and the subordination of such hollows to a given plane
certainly suggests marine action.

In the neighbourhood of Newmarket, however, there are
some gravels which resemble those on the Gog-Magogs in being
newer than the Boulder Clay, and in resting either on it or on
the Chalk; but I have not been able to work out the relations
of the several patches to one another, and will therefore simply
describe the sections I have seen.

First are the gravel pits half a mile 8.E. of Newmarket
Station, where about 18 feet of gravel and sand are shown, the
lower six feet consisting of fine gravel and sand interbedded, the
upper twelve feet of rougher and coarser material, flints being
the chief component; the gravel appears to occupy the southern
slope of the valley, and from its character and position, I am
inclined to think that it most probably belongs to the series of
old valley gravels, which will be presently described.

45

The next pit lies at a much higher level, being about a
quarter of a mile N.N.E. of Ashley Church; in this 10 feet of
roughly-bedded chalky gravel is seen, nearly 80 per cent. of the
stones being large rounded chalk pebbles, the rest are flint,
with a few pieces of quartzite, Gryphea, &c., the whole assem-
blage looking as if directly derived from the Boulder Clay; this
gravel appears to spread over the high ground about Ashley,
and may be partially underlaid by Boulder Clay, though a hasty
traverse did not lead to the discovery of any direct evidence
showing this to be the case.

No doubt however exists about the position of the gravel at
Lipsie Wood near Dalham, this has been worked off a platform
of Boulder Clay which may be seen near the entrance to the pit,
and contains fragments of chalk, flint, quartzite, Septaria and
Gryphea shells. The gravel above is composed of exactly the
same materials, and its present face is about 18 feet in height ;
some of the layers are coarse and others fine, and there are a
few patches of false bedded sand; the chalk pebbles are mostly
small and the flints large, a few of them being slightly worn
and rounded; the general matrix is iron-stained sand, but in
one place the stones were impacted in a hard clayey material
that looked like re-arranged Boulder Clay.

It is possible that these Gravels are the southernmost exten-
sions of those which spread over the country round Icklingham,
Mildenhall, Lakenheath, and Brandon, and are noted for contain-
ing flint implements. This district is now being surveyed by
my colleague, Mr Skertchly; and he informs me that though
previous writers have described the gravels as confined to the
river valleys, they really spread far and wide over the country,
only as they are of greater thickness in the valleys, they have
been more worked there than on the highlands. Much of the
gravel is coarse and unstratified, but beds of sand occur in
some places. These deposits overlie the Boulder Clay where it
occurs and occupy the highest grounds as well as the lowest ; the

land hereabouts however never rises above a height of 160 or
170 feet.

CHAPTER V,

VALLEY GRAVELS OF THE EARLY RIVER SYSTEM.

In the higher parts of the tributary valleys, as well as in other
localities nearer Cambridge, there exist certain patches of
gravel and loam, regarding the age of which there has lately
been much difference of opinion among Cambridge geologists,
and the relations of which could perhaps hardly have been
ascertained until the country was mapped in some detail.

Although similar in composition to the gravels previously
described, they occur mostly at much lower levels and are
entirely separated from the glacial deposits; they appear to
have a distinct relation to the valley systems in which they le,
and they behave in all respects like ancient river gravels.
The correspondence of these deposits with the direction of the
present valleys is not however preserved in their lower pro-
longations, indeed so great is the divergence that near Cam-
bridge they strike across the Cam Valley almost at right angles
to its present course; at the same time their fluviatile origin
becomes more apparent, for they preserve a definite line across
the country, forming a nearly continuous ridge, which may be
followed with few interruptions far into the regions of the Fens.
We are thus led to the inference that these old gravels indicate
the course taken by the first river system of the district, and we
may expect them therefore to throw much light upon the
history of its denudation, and upon the relative age of some of
its principal physical features.

The southernmost patches of these old valley gravels are to
be found in a curious hollow among the Chalk Hills near
Royston, called Wardington Bottom. The beds of the lower
Chalk are here affected by a remarkable disturbance which has

47

caused considerable deviation from their normal dip, and which
may have led to the formation of the Wardington Bottom by
determining the outflow of the springs. The combe is certainly
of very ancient date, so old indeed, as we shall presently see,
that all the rest of the valley into which it originally led has
been swept away by post-glacia] denudation.

At the head of this valley, about one mile and a half east of
Barley Church, is a small gravelly patch, but no exposure is
now to be seen in it. Lower down there is a larger patch
which sends a prolongation up the hollow towards Burloes Hill,
and about half a mile §.W. of Known’s Folly there is a gravel
pit exposing—

Chalky sand (2 feet) resting unevenly upon

Fine chalky gravel, with some large subangular flints and

pebbles of quartzite, sandstone, hmestone, schist, &c. ...9 feet.

Large bones are said to have been found in this gravel by
the workmen.

Below Known’s Folly the modern little stream deserts the
course of the more ancient channel, and has excavated for
itself a shallow valley in which it runs north-westward towards
Foulmire, while the older gravels are continued along a more
easterly line, outliers of them being found on the slope of the
hills by North Hall, Sharpens, Heydon Grange and onwards to
Whittlesford.

About North Hall some thickness of chalky gravel and sand
is found, the stones being mostly pebbles of chalk and flint, but
there are many boulders of quartzite, grit and basalt. Near
the farm called Sharpens a small pit exposes 10 feet of very
chalky gravel, evidently occupying the old channel in the
chalk, but now forming a ridge into which the beds dip on
each side; sandy and loamy layers are interbedded with the
gravel, and the proportion of chalk stones is in places more
than 50 per cent.” North-eastward by Heydon Grange the

1 Details regarding this disturbance and depression are given in the Geo-
logical Survey Memoir, on sheet 47, now in the press.

2 For the notes on these and other Gravel pits I am indebted to Mr W. H.
Penning, of H. M. Geological Survey, and I have since had the advantage of
visiting some of them under his guidance,

48

direction of the old river course may be traced by the gravelly
surface of the ground.

Further still another large mass of gravel is met with,
covering the country north of Chrishall Grange; about a mile
N. of this place it has been excavated for road material, and
when seen in 1875 the pit disclosed 8 feet of rough chalky
gravel underlaid by 3 feet of fine chalky.sand, with a lenticular
bed of fine gravel composed entirely of small chalk pebbles.
The gravel was roughly stratified, and one layer was stained
black by manganese or iron; a few large boulders occurred, and
many subangular flints, some of them standing on end; there
were also two or three small patches of contorted loam enclosing
shells (Succinea and Pupa?), these appeared to have been
contemporaneously interbedded, and if so, they would indicate
clearly the fluviatile origin of the gravel. .

This pit is situate on a flat or gentle slope, but the base of
the gravel appears to be uneven, and to rise towards the North,
for it runs out into the high ground, which extends as a gravel-
covered ridge northward towards Thriplow, but bends eastward
before reaching that village, and peints towards the mass of
loam and gravel to be next described.

This is first seen in a gravel-pit near the main road about a
mile west of Whittlesford station, but the best section is to
be found in a large pit close to the station on the south side of
the road. Along the eastern face of this a sandy buff-coloured
loam is seen which is underlaid at the southern end by fine
chalky gravel, containing on a rough calculation about 50 per
cent. of chalk pebbles, the rest being chiefly flints ; a small cave
here excavated in the gravel is roofed by the overlying loam.

Turning back and descending into the lower part of the pit,
we find it worked in roughly bedded gravel, chiefly composed of
small stones, but with occasional layers of coarser material,
made up of flints and large chalk stones, with quartzites, shelly
oolites and fragments of Grypheeee ; several pieces of laminated
loam with shelly partings were also found. Farther on the
gravel becomes strongly false-bedded, with intercalated patches
of fine sharp sand, and the whole is cut into by a descending
scoop of the overlying loam, which is strong and clayey near the
base, but yellow and sandy above.

49

Beyond this the section is much obscured by talus, but the
second bed of gravel (c) appeared to descend from above and
cut into the loam in a similar way; and this view of the facts is
shown in the annexed representation of the eastern side of the

pit.
Fig, 2,

Diagrammatic Sketch of Whittlesford Gravel Pit,
N.W, Bj S.E.

ca

a=lower gravel. d=roadway.
b=loam. e=supposed fault,
c=upper gravel. f=the cave,

There is no evidence of a fault at e, as some have supposed;
the loam simply fills a hollow eroded out of the gravels by
current action and passes above them undisturbed. On the
west side of the pit nothing but loam is exposed; but in the
next field another excavation shows gravel again with inter-
bedded contorted loams and sands, the collocation here giving
colour to the interpretation above given of the section in the
larger pit. Nowhere could any shells or contemporaneous
fossils be found.

