Devon & Cornwall Notes & Queries

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THE HISTORY

OF

DEVONSHIRE SCENERY

G

THE HISTORY

OF

DEVONSHIRE SCENERY

AN ESSAY IN

Geographical Evolution

BY

ARTHUR W. CLAYDEN M.A.

Principal of the Royal Albert Memorial CoOege, Exeter

JAMES G. COMMIN CHATTO AND WINDUS

EzBTBR. London.

1906

r

I

^POM THE LIBRARY

CONTENTS.

Page.

Chapter I. Introduction i

„ II. The Devonian Rocks of North Devon 14

„ III. The South Devon Rocks 29

„ IV. The Culm of Devon 41

„ V. The Great Upheaval 56

„ VI. Volcanic Rocks 65

y, VII. The Dartmoor Granite and Exeter Lavas 77

VIII. The Salt Lake Period

IX. The Age of Reptiles

X. The Return of the Sea

XI. The Chalk

XII. The Plateau Gravels

XIII. The Bovey Lake

XIV. The Rivers of Devon
XV. The Modem Scenery

95

108

122

169
185

LIST OF ILLUSTRATIONS.

1. The Valley of Rocks, Lynion

2. Radtolariay etc.

3. Old Red Sandstone Geography

4. Under the Torrs^ Ilfracomhe^ and Key ...

5. Under the TorrSy Ilfracomhey and Key

6. Morte Slates ... ...

7. Lantern Roch Hfracombe ...

8. Devonian Limestone^ Section

9. Wavy Structure near Kingsbridge

10. Thin Bedded Black Limestone^ Drewsteignion

11. Thick Bedded Grey Limestone y Westleigh

12. Post-Carboniferous Geography

13. Volcanic Rocks y near Br idf or d

14. Heltor

15. Pocombe Quarry

16. Lava on Culniy Pocombe ...

17. Ide Cutting

18. Breccia near Dawlish

19. Fossil Salt Crystals

20. Spongy Lava

2 1 . Budleigh Pebble-Bed on Marls

22. Gypsum Veins in Red Marls

23. Red Marls with Green BandSy Seaton

24. Culverhole

25. West Cliffy Lyme Regis

26. Church Cliffy Lyme Regis

27. Liassic Geography

28. Haven Cliffy Axmouth

29. WhiU Cliffy Seaton

. . . Frontispiece
To face page 7

16
22
23
24
24
38
38
48
48
62

65
77
91
91
92
92
95

95
100
100
104
104
no
no

"3
128

134

ILLUSTRA TIONS—coniinued.

'30. Cenomanian Limestone on Greensand

31. Hooken Cliff and Under Hooken ...

32. Beer Cave and Key to Zones

33. Zone Fossils from Beer and Seaton

34. The Bovey Clays and Lignites

35. Heathfield Clay Pit

36. 77ie Rivers qf Devon at Present

37. The Rivers of Devon in Eocene Time

38. The Valley of the Otter: Honiton

39. Bindon Landslip : The Great Chasm

40. Lydford Gorge : Pot-holes

41. Lydford Gorge : The Deep Cleft ...

42. The Crown of the Moor: Yes Tor..,

43. The Edge of the Moor : Meldon ...

136

137
141
142
161
161
172
173
185
185
189
189
193
193

PREFACE.

To geologists geDerally, but especially to those who are
working in the same field, I hope these pages may be of
interest and use, not only as the expression of conclusions
to which I have come after many years' work in the
County of Devon, but also as a summary of the
problems presented by its complicated structure, and the
various solutions of them which have been proposed.

Some of the views I have expressed are novel, and
in certain instances I have felt compelled to dissent from
explanations which others have offered. In such cases I
have endeavoured to make clear my reasons for preferring a
new interpretation of the facts observed, and have given
references to the original papers concerned, so that the
writer's arguments can be followed in full.

To students, I hope the book may be useful as supply-
ing a simple connected narrative by which the facts of
geology may be linked into a whole. This has been
done in a different way by Professor Hull in his
Contributions to the Physical History of the British IsleSy and
by Mr. A. J. Jukes-Browne in his book The Building of the
British Isles. To both of these works, but especially the
latter, I must acknowledge considerable indebtedness when
dealing with distant parts of the kingdom.

