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THE

POST-TERTIARY GEOLOGY

CORNWALL.

W. A. E. USSHEE, F.G.S.,

OF H.M. GEOLOGICAL SURVEY OF ENGLAND AND WALES.

1879.

Printed foe Phivate Circulation,
By Stephen Austin and Sons, Hertford.

c..e Geology of Copnwall

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THE

POST-TERTIARY GEOLOGY

CORNWALL

■W. A. E. USSHEE, F.G.S.,

OF H.M. GEOLOGICAL SURVEY OF ENGLAND AND WALES.

1879.

Printed for Private Circulation,
Bt Stephen Austin and Sons, Hertford.

CONTENTS.

Prefatory Statement 1

Part I. — The Pleistocene Deposits of Cornwall 9

Part II. — A Classification of the Pleistocene Deposits of

Cornwall 37

Table of Classification 50

Notes on the Pleistocene Deposits of the Cornish Coast near

Padstow 53

i

ox

CORNISH POST-TERTIARY GEOLOGY.

PEEFATOKY STATEMENT.

In the course of a series of articles on the recent geology of Corn-
wall, begun in January last, in the "Geological Magazine," I referred
in the March number, p. 102, to papers on the same subject which
I had submitted to the Geological Society. These papers contain the
Inilk of original observations made by me during leaves of absence
in 1876, and also embody such quotations as are necessary to
establish the classification put forward, being the records of pheno-
mena which could in no way come under my personal observation.
The articles in the "Geological Magazine" were intended to supple-
ment this general work of description and classification, by bringing
out the historical part of the subject, the mass of bibliography, and
detailed accounts of each section of the paper : so that the com-
bined papers might bring into one view all that had previously
been written on the subject, and show that the reasoning was
logically founded on fact, and that facts not coming within the
author's direct observation had not been distorted to accord with his
views. The whole subject was originally embodied in a single
paper too voluminous to obtain admission in any Society's Journal.
It lay dormant for two years, during which I neglected no oppor-
tunity of adding to the details which a survey of the superficial
deposits of Devon and Somerset, extending over the six previous
years, had enabled me to accumulate. The general results of my
survey of the recent deposits of Devon and Cornwall are to be

1

'i CORNISH POST-TEKTIARY GEOLOGY.

found in a paper, entitled '-'The Chronological Value of the Pleis-
tocene Deposits of Devon," Quart. Journ. Geol. Soc, 1878, vol.
xxxiv. pp. 449-458. Finding the results arrived at by independent
studies of Devon and Cornwall dovetail, I felt bound to bring out
my views respecting the latter county, and accordingly recon-
structed the original MSS., giving the general results in the
papers here prefaced, viz. a General Description (Part I.) and
Classification (Part II.), and a separate account of the most in-
teresting combination of recent geological phenomena anywhere
to be found on the south-western coasts of England.

In transmitting these papers to the Geological Societ3S in October,

1878, I stipulated that in the event of any abridgment being decided
on by the Council, the MSS. should be returned to me, and no
abstracts printed in the Journal. On December 4th, 1878, brief
abstracts of the papers were read, in my unavoidable absence ; and,
considering the nature of the subject, I do not think better abstracts
could have been made, as far as one can judge from the resumes in
the fortnightly "Abstracts of Proceedings." On February 19th,

1879, I received the following letter : .

Geological Society, Burlington House, W. ^
My dear Mr. Ussher, — The resolution passed by the Council
was to the effect that your two papers on Cornish Pleistocene
Geology should be printed "in short abstract in accordance with
the opinion of the Referee." The opinions expressed by the
Pieferee I have copied, and now inclose. — Yours truly,

W. S. Dallas.

Tlie form for the guidance of the Referee is as follows : —

1st. Is it desirable that the paper, as it stands, should be
published in the Quarterly Journal of the Society, as containing
new facts, or new views of the bearing of admitted facts, or appa-
rently well-founded corrections of important errors as to matters of
fact, published in the Journal of the Society or elsewhere ? or,

2nd. Is it desirable that any part of the paper should be omitted,
as merely general observations, or as unnecessarily controvei'sial,
or as containing expressions liable to give just cause of offence, by
reason of their personality, or otherwise ? or,

3rd. Can the Paper, for other reasons, be altered or abridged,

PREFATORY STATEMENT. <i

without detriment, either in the text or in the illustrations ? if so,
you will please to mark, in pencil, the parts which, in your opinion,
may be so altered or abridged ; or,

4th. Would an abstract, only, give all that is important in the
paper ? and would such abstract require any woodcut or other
illustration, regard being had to previous publications on the same
class of subjects ?.

5th. If any illustrations accompany the paper, can any one, or
more, or all of them be dispensed with, being of a kind either well
known, or merely ideal, or too indefinite, or incorrect?

The following is the opinion of the Keferee : —

The Pleistocene History of Cornwall. Part I.

(1), "This paper does not comply with any of the requirements
under the first query (see form herewith inclosed). The avowed
object of the communication was not to record any original personal
observations, but to arrange the plentiful material of Messrs. Boase,
Carne, Henwood, and others, in a connected history of the Pleis-
tocene period in Cornwall, an attempt not hitherto made.

" The author was in Cornwall in 1876, and visited certain
localities, of which sections and descriptions had already been
given in well-known publications. Such being the nature of the
paper, it cannot be recommended for publication in the Quarterly
Journal, in accordance with first query.

(4). "An abstract would suffice."

Pleistocene History of Cornwall. Part II.

" A. classification of the Pleistocene deposits of Cornwall. The
author's method of treating this part of his subject leads to a great
deal of repetition of Part I. There are not any new views to
warrant the publication, in extenso, of such a memoir in the
Journal. I would point out the age assigned to the oldest deposits,
Crousa Downs, etc., etc., which is just that which Sir H. de la
Beche speculated upon.

"So also the ' Classification' is merely the order of sequence for
the rest of the series, which that geologist has adopted in his
report."

* cornish rost-tertiary geology.

Pleistocene Notes on the Coast of Cornwall, near Padstow.

'■' This locality was visited and described by Mr. Henwood in
1858. The several phenomena of blown sands, either loose or
cemented, with littoral and sand-hill shells, with an under-layer
of old vegetable surface, all occur there, but not with so distinct
relations as at so many other places on the Western Coasts.

"In the greater portion of the paper tlie author argues out
certain hypothetical considerations, which, however, do not conduce
to any very definite views. In this communication, as in the two
former, the term Pleistocene has been adopted, but there is no
definite explanation as to the precise portion of geological time
which is thereby meant.

" Abstracts of these communications will suffice."

Such is the substance of the Eeferee's report.

Having called attention to the state of the Eeferee system at the
Anniversary Meeting of the Society, on February 21st, I sent in
tlie following reply to Mr. Dallas's letter of the 19th : —

Dear Sir, — I have to acknowledge the receipt of the decision
of the Council respecting certain papers of mine on the Pleistocene
Geology of Cornwall. In transmitting the papers in question to
you, I signified my desire that the MSS. should be returned, and
no abstract, however brief, printed in the Quarterly Journal, in the
event of the least abstraction being decided on by the Council,
except in the matter of illustrations, of which some were marked
as capable of being dispensed with. I now ask that this request
should be complied with, unless the Council decide that the papers
in question be printed in full, after consideration of the accom-
panying memoranda, embodying my objections to the decision of
the Referee. — I am. Sir, yours faithfully, W. A. E. Ussher.

The following answer to the Eeferee was accompanied by the
original notes made by me in Cornwall on maps and in note book,
to vindicate the title of the paper to originality in substance as well
as in form.

Answers to the Eeferee's Eerort on Papers relating to the
Pleistocene History of Cornwall.
In answer to the first objection, I have to adduce the Eeferee's
quotation of the words, " in a connected history of the Pleistocene

PREFATORY STATEMENT. 5

Period in Cornwall ; " such a histonj having never before been
attempted, it was absolutely necessary to collect the scattered, and
often casual, observations of jDrevious workers, more especially
those relating to submerged forests and stream-tin sections, which
I could have no opportunities of observing ; but the major part of
these quotations were reserved for separate publication, such only
as were considered indispensable to illustrate the inferences drawn,
and for purposes of classification, being retained in the papers under
consideration.

As to original observations, I can only submit to the Council the
maps on which my observations were made and the notes written
on the spot. These will establish my claim to have exceeded all
previous observers in amount of original observation respecting the
Post-Tertiary Geology of Cornwall. The Eeferee states that the
localities visited by me had previously been described with sections.
Many localities had been described, and a few sections had been
given ; but the descriptions were wanting in essential particulars,
and the sections mere sketches. In almost all of them the Head
was barely mentioned, whereas in my paper it has been assigned
an important place ; De la Beche neglected it, and Mr. Godwin-
Austen gave very few observations of its occurrence in Cornwall,
and applied solutions to account for it, which I consider inad-
missible in some cases. Even if, in other respects, my paper were
a replica of De la Beche's general observations on the recent
geology of Cornwall, the descriptions of this stony loam, or Head, and
its insertion in the sequence of deposits, looidd redeem the paper from
every objection brought against it by the Beferee.

The repetition complained of in Part 11. was occasioned by the
construction of the paper to permit of division into separate parts
both in reading and printing, if necessary.

Notwithstanding this alleged repetition, I have been accused of
adopting De la Beche's views, whereas in the essential particulars of
the relative age of the Submerged Forests and Baised Beaches,
a reference to p. 425, lines 20, etc., of the Beport, ivill show that I
entertain a diametrically opposite opinion.

Sir H. de la Beche embodied his views in chapters, and gave no

6

CORNISH POST-TERTIARY GEOLOGY.

dlstiact classification.^ He described the St. Agnes and Crousa Down
deposits as supra-Cretaceous ; my opinion respecting them is derived
from original observations made in Cornwall, Dorset, and Somerset ;
from a minute survey of about 800 square miles in Devonshire ; and
from the facts, not opinions, of previous and contemporary observers.
By accumulating these materials during several years, I have
endeavoured to bridge over the gaps in the chain of Post-Tertiary
chronology in Devon and Cornwall occasioned by the general
absence of the earlier deposits ; but, as negative evidence and
I'oasoning from analogies are, in some cases, the only modus
operandi, I availed myself of them, and this has laid me open to
the charge of entertaining "not very definite" views, brought
against me by the Referee, on a subject where very definite views
could not be put forward without evoking imaginary deposits, or
binding myself to hypotheses which, although I have now strong
grounds for entertaining them, might have to be modified, or
possibly abandoned, in the light of future discoveries.

Next, as to my paper on Pleistocene, or Post-Tertiary, phenomena
near Padstow. These observations were not included in the larger
paper, owing to their extreme importance. In no other part of the
South-Western counties has so interesting a collection of Pleistocene,
or Post-Tertiary, phenomena been observed within so small a space.

The Eeferee's remarks on this paper are irrelevant. I have
given Mr. Kenwood's notes on the Dunbar (Doombar) submerged
ibrest in MSS. for articles in the " Geological Magazine," containing
a mass of details not embraced in the papers submitted to the
Society. Mr. Hemcood did not observe the old consolidated beach on
Dunbar Sands, which is exceedingly interesting, and has, as far as
I am awai'e, never been noticed before.

The Greenway Clifi" section is also exceedingly interesting. If I

could find a few more sections resembling it, the Referee would have

less cause to find faidt with the indefinite parts of my classification.

This observation is quite original ; it stands alone ; and either of the

hypotheses i:>ut forward to account for it by me are warranted by

the facts.

' In the second edition of his Geological Manual (1832), p. 159, a distinct classifi-
cation is given by De la Beche, but its application is restricted to the Plymouth
raised beach. This classification resembles mine, and would have been mentioned
had I noticed it. Although it is not quite relevant. — May 23, 1879.

PREFATORY STATEMENT. /

As to any objection to the term Pleistocene, I would willingly
have altered it to Post-Tertiary, Post-Cretaceous, or some equally
suitable title, bad such emendation, been suggested by the Council
on admission of the paper for reading. I trust. Gentlemen, that
the above statement of the case may suffice to show that it is
impossible for me to allow the papers to appear in the form recom-
mended by the Eeferee, or with any abridgment whatever.

W. A. E. USSHER.

On March 2nd I was informed that the Council would not
reconsider their original determination. On March 3rd I received
the MSS. from Mr. Dallas, which I now publish without any
alteration, addition, or elision (except as regards the supposed fault
in Mr. Pattison's Fowey section).

If the decision of the Eeferee were taken upon papers prior to
their admission for reading, authors would have the option of with-
drawing their papers or not in the event of an adverse decision ;
and by incorporating my papers with the articles in the " Geological
Magazine," I should have been spared this unpalatable preface.

By the present system very few long papers can be done justice
to in the brief extracts or abstracts to which the author is obliged
to confine himself in reading, so that if such papers be afterward
printed in short abstract, it is impossible for any one but the
Eeferee to judge of their contents. Whilst the universal admission
of papers for reading tends, on the one hand, to crowd out the longer
and more general papers, by placing a hasty observation of an
isolated section on a level with the geology of a county ; it entails,
on the other, the disagreeable necessity of curtailing lengthy papers,
not because they, in any way, transgress the rules laid down for
admission in extenso to the Society's Journal, but because their
publication would cause its "expansion be3'ond the limits which
economy prescribes. If a limit as to length were assigned to
general papers, and rules so clear and concise laid down that there
could be no misconstruction or misconception on the part of the
Referee, less scope for occult attacks would be afforded to indi-
viduals who, prejudiced perhaps with preconceived notions, may
now put their veto on the expression of contrary opinions, and
negative questions seen from a different point of view to their own.

0 CORNISH POST-TERTIARY GEOLOGY.

Whilst the abstract of a long paper when read may provoke but
a partial discussion, the Keferee has the power, as in my case, of
creating objections against a paper, which could be fairly quashed
in discussion, with the questionable satisfaction of knowing that his
victim is perfectly defenceless. I have, therefore, availed myself of
the only possible means of redress, as I conceive that the suppression
of opinions founded on facts and long investigation, and put forward
solely to supply a deficiency and arrive at the truth, is very likely
to prejudice their subsequent communications, unless (as I think the
foregoing correspondence will show) it can be proved that the
papers in every way fulfilled the requirements of the rules laid
down for the Eeferee's guidance, and that his recommendation to
print them in short abstract must therefore be attributed to ignorance
of their contents, and of the well-known work of previous observers
in the same field.