The hill to the North appears to be chiefly composed of
loam, and in a small brickyard just N.W. of the cross-roads the
following section is shown :

feet
PGP SOUND Hes ton pre coca gasacs hadusadecdan ens 1
Laminated yellowish loam .................. 2
Wellowish clayey (0am .....5..cfeseeauscsses 4
Hard bufFcoloured loam................eceee 8
poler blaishi-grey leant’... 02 22kthw.s test 2+

The lowest loam here seen is somewhat the colour of blue
Boulder Clay, but its intimate structure or texture is entirely
different, and it passes up into a stiff buff loam breaking with
a kind of hackly fracture. The bluish tinge of the deeper
portion was no doubt the original colour of the whole mass, the
upper part having weathered to its present colour. These

loams are doubtless to a great extent sifted and re-arranged
4

50

Boulder Clay, mixed with a considerable proportion of sand, and
an occasional chalk-pebble occurs here and there in the mass,

This ancient series of river deposits has now been traced
to a point where it is cut off by the present valley of the Cam,
and before proceeding to consider the direction in which it was
continued it will be desirable to notice some similar deposits on
the flank of this valley.

The section in the railway cutting near Chesterford station
has long been known as exhibiting 7 or 8 feet of contorted
yellow and brown loam overlaid by a few feet of coarse rubbly
gravel. By some geologists it has been thought that the loam
belonged to the Mid-Glacial series, and that it was overlapped
by a high terrace of valley gravel.

There is no doubt that recent valley gravel intervenes
between the loam and the river, but I am inclined to think that
this is much more recent and altogether at a lower level than
the gravel overlying the loam. With regard to the age of the
latter, its entire separation from other glacial deposits, and its
disposition along the slope of the valley, are sufficient to create
grave doubts as to the propriety of grouping it with Middle
Drift; while from the great similarity of both loam and gravel
to the deposits above described near Whittlesford, I am strongly
inclined to consider them as belonging to a similar series and as
having originated in a similar manner; (indeed, a little north
of Ickleton inclined beds of yellow and grey loam occur, which
may have formed part of their continuation towards Whittles-
ford.)

Southward the loam can be traced along the railway for
more than half a mile, and patches which have evidently once
been connected with it trend southward along the slope above
the line. It is not improbable that some of the loams and
gravels about Wenden and Newport may be of the same age,
but they are so mixed up with beds of later date as to make
any attempt to separate them a very difficult task.

I think, however, that there is sufficient evidence to prove
that a series of deposits once existed along this valley, similar
in age and origin to those which have been traced from
Wardington Bottom to Whittlesford; but in consequence of
this valley having ever since continued to be a main line of

51

drainage, they have been exposed to greater denudation and
fewer portions have escaped destruction ; in the other case the
stream has been diverted into another channel, and the older
beds have been left in a much less patchy and discontinuous
state.

In the Linton valley, 8.W. of Bartlow, there is a patch of
gravel which has also been referred to the Middle Drift, but
which may not improbably belong to a branch of the present
series. It is well seen in a large pit near the station, which
exposes some forty feet of fine chalky gravel, iron-stained, and
piped at the top, with many thin bands of sand and loam in the
central part, and very chalky gravels below, all the beds
dipping 8.S.W. at an angle of 15°.

Two smaller neighbouring pits present the same features,
and the whole mass appears to be banked up against the chalk
slope; Boulder Clay caps the hill above and comes very near
to the edge of the gravel, but does not appear to overlap it.
Patches of gravel occur at about the same level further down
the stream on either side of Linton; that which is seen about
Pampisford Station and Abington Park may be of the same
age, though it is difficult to separate it from lower and more
recent gravels. But in the cutting half-a mile N.W. of the
Station gravel is again seen lying in a hollow of the chalk, and
thus appears to be continued into an elongated patch capping
the high ground by Pampisford Hall. The end of this outlier
points directly for the Whittlesford mass, and may once have
been continuous with it before the excavation of the present
valley; it seems probable therefore that somewhere in this
neighbourhood the three streams whose gravels we have traced
down their several valleys were united into one river.

But what course did the confluent waters subsequently
take? This is a question by no means easy to answer; there
are beds of gravel at various altitudes lower down the valley,
but even the highest of these appear to belong to a series which
is the production of later times. Moreover the probable con-
nection of the Whittlesford and Pampisford patches seems to
indicate that the old river flowed either in an easterly or a
westerly direction. Now it is to be noticed that the Whittles-
ford ridge is prolonged for some distance to the N.W., and

4—2

52

although it appears to be almost denuded of the deposit to
which it doubtless owes its existence as a feature, a small patch
of gravel still remains near Stanmoor Hall. Still further to the
north-east between Newton and Harston is Red-land Hill, capped
by the patch of gravel described by Warburton in Prof. Hail-
stone’s paper on the Geology of Cambridgeshire (see p. 11). As
no exposure is now to be seen on the hill, I will quote Mr War-
burton’s description—he remarks “that three-fourths of the
rubbly mass” is composed of rounded pebbles of very hard
chalk; that the gravel also contains “numerous angular masses
of striped flint, fragments of septaria, shelly limestones, and
angular pebbles of trap or greenstone,” likewise some ochreous
balls which he looks upon as decomposed pyrites nodules,
together with derived Belemnites and Gryphea shells.

He notices the peculiar position occupied by this outlying
stratum, which looks, he says, “like the partial destruction of
an alluvial level by some subsequent cause.” This small patch
may possibly be a remnant of the series we have been following,
or at any rate of some contemporaneous affluent, but beyond
this point all traces are lost, having probably been carried away
by the excessive denudation which this part of the valley has
undergone. Leaving therefore the question of the northward
continuation of this series in some doubt, we will now pass to
another system of drainage in which the deposits have been
much better preserved.

Crossing the watershed of the hills above Hildersham with
their patches of clay and gravel, several deep and generally dry
valleys will be found proceeding from these and the Balsham
hills, and running in a northerly or north-westerly direction.

In one of these at some gravel pits marked on the map a
little east of Gunners Hall, a curious section is exposed, viz. a
succession of finely-bedded loams, sands and gravels, mostly of a
yellow colour, and many of them false-bedded; they are all bent
over into an anticlinal from N.W. to S.E., dipping very sharply
on each side; this is best seen at the S.E. end, the north part
appears to be chiefly composed of yellow loam. The patch does
not seem to be of large extent, but is elongated in the direction
of the valley.

Nothing is seen northward till the pits near Dungate are

53
reached ; these show 6 or 8 feet of chalky and somewhat clayey
gravel, containing patches of light sand, and covered in places
by a reddish-brown sand; the whole is apparently made up of
waste from Boulder Clay, it contains many rounded pebbles of
chalk, many flints (mostly angular), pieces of limestone, sand-
stone, quartzite, red chalk and derived fossils. This patch les
on the slope of the hill, and similar sand and gravel may be
traced northward along the ridge and also down the slope into
Wratting Valley; half the hollow of the ancient watercourse is
therefore preserved, while the opposite slope has been worn
back, but once stood, no doubt, over the ground of the present
valley, as shown by the dotted line in Fig. 3, The same feature

Fig. 3. Section across Wratting Valley.

a=chalk. b= gravel.

was remarked near Duxford Grange in the “ Wardington
Bottom” series, in both cases the gravels lying half on the hill
and half in the valley. In both cases also the present valley or
“bottom” only coincides with the line of the ancient watercourse
in its upper and deeper portions, while lower down the old
gravels gradually get up on the slopes of the valley, and
eventually deserting it altogether they form long ridges raised
above the level of the country beyond ; such behaviour indicates
at once their great antiquity, and the enormous amount of
denudation which has taken place since the period of their
formation.

In the present case this feature is very marked, the next
outlier of gravel occurring along the high ridge which is cut
through by the junction of the old and new railways to
Newmarket.

A chalk pit near its southern extremity shows about 8 feet
of hard chalky sand containing scattered flints, but few chalk
pebbles of any size; the sandy matrix is an intimate mixture of
chalk grains and flint sand, but the former has been dissolved
from the uppermost foot or two, leaving the flints embedded in

54

a brown sandy soil; the base is piped, and pockets of light-
coloured sand full of flints descend into the chalk below.

A small excavation north-west of this exhibited 10 feet of
coarse flint gravel, a few lenticular patches of similar chalky
sand producing a rough appearance of bedding; the whole
deposit has the appearance of being quickly accumulated from
the rapid denudation of Gravel, Boulder Clay, and Chalk, for the
flints though sometimes cracked, are angular and unworn, and
certainly have not been transported from any great distance.

About six feet of the same gravelly material is seen in the
railway cuttings. And beyond this the ridge is prolonged till it
is cut off by the hollow in which Great Wilbraham lies, across
which it has clearly once extended to join the long gravel-capped
ridge presently described.

An examination of the other valleys which furrow the
northward slopes of the Balsham and Wratting hills discloses in
them also the existence of similar deposits, and small patches
near Larks Hall have yielded Mammalian bones in some abun-
dance; specimens are now in the Woodwardian Museum, and
among them can be recognised teeth and bones of Elephas,
Rhinoceros, Hippopotamus, and Cervus.