By confining myself mainly to a single district, it has
been possible to give references to sections and scenes which
may be visited within the limits of one or two summer
vacations; and Devonshire is not only the county with
which I am most familiar, but serves my purpose best, by
illustrating a greater number of geological principles than
any other.

Geology is too frequently studied as a vast accumu-
lation of disconnected £acts, which have to be learnt before
they are put together. My own experience is that it is
better to begin with a connected story from the first.
The science is ^made more interesting, the details become
easier to remember, and the use and meaning of principles
is better understood.

In writing the following pages I have used the minimum
of technical language, with the object of making them
suitable for the beginner and the ordinary reader who has
no previous knowledge of the subject, but who cares to
know how Devonshire came to be what it is.

If a few should be led to a further study of a fascinating
science, or if a few should gain a keener pleasure in the
open moors and wooded valleys, tumbling streams, and
rugged coast line of Devon, by learning something of their
history and meaning, the book will have fulfilled its aim.

In conclusion, I have to express my indebtedness to the
maps and memoirs of the Geological Survey, to the
numerous geologists who have worked in Devon, and
especially to the various publications of Mr. W. A. E.
Ussher.

ARTHUR W. CLAYDEN.
5, The Crescentf
Mount Radford^ Exeter.

The History

OF

Devonshire Scenery

BY

ARTHUR W. CLAYDEN, M.A.

PRINCIPAL OF THE
ROYAL ALBERT MEMORIAL COLLEGE, EXETER

The History

OF

Devonshire Scenery.

CHAPTER I.

Introduction.

The story of Devonshire scenery begins far back in the
dim antiquity of geological time, when the distribution of
land and water on the face of the globe was very di£ferent
from what we see on modern maps ; when mountain ranges
stood where there is now the open sea, and when the very
rocks which go to build some of the loftiest heights of to-day
were yet unformed. Through all time, since the world
assumed anything like its present condition of temperature,
change has followed change, and each interval has left some
record of its character, which may be read by those who know
the language in which it is written.

We are thus enabled to reconstruct, often with great
accuracy, the physical geography of the past, but, just as with
human history, the further we trace things back the more
fragmentary become our sources of information. The earlier
documents have too often been more than half obliterated,
others have been written in a language which we cannot at
present translate with confidence, and some are so ambiguously
worded that they seem equally open to more than one
interpretation.

In the long story of Devonshire there are many contentious
and difficult points which await solution. Some will, no
doubt, in time be solved by the diligent co-operation of local
geologists, others will perchance have to await the discovery

2 The History of Devonshire Scenery*

of clues to their interpretation in other parts of the world. To
the man of science it is, of course, just these uncertainties
which have by far the greatest interest, but, after all, they are
mostly details, while the broad general facts are clear enough
to satisfy the most determined sceptic. On the whole it is easy
to see how, step by step, the rocks of Devon came to be where
they are and what they are ; how, age after age, the scenery
was modified, and yet how the physical geography of one time
was more or less determined by that which had gone before,
until in the fulness of time, that which we see around us
is the result of all the long and chequered past.

The historian who wishes to make plain the why and
wherefore of the events which make up the story of a people
cannot avoid dealing more or less with the nations with whom
they came in contact. Neither can he well omit all account
of the still earlier races from whom it is possible to trace the
descent of those who form his theme. In the same manner if
we are to correctly understand the geological records of our
own county it is absolutely necessary to study in a general
way the changes which have affected a wider area, sometimes
even one which embraces considerable portions of the Euro-
pean Continent, or what is now the North Atlantic. In other
words we must consider the physical geography of a much
wider region and the place which Devon has occupied in
each of the pictures we attempt to draw.

Time is not measured by centuries in geological history.
It is divided into five great eras, and each of them is sub-
divided into a number of periods. The names of these divisions
of time are derived in some cases from the living things whose
fossil remains are characteristic of the age, in others from
the geographical district in which the rocks formed during the
period are best shown or were first studied, and in others from
the kind of rock formed at the time in some typical district.
Unfortunately the sequence and nature of the records differs
greatly in different parts of the world, and various attempts
have been made to reform the system of nomenclature in order
to make it as applicable to the geology of Europe as it is
to that of Great Britain, which was the cradle of geological
science. But these changes are only creeping slowly into

The Dawn of Life* 3

our English text-books, so the old system and the familiar
terms will be used in the following pages.