If future discoveries should prove the classification I have adopted
to be erroneous, they would be none the less welcome for presenting
new lights, which, in the present state of the subject, are much to be
desired, and for settling the object in view, namely, a true statement
of the recent geological vicissitudes experienced by Cornwall, though
that statement should necessitate the complete abandonment of ray
present opinions. The absence of connecting links, and the isola-
tion of the older superficial deposits in Devon and Cornwall, taught
me the value of guarded opinions in the face of doubtful or negative
evidence ; and no better proof of the value of waiting on facts can
be adduced than the admirable work of Sir H. de la Beche, as
embodied in his Eeport on the Geology of Devon, Cornwall, and
West Somerset, which owes its imperishable excellence to the extent
and accuracy of his observations, and tlie discrimination which he
displayed in not committing himself to definite opinions where direct
evidence was not obtainable.

To conclude, had the Eeferee simply recommended the printing
of the following papers in brief abstract on account of their length
and the number of quotations, I should have printed them without
this preface, which is written in vindication of my work, and in
answer to objections which I should hardly have deemed worthy a
reply had they been urged in discussion. W. A. E. U.

PART I.
THE PLEISTOCENE ' DEPOSITS OF CORNWALL.

INTRODUCTION.

Notwithstanding the excellent observations of Messrs. Boase,
Carne, Henvvootl, and others, which afford plentiful material for a
connected history of the later part of the Pleistocene period in
Cornwall, such an attempt has not hitherto been made.

With the intention of supplying this want, I visited Cornwall in
the summer of 1876, carefully observing the coast-line as far as
practicable in the following districts. From Polkerris, near Par, to
Coverack Cove in the Lizard district ; thence over Goonhilly Downs
to ]\Iullion ; from Mullion to Penzance ; from St. Loy Cove to the
Logan Rock ; from Cape Cornwall to the Land's End ; from St.
Ives to Godrevy Island ; St. Agnes Beacon ; from Porth Towan (to
the south of Peri-an Sands) to Tintagel. A thorough survey of the
inland districts, with which I am unacquainted, would, doubtless,
furnish a very valuable addition to the inquiry, notwithstanding the
numerous facts accumulated, selections from which are alone given
in this papei', so far as they are necessary to establish the conclusions
embodied in the Second Part (Classification).

The early Pleistocene history of Cornwall, like that of Devon, is
very obscure. The absence of any records of Boulder-clay, rocJies
moutonnes, or striations, gives no colour to the hypothesis that Corn-
wall was submerged during the Glacial epoch, or that it was invaded
by foreign ice. If land-ice helped to mould the contour, it must
have been local, and all traces must have been expunged by subse-
quent subaerial waste. The quartz gravels of Crousa Down and

^ The term Pleistocene is used in an indefinite sense, as the oldest deposits cannot
with propriety be included under that name in its ordinary acceptation; but as, with
their exception, the phenomena discussed, from Raised Beaches to the present time,
are Pleistocene, and with them the classification is principally concerned, no better
titles than Pleistocene and Post-Tertiary occurred to me. — W. U., Aug. 9th, 1879.

10 CORNISH POST-TERTIARY GEOLOGY.

Crowan, and tlie sands and clays of St. Agnes, are the oldest deposits
on record, and might be even referred to the Tertiary period.
Between these and the Kaised Beaches, with which the unbroken
record commences, save in occasional Boulder-gravels at high levels,
we have no connecting links. The numerous excellent examples of
Raised Beaches and stony loam, or * Head,' Avhich Cornwall affords,
owing to the greater extent of its Palaeozoic coast-line, and the com-
pleteness of the stream-tin sections, not only make the Pleistocene
history of Cornwall more interesting than that of Devon, but to a
certain extent make up for the absence of cavern deposits. As it is
not possible to treat deposits of different ages, when associated in
the same sections, separately, I have noticed Head and Raised
Beaches together, and embraced under the head of stream-tin the
deposits overlying the submerged forests, reserving the last place
for a brief notice of Blown Sands and Gravel Bars. In the second
part of the paper I propose to weave these materials into chrono-
logical order.

OLDEST DEPOSITS.
CroHsn Down Gravel.
Upon Crousa Down, in the Lizard District, a patch of quartz
gravel occurs at a height of about 360 feet above the sea, or about
20 feet lower than Roskruge Beacon. The ground is nearly level,
with a slight slope toward the south. It has been described by the
Rev. E. Budge.' I obtained the following section of the gravel pits,
which are from six to twelve feet in depth :

1. Brown earthy soil, vrith angular stones and pebbles of qnartz,

lying unevenly upon 1ft. to 4ft.

2. Eeddish-brown earthy sand, with angular fragments of quartz \

3. Light-brown and grey clay, containing patches of tine quartz ) 6ft.

gravel and loamy sand in places )

Below this the section was concealed by talus. The base of the
gravel is not shown ; the sides of two ponds at the bottom of tlie
pits are composed of quartz gravel. ,

On the opposite side of the pit to the foregoing, the deposit is

represented by quartz gravel of irregular pebbles and subangular

fragments, those of small size predominating, in brownish loam,

exhibiting no signs of bedding. On some parts of Crousa Down

1 Trans. Roy. Geol. Soc. Corn. vol. vi. pp. 1 and 91.

CORNISH POST-TERTIARY GEOLOGY. 11

the surface is studded with diallage boulders. Near Cowissack I
noticed that the boulders rested on soil of drab and light-brown
sandy loam, with small angular pieces of quartz, which was exposed
by a pond to the depth of one foot.

Mr. Budge ' says : " The whole country from Porthoustock to
Gwinter, four miles, is strewn with a broad band of scattered
boulders of a rock locally called Ironstone. A little to the west of
Crousa Down a stratum, commonly termed Marie, of decomposed
syenitic rock of the same character as the boulders on the Down, is
met with."

Quartz Gravel in the Parish of Crow an.

Mr. Tyack - notices the occurrence of quartz pebbles (evidently
derived from veins in the Killas) resting on granite, near Polorebo,
in the parish of Crowan, at about 400 feet above the sea, and about
150 feet lower than the lowest part of the adjacent watershed,
which separates the basins of the rivers Cober and Hayle. The
pebbles vary from the size of a pumpkin to that of a hazel nut ;
they are less rounded than beach pebbles, but more worn than those
in the river gravels of the neighbourhood. The pebbles occur in
surface soil, and in a subsoil of yellow clay, resulting from decom-
position of granite ; the larger pebbles have been found here and
there in the clay subsoil, in pits sunk to depths of from two to eight
feet. The area covered by the gravel is about 800 yards from north
to south, and 500 from east to west. The neighbouring granite hills
rise at least 100 feet higher than the site of the gravel, but it occurs at
a greater elevation " than any clay slate anywhere near it." In the
valley below the gravel patch, and one mile distant from it, similar
pebbles have been found mixed with refuse from the stream-tin
works.

Between Trewavas Head and PortMeven.

South of Tremearne houses, I noticed five feet of drab loamy clay
or earthy soil, with small angular slate fragments, and containing
near the surface numerous small well-rounded and smoothed flint
and quartz pebbles. The pebbles are found in brown earthy top
soil, for five chains eastward from a little stream which trickles

1 Trans. Eoy. Geol. Soc. Corn. vol. vi. p. 95.

2 Trans. Eoy. Geol. Soc. Corn. vol. ix. part 2, p. 177, etc.

12 CORNISH POST-TERTIARY GEOI^OGY.

down tlie cliff face. From the height of the cliffs it is very nnlikeh*
that these i^ebbles should have been hurled up by storm waves and
S25ray from time to time from the beacli below ; and as there is no
reason to suppose that they were brought to their present site b}'
human agency, I am inclined to regard them as relics of an old
gravel deposit, perhaps roughly contemporaneous with the gravels
of Crousa Down and Crowan.

Sands and Clays of St. Agnes.

St. Agnes Beacon is encircled on three sides by a deposit of sand
and clay, generally resting on stream-tin, and covered on the surface
by stony clay. This deposit occurs at more than 360 feet above the
sea, and rests on slate, except on the east of the Beacon, where an
isolated patch rests upon granite. De la Beche ' gives a section of
the deposits. Dr. Boase- another. Mr. Hawkins^ gives four sections
of pits at 375 feet above spring-tide high- water. Mr. Henwood *
gives a section, and quotes four others given by Mr. Thomas at
heights of 383, 377, and 418 feet above high-water. The most
complete set of observations is given in a paper by Messrs. Kitto and
Davies,* accompanied b}^ a map. A year previous to the publication
of this paper, Mr. Eobt. Hunt, F.R.S., Keeper of the Mining Records,
kindl}^ lent me ten sections of the St. Agnes deposits, beautifully
executed by Mr. A. T. Davies ; also a map. In Mr. Davies' paper I
find six of these sections given without illustrations. I have reduced
the following four sections from Mr. Davies' illustrations. (See
Plate.) The details of those marked C and E are not given in Mr.
Davies' paj)er ; section F is noticed, and corresponds to H on the
map accompanj'ing the paper; while section A corresponds to J on
the paper, being taken in the isolated patch on the granite where
the clays attain their maximum thickness.

(Plate, Fig. 1.) Section A, 24 chains distant from the Beacon

in the direction of W. 18^ S.

Soil and overburden 9ft. lin.

Candle clay 19ft. 7iu.

Pebbles, boulders, and sand, with a seam of sandstone oft. 2iii.

Upon waterworn granite.

' Report on Geol. of Com. and Devon, p. 260.

2 Trans. Roy. Geol. Soc. Corn. vol. iv. p. 296.

3 Ibid. p. 135, etc. * J/nd. vol. v.
6 Ibid. vol. ix. part 3, p. 196, etc.

CORNISH POST-TERTIARY GEOLOGY. 13

(Plate, Fig. 2.) Section C is nearly 45 cliains from the Beacon,
in the direction of N. 29° W.

Soil and overburdea 5ft. 9in.

Sandy overburden 1ft. lin.

Fireclay 6ft. 2in.

Sand 7ft. Oin.

Sandstone on sand 2ft. Oin.

Waterworn rock.
(Plate, Fig. 3.) Section E is 41 chains from the Beacon, in the
direction of N. 11° E.

Soil and overburden 6ft. lOin.

Candle clay 1ft. Sin.

Sand 14ft. Sin.

Sandstone oft. lOin.

Sand Oft. 4in.

Ou waterworn rock.
(Plate, Fig. 4.) Section F is 16^ chains from the Beacon, in the
direction of N. 9° E. It shows a cliff as laid open in mining
operations at Wheal Coit. The cliff facing north was first exposed,
and a level was then driven into it southwards (dotted line), when
sand was again found. " From which," says Mr. Davies, " it may
be concluded that we have here a wedge-shaped promontory from
the main cliff to the west."

Soil 2ft. Oin.

Overburden 20ft. Oin.

Bluish-grey candle clay 0 to 2ft. Oin.

Sand, with pebbles and boulders of granite and stream tin ore 2 to 7ft. Oin.

On waterworn Killas rock.
The candle clay is bluish, plastic, adhesive, and very tough. The
fire clay is bluish or yellowish, is coarse through admixture of sand
and gravel, but yields candle clay when well washed. The sand is
nearly pure silica, the grains being perfectly i-ounded and polished.
Its colour is in most cases removable by washing. The sandstone
is produced by cementing oxide of iron, and occurs sometimes in
cores with a sand centre, sometimes in flat uneven layers. The
pebbles vary from the size of a hazel nut to large boulders " weigh-
ing a ton or more." They are all from local rocks, and " vary with
the different districts, and may often be referred to the rock above
which they lie."

The variability and impersistence of the beds may be still further
seen from the following sections, which I obtained on the occasion
of my visit.

14

CORNISH POST-TERTIARY GEOLOGY.

1ft.

6in.

Oft.

6iu.

2 ft.

Oin.

4 ft.

Oin.

2ft.

Oin.

1ft.

Oil).

(Fig. 5.) Pit No. 1. Distant from the Beacon more tlian 40
chains, in direction W. 39° N. In one part we have : —

Blackish sandy soil with angular stones 1ft. Oin.

Reddish and yellowish-brown sandy loam, full of angular frag-
ments of grit and quartz

Loamy sand, red

Bluish-grey and brownish loamy sand, occasionally containing
small angular fragments of dark-grey slate, and quartz, passing
horizontally into 0 to

Fine bluish-grey sand 3 to

Drab and yellowish loam

Stiff light-di-ab clay, passing downwards into

Orange and yellow sand, not penetrated.

(Fig. 6.) Pit No. 1. In another part, where the section is about
9 feet in depth.

Eed-brown loam, with angular stones; of a lighter colour and with fewer
and smaller fragments at (a'); drab-coloured at (a-). Greenish and drab-
grey, tough sandy loam, containing, at (xx), bluish-grey, impersistent,
slightly clayey, bands ; fine bluish-grey sand, with small angular stones of
quartz, and dark-grey slate, here and there.

In another part of the pit :

Brownish and grey clay 3ft. Oin.

Stiff bluish clay, with a thin band of granitic sand near the top 4ft. Oin.
Fine orange sand, yellowish in places, compact, exposed to a

depth of 2ft. Gin.

Fig. 5. Pit Xo. 1.
Vertical Scale 1 in. = 12 ft.

Fig. 7. Pit No

jOrojOrO-Or o^O-

FiG. 6. Pit No. 1.

(Fig. 7.) Pit No. 2 is about 45 chains from the Boacon, in a direc-
tion N. 39° W. The section is about 10 feet in depth :
Blackish sandy soil, with angular stones.
Dark-brown sand with small yellowish-red spots in places.
Yellowish and orange sand.
Buff and grey sand.
Light-brown sand.