It is worthy of note also that the bottom of the neighbouring
valley is occupied in places with a recent wash of sand and

‘flints, very similar in character to the old gravels on the slope

above; it has no doubt been largely derived from these, and
while serving to indicate their once greater extension up the
valley, it shows at the same time that even this second trans-
portation has failed to reduce the flints to a rounded shape ;
long attrition is required to effect this, and the rapidity of the
process here has not allowed sufficient time, for the valley is
usually dry, and the detritus is only brought down by heavy
rains and floods such as I was a witness of in 1875,

-The patches above mentioned lead on to an elongated outlier
which is cut through by the Newmarket railway near Six-Mile
Bottom Station. Here material is seen precisely similar to that
in the former cutting S. of Wilbraham; and beyond this point
a long ridge may be followed in a north-westerly direction, till
it turns westward below Quy-cum-Stow. This ridge is indeed
the line of the old river-course, and it owes its existence as a

55

ridge to the river-gravels which rest upon it, and have protected
the underlying chalk from denudation ; the bottom therefore of
the ancient valley is here preserved, while the hills and slopes
which once formed its sides have been long since destroyed and
washed away. The dotted lines in Fig. 4 (kindly lent by H.M.
Geol. Survey) will give an idea of the probable configuration of
the country at the time when these beds were deposited.

Fig. 4. Section across the Wilbraham Grayels.
Droveway. Road. Road, Stream. Bottisham.

Horizontal scale, 2 in. toa mile. Vertical scale, 200 feet to an inch.
a=chalk. b=ancient river gravel. c=gravels of Wilbraham Fen.

Some small excavations north-west of Great Wilbraham Hall
exposed about 9 feet of rough flint gravel and sand; from the
bottom of one of the pits I obtained the tooth of a deer, and
was told that bones were frequently found. The stones here
had lost some of their angularity, and the further the distance
from the hills, the more rolled and rounded do the pebbles
become, affording, were it needed, another proof of the fluviatile
origin of the beds. The sand-pit by the wood opposite the Hall
is at a lower level, and is probably near the spot where the
Wratting Valley stream joined that we have been tracing, the
channel of the former being intersected by the watercourse
running westward from the present springs.

Close by Little Wilbraham Church there is an extensive
pit, the recent diggings in which show loamy sand and sandy
gravel, the former containing in one place small specimens of
Succinea and Pisidium. Gravel has also been obtained from
numerous holes dug in the fields north of Little Wilbraham,
and a bed of loamy marl overlying gravel in one of these yielded
several specimens of Succinea, Helix and Pupa; bones also are
said to have been found. The ridge here is about half a mile
wide, but it becomes somewhat narrower to the N.W., where the
above section (Fig. 4) is taken, to show its relations to the
present surface of the ground, and especially to Wilbraham Fen,

56

Between Bottisham and Quy it bends to the S.W., and extends
about a mile in that direction, terminating a little beyond Quy
Church, where the height of the surface is given as 60 feet
above sea-level. At Quy-Water Bridge it is cut through by a
more recent line of drainage; but gravelly soil is again found on
the hill to the 8.W.,and another elongated outlier of gravel and
sand extends along the Newmarket road from Greenhouse Farm
to within half a mile of the railway bridge.

The direction of this patch and consequently of the old
valley which it represents, strikes directly west across the
present valley of the Cam, so that we might expect to find its
continuation about Castle bill, and the Observatory. This is
indeed the case, a small patch of gravelly soil being observable
when the coprolites were worked opposite the Alms-houses
at Mount Pleasant, while just beyond the Observatory there are
large pits by Gravel Hill Farm, which have been worked for
many years, and where the gravel is said to be 20 feet deep. —

A. recent excavation here discloses about twelve feet of
gravel, the lower six feet being fine and irregularly bedded,
containing nearly 50 per cent. of chalk pebbles, the rest being
flints with a few pieces of hornstone, quartzite, &e. The upper
six feet are disturbed and piped, the pockets being filled with
brown sand and occasional flints, and their bottoms lined in
places with films of carbonate of lime, from which we may
conclude that the contortions have arisen from the solution of
the chalky portion of the mass, the carbonated water having
probably been guided by roots of trees in the first instance.

I did not succeed in finding any shells, though Mr Seeley
states that he found fresh-water shells under the Observatory.

It is remarkable that the base of the gravel here is some-
what higher than it is further back, for its surface being 85
feet above sea-level, its base would be 65 feet, while near Quy
Church it is not quite 60 feet; this would apparently indicate
that there has been a slightly unequal upheaval of the area at
some subsequent time ; other facts bearing in the same direction
will be noticed in the sequel.

In 1873 I was fortunate enough to see the northern bank
of the old watercourse exposed in the coprolite diggings then
opened behind the Observatory; the section ran from N.E. to

57

S.W., and showed a hollow filled with gravel, shelving up to the
North but gradually deepening towards the Observatory grounds,
and about 8 ft. deep at S.W. end.

I think it may have been hereabouts that the series of
deposits first described in the higher parts of the Cam Valley
was united to that coming from the east ; the former must have
descended the valley, and since the gravel-covered ridge now
makes a sharp turn to the N.W., this may have been consequent
upon the junction above suggested.

Several old gravel pits occur along the high ground between
the Observatory and Girton College; at the latter place a well
was sunk 10 feet into gravel without touching the gault below.

Most. of Girton stands on gravel or sand, and where exposed
the pebbles are seen to be “mall and much rolled. From Girton
the ridge bends slightly to the north-east, and then turns again
to the north-west; below Histon Church however it is cut
through by a little brook which flows off the lower gravel plain
to the eastward, and has made a valley for itself through this
still older series of deposits. Another breach is made by two
small streams coming in from the south-west near Oakington,
and re-deposited gravel occurs in both valleys, so that there is
much confusion in the gravels here.

Above Oakington however the high ridge commences again,
and continues steadily towards the north-west between Long
Stanton and the Huntingdon railway; in the cutting on this
line, about midway between the Long Stanton and Swavesey
Stations, gravel is seen overlying Oxford Clay, and thence a
gravelly soil extends on the north side of the line as far as Over,
where gravel has been obtained from pits along the slope facing
the river Ouse. This river, like the Cam, has cut directly through
the ancient line of drainage, which appears to have taken a bend
to the north hereabouts, washing past the clay slopes which jut
out above Bluntisham and Colne. Gravel occurs at and west of
these places, but its precise relations are rather difficult to
ascertain; it is furrowed by transverse valleys and appears to be
flanked by more recent Fen-gravels.

At Somersham its disposition is more readily comprehended :
it underlies the whole of the town, and caps the high ground to
the north and north-west. A good section of it was visible

58

(1876) in a field near the Rectory, the pits exposing 12 or 14
feet of finely bedded sand and gravel, the latter composed
chiefly of small rounded flint- and chalk-pebbles, with a few
rolled pieces of yellow quartz and brown quartzite, and many
broken fragments of Gryphea dilatata. The total depth was
said to be about 20 feet; the sands had a somewhat crag-like
appearance, but appeared to be quite unfossiliferous, North-
ward its edge or base is very little above the level of the
Fen.

About Chatteris again its position is clearly defined, as it
here forms a low island or bank rising up from amidst the
surrounding fens, and the town is entirely situated on this
bank, which is here about three-quarters of a mile wide. Small
excavations in the Nursery gardens near the Station showed
4 or 5 feet of gravel similar to that at Somersham banked up
against a clayey loam; I was informed that the whole deposit
was from 5 to 7 feet deep and rested irregularly upon stiff clay
with occasional “large oysters” in it, but could not ascertain
whether this was Boulder Clay or Oxford Clay.

The clayey loam occurs in patches among the gravel, and is
left in working out the latter; they evidently bear much
the same relations to one another as the loam and gravel at
Whittlesford.

The gravel extends southward beyond the Mill Field and
northward beyond the Gas Works, near which place it is also
worked. I could discover no shells, but Mr Skertchly informs
me that Cyrena fluminalis has been found here together with
Cardium edule and Tellina solidula (balthica).

Near Doddington the railway cuts through gravel, but the
pit near the Station at Wimblington is now grown over and
no longer worked; many shells (chiefly marine) used to be
obtained from this pit, which is probably that mentioned by Mr
Seeley as disclosing a floor of Oolitic rock pierced by Pholades.

The gravel pit in the immediate vicinity of March Station is
likewise grown over, but gravel full of marine shells is seen in
the ditches leading into it.

[The beds were well exposed in 1872, when part of the
section described by Prof. Seeley in 1866 still remained (see
ante, p. 18); the succession being as follows.

59

Brownish clay, about 3 feet.

Shelly gravel, with false-bedding, 2 feet shown.

Talus and water, apparently hiding the base of the gravel and
its junction with blue Boulder Clay below’.

The uppermost clay was certainly not Boulder Clay, but true
Glacial Clay was seen below the gravel in other paris of the
pit.

A good section was observed by Mr Skertchly in Hutchison’s
brickyard, and noted as follows’.

Gravel, with marine shells, now almost removed, formerly from
6 to 20 feet thick.