The first era is naturally the one about which least
is known. Until recently no fossils had been found in its
rocks except some markings which looked like worm tracks,
but which might have been due to some other cause. Hence
it was named the Azoic or Lifeless Era. But the series of
rocks lying immediately above, and therefore presumably next
in age, contain so large a variety of organisms and some so
highly developed that it seems impossible on any theory of
animal evolution to suppose they had no progenitors, a doubt
which has been efifectually settled by the discovery of several
undoubted fossils in the earlier rocks of America. The term
Azoic is therefore a misnomer, and its place is now being taken
by the word Eozoic which means the dawn of life. The rocks
formed during the time are frequently spoken of as Archaean,
but they only peep up here and there through the later
deposits, and the various exposures show such di£ferent fea-
tures that there may really be a greater separation in time
between the Eozoic rocks of one place and those of another
than there is between the latest of them and the earliest
deposit of the following great division of time. It seems,
therefore, undesirable to give the same name to all, and make
that a definite name, for fear that it should be taken to imply
an identity of age which does not exist. The oldest fossil
bearing system which lies above them is the Cambrian system,
and the Eozoic rocks are therefore now generally classed
together under the name Pre-Cambrian.

We know little of Pre-Cambrian geology. There were
volcanoes from which great floods of lava were outpoured.
There were seas or lakes in which beds of pebbles and sand
and mud were laid down, but although the similarity of con-
ditions is obvious there are not wanting numerous indications
that the action of those forces which result in the wear
and tear of the land and the deposit of sediments was more
vigorous then than it is to-day.

We have no certain glimpse of Devon in Pre-Cambrian
time. The serpentine rocks of the Lizard peninsula and the
green and grey crystalline rocks which make up the country

4 Tlie History of Derooshife Scenery*

by Saloombe, and reach from the Bolt Tail to beyond the
Start, are believed by some geologists to be of Eozoic age.
But there is no proof, and if the guess is correct they tell us
no more than that volcanoes were busy in the district. As
a matter of fact the rocks of both places belong to a great
section known as Metamorphoric, which means that they have
been profoundly altered. In neither case can we say what
they originally were. Probably they were partly volcanic,
partly sedimentary, but their original structures have been
destroyed and even their mineral constituents rearranged*
They are documents, so to say, in which new things have
been written on faded sheets so that the older writing has
become quite illegible. It is on the whole more likely that
they belong to a much later time, and we shall consider them
again when we come to discuss the period at which the
changes were most probably brought about.

The second great era is known as the Palaeozoic, or time
of the ancient forms of life. It covers a long and im-
portant series of events during which great alterations took
place in the map of the world, and since changes in geography
with their consequent effects upon climate and environment
are among the most potent agents of animal variation, we find
that at the end of the era the world's inhabitants had made
great progress in evolution.

So far as the British area is concerned the era falls
naturally into two divisions known as Protozoic, or first
life, and Deutozoic, or second life. The history of each
of these follows a definite course, so that they form a
couple of cycles during the second of which the events of the
first were repeated with curious similarity. Each began with
a land surface occupying a large part of the British area.
The sea then advanced over the plains and up the valleys^
driving the coast line further and further towards the north
and west until our area was mostly covered by the ocean
waters* Rain and rivers, wind and wave, swept down the
debris from the land and spread it over the sea bottom in
sheets of gravel, sand and mud. Organic things contributed
their quota in the form of shells, reefs of coral, and limestone
mud until thousands of feet of new rocks had been laid

Pfotocoic Tunc* 5

down. The long period of deposition was then converted
into an upheaval, at first gentle and accompanied by broad
tindalations of the strata, but later on the ascent became
more rapid and was attended by enormous crushing, folding,
and crumpling of the earth's crust, lifting the new formed
rocks higher and higher above the sea until they stood up
as a series of ranges making a mountain chain comparable
with the Alps or Rocky Mountains of to-day, and dominating,
as those chains do, a continental land.