Impersistent seam of bluish-grey clay.
The colours of the sands merge insensibly into one another.

CORNISH POST-TERTIARY GEOLOGY.

15

(Fig. 8.) Pit No. 3 is about 50 chains N. 25^^ W. from tlie Beacon :

a. Brown clay with angular stones.

b. Dark reddish-brown clay and loam, with angular stones.

c. Orange, bright reddish, and yellow, fine sand.

(a, b, and c dovetail, a being above, and c below.)

d. Grey and light bluish-grey clay, loamy in places, and of a light
brown tinge toward the base, about four- feet thick.

e. Fine light-grey sand, about four feet thick.

f . Fine gamboge-coloured sand, orange in places, not penetrated.

(Fig. 9.) Pit No. 4 is about 47 chains N. Q"" E. from the Beacon :

Grey and blackish soil, with small angular stones, yellowish at

the base 1ft. Oin.

Brown loam, with angular stones resting irregularly on buff and
light-yellow fine sand, with angular fragments of slaty grit,
sometimes of large size 6ft. Oin.

Fig. 8. Pit No. 3.

Fig. 9. Pit No. 4.

BOULDER BEDS.

Mr. Hen wood * mentioned the occurrence of boulders at Morrab
Place, in Penzance, at 80 feet above the sea-level. At Lamorna
Cove, Mr. Came ^ noticed boulders of immense size in the roof of a
cavern ten feet above the highest tide. Between Lamorna Cove and
Mousehole he observed three to eight feet of boulders under 30
feet of angular fragments in clay, to the north-west of Carndu.

Near Carn Bargis he noticed a mixture of boulders and angular
fragments, about 20 feet above high-tide level. The roof of Gamper
Hole is composed of granite boulders, under 20 feet of granite frag-
ments in clay, and is 40 feet above high-tide level.

1 Trans. Roy. Geol. Soc. Corn. vol. v. p. 112.

2 Jbid. vol iii. p. 229, etc.

16 CORNISH POST-TERTIARY GEOLOGY.

At Pecln-men-du Mr. Carne observed a few boulders at 30 feet
above tbe sea. The same observer records the occurrence of a bed
of boulders 15 feet tbick, in a disintegrated granite and clay matrix,
at 50 feet from tbe surface, and about 500 feet above tbe sea, in
sinking a sbaft at Huel Carn tin mine. No boulders were found in
tbe lode.

Mr. Salmon mentioned tbe discovery of granite boulders at 74
fathoms from tbe surface in West Eosewarne Mine, Gwinear, which
he thought had been introduced by fissures from the surface.

At Eelistan Mine Mr. Carne mentioned the occurrence of a mass
of slate pebbles at 100 fathoms from the surface, but he commented
on the presence of spheroidal concretions in the slates in the vicinity^

Mr. Whitley ^ gives a sketch section from Zennor Castle to the
coast on the north of it, showing boulders of granite on the surface
of a bed of decomposed granitic loam, thin on the slope, but as much
as 10 feet thick on level ground, and resting alike on granite and
killas. Though the above may be due to early Pleistocene denuda-
tion, it is more probably ascribable to the period during which the
Head was accumulated. Diallage boulders are similarly separated
by soil from their parent rock in the Lizard District.

EAISED BEACHES AND HEAD.

In the garden of a house by Par Harbour, near Spit Point, I
observed gravel (composed of small rounded pebbles of quartzite and
granitic rocks, generally of small size, with rounded and subangular
boulders) and beds of greenish grey sand (with reddish streaks and
fragments of shale), about 6 feet in thickness, and 8 feet above high-
water mark at its base.

On the north side of Spit Point, I obtained the following section :

Brown sandy soil : gravel of pebbles, principally quartz 4ft. Oin.

Brown gravel finer than the above : gravel with boulders 3ft. Oin.

Grey loam with quartz pebbles 1ft. Oin.

resting on slates at 8 feet above the present beach.

On the south of Spit Point the base of the gravel is about 10 feet
above high-water maik.

1 Jouru. Eoy. Inst. Corn. Xo. 11, p. 184.

CORNISH POST-TERTIARY GEOLOGY, 17

(Fig. 10.) Gerran's Bay. The base of tlie Eaised Beacli is only
a foot or two above the reach of spring-tides in some spots, although
its average elevation is between 5 and 15 feet above high- water mark.

In one place the section consists of :

Brown loam with angular stones of slate and quartz 10 to 15ft.

Orange-colom-ed sand or loam 1ft.

Eeddisli-brown sand with coarse and fine quartz gravel, and

angular fragments of slaty rock, sometimes of large size ... 6ft.

Fig. 10. Gkrean's Bat. Vertical Height of Cliflf, 25 to 30 feet.

A ^Afl^

Near Pendowa, the beach is absent, and the angular accumulation
rests directly upon the slates.

Falmouth. To the west of Pendennis Point, Head of flattish
angular slate fragments and large angular pieces of quartz in grey
loam, becoming reddish-brown near the base, rests upon — light
yellowish-brown loamy clay, containing a few small angular stones
on — dark-grey slates with quartz veins.

South of the. Falmouth Hotel.

Under Head, traces of a beacli or old river gravel of quartz pebbles
in a brown and blackish sandy matrix, consolidated in j)laces, rest
on a waterworn rock platform at from 3 to 6 feet above high- water
mark.

Between the above and Swanpool Point, a bed of quartz pebbles,
2 feet in thickness, rests on slates at about 10 feet above high-water
mark.

Near Bream, to the south of Maen Porth, under stony loam, 4 feet
of blackish and brown sand, with angular slate fragments, is exposed
in the cliffs at from 10 to 15 feet above high-water mark. Beefs of

2

18 CORNISH POST-TERTIARY GEOLOGY.

rock in the vicipity exhibit planed surfaces at about 6 feet above
high-water mark, being probably remnants of the old beach bed.

During the accumulation of the Head in this section, the beach
appears to have been mixed with it.

In the Cove near Eosemullion Head, to the south of Bream, the
cliffs exhibit — Head of yellowish and brown loam, with angular
stones, on — blackish and brown sand, with quartz pebbles, 4 to
5 feet in thickness, and from 5 to 10 feet above high-water mai-k.

In Coverack Cove, the cliff to the north of the village is composed
of brown earthy sand with angular stones (the distribution of which
gives an appearance of bedding), upon — sand, with pebbles and
boulders of th6 neighbouring rocks, at base about 8 feet above high-
water mark. To the north of the above, 5 to 12 feet of buff and
greyish loamy sand, with iron-stained bands, contains pebbles and
boulders, in places, at its base from 5 to 10 feet above high-water
mark. I

In Porthbeer Cove, to the south of Coverack, pebbles and large j
boulders of diallage rock, and occasional small flints, in brownish
earthy loam, occur at about 10 feet above high- water mark. The
face of the low cliffs is composed of brownish sand, probably blown
against them.

Between Trewavas Head and Porthleven, south of Tremearne

houses, the cliff section shows :

Grey loamy soil, with flint and quartz pebbles 2ft.

Grey loam, with angular slate and granite fragments of rather

small size 3ft. to 5ft.'

Grey loam, with angular fragments of slate and granite, and

rough granite boulders 5ft. to 6ft.

resting upon nearly horizontal grey slates with quartz veins, at

from 12ft. to loft, above high-water mark.

(Fig. 11.) The low cliffs between Pra and Sydney Cove are com-
posed of Head, with the exception of the upper part, which consists (
of blown sand 2 to 3 feet in thickness. In one place, where the
cliff is about 14 feet in height, a trace of consolidated blackish sand,
made up chiefly of comminuted slate fragments, is visible at the
base of the cliffs about 2 feet above high-water mark ; it is overlain
by 12 feet of coarse granitic loam, containing angular fragments of
slate, granite, and quartz, and some subangular boulders.

Toward Sydney Cove the cliff becomes lower, and the Head

CORNISH POST-TERTIARY GEOLOGY. 19

varies, the upper part, for 4 feet, consisting of yellowish loam, with
small angular stones unequally distributed, upon — 5 feet of brown
loam, with small angular fragments of slate, and larger angular
slate, quartz, and occasionally elvan, stones. A few small flint and
quartz pebbles and angular stones are visible in a grey sandy top
soil.

Fig. 11. Pra Sands.
Vertical Scale— 1 inch = 96 feet. Horizontal Scale— 5 inches = 1 mile.

b h V

h Blown Sand. H H Head.

b' V Blown Sand mixing with Beach Sand obscures B Portion of a Raised Beach.

the section. S S Killas.

The cliffs to the west of Sydney Cove are composed of Head,
brown loamy clay, with angular fragments of slate and granite,
containing seams of brown clay with fewer stones, and passing into
stiff drab clay at the base of the cliff.

Near the above the cliffs are about 50 feet in height, and com-
posed entirely of greyish-brown loam and clay, with angular frag-
ments of granite and slate.

On a little promontory near the above, a trace of Eaised Beach is
visible ; it consists of 4 feet of reddish quartzose loamy sand,
containing pebbles, subangular slate boulders, and angular and
subangular fragments of quartz and slate. The base of the deposit
is about 5 feet above high-water mark ; it is capped by 10 feet of
Head, grey loam, with angular fragments. In another spot drab
clay overlies 2 feet of pebbles and angular and subangular fragments.

At Trevean Cove the cliff presents the following section :

Grey and brownish loam, containing angular stones (not of the
subjacent slates), occasionally presenting a stratified appear-
ance with a seaward inclination 8ft. 6in.

Coarse blackish and grey sand with quartz pebbles, and sub-
angular fragments, also large subangular boulders of green-
stone, one of which measured oft. by 2ft. 6in. by 2it 4ft. Oin.

A small piece of a broken flint pebble was obtained from this bed.
The base of the deposit is from 5 to 8 feet above high- water mark.

20

CORNISH POST-TERTIARY GEOLOGY.

The following section was obtained in the cliifs to the south of
Perranuthno :

Head of angular greenstone fragments in loam, in places stained
reddish, and with few stones toward the base, upon — fine quartz
gravel, or coarse waterworn sand mixed with earthy matter
from the Head above, 5 feet thick, and, at base, about 8 feet
above high-water mark.

Kear the above, under Head as before :

Coarse sand with earthy matter, cemented by iron into nodular

1ft.

Coarse sand, cemented in veins by iron

Coarse sand or fine gi-avel, chiefly composed of quartz ; grit,
slate and flint being also present ; containing angular and sub-
angular fragments of quartz and greenstone

3ft. Gin.
h-water

The base of the deposit is from 8 to 10 feet above h
mark.

(Fig. 12.) In St. Loy Cove, south of St. Buryan, to the east of
the stream, the clifi" section consists of:

Angular and subangular blocks of granite and stones of quartz,

slate and fine slaty grit in brown sandy loam 10ft. to 15ft.

Yellowish-brown loam, with angular stones and pebbles, of
granite, grit, and quartz, presenting an appearance of

irregular bedding 2ft.

Coarse angular granitic sand (Growan), with large rounded
granite houlders and pebbles of quartz, dark- bluish slate,
granite, etc. At base, about 10 feet above high-water mark... 4ft.

St. Loy Cote. 1 inch = 24 feet.

Land's End District.
In Sennen Cove, Whitesand Bay, here and there at the base of the
low cliffs, pebbles are visible under stony loam ; in one place a trace
of black, consolidated coarse sand binds two boulders of gi-anite, at

CORNISH POST-TERTIARY GEOLOGY. 21

about high-water mark. It is possible that this may be a relic of a
raised beach, destroyed at a higher level.

Between Pornanvon and Pol Pry, near the latter, the following
section was shown in the cliff :

Large granite boulders in soil

Yellowish-brown, coarse granitic debris (Growan) with large

angular fragments 15ft.

As above, with great angular boulders, and small fragments of
schorlaceous and porphyritic granite. The matrix becomes
darker in the lower part, and for 5 feet upward from its base,

exhibits an appearance resembling false bedding 2oft.

Granite boulders, round and subangular, with a few pebbles of
dark bluish-grey slate, resting upon decomposing granite, at
from 10 to 20 feet above high-water mark 2ft. to 5ft.

(Fig. 13.) Pornanvon Cove. The cliffs near the mouth of the
stream give the following section :

Head, of angular fragments of granite, some of great size, in

coarse granitic c^e'Sri* (Growan) 20ft.

Large granite boulders, smooth and well rounded, lying irregu-
larly on granite which in one place separates the bed altogether 5ft. to 15ft.

Fig. 13. Poknanvon. 1 inch = 32 feet.

The base of the boulder bed is from 5 to 15 feet above high-water
mark ; occasional smaller pebbles of slate and quartz occur in it.
In Priest Cove the following cliff section was obtained :

Head, of light-brown loam, with angular slate, and, occasionally,
granitic fragments, becoming darker in colour, and containing
fewer stones for from 5 to 10 feet from its base 10ft. to 15ft.

Blackish and brown coarse earthy sand 6in. to lit.

Gravel, chiefly composed of pebbles of altered slate, greenstone,

quartz, and, occasionally, flint 3in. to 2ft.

At base 5 to 10 feet above high- water mark.

12ft.

Oin.

Oft.

6iii.

5ft.

Oin

1ft.

Oin.

22 CORNISH POST-TERTIAR"t GEOLOGY.

The following section was obtained from the cliffs, near Cape
Cornwall.

Brown loam, with numerous angular fragments

Impersistent band of blackish loam

Dark-bro^\Ti loam, with fewer angular stones than the upper bed

Brownish-yellow sandy loam, with a few angular fragments ...

Brownish sandy loam, with angular fragments, and pebbles of

quartz, slate, and greenstone, and boulders near its base which

is in places on the level of the present beach 4ft. Oin.

Head is shown on a rock isolated from the cliffs, near Cape
Cornwall. Mr. Came ^ describes a Eaised Beach in Treen Cove, to
the east of Gurnard's Head Promontory, near St. Ives, composed of
pebbles and boulders of the subjacent rock of various sizes, in clayey
and sandy matrixes ; about 60 yards in length, 15 feet in thickness,
20 feet above spring-tide high- water ; and overlain by Head, earthy
clay with angular fragments.