Boulder Clay, dark blue in colour, with many rounded and
striated chalk-pebbles.

Kimmeridge Clay, dark blue, with Ostrea deltoidea in the upper
part, dug to 40 feet. |

Mr Skertchly has not seen anything like true Boulder Clay
overlying the gravel either in this or in any other pits, and
agrees with me in thinking the whole series to be of Post-glacial
age, and the general relations of the gravel to be as shown
in Fig. 5.

Fig. 5. Diagram Section across the March Gravels,

a=Kimmeridge Clay. b=Boulder Clay. - e=gravel.
d=loam. f=fen series.

About half a mile north of the Station are more recent
excavations, showing fine gravels and sands full of marine shells ;
they are overlaid near the railway by a bed of yellowish loamy
clay, somewhat similar to that mistaken for Glacial Clay by
Prof. Seeley and possibly once continuous with that deposit.

I collected in these pits the following shells:

Ostrea edulis. Buccinum undatum, Bela turricula.
Cardium edule. Purpura lapillus. Littorina littorea,
Tellina solidula. Turritella communis, Natica Alderi 2?

1 Having lost my notes of this section, I am indebted for the above details to
Prof. Bonney, with whom I visited the locality,
2 See Geology of the Fenland, p. 192.

60

Westward of this section is a brickyard disclosing a surface
of clay from which 5 or 6 feet of gravel have been removed. The
top 2 or 3 feet of this clay are yellowish in colour and contain a
few stones and pebbles, so that it may be the base of the
Boulder Clay, the old river having here nearly, but not quite,
cut down to the Kimmeridge Clay below the plain of Boulder
Clay.

[This section is the same as that numbered 96 in the
Appendix to Skertchly’s Geology of the Fenland. ]

Below is a full list of the fauna hitherto collected, 40 species
in all.

Buccinum undatum.
Purpura lapillus.
Trophon scalariformis.
$3 Bamfius.
Bela turricula.
9» pyramidalis.
Mangelia rufa.

Aporrhais pes pelicani,

Turritella communis.
Scalaria communis.
Littorina littorea.
BE rudis.
Lacuna vincta.
9 _-crassior.
* Hydrobia ulva,
Natica Alderi.
» helicoides.
*>7;;, _, Gaveue,
Trochus cinerarius.
at tss helicinus.

Cyrena fluminalis.
Ostrea edulis.
Mytilus edulis.
Tellina solidula.

Ph bata
Scrobicularia plana.
Cardium edule.
Astarte borealis.

3 sulcata.

* Modiola modiolus.

* Artemis exoleta.
Cyprina islandica.
Mactra ovalis.

3) oasolida.
Corbula striata.
* Gi elloua.

Mya arenaria.

», truncata.
Pholas crispata.
Rhynchonella psittacea.

* On the authority of Mr Harmer.
+ On the authority of Mr 8. Wood.

CHAPTER VI.

VALLEY GRAVELS OF THE PRESENT RIVER SYSTEM.

THE gravels which occur in the present valley of the Cam, and
along the banks of its tributaries, offer rather a complicated
subject for study, inasmuch as they have been deposited at
different times and at different levels, according to the changes
in the courses of the streams and the depths to which they had
successively excavated their channels.

Indeed it would not be possible to unravel the relations of
all the ridges, terraces and patches of gravel which occur at
various heights above the present streams, without carrying out
a far more detailed survey of the whole valley than has yet been
made, and accurately determining the height of every such
terrace and patch above ordnance datum. The following pages,
therefore, must be regarded as containing only a first attempt at
giving a connected historical account of the river-gravels of this
valley.

By Prof. Sedgwick these deposits were all classed together
under the name of the Fine Gravel of the Plains, and all such
beds were at that time considered to be of marine origin.
Prof. Seeley perpetuated this idea, and was even bold enough to
correlate them with the Upper Boulder Clay of Norfolk (see
ante, p. 20), but their fluviatile origin has since been acknow-
ledged by Prof. Bonney and other observers.

Before proceeding to describe the several terraces of gravel,
I will offer a few remarks upon their general mode of occurrence,
and upon the extent to which they are likely to be preserved in
different parts of a valley such as that of the Cam,

62

The river system is composed of several streams, flowing off
comparatively high ground, and uniting to form a river which
opens on to a low flat country ; hence, as the power of a stream
to deepen its channel depends more on its velocity than its
volume, it is obvious that erosion will proceed much more
rapidly in the higher portions of the valley, and that the oldest
gravels in these localities will be left at a much higher level
above the river than those of the same age lower down the
valley. Moreover, if the river lose so much of its velocity before
reaching the sea as to deposit material instead of deepening its
channel, the positions and ages of the gravels will be reversed,
the lowest beds in the delta and the highest beds on the steeper
slopes being respectively the oldest, while between the two
there will be a space where the valley opens out, and where
there is little difference of level between the oldest and newest
deposits.

It might therefore be expected that the terraces of gravel
would be found more widely separated, and more distinetly
marked, as the sources of the river were approached ; this is
indeed the case as far as they are preserved, but it must be
remembered that the atmospheric agencies of denudation take
much greater effect on the steeper slopes, so that the oldest
terraces in the higher parts of the tributary valleys will often
have been entirely destroyed and washed down into the more
recent gravels.

Consequently it is in the lower parts of these valleys and in
the higher portion of the resultant main valley, where the
erosive power of the stream is still considerable, but the lateral
denudation is not so great, that we should expect to find these
terraces best preserved and at the same time tolerably distinct
from one another.

This is the case in the valley of the Cam; and for some
distance south of Cambridge three sets of gravels can be clearly
distinguished, but north of the town they spread out over a
wide area, and there is not so much difference in level between
the highest and lowest of the terraces, so that it becomes more
difficult to separate them one from another. _

Leaving these lower plains for the present, I will first
describe the river gravels above Cambridge, taking the several

63

terraces separately, and endeavouring to trace them as far as
possible up the tributary valleys southward, westward and east-
ward,

§ a. The highest and oldest terrace to be found in the
present valley of the Cam or Granta, near Cambridge, occurs
along the low ridge which runs southward from Barnwell at a
level of about 45 to 50 feet above the sea. At the northern
end of this are the well-known gravel pits of Barnwell Abbey ;
these are now nearly exhausted, and no deep sections are
exposed, so that I am obliged to quote the following facts
from Mr Seeley’s account of the pit’, which agree with my own
recollections between the years 1871 and 1874. “ Examined
generally, the gravel is formed of layers which extend pretty
continuously round the pit. The lowest bed exhibited is quite
a coarse bed with the pebbles mostly rounded. About 2 feet
above this is a bed of yellowish brown marl, almost clay, irregu-
lar in thickness from a few inches to four feet. At times,
cuttings display one or two similar but thinner beds in the
upper part of the section.” As the pit was cut back, these thin
bands appear to have thickened into a bed of gréyish white
marl, which is still visible on the west side of the pit and is
underlaid by false-bedded sands containing shells.

“The most important stratum is the marl-bed (ze. the
lower marl), first described by the Rev. P. B. Brodie, see Camb.
Phil. Trans. vu. p. 138 (ante p. 13); in this are found
fragments of- plants, seed-vessels of Chara, and many shells,
some fresh-water, others land forms, nearly all now living in
Britain,...Here too are found the bones of various mammals,
nearly all extinct ; and in the same bed is evidence of man in
his work.”

This evidence consists of an incised bone described by
Mr Seeley as being apparently part of a rib of an Elephant, the
incisions on which he considers to have been the handiwork of
Paleolithic man”*. No flint implements have ever occurred
here, though one or two flakes are said to have been found °,

1 Quart. Journ. Geol. Soc., Vol. xx11. p. 476.

2 See Brit. Ass. Rep., 1862, Trans. Sec., p. 94.

3 A fine specimen of the ‘‘hache” type has however recently been obtained
(1878) by Mr A, J. Griffith from the pit on the other side of the Newmarket
road,

64

A full list of the Mollusca yielded by the marl and sand is
given below (58 species in all). I am indebted to Mr A. Bell
for the names of many species not hitherto recorded from
Barnwell.

Freshwater species. Land species.

Cyrena fluminalis (common). Helix hortensis (nemoralis).

Unio littoralis (common). », arbustorum (common).
» limosus. »» cantiana? (or fruticum).
5, pictorum. 5 ericetorum,

Cyclas cornea. » hispida,
» calyculata. » .concinna.

Pisidium amnicum (common). 5, rufescens.

a fontinale. », rotundata.

as pulchellum. » pygmerea,

=e nitidum. 5» pulchella.

+s Henslowianum. Helicella cellaria.
Limnea palustris. wi radiatula.

a peregra. i nitida.

& auricularia, “r nitidula,

5 truncatula. FA fulva.
Planorbis marginatus. Bulimus montanus.

as carinatus. ¥ Lackamensis.

* spirorbis. 5» (Zua) lubrica.

5 vortex. 5, (Azeca) tridens.

a nitidus. Clausilia biplicata.