Protozoic time includes three periods which are generally
known as Cambrian, Ordovician, and Silurian, but geologists
have not yet come into complete agreement over the use of
the second name. The beds now classed as Ordovician were
formerly named Upper Cambrian by the great Cambridge
geologist, Sedgwick, and were independently called Lower
Silurian by Murchison, the head of the geological survey.
For many years the followers of these two great pioneers
adhered obstinately to the use of the name adopted by their
chief. Finally, as agreement seemed impossible, it was
reserved for Professor Lapworth to invent a new term. The
word Cambrian is derived from the fact that rocks of this
age were first studied by Sedgwick in North Wales. Mur-
chison first investigated the Silurian rocks in South Central
Wales, the district once inhabited by the tribe of Ancient
Britons known as the Silures. The debatable deposits lay
between the two, not only in order of time, bat also geo-
graphically. This was the district where the Ordovici lived,
why not bury the hatchet then, and agree to drop both Upper
Cambrian and Lower Silurian, and give a distinct name to a
series of deposits which bore no nearer relationship to either
the previous series or the succeeding series than it did to the
other. The reasonableness of the suggestion has been ap-
preciated and there are now only a few, such as Sir A. Geikie,
who still adhere to the Lower Silurian of his predecessor in
office.

The Cambrian rocks bear abundant evidence of having
been deposited at no great distance from a steep sloping shore
in shallow water, and in shifting currents. Where their base
can be seen they are often seen to rest on the upturned,

6 The History of Deyonshire Scenery*

denuded edges of the earlier rocks, showing that they were
formed on a submerged land surface. The upper beds of the
system are finer and more evenly laid down, and consist of
materials which would naturally have come to rest further
away from the receding coast and in deeper water. They are
interspersed with beds of lava and fine volcanic ash which
suffice to show that in North Wales, at least, the volcanic
activity so characteristic of Pre-Cambrian time was still alive.
Indeed, much of the fine mud which made up the slates
among which the undoubted volcanic rocks are found may
very well have owed its origin to eruptive outbursts.

A study of the Cambrian rocks of other countries points
to the remarkable conclusion that the great continent from
which their materials were borne occupied the site of the
Northern Atlantic, while the oceanic areas lay where Russia
is on the one hand, and the Western States of America on
the other.

The volcanoes of Cambrian days seem to have been a
feebler link between two periods of intense action. Ordovi-
cian time witnessed the growth of several important groups
of volcanic mountains in the British area, the chief of which
occupied the site of North Wales, while another of almost
equal importance marked the place now occupied by the
English I^ake district. Great Hoods of lava were poured out,
and these alternated with vast deposits of volcanic ash which
were spread far and wide over the floor of the sea. There
is little doubt that these two districts formed volcanic islands
built up from the ocean bottom like the Sandwich Islands
and some of the West Indies of to-day. Like all other great
volcanic piles they were built up of materials which varied
enormously in their power of resisting the wear and tear of
time, and it is to this fact that North Wales and the Lake
district owe the rugged grandeur of their scenery.

The depth and wide extent of the Ordovician sea is
shown in many ways. We cannot here do more than
briefly indicate a few of the reasons for the conclusion. In
the first place we have the character of the materials.
Apart from the volcanic masses already mentioned, Ordovician
rocks are generally very fine grained, made up of thin beds

7

1 & 2« Radiolaria (highly magnified),
3t 4 & 5. Foraminifera (highly magnified).
6, 7 & 8* Graptolites (two-thirds natural size).

Deep Sea Organisms* 7

and often partly limestone, which can only form in water
sufficiently free from land derived material. Over very large
areas the deposits consist of thin black shales full of the
remains of a peculiar order of creatures known as Graptolites,
and these are not infrequently associated with other animals
called Trilobites.

Graptolites are so called from the fact that their fossil
remains are always very thin and flat, looking more like
things drawn upon the rock with a brush or pencil than
included organisms. The whole order has long been extinct,
but careful study of the best preserved fossils shows that they
were Hydrozoons and probably lived in the ocean waters
floating about attached to drifting weed, or perhaps to
gelatinous floats similar to that of the modern Portuguese
Man of War. Many of the same species occur in such
widely separated regions as Sweden, Britain, France and
Canada, and the beds in which they are found are themselves
similar, facts which are difficult to explain on any other
hypothesis than that of a widespread continuous ocean. It
may easily be argued that as the order is extinct it is
impossible to know what was their mode of life. But there
are other facts.