(Fig. 14.) St. Ives. Cliff sections in Porthgwidden Cove, under
Head, of light brown and yellowish brown loam, from 5 to 15 feet
thick, shown in the north part of the cove.

Yellowish-brown loam 3ft.

Pebbles of grit, quartz, slate, and, occasionally, flint 3ft. to 6ft.

Fig. 14. Porthgwidden Cove, St. Ives.
1 inch = 24 feet.

In another part of the Cove :

Quartz, slate, grit, greenstone, and, occasionally, flint pebbles in

yellowish-brown sand 4ft. Oin.

Strip of rather fine yellowish sand 4iu. to 6in.

Quartz, grit, slate, and occasional flint and granite pebbles in

yellowish-brown sand 3ft. to 4ft.

The base of the pebble deposits is about 5 feet above high-water

mark.

1 T. 11. G. S. Corn. vol. vii. p. 176.

CORNISH POST-TERTIARY GEOLOGY.

23

The cliffs from a point west of Gwythian to Godrevy Island
exhibit a very fine example of a raised beach, at base from 5 to 8
feet above high-water mark.

In one spot, west of Gwythian, the low cliff consists of:

Blown sand 2ft. Oin.

Brown sand 5ft. Oin.

Gravel of grit, slate, quartz, and a few flint pebbles near the base,
at about 5 feet above high- water mark ; coarse black consoli-
dated sand, containing pebbles, fills up the inequalities in the
subjacent grey slate platform 2ft. Oin.

(Fig. 15.) At nearly three-quarters of a mile to the south of
Godrevy Island, I obtained the following section :

1. Head, of light-brown and grey loam, with angular fragments.

stained blackish at the base 15ft.

2. Brown and drab iron-stained sand, with bands of pebbles in places 10ft. to 15ft.

3. Pebbles of quartz and slate, of various sizes, with subangular

fragments of slate in coarse sand, consolidated near the base
in which a large boulder was noticed. Base of pebbles, 5 feet
above high-water mark 1ft. to 5ft.

Fig. 15. Godrevy Cliffs looking toward Gwythian.
Vertical height represented in foreground = 34 feet.

Near the above the old consolidated pebble beach forms the roof
of cavernous hollows in the slates in two places. Where the con-

24 CORNISH POST-TERTIARY GEOLOGY.

solidated sand beds attain their maximum development near Godrevy
Island, the section consists of :

Brown loam, mth angular stones Sft. Oin.

Coarse grej' and buff consolidated sand, with angular grains, in

beds apparently dipping inland. (Probably old blown sand.) 10ft. Oin.
Coarse grey sand, with pebbles scattered through it, and traversed

by a line of pebbles 6ft. Oin.

Coarse sand of qua»tz grains and comminuted shells, full of quartz

and slate pebbles and subangular fragments, and containing a

few pieces of flint ; a fragment of a Miirex was also obtained... 3ft. to 4ft.

Tlie base of the deposit is about 4 feet above high-water mark.

Eock platforms abound on this coast, their surfaces being planed
at about the level of spring-tide high-water.

(Fig. 16.) Near the point where the foregoing section was
obtained, a reef of rocks is noticeable at 70 j-ards from the cliffs,
and is capped by a pinnacle of Head, consisting of light-brown loam
with angular slate fragments. Just below the Head traces of
reddish and black consolidated sand fill up inequalities in the reef,
at about 10 feet above high- water mark. A pebble bed, at base not
much above high-water mark, occurs under Head, capped by blown
sand in the adjacent cliffs.

Fig. 16. O.v Godrevy Beach.

Kock Reef 70 yards from the Cliffs, bearing: traces of Raised Beach and capped by
a Pinnacle of Head.

CORNISH POST-TERTIARY GEOLOGY. 25

(Fig. 17.) Fistral Bay. General section :

Fig. 17. Fistral Bat.

1ft.

Oin.

Oft.

6in.

1ft.

6in.

1ft.

6in.

2ft.

Oin.

A. Pebbles of slate and quartz in coarse black consolidated sand.
BB. Boulders of quartz in the pebble bed A.

C. Cliff section — Angular quartz stones in sand and loam, upon — 10 feet of

sand and gravel, upon — 2 feet of gravel.

D, Cliff section — Head — upon coarse brownish consolidated sand beds, upon

— pebbles in black consolidated sand.
XX. Line of Eaised Beach, base about o feet above high-water-mark.

The following sections have been selected out of many observa-
tions which I made of the cliffs in Fistral Bay. Near the centre of
the Bay, under Head :

Coarse consolidated sand

Quartz pebbles

Coarse consolidated sand

Sand, with numerous small pieces of slate

Coarse consolidated sand

Coarse black sand, with bands of gravel, of pebbles, and sub-
angular fragments of quartz and slate ; occasional boulders
near its base, which is from 5 to 6 feet above high- water mark 3ft. Oin.

Near the north end of the bay, loam with angular slate fragments
rests on beds of consolidated sand, which appear to overlie —a Head
of angular fragments with occasional pebbles, resting on— -the Eaised
Beach sand and gravel.

In this case the old blown sand seems to have accumulated upon
talus resting on the Eaised Beach prior to the formation of the
Head above.

(Fig. 18.) At To wan Head, on the north of Fistral Bay :
Coarse brown consolidated sand beds, with a seaward dip of about

15° 6ft. Oin.

Coarse brown consolidated sand, with large angular and sub-
angular fragments and pebbles of quartz, slate, and granite ... 2ft. 6in.
Fine gravel, chiefly composed of quartz pebbles, containing large

angular fragments of slate , 1ft. Oin.

At base, from o to 6 feet above high-water mark.

26

CORNISH POST-TERTIARY GEOLOGY.

Fig. 18. Towan Head.
Vertical Scale— 1 inch = 20 feet.

"%^

Near Xew Quay Pier, a raised beach occurs on a rocky platform
about 20 yards in widtb, and from 5 to
6 feet above high-water mark. It con-
sists of tough, buff, sand rock, weather-
ing dark grey (frequently emitting
sparks when struck), containing large
slate and limestone boulders, quartz,
slate, and, occasionally, flint pebbles.
The boulders might have fallen from
cliffs overhanging the old beach during -_-::= ^"""^z^^"^-^^^^^ - ~
its formation.

Consolidated sand beds (old blown sands) are visible in the
adjacent cliffs. Bones of oxen are said to have been found in the
consolidated sands of New Quay.^

De la Beche says that the consolidated sands of New Quay are
sometimes cemented by oxide of iron or calcareous matter, and
sometimes by both.^ In the Fistral Bay raised beach, Mr. S. E.
Pattison ^ found Modiola vulgaris, Cytherea cliione, Patella, Ostrea.

(Fig. 19). Constantine Island is capped by brown sand, with
tests oi Patellce and broken Mytili to a depth of from 1 to 2 feet;
under which, toward the north part of the island, angular fragments
of slate and quartz, and occasionally gi-eenstone pebbles, are shown,
forming an impersistent bed 3 feet in maximum thickness, and at
base, from 5 to 8 feet above hiojh-water mark.

Fig. 19. Constantine Island.
1 inch = 24 feet.

^ii^^:p^^

1 From the small quantity of sand now drifted on the old consolidated sand dunes
of Xew Quay, De la Beche considered that the change of level had rendered the
locality less fit for .such accumulations than it was during the Eaised Beach forma-
tion.—De la Beche, Report on the Geology of Cornwall and Devon, p. 428.

2 md. p. 431.

* Trans. Hoy. Geol. Soc. Corn. vol. vii. p. 50.

CORNISH POST-TERTIARY GEOLOGY.

27

STREAM-TIN SECTIONS.

The records of stream-tin sections are so numerous and interesting
that it is difficult to make a selection without giving the stock
instances of Par and Pentuan and Carnon ; these, as well as some
interesting sections given by Mr. Henwood, in which probably con-
temporaneous beds are marked, have been omitted through want of
space, and a host of lesser sections are represented by samples here
and there.

(Fig. 20). By Mr. S. R. Pattison.' Fowey Valley Works :

Fig. 20. FowEV Valley Works.

14ft. Oin.
2ft. to 3ft.

4ft. to 5ft.
1ft. to 7ft.
3ft. Oin.

a. Peat

b. Fine washed sand

c. Peat, containing wood, ferns, hazel nuts, etc., well preserved,
also the horns of deer

d. Sand and rounded stones, with much tin

e. Peat, very hard and black, containing numerous trees, etc. ...

f. Peat, with a large tree trunk, found in June, 1847.

G. Granite shelf, on which large quantities of tin were found.

F. Possible fault, downthrow 5 feet, lined with small quartz
crystals. [Mr. Pattison has since informed me that he is in-
clined to refer this faulted appearance to unequal erosion of the
shelf at a quartz vein.]

Par and Pentuan.

In a shaft in the lower ground, near Par Estuary, a bed of sea

sand 4 feet thick, containing shells, was met with at 16 feet 6 inches

from the surface, between two beds containing traces of vegetation

mixed with debris. The description^ of this section is not suffi-

• Trans. Roy. Geol. Soc Corn. vol. vii. p. 34.

^ Report on the Geology of Cornwall and Devon, p. 403.

28 CORNISH POST-TERTIARY GEOLOGY.

ciently definite to enable one to make a rough correlation with the
beds given in Mr. Colenso's section' of the Happy Union Works,
Pentuan, where a bed of sea sand with shells, 4 inches thick, occurs
between beds containing forest remains, at 42 feet from the surface ;
but in the uppermost bed, 20 feet thick, sea sand is intercalated with
river sediments ; and a row of wooden piles was met with, their tops
being 24 feet from the surface, and on a level with spring-tide low-
water mark. Mr. Henwood ^ says that the tin ground in Pentuan
Works, near the sea, is below the sea-level and covered by sea sand
and shells, whilst in the stream works higher up the valley, the tin
ground rests on granite, and is covered by recent alluvia.

Mr. Rashleigh described^ the stream works of Poth and Sandry-
cock, in the valley between St. Austell and St. Blazey. The vale has
so gentle a slope that, but for a flood hatch, the salt water would flow
into Poth. It opens into the Par Estuary, the level of its basin being
considerably below low-water mark. The accumulation of a beach
bar prevents the sea from going up the moor, except by the adit.

Section of Stream Works at Poth, near the sea, and Sandrycock,
near the middle of the vale.

1. Vegetable mould about

2. Gravel and micaceous sand, mixed with loam in alternate beds

3. Light-coloured clay with a little mica, with traces of decaying

roots

4. Black peat

6. Light-coloured clay

6. Stiff light-brown clay, with light-bluish spots, containing de-

cayed vegetable matter ,

7. Sea sand and clay mixed

8. Very fine micaceous sea sand, with comminuted shells and bits

of slate

9. Coarser sand without shells

10. Solid black fen, with few vegetable remains (not used for fuel)

11. Tin ground and loose stones of various kinds

12. Killas, on which tin ground and in some places yellow clay rests

At Poth, near the bottom of the sea sand, and upon the sea mud,
horns of deer and wild oxen were found. A pair of the latter
measured 15 inches in circumference at the base.

1 lUd. pp. 401, 402, 403.

- Trans. Eoy. Geol. Soc. Corn. vol. v. p. 129.

3 Ibid. Tol. ii. pp. 282, 284, 286.

Oft.

Sin.

8ft.

Sin.

oft.

Sin

4 ft.

lin.

1ft.

4in

3ft.

lOin.

3 ft.

Oin.

4ft.

Gin.

6ft.

Oin.

2ft.

lOin.

1ft. to 6ft

CORKISH POST-TERTIARY GEOLOGY. 29

Section at Pendelow, St. Austell Valley ' Deposits wrouglit in
1873:

1. Granitic sand and gravel, divided by tliin partings of silt into

many separate beds , 6ft. to 8ft.

2. Peat (fen) often mixed witb and sometimes interlaid by micro-

scopic layers of granitic sand T^jft. to 2ft.

3. Granitic sand and gravel in many layers, the lower part being

much mixed with hardened mud 7ft. to 8ft.

4. Peat, very closely resembling No. 2

5. Granitic sand and clay, scarcely differing from No. 1 Sin. to 6in.

6. Peat, sometimes mixed with stems of fern, nuts, leaves, branches

of furze, alder, and hazel, and trunks of oaks; here and there

a few flints have been very rarely discovered 1ft. Oin.

7. Tin ground, of granitic, schorlaceous and quartzose, matter,

mixed with the oxide of tin, usually as sand and gravel, but
sometimes including subangular masses of granitic rocks and

vein stones, and more rarely thin scales of slate 2ft. to 4ft.

Upon granite shelf unequally eroded.

Section of Lower Creamy Works,- in a part of Ked Moor, in
Lanlivery. (N. of St. Austell.)

1. Peat 2ft. to 3ft.

2. Granitic, though slightly quartzose, clay of a greyish hue,

mixed with lamina3 of slate 1ft. to 3ft.

3. Tin ground of angular, subangular, and spheroidal masses of

pale-brown quartz, fragments of felspar mottled dark blue
and yellowish brown, clay and granitic gravel, thinly mixed
with rounded masses of tin stone. Flints of considerable size
occur at intervals, and particles of gold less frequently ... 4ft. to 5ft.

The roots of marsh plants peneti-ate to a depth of from 2 to 3
feet into the tin ground.

Shelf of pale-buff coloured clay.

The occurrence of flints in the tin ground is remarkable, unless
by that name siliceous fragments of Palaeozoic rocks are meant.
Section of Carnon Works, in 1807, by Mr. E. Smith r^

1. Mud and sand 7ft. Oin.

2. Granitic gravel, with a few shells (charcoal P) 4ft. Oin.

3. Pine gravel, shells, mud; irregular strata of oysters extend to

within 4 or 0 feet of the tin ground 12it. Oin.

4. Closer mud, shells, trunks and branches, sometimes exhibiting

the appearance of having been cut by an axe ; horns and

bones of stags, human skulls 19ft. Oin.