5 glaber. 3 rugosa,

55 contortus. Pupa muscorum,

3 corneus ? » Mmarginata.
Bithinia tentaculata (common). Vertigo pygmeea.
Valvata piscinalis, » antivertigo.

cristata. moulinsiana.

”
Ancylus fluviatilis.

. oblongus.

Hydrobia marginata (rare).

””

Carychium minimum.
Succinea putris.

”

gracilis.

The following remains of Mammalia have been found :

Bos primigenius.
», longifrons ?
Equus fossilis.
Cervus megaceros.
» Sp. (small),

Elephas primigenius.

3?

antiquus (rare).

Rhinoceros tichorhinus.
Hippopotamus (major 1).
Felis spelea.

65

Conspicuous by their presence in the above list are firstly
the Mammalian remains which indicate considerable antiquity ;
Elephas antiquus is, I believe, only known by a single tooth, and
it has been suggested that this may have been derived from
some older gravels; secondly, the occurrence of Cyrena fluminalis,
Unio littoralis and Hydrobia marginata must be noted, as they
are all now extinct in Britain.

Conspicuous by their absence are Unio tumidus, Neritina
fluviatilis, Paludina Listeri and Lymnea stagnalis, since all
these are now common in the Cam and its alluvium, associated
with most of the other freshwater shells named in the above list;
the former two however are generally found in the full strength
of the current, while the latter two prefer stagnant marsh pools;
but this is hardly sufficient to account for their total absence
(even as drifted shells) in the Barnwell sand.

Gravel is found behind the wall of the old Abbey, it is only
7 or 8 feet deep, and is said by the workmen to rest on “clunch”
or chalk marl. This is certainly the case in a pit behind the
houses on the opposite side of the road to the Abbey Church,
whence large quantities of gravel and sand are now being
removed, the total depth being about 12 feet; underlying these
are one or two feet of marl resting immediately on the clunch
from which it has been mainly formed. Clunch comes to the
surface on the East, and coprolites are worked at a depth of
20 feet, thus a section through the above pits from N.W. to S.E.
would appear as in Fig. 6, for the use of which I am indebted to
H. M. Geological Survey.

Fig. 6. Section through the Barnwell gravels.
Priory Road Pit

e
B

Horizontal scale 9 in. to a mile; vertical, 100 feet to an inch,

a= Gault. b=Chalk. c=Gravel.

The gravel may be traced southward to the railway station,
where a long section was exposed in 1875, showing beds of
5

66

gravel, sand and loam; the depth of these deposits near the
goods-sheds is said to be about 16 feet, but opposite the main
platform it is not more than 10 or 12 feet, and along the
Newmarket line it shallows to 7 feet, and was seen to rest upon
an irregular surface of stiff grey marl (probably the Chalk Marl
in situ, though containing impacted sand and pebbles).

In the cutting near Polecat Farm the gravel is found again
and thus caps the highest part of the ridge overlooking the old
Cherry Hinton mere; at the time therefore when the river ran
at the height indicated by this terrace or ridge, the mere could
hardly have been in existence, and its site was probably occupied
by ground that sloped upwards toward the Gog-Magog hills of
that period, the lower spurs of which have so far receded in the
interval between that time and the present, as to allow of the
formation of the mere.

The Barnwell terrace is here about half a mile wide, and is
separated from the lower terrace on the west by astrip of chalk ;
southwards the terrace declines gradually towards Brooklands,
and the beds have been washed down into the newer gravels,
which are here banked against the older series.

The southernmost pit is situated in the angle between the
railway and the Hills Road, and shows from ten to six feet of
sandy gravel, with a band of marl near the bottom. The
ballast pits between the railway and Brookland Farm expose
about 8 feet of sand and gravel, resting on Chalk Marl.

Having now described the position, character and contents
of the Barnwell gravels, it will be sufficient to trace their
continuation southwards.

Crossing the shallow valley through which Vicar’s Brook now
runs, and which we shall find to have been the course of the
Cam at a subsequent date, the higher series of gravels are
continued by Trumpington; gravel and sand to a depth of 16 or
20 feet underlie the greater part of this village, but thin out
towards the church’.

The railway cutting between the branching roads south of
Trumpington intersects this ridge of gravel, which appears to
thin out both eastward and westward, for near the 28th mile on

1 The Rev. O. Fisher informs me that a tooth of Elephas primigenius was
found in sinking a well at the Vicarage.

67

the railway, chalk appears in the ditch, and thus the older gravels
are probably separated from the newer deposits in the low
ground to the east (see Fig. 7, lent by H. M. Geological Survey),

Fig. 7. Section through the Trumpington gravels.

=

Nine Wells.

a
="
-_-_-

-—
=
oes
=-
=

a=lowest terrace, b=second terrace. c=highest terrace. d=chalk.

The gravel pits marked on the ordnance map near Vicarage
Farm are ploughed over, and the next section to be found is at
the S.W. end of the cutting on the Great Northern line near
Shelford. Here soft white sand is exposed, covered in one place
with a bed of white marl, shells occur in the former, and are the
same as those found at Barnwell.

Cyrena fluminalis. Helix ericetorum.
Pisidium (amnicum ?), 5 arbustorum.
Bithinia tentaculata. » hispida ?

Valvata piscinalis.

It is difficult to trace this series of gravels any further south,
but there is a patch capping the high ground midway between
Stapleford and Sawston that may possibly be of the same age,
and just north of Sawston the ridge bends eastward towards
Babraham, so that some of the higher gravels near Babraham and
Abington may belong to the same series. It is no easy matter
however to separate this set of gravels from the older series
previously described as crossing the country hereabouts, though
I think it would be possible to do so if accurate observations
were made of the heights of the different patches.

In the main valley of the Cam I can point to no deposits of
this age, they have probably all been swept down to lower levels,
for reasons given in the first instance.

Neither have I seen any similar terrace of gravel in the
valley of the Rhee, which appears to be of later date than any
of the other tributary valleys. No beds of gravel occur along
the banks of the Rhee from its sources near Ashwell as far down
as Barrington, and I am inclined to think that this portion of

5—2

E.

68

the valley had no existence until the Boulder Clay had been
entirely removed from this district, and the springs issuing from
the base of the Chalk were brought into play. Opposite
Barrington the Rhee receives an affluent which comes down
from Wardington Bottom, and running through Foulmire passes
between Shepreth and Foxton, It will be remembered that
when describing the early river-system (p. 47), it was mentioned
that this stream had deserted the course which it took in older
times by Heydon Grange and the Crowley Hills to Whittlesford,
and that it now followed the direction above indicated.

It is impossible to say exactly when this deviation took
place, but from the patches of gravel occurring along the course
which it now follows, it seems likely to have been a main line of
drainage at some period intermediate between the formation of
the Whittlesford gravels, and the excavation of the present
valley of the Rhee above Barrington.

It may be therefore that the gravels about Foulmire and
Foxton were deposited about the same time as those about
Barnwell and Trumpington, but on the whole it seems likely
that they belong to a somewhat later period.

The valley of the Bourn, on the other hand, appears to have
existed from very early times, and remains of the three principal
terraces occur along its slopes. The highest of these has been
mentioned by Prof. Seeley as forming a ridge between Barton
and Grantchester', and in all probability this was originally

continuous with the Trumpington gravels, from which it is now
separated by the modern valley of the Granta.

In the old pits behind Grantchester church about 10 feet of
fine gravel and sand was exposed in 1874, and I was informed
that large bones and teeth had been found here. From this
point the gravels extend westwards and occupy a hollow along
the top of the chalk ridge, bearing the same relations to a
previous surface as the long gravel-capped ridges previously
described.

Beyond Barton the continuity of the series is interrupted by
a watercourse draining off the Boulder Clay on Comberton
Field, but a large patch again occurs in the upper part of

1 Quart. Journ. Geol. Soc. Vol. xxi. p. 475.

69

Comberton, and it was from this I presume that the tooth of Rh.
tichorhinus mentioned by Mr Seeley was obtained.

Beyond this point the terrace cannot be traced, and it has
probably been carried away by subsequent denudation into the
newer gravels below.

§ b. Returning again to Cambridge as the starting point,
the gravel which underlies Downing College, New Town and
the Botanical Gardens, and presents an evident bank to the
river near Mr Bland’s farm, is found to stretch up both sides of
Vicar’s Brook, and to occupy the shallow valley previously
mentioned as cutting through the older (Barnwell) series between
Brookland Farm and Trumpington Mill (see also Fig. 7). At
the cottage where the Mill Road crosses the railway, there is said
to be 12 or 15 feet of gravel, and the same material continues to
occupy the low ground as far as Shelford, where it may be seen
in pits near the bridge over the Cambridge and Hitchin railway;
gravel underlies most of Great Shelford and is from 8 to 12 feet
deep in various parts of the village, ending abruptly against the
river; but on the other side of the alluvium it appears to be
continued by Frog Hall to Whittlesford. Beyond this it is not
easy to separate it from gravels of later date, and the same may
be said of its continuation up the Linton Valley by Howe Field,
Babraham and Abington, for gravel is found along the banks of
both streams at all levels from the recent alluvium to a height
of thirty or forty feet above it.