5. Tin ground 1ft. to 6ft.

1 Henwood, Journ. Eoy. Instit. Corn. vol. iv. p. 213.

2 Ibid. p. 214.

3 Trans. Eoy. Geol. Soc. Corn. vol. iv. p. 408.

30 CORNISH POST-TERTIARY GEOLOGY.

Mr. Henwood gives a section of Carnon Works,' evidently at some
distance from the above, for a bed containing moss, leaves, nuts,
wood, oyster shells, animal remains, chiefly cervine, and human
skulls ; 18 inches thick ; rests on the tin ground, and, when traced
seaward, gives place to silt, the lowermost bed of the overlying 53
feet of sand, mud, silt and shells.

De la Beche,^ commenting on these sections, says that the name
Carnon applies to a long line of works down the valley, and that
the shells in both sections correspond to species now living in the
Falmouth Estuary.

At Perranwell, an open work, moi-e than 50 years ago, showed : '

1. Angular gravel, sand and silt, -witli worn masses of granite and

slate, in thin beds ; deer remains were found at a considerable

depth, and still deeper oyster shells 12ft. to 15ft.

2. Fine silt, mixed with oyster shells, leaves, nuts, branches of

trees, and very rarely wing cases of beetles 6in.tolft. 6iu.

3. Tin ground, small rounded tin stones, angular and subangular

blocks of schorl rock, granite, quartz, quartzose slate, and

other vein stones. On shelf of clay slate 2ft. to 3ft.

In Gwennap,* toward the middle of the vale, half-way from
Tarnon Dean (?Tannerdane on the map) to the Arsenic Manufactory,
large rough angular masses of quartz, two or three tons in weight,
rested on a bed of silt, shells, and vegetable matter, at 16 feet below
the surface ; beneath this, at about 22 feet below high-, and 4 or 5
feet below low-watermark, an entire human skeleton was discovered
within the compass of the layer of animal, vegetable, and mineral
substances.

Cober Valley to North of the Loo Pool.
Mr. J. Eogers ^ says that in one part of the Cober Valley, 28 feet
from the surface and directly superimposed on the tin ground, a
vegetable stratum, containing leaves and trunks of trees, also hazel
nuts, was met with, there being no indications of vegetable growth
in the overlying deposits. At Wheal Cober no indications of marine
deposits were found on the Killas ; nor at Helston Gas Works, where
an excavation was made to a depth of 21 feet, or 7 feet below high-
water mark.

1 Journ. Eoy. Instit. Corn. vol. iv.

* Eeport on Geol. of Corn, and Devon, p. 404.

3 Ilenwood, Journ. Roy. Instit. Corn. vol. iv. * Jbicl. p. 206.

^ Trans. Roy. Geol. Soc. Corn. vol. vii, p. 352.

CORNISH POST-TERTIARY GEOLOGY. 31

Drift Moor Worlcs near Newhjn.

Mr. Carne ' says the tin ground in these works rested on the sides
and bottom of a clay-lined basin, on all sides except the north, the
point at which alluvial deposits resting on mounds of old workings
(carried on to a depth of 36 feet) came in. The tin ground was no
thicker at the bottom of the basin, 40 feet from the surface, than on
its sides, which are so steep as to come within a foot of it. An old
rag and chain pump and three copper coins, one Portuguese, with
the figures 169 still legible on it, were found in the alluvial debris,
the engine being 15 feet from the surface.

Mr. Carne - mentioned some stream tin works at Douran, noticed
by Borlase in 1738. The tin ore was pulverized, and occurred under
2 feet of sand and gravel, which becomes 40 feet thick at Douran
Hill on the east.

Treloy, in Parish of St. Columh Minor.

De la Beche ^ was informed that the tin ground in the Valley of
Treloy rests on an unequal surface ; that above the inequality, the
tin ground was poor, below it, abundant and mixed with mussel
shells, some of which were attached to the rock, as if they had
existed prior to the stream-tin formation, at a time when the sea
extended up the valley thus far.

Mr. Henwood * mentioned the occurrence of a thin bed of tin ore
at Treloy, covered by 8 to 10 feet of silt, vegetable matter, sand, and
mould, and betraying signs of old workings. Celts, coins, rings,
brass brooches were found. The rings were supposed to have been
magic rings of the Druids ; the coins appeared to be Eoman, a slight
crystalline incrustation was noticed on one or two of them. In a
later paper ° ]\Ir. Henwood gives the following section of the Treloy
works, probably those referred to above :

1. Successive layers of sand and gravel 8ft. or 1 Oft,

2. Vegetable remains 2in. to 6m.

3. Tin ground ..from 6in. to 2ft.

' Ibid. vol. iv. p. 47.

2 Ibid. vol. iii. p. 332.

^ Eeport on Geol. of Corn, and Devon, p. 405.

* Trans. Eoy. Geol. Soc. Corn. vol. iv. p. 63.

* Journ. Eoy. Instit. Corn. vol. iv. p. 219.

32 CORNISH POST-TERTIARY GEOLOGY.

He adds : " As every part of this deposit, wrought during the
memory of the generation now passing away, was beyond high-
water mark at Forth, and even above the level of the Kaised Beach
at Fistral, near New Quay, it contained neither shell nor other
substance of marine origin, but frequently afforded granules of
gold." The shelf consists of clay slate.

If De la Beche was not misinformed, we must suppose that the
Treloy Valley was excavated j^rior to the formation of the Raised
Beaches, or that the occurrence he describes occupies a very different
site from Mr. Henwood's section. If, however, it lay below high-
water mark, we might be justified in considering its formation as
subsequent to the submergence of the forests, and refer the tin
ground in this valley to a still more modern date.

sub:\ierged forests.

Looe.
Mr. Box ' noticed the exposure of oak, alder, ash, and elm trees
under sand and shingle, below high-water mark, on Millendreath
Beach, east of Looe. The trees were imbedded in compact peat,
chiefly composed of marsh plants.

Foicey.
Mr. Peach - states " that portions of trunks and roots of trees, in
situ, were exposed at Ready Money, in Fowey Harbour, by a heavy
gale of wind ; they were rooted in a stiff clay over which leaves,
flags, etc., and the elytra of beetles, are found."

PorthneUia (near Ilevagissrj).
Mr. Peach ' observed roots and parts of stems of trees, in situ, on
clay, surrounded by alluvial matter containing flags and the elytra
of beetles, on Porthmellin Beach, after a heavy gale.

Fahaoutli.
Mr. E. Claypole ^ notices the occurrence of peat, seldom exposed
except at spring-tide low- water, and after heavy south-easterly gales,
in the curve of the shore at Gyllyngvaes, Falmouth. The peat

' Twenty-sixth Ann. Rep. Roy. Instit. Corn, for 1844.

2 Trans. Roy. Geol. Soc. Corn. vol. vii. p. 12. ^ zbid. vol. vi.

* Proc. Rrist. Nat. Soc. vol. v. p. 3<5, lor 1870.

CORNISH POST-TERTIARY GEOLOGY. 33'.

contained trunks of alder, oak, and hazel (the latter frequently with
nuts and twigs attached), also apparently yew; and remains of red
deer, oxen, human skulls, and cut branches. The peat rested on
very tenacious clay, and continued down to low-water mark, being
overlain by a quartz pebble beach, rising to the level of the highest
spring-tides.

Maen Forth, near Falmouth.
The Rev. J. Eogers ^ observed the roots of an oak in peaty matter,
Avith leaves and roots of Iris pseudacorus beneath the surface of the
sand below high-water mark, on Maen Forth Beach. The roots
were in clay, resting on the solid rock. Pieces of peat were washed
ashore during gales.

Forthleven, West of Loo Fool.
The Eev. J. Eogers - mentioned the occurrence of stumps of oak
and willow, apparently in situ, imbedded in vegetable mould, under
10 feet of sand, at Forthleven, a little below low-water mark.

Mounts Bay.
The Mounts Bay Submerged Forest has been noticed by Leland ;
by Dr. Borlase,^ who says that the trees occurred 300 yards within
full sea-mark, and at high tide had at least 12 feet of water over
them ; by Dr. Boase,* who inferred, from the occurrence of nuts and
leaves in the vegetable mould, that the submergence had taken place
in the autumn. I select Mr. Game's ° account as giving the best
general description : "A mass of decayed plants, full of small
branches, twigs, and leaves, generally of hazel or birch, forming a
spongy brown substance, occurs under 4 inches to 1 foot of fine
sand, on the east of Fenzance, continuing for half a mile from east
to west, and being in its most southern i3arts, as far as ascertained,
20 to 30 feet below spring-tide level. Numerous prostrate tree
trunks, amongst which oak was noticed, were imbedded in brownish
earth full of woody fibre, beyond the pile of rocks near the Chyan-
dower Eiver."

1 Trans. Roy. Geol. Soc. Corn. vol. iv. p. 481.

2 Trans. Roy. Geol. Soc. Corn. vol. i. p. 236.

3 Trans. Roy. Soc. for 1757, p. 80.

* Trans. Roy. Geol. Soc. Corn. vol. iii. p. 131.
5 Ibid. vol. vi. p. 230.

8ft.

Oin.

4ft.

Oin.

12ft.

Oin.

1ft. to '2ft.

3ft.

Oin.

4 ft.

Oin.

34 CORNISH POST-TERTIARY GEOLOGY.

Further eastward the vegetable bed was 4 feet thick, consisting
of branches and twigs of hazel and birch in the upper part, and of
leaves and woody fibre in the lower part ; it extended to the eastern
Cressets rocks.^

The vegetable stratum generally rests on clay slates, or on a Ijluish
sand, and in one place on a mass of gravel. At Huel Darlington
Mine, in Marazion Marsh, Mr. Came obtained the following section,
in a pit near Marazion River :

1. Slime (? river) tjravel, and loose ground

2. Peat, with minute woody fibre (fit for fuel)

3. White sand, with Cardium edule

4. Oak and hazel trees lying in all directions ; hazel nuts loose

and on their branches ; a piece of oak, shaped as if for a boat
keel

5. Solid hard peat, closer than the upper bed (good for fuel) ...

6. Alluvial tin ground on clay slate rock

In a part of Huel Darlington Mine, where the tin ground was at
a higher level, bed 3 of the preceding section rested directly on the
tin ground.

Mr. Carne considered bed 4 to be a continuation inland of the
Mounts Bay Submerged Forest, the difference in level between them
being small.

Traces of submarine forests are said to occur at Perran Forth, St.
Colurnb Forth, and Mawgan Forth."

The forest near Fadstow, on Dunbar Sands, has been described by
Mr. Henwood.^

Mr. S. R. Fattison* notes the discovery of 20 feet of soil, between
high- and low- water mark, at Maer Lake, near Bude Haven ; ti-ees
of large size, and roots apparently in situ in dark clay, have been
found; also a bullock's horn 4 feet long and 18 inches in circum-
ference, and a stag's horn 5 feet in length.

1 Dr. Boase (Trans. Roy. Geol. Soc. Corn. vol. iii p. 172) describes the forest
stratum, traceable on the seaward side of the "West Green Sand Bank for 200 yards
in width, at low water, from Larrigan rocks to Newlyn, as " trunks and branches
of hazel, alder, elm, and oak (with leaves and the elytra of beetles), lying in all
directions; the larger ti'unks lie N.E. and S."W., they are split and frequently
perforated by Pholns daetyliis.

2 De la Beche, Report on Geology of Cornwall, etc., p. 419.

3 Fortieth Ann. Rep. Roy. Instit. Corn, for 1858.
* Trans Roy. Geol. Soc. Corn. vol. vii. p. 34.

CORNISH POST-TERTIARY GEOLOGY.

35

BLOWN SANDS AND GRAVEL AND SAND BARS.

From its more exposed situation the north-western coast-line of
Cornwall exhibits by far the most considerable accumulations of
blown sand. On either side of the Hayle Estuary, and extending
as far north as Godrevy Farm, the lower lands are buried beneath
sand dunes. The Perran Sands, in which traces of the ruins of
Constantine Chapel are still visible, cover a considerable area, attain-
ing in places to more than 300 feet above the sea-level. To the
south of Trevose Head the flat land lying on the west of the Camel
Estuary is covered by blown sand ; also tlie low-lying tract on the
east side of the estuary, in which St. Enodock's Chapel is situated.
Blown sand occurs between the latter spot and Tintagel in several
places, but of inconsiderable extent. The old consolidated blown
sands of the coast near Gwythian and Godrevy, and in Fistral Bay,
etc., show that a similar drift of sand prevailed during the Raised
Beach formation. A small patch of sand dunes borders Whitesand
Bay near the Land's End ; blown sand also caps tolerably high land
at Gunwalloe near Mullion, in the Lizard District.

Mr. Boase ' commented on the absence of documentary evidence,
or even popular tradition, of the devastation of considerable tracts of
land, and the engulphment of a number of churches by the blown
sand : " The particular circumstances of the catastrophe seem to
have been already forgotten when Leland visited the place, about
300 years ago ; and yet the period of its occurrence could not then
have been very remote, because ' the churches ' still extant are
evidently not of an age much anterior to that of Leland himself."
As, however, this devastation was most probably gradual, no sudden
influx of sand worthy of record may have taken place.

Blown sand sometimes forms the crest of sand or gravel bars on
the south-east coast. In the upper part of the West Green Sand-
bank, near Marazion Bridge, Mr. Edmonds - discovered numerous
land shells to a depth of from 7 to 8 feet from the surface. The

1 Trans. Roy. Geol. Soc. Corn. vol. ii. p. 141.

2 Ibid. vol. vi. pp. 303, 304.

36 CORNISH POST-TERTIARY GEOLOGY.

crest of the bank being 18 feet above high-water mark, proving its
^olian origin. Dr. Boase ' gives the following section of the bank :

1. Granitic sand, of quartz, mica, and hornblende slates, with a

little tin ore, quartz predominating 10ft. Oin.

2. Gravel, pebbles of hornblende slates from 1 to 3 inches in

diameter ICft. Oin.

Eesting on the forest bed, which ranges from 12 to 20 feet
below high-water mark, and rests on decomposed slates.

The West Green Sandbank is much shortened and greatly diminished
in area, there being evidence- to show that in Charles the Second's
time it afforded 36 acres of pasturage, whilst it is now but 2 or
3 acres in extent ; a diminution for which the large quantity of sand
abstracted for agricultural purposes ^ does not satisfactorily account.

Gravel and Sand Bars are almost entirely confined to the south-
eastern coast-line. The Loo Bar consists of coarse sand and fine
quartz gravel, with occasional pebbles of slate and flint. In 1837 *
a boring was made in the middle of the Loo Bar to a depth of 68
feet, or 30 feet below low-water, without meeting rock. The details
of the boring are not given. The waters of the Loo Pool, at a
point 400 yards within the bar, are 40 feet in depth at their ordinary
level.'

Swan Pool is dammed by a bar, chiefly composed of small quartz
pebble shingle, 80 yards in breadth, and from 3 to 5 feet above high-
water mark on its crest.

At the mouth of the Pentuau Valley a bank of coarse granitic
sand, in alternate light and dark (schorlaceous) layers, showing false
bedding, and rising to a height of 5 feet above high-water mark,
separates the alluvial land (also superficially composed of granitic
sand) from the sea. A second ridge is formed by a low range of
sand dunes at 6 chains inland, probably the sun-dried drift from the
bank which dams the sea from the low-lying land at the mouth of
the valley.

A low range of sand dunes runs across the head of the Par
Estuary, separating the alluvium from the sea-sands. Par Sands,
being of considerable extent, and uncovered for a long time between
the tides, would furnish the material for this ^a^olian drift.

' Trans. Roy. Geol. Soc. Corn. vol. iii. p. 131.

2 Ibid. vol. ii. p. 136, and vol. iii. p. 131. ^ Ibid. vol. vii. p. 31.

* Mr. J. Rogers, ibid. vol. vii. p. 352. « UiU.

37

PART II.

A CLASSIFICATION OF THE PLEISTOCENE
DEPOSITS OF CORNWALL.

OLDEST DEPOSITS.

The existence of a quartz gravel in a district composed of Diallage
and Serpentine on Crousa Down, and the occurrence of a similar
gravel resting on granite in Crowan, both patches being not only
disconnected with the pi-esent drainage system, but situated at such
altitudes as to preclude the idea of transport from adjacent sources,
lead one to infer :

1st. That (a) they were formed from the degradation of the Killas
and its associated quartz veins ; or (fe) from the disintegra-
tion and transport of a quartz conglomerate rock.

2nd. That they are the relics of deposits originally much more
extensive, formed at a time when the country possessed an
entirely different configuration.'

There being no means of arriving at a definite conclusion as to
the age of these gravels, or of the sands and clays of St. Agnes
Beacon, I can only include them within a long period ranging from
Cretaceous to early Pleistocene times, at the same time inclining to
the belief that the quartz gravels are either of Tertiary age or a
re-assortment of Tertiary gravels.

This indefinite chronology is not to be wondered at, when we
reflect on the absence of evidence respecting the extension of Creta-
ceous and Tertiary deposits to the westward of Haldon ; and specu-
late, in the event of such extension of either formation having
taken place, on the influence local sources of supply would have had
on the marginal sediments there thrown down.

1 This is also Mr. Tyack's opinion.

38 CORNISH POST-TERTIARY GEOLOGY.

The small flint and quai'tz pebbles noticed in soil on the top of
the clitfs near Trewavas Head, might likewise be considered as
of Tertiary origin,

Mr. A. Smith ' mentions the occurrence of small chalk flints not
much worn, and of fragmentary stones of Greensand on the surface
of Castle Down, on the north part of Tresco Island.

Mr. Peach ^ speaks of the " Chalk of No Best " off the Dodman
Point. Both these observations require confirmation, especially the
latter, so I give them without further comment.

The sands and clays of St. Agnes, occurring at a lieight of from
350 to 400 feet above the sea, and occupying a site quite disconnected
with the present drainage system, carry us back to a time so far
removed from the present, that subsequent agencies have obliterated
the relations of their site to its original surroundings, in the elabo-
ration of a new drainage system. If, as De la Beche suggested,
they are of marine origin, deposited, as Messrs. Kitto and Davies
think, in " a sheltered arm of the sea, into which a river emptied its
waters," the land must have been submerged to a depth of 400 feet,
and therefore their origin must be put back to a time very much
more remote than that during which the Eaised Beaches were
formed.

The exceptional development of clay where the deposit rests on
granite, and the peculiarly local character of the pebbles and
boulders met with in the different pits, seems to me to forbid a
marine origin. The thinning out of the clay toward the edges of
the main deposit, as shown in Section F and Pit No. 2, and in Section
B in Messrs. Kitto and Davies's paper ; the impersistent character
of the beds, as shown in the three sections of Pit No. 1 ; the absence
of all organic remains, save a very doubtful plant-like marking, are
much more easily explainable by fluviatile than marine action. The
exposure in 1875 of a cliff face (part of which is shown in Section
¥) 16 feet high, at 15 feet from the surface, with very large pebbles,
l)oulders, and angular fragments near its base, corroborates the
information De la Beche obtained, and might be taken as proving
marine action ; but, on the other hand, the very great irregularity
in the shelf in some stream-tin sections, the existence of false shelf

' Trans. Roy. Geol. Soc. Com. vol. vii. p. 313.
* Ibid. vol. v. p. 55.

CORNISH POST-TERTIARY GEOLOGY. 39

in some places, and of large masses of slate in tlie gravels (from
the disintegration and fall of rugosities in the river-bed or banks)
in others, renders it possible that the water-worn face and out-
standing pinnacle of the cliff may be due to fluviatile agencies.

The preservation of the sands and clays is probably due to an
envelope of talus shed from time to time through the weathering of
the high land of the Beacon (620 feet above the sea), and repre-
sented by the overburden or Head in the sections. This Head was,
in all probability, accumulated after a considerable denudation of
the deposits had taken place, so that it rested directly on the sands
on tlie edges of the patch. Such appearances as the inosculation of
the Head with the upper bed of sand in pit No. 3 might be explained
by rain floods carrying debris over an eroded surface of sand, and by
the penetration of winter frosts, causing the intrusion of the earthy
material in the hollows of the surface on which it rested. I see no
reason to doubt the contemporaneity of the overburden with the
Head on the cliff-line.

The local character of the pebbles in the deposit might be con-
sidered as an objection to the fluviatile theory. I assume, however,
the former existence of a stream draining districts of similar con-
stitution to the present surroundings of the patch, and account for
the variety of the sediments not only by fluctuations in the condition
of the stream, but by its conversion into a tarn through the stopping
of its seaward outlet. The varied alternations of sand and clay
would then result from the deposition of a stream, whose finer
sediments would be precipitated in the deeper parts of the lake,
their precipitation being interrupted by influxes of coarser material
when the stream was swollen or the dam temporarily removed.

Their isolation prevents one from assuming that the formation of
the sands and clays of St. Agnes was contemporary with the
deposition of the Crousa Down and Crowan gravels, but in the
absence of connecting links, they may be classed together within a
period ranging from Tertiary to early Pleistocene times, when the
contour presented a vastly different aspect from its present outlines,
before the selection of the present lines of drainage.

40 CORNISH POST-TERTIARY GEOLOGY.

BOULDER GRAVELS.

As in the granitic districts of the Land's End, the modern beacbes
are often almost entirely composed of large rounded granite boulders,
it is not improbable that many of the boulder gravels alluded to by
Messrs. Came and Henwood ; at Pornanvon, St. Loy, and St. Just,
for instance; may represent raised beaches or contemporaneous
fluviatile deposits, whilst others in valley bottoms of the present
lines of drainage may be equivalent to stanniferous gravels else-
where. But boulder gravels, such as those mentioned by Mr.
Henwood as occurring at a height of 80 feet above the sea at
Morrab Place, Penzance, or even the boulder-bed forming the roof
of Gamper Hole, at 40 feet above the sea, mentioned by Mr. Came,
cannot be classified with the Raised Beaches, even on the supposition
of unequal elevation, as well as a local rise of tide : and still less
can they be regarded as equivalent to stanniferous gravels.

It is vei"y difficult to believe that no traces of old fluviatile depo-
sition, prior to the formation of the old beach cliffs (i.e. before and
during the subsidence which culminated in the formation of the
Raised Beaches), were preserved. Before and during the elaboration
of the present drainage system, deposits would no doubt have been
formed marking the progress of denudation by the rivers. Whilst
in inland districts the great surface waste during the period of the
accumulation of the Head on the coasts would have tended to the
dispersion and concealment of such old fluviatile relics on the slopes,
mining excavations, and the wearing back of the coast-line would
naturally bring them to light. The boulders at Huel Carn Mine,
50 feet from the surface and 500 feet above the sea, mentioned by
Mr. Carne as occurring beneath a mass of disintegrated granite and
clay, are probably explainable in this way. The boulders of granite
in Rosewarne Mine, Gwinear, at 74 fathoms from the surface, noticed
by Mr. Salmon who considered that they had been introduced by
fissures from the surface, are so difiicult of explanation without
further particulars, especially the description of the structure of the
granite in their vicinity, that I hesitate to hazard a conjecture re-
specting them. At Relistian Mine, on the contrary, though the
slate pebbles observed by Mr. Carne were met with at 100 fathoms
from the surface, his mention of spheroidal concretions in the slate
in their vicinity seems to offer at once the simplest and most reason-

CORNISH POST-TERTIARY GEOLOGY. 41

able explanation. Numerous localities in the Land's End District,
in which boulders occur, have been cited by Mr. Carne in Trans.
Koy. Geol. Soc. Corn. vol. iii. It is to be regretted that the absence
of similar notices of the old gravels in the central and eastern part
of Cornwall renders this part of the subject so defective.

When we reconstruct, in imagination, the Cornwall of early
Pleistocene times, before the submergence which led to the Raised
Beach formation had begun, we can scarcely consider the present
extent of the county as embracing more than the main watershed
boundary and sources of the old drainage system, so that the paucity
of old river gravels is not to be wondered at.

EAISED BEACHES.

Erom the sections given, the average height of the base of the
Eaised Beaches may be taken as from 5 to 10 feet above high-water
mark ; but, as a considerable thickness of beach has been denuded
away from the sites, where traces are only now visible, and as in
many places the Head, or talus, was shed upon it while in an uncon-
solidated state, partly sweeping away and partly becoming mixed
with its sands and pebbles, sections where the whole thickness of
beach seems to be present (as in Gerran's Bay, St. Ives, Godrevy
Beach, and Fistral Bay) must be taken, which would raise the
average extent of subsidence during the Raised Beach formation to
15 feet above high- water mark.

As, no doubt, beaches were in some cases heaped up to a few feet
above S2:)ring-tide high-water, or were, like the modern West Green
Sandbank near Marazion, overspread by the shifting sand grains
drifted from the foreshore, the actual thickness of Eaised Beaches,
where undenuded, is not always a safe index of the amount of sub-
sidence.

The height of the old beaches would naturally be greater in
proximity to their cliff-line, so that isolated portions, on reefs at the
level of spring-tide high-water, or exposed at the base of a consider-
able thickness of Head, masking an old cliff some distance inland,
are no indices of the local amount of elevation of the beaches.'

1 Vide De la Beche, Geological Manual, p. 157 ; and Pengelly, " On Raised
Beaches," Trans. Dev. Assoc, for 1866.

42 CORNISH POST-TERTIARY GEOLOGY.

The section at Treen Cove, given by Mr. Carne, if an instance of
Eaised Beach, is of very exceptional height (20 feet above spring-
tide high- water), and it is not clear whether he regarded the whole
mass, 15 feet thick under the Head, as Eaised Beach, or only the
lower part of it.

The paucity of shells in the Eaised Beaches, and their very local
occurrence, is worthy of note.'

OLD BLOWN SANDS.

It is not easy to fix a definite junction between Old Blown Sands
and Eaised Beaches, where both are similarly bedded and consoli-
dated. In the lower parts of the Old Blown Sands of Fistral Bay
and Godrevy Beach pebbles are sparsely disseminated, sometimes
in impersistent lines, having been probably cast up by storm waves.
In the clifi"s of Godrevy, Fistral Bay, Towan Head, New Quay,
Green way (N. of Padstow), the best examples of Old Blown Sands
ai-e shovsm, attaining in places to 20 feet in thickness.

In Greenway Clifi", and in parts of Fistral Bay, the Old Blown
Sand projects from the cliif face in hard corrugated laminae of
siliceous sandstone.

In parts of Godrev}^ Cliff, and near New Quay Pier, the Old
Blown Sand is consolidated in hard thick beds.

HEAD.

Though from its general appearance the Head might be regarded
merely as an old talus, shed from the adjacent heights upon the
raised platform of the old beaches, in some cases fragments have
been incorporated which could not have been derived by mere
weathering, but were probably carried down by torrential surface
waters or melting snows from higher lands not far off", but not in the
immediate vicinity. "Where the Head, for instance, cajDS cliffs form-
ing the seaward termination of a valley, one might expect to find
fragments in it which had travelled some distance. The appearance
of stratification sometimes exhibited might be satisfactorily exj^lained
by seasonal changes. Thus the disintegration and slip of numerous

' 'When the fra^entary condition^of the Raised Beaches is taken into account,
as well as, in many cases, the unfavourable nature of their materials for the pre-
Bervatiun of shulls, uxcept in a microscopically coumuiiuted state, objections to
unfossiliferous deposits being regarded as Kaised Beaches will be shown to be
unfounded.— W. U., Sept. 1879.

CORNISH POST-TERTIARY GEOLOGY. 43

fragments of earth and soil, through, the wedging of frosts and
melting snows, might be temporarily succeeded by a finer talus,
containing smaller and fewer stones, during milder seasons.