It would appear, therefore, that at the period in the history
of the Cam valley which we have now reached, these united
streams did not take their present course by Little Shelford and
Hauxton, but ran nearly due north, as far as Cambridge, before
they were joined by the Rhee and Bourn.

As regards the Rhee, indeed, we have already shown that it
could hardly be said to have any existence; the upper part of
its course being so very different from that which it now
follows, and the main stream at this time being probably that
which descends from Wardington Bottom.

Gravel occurs on the east side of the Rhee, both north and
south of Harston, but at no great height above the river, and
these patches seem to lead on to a much larger spread of gravel

70

near Foxton, which keeps away from the present stream and points
up the older valley towards Foulmire, so that the gravel occurring
near the latter place would appear to belong to the same series.

Along the valley of the Bourn Brook there are several
patches of gravel at levels intermediate between the Barton
ridge and the more recent beds which flank the present brook.
The largest of these is at Toft, another occurs near Lords Bridge,
and a third lies midway between Spring Hall and Cantalupe
Farm; some of the gravel east of the latter place is much about
the same level and may be of the same age, with more recent
gravel banked up against it.

The stream in the channel of which these gravels were
deposited probably united its waters with those of the Rhee near
the junction of the present streams, and the gravel bank
extending from Byron’s Pool to the vicinity of Trumpington
House appears to belong to the same intermediate series.

The gravel which underlies Croft Town and Newnham is at
nearly the same relative level, and it must have been somewhere
about this locality that the two rivers, which then flowed north-
wards, one on each side of the Trumpington ridge, met to form
the Cam or Granta of that period.

Such appears to have been the aspect of the Cam valley
before the time when the river changed its channel for the last
time, and took its present course by Little Shelford and
Hauxton to join the Rhee near Cantalupe Farm.

§c. The gravels which flank the alluvium of the present
river hardly merit any particular description, and it will be
sufficient to indicate the principal localities where they occur,
especially where they have yielded any fossil remains. It may
however be worth while pausing to consider how the last
change in the channel, introducing the present state of things,
was brought about.

We have seen that the main stream of the Cam, after
receiving the Linton brook, continued its northerly course
beyond Great Shelford, its western bank being apparently
formed by a low ridge of Chalk which stretched across the
present site of Little Shelford, and part of which still remains as
a narrow strip between the two villages.

a1

This old northward course of the river appears to have been
gradually silted up, a bank being probably formed by the gravel
brought down from the Linton valley, so that it was slowly
converted into a series of marshy pools, remains of which are
now discoverable over the surface north of Shelford, where
patches of whitish clay overlie the gravel and contain recent
shells in abundance, such as are now found in the pools on
Sheeps Green.

In the meantime the chalk barrier on the west was gradually
overflowed and breached, the initial impulse being probably
given during some flood time, and the immediate result appears
to have been the production of a lake in the hollow where
Hauxton now stands, and the spreading out of gravel over its
bottom. For the drainage would at first be blocked by the
second ridge of Chalk Marl, which then in all probability
extended continuously from Harston to Trumpington, and the
waters would be ponded back until they could overflow at
Hauxton Bridge; this they ultimately did, and by the deepen-
ing of this narrow outlet the lake has been gradually drained.

Such I believe to have been the history of the gravels about
Little Shelford and Hauxton, which therefore belong to a
somewhat later period than those previously described, and may
be classed with the more recent gravel flats.

This lowermost series of gravels is nearly continuous up the
valley to Linton, and small pits have been dug here and there.
Near Bartlow station there are pits showing about 10 feet of
gravel and loam, in which elephant tusks have been found, as
well as shells of the genera Helix, Pupa, Bithinia, and Succinea.

Along the main valley of the Cam larger spreads of gravel
are met with, now on one side of the present channel and now
on the other, extending thus for a distance of 13 miles from
Shelford to beyond Newport in Essex. The principal pits along
this line occur at the following places.

Whittlesford. ast of the station, in gravel and sand.

Little Chesterford. A large pit just south of this place
exposes about 30 feet of gravel and sand in horizontal layers.
Teeth of Llephas primigenius have been found here.

Wenden. At pits near the river 15feetof loamy gravelis shown,
from which elephant bones have been extracted.

72

Newport. Half a mile south of the village is a pit exhibit-
ing sandy brick-earth, underlain by fine light sand, the latter
also enclosing mammalian remains.

Passing now to the gravels which stretch northward from
Cambridge, we find them spread out over a wide extent of
country, bounded on the west by the long ridge of the Girton
and Observatory gravels, and on the east by the alluvium of the
present river. This sudden wide extension of the gravels may
be accounted for in two ways; either it indicates the previous
existence of an estuary in which the deposits were spread out,
as Prof. Seeley believes; or else it is due to the river having
continually cut back its eastern bank, so as to leave a series of
undisturbed gravels on its western side.

It is true that the outspread of gravel between Cambridge
and Histon has somewhat the appearance of an estuarine
arrangement ; at least it is difficult to conceive how some of it
could ever have been formed in any river channel. It may be
however that this is only the result of excessive subsequent de-
nudation, and the area appears to be highest in the centre
about Arbury, King’s Hedges and Landbeach, the height of the
ground between the two latter places being given by Fitton as
55 feet above sea-level; from this central line it slopes evenly
and gradually down to the present alluvium on the one side,
and irregularly towards Histon on the other, as if there had
been some slight local elevation over the intermediate tract.

Again, one would not expect to find a watershed in a plain of
river-gravel ; but a marshy field between the old semi-circular
encampment called Arbury and the main road to Histon
appears to occupy such a position, the water soaking off eastward
and westward from this spot to supply ditches and streams
which flow respectively into the Cam and the Ouse.

It is worth while noting these circumstances, even if they
cannot be held to prove any postglacial disturbance of the surface.

The true explanation of this wide spread of gravel is
probably to be found in the second alternative, viz. that the
river has always had a tendency to encroach upon its eastern
bank, and has gradually changed the direction of its course

from N.W. to N. and finally to N.E.

73

The more recent changes of the channel certainly seem to
have been in this direction, and the present river, which keeps
nearly parallel to the low terrace of gravel stretching away
from Chesterton through Milton to Waterbeach, begins to take
a more easterly course near the latter place, and has left a strip
of Gault-land between the gravels and the alluvium.

I think therefore the westernmost deposits of loam and
gravel may safely be taken as the oldest, and those nearer the
present river as successively newer; it is possible also to group
them in three series, which may be the continuations of the
three terraces described as existing in the higher portion of the
valley. Thus the gravel which occupies the ground north of
Cambridge towards Impington and Histon may be a continua-
tion of the Barnwell series ; patches of loam occur in it here and
there, but these are not exposed in any pits where a search for
shells might be made. About Impington the Gault comes to
the surface in many places, and the gravel only occurs in hollows
and channels, but north of Histon there is a large patch forming
a low plateau which is cut off abruptly along its northern edge;
from this a Gault slope leads down to the valley of a little
brook or ditch draining into the Ouse.

Gravel is also seen along the Roman road between King’s
Hedges and Landbeach; indeed the whole country hereabouts
seems to have been once covered with gravel, though little more
than a gravelly soil now remains to indicate its former
presence.

The Chesterton gravel is at a lower level, and forms part of
the terrace above mentioned as stretching for some distance to the
N.N.E. in a direction nearly parallel to that of the present
river; beyond Milton however it bears nearly due north, and
passes between Landbeach and Waterbeach towards Goose
Farm and Denny Abbey, disappearing finally under the peaty
soil of Cottenham Common and Chaff Fen.

There are numerous small gravel pits scattered along this
strip of country, but they do not show any good sections, and I
did not succeed in finding any organic remains. Prof. Seeley
says’ that he has found shells at Chesterton and other places,
“but in every case they were land or freshwater forms, though

1 Quart. Journ. Geol, Soc. xx11. p. 475.

74

from the gravel of Waterbeach the Woodwardian Museum has
the vertebree of a whale, which from its preservation was
evidently contemporaneous with the bed.” It would be desira-
ble to know whereabouts in Waterbeach this was found, whether
in gravel under alluvium or in the higher series westward of the
town, for the village itself is situated mainly on a strip of gault
which separates the two sets of gravels. The gravel and sand
underlying Waterbeach Fen and bordering the alluvium near
Chesterton and Milton are comparable with the low level
deposits previously mentioned.

Wilbraham Fens. To enter upon a general description of
the Cambridgeshire Fens would be beyond what I understand
to be the scope of the subject proposed, and would certainly
prolong this Essay to an inordinate length. There is however
one isolated tract that merits description here, inasmuch as its
origin is connected with that series of ancient river-gravels
which form so noteworthy a feature in the vicinity. This is the
fenny district which stretches southward from Quy between
Wilbraham and Fulbourn, and is known as Wilbraham Fen;
its history appears to have been somewhat as follows.