The frequent cliff-sections, composed of a thick masking film of
Head resting, as no modern talus could rest, against a rock-face a
few feet from its cliffs, coupled with occasional instances of its
isolation from the main cliffs, upon rocky reefs on the foreshore, as
at Godrevy and Cape Cornwall, point to a very much greater exten-
sion of land during its accumulation.
Next as to its age :

1st. It is more recent than the Kaised Beaches, because, as Mr.
Carne pointed out, where both are present in the same cliff,
it invariably rests upon them. A possible exception may
be furnished by the Greenway Cliff section, mentioned in
the supplementary paper on Padstow.
2nd. It is older than the commencement of the forest growth, for
the following reasons :
(a) The Head evidences a period of great subaerial waste, a
more rigid climate; both likely to occur when the old
beaches attained their maximum elevation, possibly pro-
ducing continental conditions. The submerged forests
must have flourished on a much more extended, though
subsiding, area, and that subsidence must have been going
on for some time prior to their growth, as the flora does
not indicate any marked change of climate from the
present : a greater extent of area is also indicated by the
depth of the stream-tin gravels at Par, Pentuan, Carnon,
etc., below the sea-level.
(h) The Head rests upon the old plane of marine denudation,
whilst the forest ground seems to occupy tracts eroded in
its surface, as on Dunbar Sands, near Padstow, etc., so that
we may infer that a considerable amount of denudation had
taken place posterior to the accumulation of the Head, and
prior to the growth of the forests,
(f) The Head is never found resting on traces of submerged
forest, as we might expect to find it near the old cliff, had
their growth been prior to its accumulation.
(d) The Kaised Beaches furnish proofs of elevation, and the

44 CORNISH POST-TERTIARY GEOLOGY.

forest growth proves that elevation to have been far greater
than might be inferred from their present positions. The
stream-tin gravels, submerged forests, and overlying de-
posits, prove the long continuance of a subsidence bringing
about the present relations of sea and land. As, from its
nature, the Head is more likely to have been accumulated
during elevation, and for some time after the ensuing
subsidence commenced, I have no hesitation in regarding
it as older than the submerged forests.

STREAM -TIN GRAVELS.
The stream-tin gravels, from their position, were evidently de-
posited prior to the growth of the forest stratum resting upon them,
and long before the submergence of the forests took place. The
depth of the tin ground below high- water mark (about 64 feet in
Mr. Henwood's section of Carnon) indicates a much more extended
coast-line. There are of course stream-tin gravels of all ages, but
those to which I refer are the deposits exposed in the valleys of Par,
Pentuan, and the Fal Estuary, etc., and all such inland gravels as
can safely be correlated with them. If these stanniferous gravels
were deposited prior to the Raised Beacli formation, we should expect
the following proofs : —

(a) Deposits in the stream-tin valleys at heights corresponding to

those of the neighbouring raised beaches. Whereas the
old estuarine gravel near the mouth of the Par Estuary,
corresponding in height to the raised beach near Spit
Point, rests on a slate platform in which the present bed
of the estuary has evidently been excavated.

(b) To find traces of marine deposition or of a marine contour on

the inland borders of flats like those of Ludgvan, between
Marazion and Penzance ; and these we do not find.

(c) That relics of old fluviatile deposits would rest directly on

the stream-tin gravels, whereas parts of the old forest-
ground rest upon them, and are overlain by fluviatile and
marine deposits, still more recent.

(d) That the detritus of stream-tin gravels would be found

amongst the materials composing the raised beaches,
which is not the case.

CORNISH POST-TERTIARY GEOLOGY. 45

Hence I conclude that the stanniferous gravels are more modern
than the raised beaches, and not only posterior to them, but sepa-
rated by a long lapse of time, during which denuding agencies were
ceaselessly at work, and great changes took place in the physical
geograph}'^ of Cornwall.

SUBMERGED FORESTS.

The growth of the old forest, the relics of which have been met
with all round the Cornish coast, must have extended over a long
period of time. The evident connexion of the Mounts Bay Forest
with the bed in Marazion Marsh overlying stream-tin, pointed out
by Mr. Carne ; and the constant presence of a distinct vegetable
stratum, or of detritus mixed with vegetable matter, on the tin
gravels in most of the principal sections, points to a general corre-
lation of the submerged forests on the coasts with the forest bed in
stream-tin sections. Although the forests may have flourished during
the deposition of the stanniferous gravels, for purposes of classifica-
tion it is more convenient to regard them as bridging over the
interval between the deposition of the principal stanniferous gravels
and the much more modern fluviatile, marine, and estuarine deposits,
beneath which they were entombed.

Several observers have cited the occurrence of hazel nuts, in some
cases with branches attached, as proof of a sudden autumnal sub-
mergence. As the forests flourished on a slightly modified marine
contour, which would probably exhibit a series of terraciform features,
during a gradual subsidence sudden encroachments of the sea would
take place as these plateaux were successively submerged.

The peaty matter so constantly associated with the forest bed,
though it might in some cases be explained by the saturation of an
old vegetable soil forming round the trees for centuries, would, as a
rule, impress one with the idea that the forest tracts were converted
into marshes, by the formation of gravel or sand bars damming back
the drainage of the valleys, for some time before the sea regained its
old cliff bounds.

The general absence of trees in the central and western parts of
Cornwall, owing to the prejudicial influences of proximity to the sea,
leads me to think that the forests began to flourish, either during

46 CORNISH POST-TERTIARY GEOLOGY.

continental conditions, or at a time when the land stood at such an
elevation as to allow of their growth over a considerable tract beyond
the present coast-line, and yet sufficiently far removed from the then
existing coasts to escape their baneful effects. In opposition to this
it might be urged that there is evidence to show that proximity to
a gradually contracting coast-line did not prove fatal to the growth
of woods on the south coast of Cornwall, till a comparatively recent
date. For in the ancient tradition of St. Michael's Mount being in a
wood, names of animals long since extinct are retained. " We thus
suppose that Caran meant stag ; Da, fallow deer ; Byk or Kidiorch,
buck ; Yorch, roe, etc."^ But the old cliflf-line, at the foot of which
the narrow belt of woodland (whose traces are alone known to us)
was situated, would ward off the inclement breezes from the north
and west, and probably allow of the growth of trees almost as near
the water's edge as they are now growing at IMount Edgecombe near
Plymouth. The absence of remains of Felidfe or Pachyderms in the
forest bed, the indications of charred matter (as in the streara-tiu
sections of Merry Meeting and Carnon), as well as of shaped wood (as
in the sections of Huel Darlington and Pentuan stream works) ; the
discovery of human skulls at Carnon and Pentuan ; and of a human
skeleton near Tarnon Dean (? Tannerdane), at 22 feet below high-
water, if not an anachronism, tend to fix the date of the submergence
of the forests at a time considerably posterior to the existence of the
extinct cave mammalia; and coupled with the tradition given by
Mr. Couch seem to indicate the contemporaneity of the old race of
men with the animals whose bones are found in association with
theirs, inducing one to think that during a thousand years, at least,
before the time of Diodorus, they witnessed the gradual diminution
of their hunting grounds and the destruction of that part of the then
existing forests that lay beyond the limits of our present coasts.

"Under the alluvial deposits, both of Pentuan and Carnon, remains
of deer were found in the forest bed. IMr. Couch, after a comparison
with specimens from Ireland, identified them Avith the Irish Elk
(3Iegaceros Hihernicus). In Truro Museum there are specimens of
Strong ijlocer OS speloeus from Pentuan, and of Koebuck (C. capreolus),
and Bos pr'uiiiijcnius from Carnon.

' Couch, Trans. Eoy. Gtol. Soc. Corn. vol. vii. p. 264, etc.

CORNISH POST -TERTIARY GEOLOGY. 47

" Bones of Euminantia, chiefly cervine, are common ; numerous
specimens have been obtained, amongst other localities, from Whit-
sand Bay (in East Cornwall) ; a few to the east of Looe ; at
Talland ; from Polperro Beach ; Lantivet Bay (near Fowey) ; and
from Marazion Beach ; but principally from Carnon and Pentuan.'

" Mr. Couch - mentions the discovery of the skeleton of a large
deer near an oak (20 feet in length, and of the circumference of a
man's waist), at 30 feet from the surface, near Villendi'eath, in the
parish of Sennen ; also of pieces of deers' and elks' horns at 20 feet
below the surface in Sennen Bay."

Mr. Hetiwood^ noticed the respective positions of the human
remains found at Carnon and Pentuan.

Feet below the
Surface.

Feet below High-
Water Mark.

Feet above or below Low-
Water Mark.

At Carnon ... ,

58

64

46 below.

At Pentuan...

20 to 40

14 to 34 ...

4 above, and 14 below.

Mr. Couch considered the human skulls unlike those of any of
the European races of the present day in their configuration.

In the old river deposits of the valley to the West of St. Austell,
remains of Diatomacece and freshwater shells were found in silt ;
and in the marine deposits beneath, sea shells, such as Cardium
ednle, of a large size and of a configuration very different from those
now inhabitino- the same shores.

KECENT MARINE AND FLUVIATILE DEPOSITS.

To particularize the events denoted by the deposits overlying the
forest bed in stream-tin sections is unnecessary, as they involve the
reiteration of estuarine, turbary, or fluviatile conditions, dependent
on the situation of the section with reference to the sea, and the
recurrence of local stoppages or diversions of drainage, etc.

Some care is necessary in distinguishing the forest bed proper
from the peat beds so often intercalated with more recent estuarine
or fluviatile deposits. These peat beds show that a decreased rain-
fall had brought about the more moderate fluviatile conditions of the

Trans. Roy. Geol. Soc. Corn. vol. vii. pp. 233, 264, etc. « Ibid.

Journ. Roy. Instit. Corn. vol. iv.

48 CORNISH POST-TERTIARY GEOLOGY.

present time, that morasses had been formed, at different times and
in different places, from alterations in river courses or stoppages of
drainage, and had in some cases perhaps been temporarily converted
into a soil favourable for the growth of underwood, as may be
inferred from bed (c) in the Fowey Valley Section,

Mr. Godwin-Austen commented on the occurrence of rock reefs
with planed surfaces occupying an intermediate position between
high-water mark and the height above it of the neighbouring raised
beaches. Numerous examples of such reefs occur, their surfaces
ranging from spring-tide high- water to 4 or 5 feet above it ; in veiy
many cases they may be regarded as relics of the old beach plane
sloping seaward, but in others Mr. Godwin-Austen's idea of a
temporary oscillation of a few feet in the later stages, of the sub-
sidence which led to the submergence of the forests may be admiss-
ible. Such an oscillation would to a great extent explain the
formation of such sand and gravel bars as those of the Loo, Swan
Pool, Par, and Pentuan ; and supposing its cessation and the resump-
tion of the downward movement to have taken place, the destruction
of the West Green Sand Banks (near Marazion), and perhaps the
entire insulation of St. Michael's Mount, can be readily conceived.

CONCLUSIOX.

In reviewing the evidence, one cannot avoid being struck with
the paucity of Pleistocene deposits in Cornwall, for, notwithstanding
their completeness, the stream-tin sections represent but a very
small portion of the denudation to which the valleys have been
subjected in Post-Tertiary times. Whether we regard the deposits
of Crousa Down, Crowan, and St. Agnes as of Tertiar}'^ or early
Pleistocene age, their positions indicate a configuration vastly
different from the present contour, that they were formed at a time
when denudation and deposition took place upon tracts of land
which have been for ages sparingly acted on by the one, and wholly
unmodified by the other.

No direct evidence of glacial action in Cornwall has been obtained.
Had the county been invaded by a foreign ice-sheet, or submerged
beneath the waters of an Arctic sea, this could not have been the

CORNISH POST-TERTIARY GEOLOGY. 49

case. Yet, to explain the thoroughness of Pleistocene denudation by-
agencies suflficiently powerful to sweep away the debris resulting
from their erosion, is in a measure to hint at the introduction of ice
in some form. There is no reason to think that Cornwall was lower
during the period preceding the formation of the old beaches than
its present altitude ; but, on the contrary, it is possible that it may
have been much higher. Supposing the erosion of the English
Channel, as Mr. Godwin-Austen suggests, to have been begun in
the early part of the Pleistocene epoch by a river flowing westward,
the transport of Cretaceous materials obtained from the eastern
districts would have furnished a plentiful supply of flints for in-
corporation in the subsequent beaches, and their presence both in
the raised and modern beaches would be easily accounted for. As
the influence of glacial conditions became felt, the highlands would
become covered by snow, liberating great quantities of surface-
water with torrential power during intermittent warmer periods,
and during the succeeding amelioration ; by these causes great
surface waste would take place, the valleys would be deepened,
and the existing deposits in exposed situations swept down with
recently derived materials to lower levels now beneath the sea.
The alternative version postulates more than this, namely, the
descent of glaciers from the snow-covered highlands. In both
cases the observation I have applied to the old boulder gravels holds
good, namely, the fact that the present area of Cornwall (at least
in its more western parts) would rej)resent but the watershed, or, in
the case of ice, the generative sources, and tracks of its nascent flow,
and all moraine material, etc., would be swept down to districts
now beneath the sea, whilst roches moutonnees, etc., would be very
unlikely to survive the subsequent extensive weathering of exposed
rock surfaces which took place during the accumulation of the Head.
Reasons have been assigned for believing that coast-ice helped
to transport some of the materials found in the raised beaches of
Brittany. 1 The large granite boulder pointed out by Mr. Williams
rests on the old beach platform in Barnstaple Bay, and is surrounded
by the raised beach materials which also rest on it. It is evidently
an erratic. Some months after my paper on the Pleistocene Deposits

1 Annales de la Soc. Geol. du Xord, T. 4, p. 186, April 18th, 1877.

4

50

CORNISH POST-TERTIARY GEOLOGY.

12. Sea Beaches, RiverGravels,
Alluvia and Peat Growth.

11. Blown Sands.

10. Eiver deposits ■with estud-
rine sediments intercalated in
some Stream-tin Sections
near the coast, also Peat
beds. River deposits with
occasional Peat beds inter-
calated in Inland districts.

9. Planed Eock reefs, Gravel
and Sand Bars.

8. Marine and estiiarine de-
posits in some Stream-tin
Sections. River Gravels and
Alluvia in inland districts.

7. Submerged Forests and
Forest Bed in some Stream-
tin sections.

The presence of man in-
dicated, with remains of
deer (including the Irish elk)
and oxen.

5. Head in inland districts
and on the cliffs. River
Gravels. Stream- tin Gravels.

5. Probably River Gravels,
as in Devon, connected with
the present drainage system.

4. Raised Beaches and Old
Blown Sands.

Erratic boulder at Saun-
ton (North Devon).

TABLE OF CLASSIFICATION.

PHYSICAL CHANGES INDICATED.

Gradual overspread of Blown Sands on parts
of the North-western coast of Cornwall, en-
tombing hamlets and churches.

Local stoppages or diversions of drainage
giving rise to peat growth and morasses in
valley bottoms. Climate of the Central and
Western parts of Cornwall only favourable tor
the growth of underwood.

3. Boulder Gravels.

2. Deposits not recognizable.
Debris swept to lower levels
beyond the existing coast-
line.

1. Gravels of Crousa Down
and Crowan ; Sands and
Clays of St. Agnes.

Possible oscillation in the subsiding move-
ment, not yet counteracted.

Advance of the sea to its old cliff bounds ;
destruction and entombment of the marshy
forest lands fringing the coasts; decay of
forests in inland districts through the preva-
lence of unfavourable conditions.

Continuance of subsidence, gradually circum-
scribing the forest plains, but allowing sudden
encroachments of the sea from time to time
as the successive terraces in -its old plain were
surmounted.

Climate ameliorating and becoming suitable
for the growth of Oak, Alder, Hazel, etc.. on
a large area beyond the limits of the present
coast-line.

Elevation, perhaps culminating in conti-
nental conditions. Seasons becoming more
marked. Considerable snow-fall and penetrat-
ing frosts. Much surface water. Cold di-
minishing. Subsidence. Rainfall greater than
now.

Land rising.

Culmination of subsidence at an average of 15
feet below the present level : Wales, etc., being
submerged, in places, to a depth of 1500 feet.

Stranding of occasional icebergs or floes
drifted from Ireland, Lundy Island or the
Northern counties.

Land subsiding. Liberation of much surface
water with torrential power by melting of
snows during intermittent warm periods and
the succeeding amelioration.

Land at considerable altitude, possibly conti-
nental Approach of cold : great quantities of
.snow accumulating on the highlands (possibly
giving rise to a local glacier system).

Old surface configuration prior to the initia-
tion of the present lines of drainage.

CORNISH POST-TERTIARY GEOLOGY. 51

of Devon had been read, I visited the spot, and am inclined to think
that the boulder vs^as brought by floating ice. These observations
lead me to conclude that Cornwall was at a much greater altitude,
but sinking during the Glacial epoch, and that although partaking
in the subsidence which caused the submergence of land to a depth
of 1,500 feet in the districts further north, its greater altitude when
the subsidence began allowed of the existence of a dry land area till
its close, which was marked by the formation of the raised beaches
when the land stood at an average of 15 feet below its present level.
It was during this last period, when glacial conditions were passing
away, that I conceive the granite boulder was floated from districts
far to the north, or from Ireland. In the accompanying table of
classification I have ventured to insert such hypotheses as the fore-
going to bridge over the breaks occasioned by the paucity of early
Pleistocene deposits in Cornwall.

NOTES ON THE PLEISTOCENE DEPOSITS

CORNISH COAST NEAR PADSTOW.

The quaint little chapel of St. Enodock rises from a hummocky
expanse of blown sand flanking the Camel Estuary opposite to
Padstovv. The broad valley occupied by the sand narrows where it
terminates in a low sand bank, to the foot of which the sea comes
at high tides ; this sand bank forms the centre of a little bay, the
horns of which are composed of purplish red and greenish banded
slates, forming low cliffs, upon which traces of a raised beach are
visible in places. The following sections were taken on the cliffs to
the north of the bay.

West of Lower Trebetherick :

Blown sand ^

Eed brown earth i

Small fragments of slate with pebbles and subangular frag- ^ 3ft. Oin.

ments of quartz |

Angular slate fragments '

Brown sand with small quartz and flint pebbles resting on slates

at 5ft. above high-water mark 4ft. Oin.

In another place to the west of Trebetherick Point.

Blown sand

Sand with fragments of Mytili and Fatellm scattered through it

(probably blown) 3ft. Oin.

Consolidated sand 1ft. Oin.

Eeddish-brown earth with small fragments of slate, and
angular, subangular, and well-worn quartz stones. A
large quartz pebble was noticed at the base 1ft. Oin.

Fine brownish sand with occasional small pieces of slate,

angular slate fragments, often large, and a few small 1 to 3ft. Oin.
quartz pebbles

Bands of sand and loam occur in this basement bed in an adjacent

spot. The base of the deposit is from 5 to 7 feet above high-water

54

PLEISTOCENE DEPOSITS NEAR rADSTO"VV,

mark. Mr. Henwood ' mentioned the occurrence of a layer of angular
stones mixed with, a few quartzose pebbles on the south side of
Trebetherick Point, at about 10 to 12 feet above the present beach.

The same observer noticed the agglutination of sand forming
patches of recent sandstone, which has been used in parts of St.
Euodock's Chapel, on the north-west of Brea Hill.-

The chief interest in the locality attaches to that part of the
Dimbar, or Doombar, sands which is left dry between mean tide
level and the sand bank in the centre of the little bay called by
Mr. Henwood " Daymer Ba3\" A small stream trickles through
the sand bank near the southern side of the bay. At from 70 to 80
j-ards from the sand bank, and at about six feet below high-water
mark, a crust of yellowish, or buff-coloured, laminated consolidated
sand, made up chiefly of comminuted shells, and containing sub-
angular fragments of quartz and slate, often of large size, firmly
imbedded in it, together with shells of Mytilus, Littorina, etc., etc.,
projects in ragged reefs through the modern sand-beach which is
strewn with fragments of slate and quartz, probably redistributed
relics of the older beach.

In one spot a large quartz boulder (Fig. 1), with its lower part
firmly cemented in the laminated sandstone, occupies a basin-shaped
depression in the reef, the laminae having a quaquaversal dip toward

Fig. 1. DcNBAR Sand?.

Keef of Old Consolidated Beach with Quartz Bouider projecting through the present Sands,

al-o a Bed of Feat [i>.)

About ^ of the natural size.
Fortieth Ann. Pup. R. lustit Corn, for 1858.

Op. cit.

PLEISTOCENE DEPOSITS NEAR PADSTOW.

55

it : thus the ordinary action of the tide in forming hollows under
any heavy substances encountered on a sand beach has been fossilized
and preserved for ages.

(Fig. 2). On the north side of the streamlet, side by side with the

old beach reef, and

pla

s only a few feet from it, I observed a
mass of blackish peaty matter contain-
ing twigs and land shells in a very
fragile condition.

Mr. Parfitt, of Exeter, kindly identi-
fied the few specimens I brought away
as Helix nemoralis var., Bytliinia tenia-
culata and a small Physa. The masses
of peaty matter were little more than
a foot above the surrounding sand when
I visited the spot, so that the base of
the stratum was nowhere observable.
During the 17 years which had elapsed
between Mr. Henwood's visit to this
spot and my own, considerable changes
must have taken place, both in the
destruction of the vegetable remains,
and in the exposure of the old con-
solidated beach reefs. Mr. Henwood^
says that, "In a small bay (called
Dayraer Bay), between Brea Hill on
the south-east and Trebetherick Point
on the north-east, a layer of earth,
often replaced by clay, and containing
fragments of slate and roots of trees
in silu, protruded through the Doom-
bar sands, traceable on slate rock from
above high-water to below ordinary
low-water mark, without reaching its
boundary in either direction." The
roots were found spreading for 20 feet
horizontally and erect ; they were of oak and hazel, and surrounded
by successive layers of leaves and nuts, alternating with thin beds
1 Op. cit.

56 PLEISTOCENE DEPOSITS NEAR PADSTOW.

of sand and earth, in which horns of red deer were found, upon
vegetable mould containing shells similar to those now living on
the adjoining sand hills.

We have here a true example of a submerged forest, which,
coupled with the raised beach on the adjacent cliffs, and the old
consolidated beach reef, gives a fair epitome of the later Pleistocene
history of Cornwall.

The beach reef is the only example that I know of, in Devon and
Cornwall, of an old beach below high-water mark, and this is the
only locality in which I have seen old beaches marking different
stages in the movement of elevation.

The raised beach indicates a depression of 5 to 10 feet, and a
subsequent elevation of more than that amount during a pause in
which the beach below high-water was formed, at a time when the
relations of sea and land were as at present. But the lower beach
must have been also elevated, to allow of its consolidation ; and
that elevation must have been of such an extent as to favour the
growth of forests on the old marine plain, partly shorn of its
deposits by subaerial denuding agencies. Finally, a period of sub-
sidence led to the advance of the sea over its old grounds, gaining
a plentiful supply of beach materials from the relics of its old
deposits, and from river gravels, and causing the decay of the forests
and their final entombment in its sands.

GREEXWAY CLIFFS.

Proceeding northwards from the Camel Estuary towards Pentire
Point, a very interesting section is presented in one part of the
coast to the south of Hayle Bay, called Greenway on the Ordnance
Map ; shown in the diagram on opposite page (Fig. 3).

The cliff face, where uncovered by drift and talus, consists of
nearly vertical grey slates, against which, in two places, old con-
solidated blown sand (A A) abuts, consisting of hard thin beds j
of calcareous buff-coloured sandstone, dipping seaward at an angle
of 20°.

Upon a narrow rocky ledge at the base of the cliff, at about five |
feet above high- water mark, traces of a raised beach (B B), con-

PLEISTOCENE DEPOSITS NEAR PADSTOW.

57

sisting of coarse consolidated sand, made up of comminuted shells
and slaty debris inclosing pebbles, were observed, in one spot,
adhering to the slate reef. The base of the old consolidated blown
sand rests upon the rocky platform. Near the traces of raised
beach the cliff face is composed of brown loam (C), with numerous
small angular slate fragments, and occasionally a few large pebbles
and blocks of quartz and slate. This stony loam or " Head " is
about 15 feet in thickness. It is capped by 4 or 5 feet of gravel (D),
consisting of large and small pebbles and angular and subangular
fragments of grit, quartz, slate, and greenstone, in grey loamy
earth. In one part near its junction with the slates, angular slate
fragments predominate in the gravel. The cliff is much obscured,
by talus concealing the junction of C and D with the slates, in
which they ajjpear to occupy an eroded hollow. The base of the
gravel (D) is rather more than 20 feet above high-water mark.

Fig. 3. Grkenway Cliff.
\ title U ^cile—1 inch = 21 feet

If the gravel D is a raised, beach, it must be either older or
newer than the old consolidated beach on the reef below. If older,
the stony loam (C) would date back to a time anterior to the raised
beach formation, and would have been subsequently submerged to
allow of a shelf being cut in it, and the deposition of a gravel beach
at 20 feet above present high-water mark. The absence of signs
of beach at this height in a neighbourhood where the raised beaches
seldom exceed 10 feet above high- water mark ; the unconsolidated
character of the gi'avel ; and the friable nature of the " Head " on
which it rests ; negative the idea that D is a raised beach of older

58 PLEISTOCEXE DEPOSITS ?sEAR PADSTOW.

date than B. Supposing D to be a raised beach of subsequent
date to B, then the beach (B) would have been raised, the stony
loam (C) precipitated upon it, and a subsidence, for which we have
no analog}' on any other part of the coast, would have taken place,
allowing the deposition of D.

Apart from the negative evidence of analogy, this hypothesis is
untenable ; for, as the old, now consolidated, blown sands bore the
same relations to the raised beaches that are exhibited by present
blown sands to the modern beaches, the sand would hardly have
had time to consolidate before the supposititious subsidence had
brought it within reach of the waves, and, if it had consolidated, one
would expect to find some trace of a shelf cut in its projecting mass
at a height corresponding to the base of the gravel a few yards
distant from it.

The gravel D must be regarded as a fluviatile deposit; but in
this case two hypotheses as to its age present themselves. First,
let us suppose D to be older than the raised beach. Then the stony
loam (C) would first have accumulated, either as an ancient talus
or flood gravel, in a channel cut in the slates, at a time when the
country stood at a higher level. In process of time, from access to
fresh materials (regarding C as fluviatile), or from the selection of
this hollow as a line of drainage (regarding C as talus), the boulder
gravel (D) would have been deposited, and when the subsidence
had progressed sufficiently to allow of the formation of an old beach
reef, the previous extension of the fluviatile deposit seaward would
have been cut back to the present cliff-line.

Let us next suppose the gravel D to have been deposited since
the raised beach formation. Then during the elevation of the beach
to a much greater height than its present level, the slow process of
agglutination would have been at work upon the existing blown
sands, and the old beach plain would have been covered with talus,
or " Head," near its cliff margin, the result of meteoric waste. In
process of time a stream channel would have been formed in the
part of the cliff where the talus (C) had accumulated, and the
gravel (D) would have been brought down and deposited on the
desertion of its channel by the stream. Between these two hj-po-
theses it is not easy to decide.

Unless the stony loam (C) is regarded as a fluviatile dejiosit, and

PLEISTOCENE DEPOSITS NEAR PADSTOW. 59

not a " Head," or atmospheric talus, its position on either of the
foregoing hypotheses furnishes a notable exception to Mr. Game's
conclusion as to the " Head " never being found below either raised
beaches or boulder gravels. In other respects the numerous ob-
servations I have made on the Cornish coast fully corroborate this
conclusion. Eegarding C as an old fluviatile deposit, which the
tendency to horizontal distribution in its contained fragments might
warrant, I should prefer to fix the date of the overlying gravel as
anterior to the raised beach formation, in accordance with the first
hypothesis.

In conclusion, I have to express my sincere obligations to Dr.
Henry Woodward for his kind advice and assistance in correcting
the proofs of these papers, and insuring the best means for their
publication.

i

STEPHEN AUSTIN AND SONS, PHINTERS, HERTFORD.

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