When the drainage of the country was carried off by the
ancient river above referred to, this fen could have had no
existence, and the springs which now rise near Wilbraham and
Fulbourn were then probably at a higher level and contributed
their supply to the river itself; but when the drainage ceased
to take this course, and the hills were gradually cut back south-
ward, the springs would retire also in that direction, while the
old river-course remaining as an elevated ridge prevented the
outflow of these waters to the north, and caused the formation
of a shallow lake in the same way as the moraine of an old
glacier ponds back a mountain stream. The level of this lake
would rise until the water overflowed the gravel ridge and made
an outlet for itself where Quy-Water Bridge now stands. This
outlet having once been made, the lake probably drained itself
to a certain extent until it was reduced to the condition of a fen
with pools or meres in the deeper portions of the area: in this
state it remained until attempts were made to bring it under
cultivation, the streams being banked up and carried along in
definite channels.

75

The northern part of the fen however still continued to lie
under water, and is remembered as a haunt of wild-fowl by
some of the neighbouring villagers.

Peat still remains here, and in patches elsewhere over the
area, but in other parts the floor of gravel and sand is exposed,
its limits still roughly marking out the extent of the old
lake.

Fulbourn Common, Coldham Common and Cherry Hinton
Mere, all marshes at one time, were doubtless formed in the
same way, the long bank of gravel blocking the drainage and
causing an accumulation of water on the southern side.

CHAPTER VII.

CORRELATION OF THE CAMBRIDGESHIRE DRIFTS WITH THOSE
OF THE EASTERN COUNTIES.

In correlating the various glacial deposits which occur in
different parts of eastern England, the presence of the great
Chalky Boulder Clay is of great assistance; from its wide
extension and the constancy of its principal characters it forms
an excellent base or reference-stratum, so that, the presence of
this clay having once been definitely determined, we are at
once able to correlate the other members of the series which
may exist in the separate areas.

This Boulder Clay, the Upper Glacial of Mr-S. V. Wood,
Junr., has been mapped both by him and by the Geological
Survey over the whole of Essex and over large parts of Cam-
bridge and Suffolk. Its extension through Cambridgeshire has
been indicated in the preceding pages, and it has been shown
that the main mass of this clay ends along the edge of the
Chalk escarpment above Royston, Saffron Walden, Linton,
Balsham, and Dullingham, at a height of from 500 to 350 feet
above the sea. It has however been pointed out by Mr W. H.
Penning’, that there are occasional outliers sloping down the
escarpment into the ancient valley of the Cam, and that the
subsequent re-excavation of this valley has resulted im the
separation of the Boulder Clay areas lying to the N.W. of the
main mass, with which they were once undoubtedly continuous.

Thus the great spread of Boulder Clay which les on the

1 Quart. Journ. Geol. Soc. Vol. xxxu. p. 198.

ve

high ground between the valleys of the Cam and the Ouse is
proved to be of Upper Glacial age not only from the similarity
of its constitution and contents, but from general physical
considerations deduced from a study of the whole county.

An examination of the heights marked on the ordnance
map shows that the basement-level of the clay in this district
gradually descends from a height of 250 feet on the south, to
that of only 120 on the north. Prolonging this gradual slope,
we are not surprised to find that the base of the same clay on
the Isle of Ely is only 60 or 70 feet above the sea, and that
northward it sinks down below the level of the fens and
ultimately below the level of the sea.

This gradual declination of the Upper Boulder Clay at once
disposes of the erroneous correlations which Mr Seeley made in
1866; it is now seen that neither the Lower Boulder Clay nor
the Contorted Drift are to be found in Cambridgeshire ; and not
only so, but it is a question whether anything that can be truly
ealled Middle Glacial occurs within the limits of the county.

Mr Searles Wood, Junr., was the first to remark that the
Mid-Glacial gravels do not occur above a height of about 300
feet, but he has never spoken of them as limited to the eastern
side of the Chalk escarpment, indeed he has mapped them as
occurring in Bedfordshire and Huntingdon, as well as beyond
the western boundary of the Boulder Clay at Saffron Walden,
Dullingham, and Newmarket.

Mr Penning, on the other hand, has seen reason to conclude
that they are so limited, and that no such sands or gravels are
to be found in the Cambridge valley; it is certain at any rate
that most of those so mapped westward of the chalk escarpment
are Post-glacial, that is to say, posterior in age to the Upper
Glacial of Mr 8. V. Wood.

Those which are actually seen to lie beneath the Boulder
Clay are, I believe, merely local lenticular patches at or near
the base of this clay ; such intercalated beds of gravel are by no
means rare in Suffolk and Essex, and may be seen for instance
near Sudbury. This I believe to be the explanation of the
series visible near Audley End and described in the early part
of this Essay; the sands and loams which here intervene
between two similar clays being probably the result of con-

78

temporaneous current action. The way in which the Boulder
Clay runs down into the valley about Newport and Wenden
shows that this was a pre-existent hollow; it would therefore
form a narrow strait at the first incidence of the Boulder Clay
(always supposing this to be a marine deposit); consequently it
is only likely that a current would set through the gap and give
rise to patches of sand and gravel, interstratifying them with
the lower portions of the Boulder Clay itself.

I agree therefore with Mr Penning, that there is no evidence
for the existence of Middle Glacial beds in the Cambridge
valley, and that the earliest glacial deposit is the Upper
Boulder Clay. Mr Searles Wood considers this as the upper-
most and latest of the glacial series, and he proposes to class as
fost-glacial all beds which can be proved to lie unconformably
on this clay. It seems to me, however, that it is more reason-
able to consider the great chalky Boulder Clay as accumulated
during the most intense period of glacial cold, and I do not see
why other beds should be excluded from the glacial series
simply because they happen to lie above this particular clay.

Supposing, with Mr 8. V. Wood, that the glacial beds are of
marine origin, and that the Boulder Clay was deposited during
the great submergence, surely marine glacial gravels are just as
likely to have been formed during the elevation as during the
depression of the shore line; it is indeed a well known fact that
there are large spreads of gravel above the Boulder Clay which
have none of the appearance of ordinary terrestrial gravels,
and which have been termed “ Plateaux Gravels” by Mr Wood.

I believe them to be in great part the Upper Erratics of
Mr Trimmer. Mr Searles Wood however appears to be only
acquainted with these Plateaux Gravels in Norfolk ; he speaks
of them in the following terms’: “This gravel is everywhere
unfossiliferous and is composed almost entirely of flints. It
is difficult in some cases to form an opinion whether it is of
glacial or post-glacial age. Most of that shown in sections is
doubtless post-glacial, but with respect to that which caps
Mousehold Heath it seems the same as the gravel which has
an extensive spread in West Norfolk, since, like it, the gravels

1 Preface to Monograph on Crag Mollusca (Paleont. Society).

79

of these places contain beds of very large flints more or less
rolled. These gravels of West Norfolk set in almost along the
same line as that about which the Middle Glacial ceases (from
Hingham on the S. to Wells on the N.). They are also com-
posed almost entirely of large flints, which are mostly so rolled
as to resemble cannon-shot.

“These cannon-shot gravels sometimes contain masses of sand
formed of chalk grains, and as they are never overlain by the
chalky clay, but in a few instances have this clay under them,
it may be that, if not of post-glacial age, they are a local modi-
fication of such clay due to the action of some powerful current
over this part of Norfolk, which dissolved all the soluble part of
the moranic material forming that clay and rolled the flints
into the cannon-shot form.

“The absence of these gravels over the southern part of East
Anglia is a peculiar feature, but some beds of gravel on the
Wolds about Speeton and Bacton seem to bear a similar
relation to the Purple Clay of those places.”

With respect to the last paragraph above quoted, it is now
found that the gravels are not absent over the more southerly
parts of East Angla, but that they extend through West
Suffolk into Cambridgeshire, and that they form quite as
important a series of deposits as the Middle Glacial beds below.
In many parts of Suffolk and Cambridge these gravels closely
resemble those of the Middle Glacial, so closely that I think
they must have originated under similar citcumstances; if
therefore the Middle Drift is a marine deposit, then these
gravels are probably marine, and they must be taken as forming
part of the Glacial Series of East Anglia. I am therefore led to
think that it may ultimately be found convenient to group this
series into an Upper and Lower Division in the way suggested
below, each division having an argillaceous member overlaid
by a set of loams, sands and gravels,

1. Cromer Till and
Contorted Drift > Lower Glacial.
2. Middle Drift

3. Chalky Boulder Clay

4, Plateaux Gravel } Upper Glacial.

2.

CONCLUSION.

HaAvine in the last chapter endeavoured to correlate such
of the glacial deposits in Cambridgeshire as seem comparable
to any in other parts of East Anglia, I conclude by offering
a few remarks upon two much-contested questions, viz. the
conditions under which these beds have been deposited, and
the age of the principal physical features of the country.

I cannot but feel that the knowledge of glacial phenomena
and glacial formations which I at present possess, although
aided by a practical acquaintance with the latter as they are
exhibited over parts of Cambridge, Suffolk and Norfolk, is
insufficient to enable me to arrive at any very decided con-
clusions regarding the first of these questions. I cannot regard
any of the rival theories as entirely satisfactory, and think that
a much larger experience, and a still greater accumulation of
facts, is yet needed before this problem can be fully and com-
pletely solved.

I shall venture however to criticise certain opinions that
have been put forward concerning the stratigrapbical relations
of some of the beds, and to state some inferences regarding the
physical geology of Cambridgeshire which seem to follow from
a consideration of the facts recorded in the preceding pages.

At the time of writing this Essay I looked upon the main
features of the country as determined before the Glacial
Period; some of them were demonstrably in existence before
the incidence of the Upper Boulder Clay, and it was equally
evident that most of the minor features were produced at a
subsequent date. I saw no grounds for supposing that there
was any marked break in the glacial series, but was disposed to
agree with Mr Penning, that, in the succession and transgressive

Sl

extension of these deposits, we had the evidence of a gradually
deepening marine area, open to the north, with land on the
south and west. I believed, moreover, that the Norfolk Lower
Glacial was a local deposit containing Scandinavian drift from
the N.E. and accumulated before the cold became great enough
to cause the formation of ice near the sea-level in Britain, but
that as the land sank and the cold increased, bergs and coast-
ice from British shores supplied the detritus found in the
superior and wider-spread deposits.

Messrs Wood and Harmer however have lately published a
long paper in which they discuss these questions, and put for-
ward two important considerations’; (1) that the Contorted
Drift, which they class with the Lower Glacial, had a much
wider southward extension than previously supposed ; (2) that a
marked unconformity exists between the Lower and the Middle
Glacial deposits, the break being of such extent and importance
that all the valley systems of East Anglia had their inception in
the intermediate period.

Suggestive as the whole paper is, I cannot consider that the
evidence for either of these propositions is at all satisfactory.
The identification of the Suffolk brick-earths with the Contorted
Drift is by no means certain; and the section mainly relied on
to show the unconformity between this deposit and the Middle
Glacial, viz. that along the coast of Norfolk, is, to say the least,
capable of a different interpretation. The conclusion to which
I came after a careful inspection of it was that the gravels
formed part of the contortions, and were closely connected with
the beds below instead of being separated from them by a
marked line of erosion and denudation’,

The last few pages of the paper are devoted to a considera-
tion of the mode in which the Middle and Upper Glacial beds
are accumulated ; the authors conjecture that a branch of the
ice-sheet, moving southwards from Yorkshire and Lincolnshire,
and being of great thickness (1200 to 1500 feet), occupied all
the low ground of the midland counties as far south as Bucks,
“in such a way that it avoided all but the extreme west of

1 Quart. Journ. Geol. Soc. Vol. xxx. p. 74.
2 My colleague, Mr C. Reid, informs me that his survey of the Cromer coast
has led him to take the same view.

82

Norfolk and Suffolk,” which counties were submerged to an
extent of 400 feet below their present level. They think that
the Middle Glacial was kept out of this midland area by the
presence of the ice-sheet, and that it was only accumulated
beyond the limit of the land-ice by the currents which washed
its edge.

All this, however, is so purely conjectural, and though it might
account for some of the facts, yet it seems to create difficulties
so much graver than those which the authors seek to explain,
that it is impossible to take it as representing, with any degree
of probability, the actual physical conditions of the period.

Admittmg therefore that at present we cannot hope to
account for all the phenomena presented by the glacial deposits,
I am still inclined to think that a modification of the older
theory, and the supposition of a gradually increasing submerg-
ence from the date of the Forest Bed, offers the fewest difficulties
in explanation of their mode of occurrence.

In this connection I would call attention to the claims of
coast-ice, recently advocated by Prof. J. Milne, to be regarded as
an important agent im glaciation. Such ice operates in less
depth of water than berg-ice, and is found to carry much
greater quantities of material; moreover it is capable of ex-
plaining the local character which the Boulder Clay almost
everywhere exhibits, and which has been thought a fatal
objection to the marine theory.

Such a gradual submergence does not of course preclude the
possibility of there having been minor oscillations of level, and
changes in the amount of cold during the whole general period ;
but it would appear that the deposition of the Chalky Boulder
Clay marks the maximum both of depth and cold, and that the
land then gradually rose again from out of the glacial sea.

Starting therefore with the supposition that at this time the
whole of Cambridgeshire was deeply submerged, let us consider
what would be the result of its gradual re-elevation. It is clear
that the clay-covered escarpment of the Chalk would first rise
as a low ridge, and would be subjected to the action of marine
currents; these would sift and re-arrange the Boulder Clay,
forming deposits of gravel such as exist eastward, northward
and westward of the highest portions of the scarp.

$3

As the land continued to rise and increase in extent, rain
would fall upon its surface, perhaps in greater quantity than at
present; streams and rivers would come into existence, still
further arranging both the Boulder Clay and the coast-gravels
previously formed; and these rivers would have a general
tendency to flow from the dominant ridge towards the N.W.
and §.E., the northerly tendency being increased in Cambridge-
shire by the slope of the country towards the estuary of the
Wash, which was in existence before the incidence of the
Upper Glacial Clay.

Taking the above as an outline of what would probably
happen during such an emergence of East Anglia as was
initially supposed, it is satisfactory to note that all the deposits
described in this Essay are fully accounted for by such a series
of events, and that their relations to one another are perfectly
explicable on this hypothesis.

The “Hill gravels” and their probable equivalents, the
“ Plateaux”’ or “ Flood gravels,” seem to have been accumulated
rapidly, and like the Middle Glacial sand and gravels they are
apparently marine; yet so closely are they connected with a
second set of gravels which are clearly of fluviatile origin, that
no long period of time can have intervened between the forma-
tion of the two series; the conditions which caused the pro-
duction of the former seem also to have led to the formation of
the latter, and from this time to the present there is no reason
for supposing that East Anglia has been subjected to any other
influences than those of rain and rivers. |

Turning now to a consideration of the changes that have
taken place since the emergence of the country from the glacial
sea, the evidence afforded by the series of ancient river gravels
leads to some interesting results.

It is indeed a significant fact that in these higher districts
the gravels have a recognisable relation to the existing valleys,
while when they emerge upon the plain country all such con-
nection is lost, and the direction which they take across the
country is quite irrespective of the present river system.

We may at once conclude that the outline of the hill
country has not changed so much as that of the plain, and that
its present valleys are but the more deeply excavated termina-

84

tions of the old valleys which these ancient rivers had formed
and which were once continued across the country; their lower
prolongations, however, have since been entirely destroyed, and
instead of valleys long ridges only now remain, cut through at
various points by channels of more recent origin. Such a
result might indeed have been anticipated, since water flowing
down a steep slope and cutting a deep groove for itself must
tend to keep approximately in the same channel for a longer
period of time than when it reaches lower and more level
ground, where very slight changes are sufficient to produce great
deviations in its course. Still it is none the less interesting to
find the result so clearly stereotyped on the country as it is by
this series of gravels, which enables us to estimate roughly the
enormous amount of denudation which has taken place since
the time when they formed valley bottoms instead of elevated
ridges.

We see therefore that while little change seems to have
taken place in the higher parts of the old valleys, where the
watercourses still preserve their original directions, and patches
even of the primeval mantle of Boulder Clay still remain upon
the bounding heights; great changes have gone on outside the
hill district, resulting in the removal of much material, and
causing many important alterations in the direction of the main
rivers.

The whole succession of post-glacial valley gravels seems
indeed to have been singularly well preserved in this part of
England, and if the various beds could be thoroughly dis-
entangled, they would mark out the courses of the streams at
different times, and present us with a picture of the successive
changes which have taken place in the river system from the
glacial period to the present time. Without attempting to give
such a history of the manner in which Cambridgeshire was
moulded, I think the following statements regarding the relative
age of its principal physical features are warranted by the
evidence which has been brought forward.

(1) That the great hollow of the north fens existed to a
great extent before the incidence of the Upper Boulder Clay ;
but that of the south fens between Ely, Newmarket, and Cam-
bridge had no such existence, having on the contrary been
formed subsequently to the removal of the Boulder Clay.

85

(2) That the valley of the Cam above Whittlesford and its
tributary valley through Linton are the oldest channels in the
district, dating from a time anterior to the formation of the
Chalky Boulder Clay.

(3) That the valleys radiating from the Chalk escarpment
had their inception in early post-glacial times, when the drain-
age system was entirely different from that of the present
rivers.

(4) That the first determination of the waters towards the
present system is marked by the series to which the Barnwell
gravels belong; that the gravel-filled hollow between Shelford
and Cambridge marks an intermediate stage; and lastly that
the present valley of the Rhee and Granta is the newest of all,
and that its direction is nearly at right angles to the earliest
lines of drainage.

CAMBRIDGE: PRINTED BY C. J. CLAY, M.A., AT THE UNIVERSITY PRESS.

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