The Trilobites are also an order of the past. They
were very abundant during all Protozoic time, being the most
characteristic feature of its fauna. They were strange animals
not altogether unlike the modern King Crab in its earlier
stages. One of them, found in the Cambrian rocks, was two
feet or more in length. They were, as a rule, provided with
well formed eyes, but, mingled with the Ordovician Graptolites,
it is found that forms frequently occur in which the eyes are
abnormally large, as if the creature lived in regions where the
light was very feeble. In others eyes are altogether absent,
as if the animals frequented waters too deep for light to
penetrate. In short they were adapted to live in the darkness
or dim light of the ocean depths.

An even more conclusive piece of evidence comes from the
neighbouring county of Cornwall. In 1893 Mr. Howard Fox
and Dr. Teall were investigating the structures of the Lizard
peninsula when they found on Mullion Island a band of a hard

8 Tlie History of Devonshite Scencf y*

flinty rock called Chert which proved to contain vast numbers
of fossil organisms called Radiolaria. The same band, or a
similar one, has since been traced on the mainland associated
with rocks which are pretty certainly of Ordovician age.
Since then similar bands of Radiolarian Chert have been
found interstratified with the thin black shales which are full
of Graptolites, thereby proving beyond a possibility of doubt
that they were formed under similar conditions and that those
conditions reached so near to Devonshire as the end of
Cornwall.

We have already hinted that the debris worn from a land
surface and carried out into the sea comes to rest in a definite
order. Nearest to the shore we get coarse shingle or rough
broken material, further out comes sand, which gets finer
and finer until we have a fine slimy mud. The coarser the
material the thicker the deposit as a whole, until we come to
a distance of a hundred miles or so from the coast, when the
land derived material thins out to nothing. It has been found
from the examination of samples of mud dredged up from
the ocean floor that this land derived material, easily recog-
nised under the microscope, is confined to a strip measuring
from loo to 300 miles in width, according to the strength of
the currents bordering the continents and islands. Beyond
this distance the mud consists generally of the skeletons and
other hard parts of the creatures which dwell in the open sea.

Thus the North Atlantic is now paved with a pale grey
slime, or ooze, which consists principally of the skeletons of
minute animals called Foraminifera, a group of creatures
whose bodies were stifiened with a framework of carbonate
of lime dotted all over with tiny holes or foramina. They
live in countless numbers in the waters and there must be a
ceaseless gentle rain of their dead sinking slowly downwards.
The protoplasm of their bodies soon decays and the little shells
fall on. Now carbonate of lime dissolves in water which con-
tains carbonic acid gas in solution, and the stronger the
solution the more rapid will be the corrosion. All sea water
contains some carbonic acid, but the greater the depth the
larger is the percentage of gas, so that at very great depths
any shell will be rapidly eaten away. The consequence is

Radtolarian CEert Beds* 9

that a specimen of ooze from a moderate depth is found to
contain abundant perfect and beautiful foraminiferal shells,
principally those known as Globigerina, but as the depth in-
creases the corrosion becomes more and more evident.
Obviously we have only to go deeper and deeper until we must
come to a stage when there will be nothing left. A rock,
then, made largely of Foraminifera is almost certainly a deep
sea deposit, but is equally certainly not an abysmal formation.

There are some other animals not very different in some
ways, but having their hard parts composed of silica, or
flinty matter, instead of carbonate of lime. These are the
Radiolaria. They are much fewer in the surface waters than
their calcareous contemporaries, but they live at all depths.
The consequence is that the greater the abyss the heavier
will be the rain of radiolarian tests. In the comparatively
shallow regions the quantity of foraminiferal shells in a
specimen of ooze is so much larger than the radiolarian that
the latter are rarely seen, but as the depth increases they
become relatively more and more frequent, until, if the ooze
has come from about 3,000 fathoms or more it will be found
that the insoluble siliceous skeletons have outlasted the
soluble calcareous ones and the mud is almost exclusively of
radiolarian origin.

Not many years ago it was frequently argued that no part
of the existing land could ever have formed the floor of a
really deep ocean, because we had nowhere found any rock
resembling a radiolarian ooze in its composition. Hence it
was maintained that the present arrangement of ocean and
continent must in the main have endured ever since there was
any division of the terrestrial surface into land and water.
But the microscope has shown that the reasoning was based
on false data. The dry land of to-day contains many layers
of Radiolarian Chert, and the MuUion Island specimen is a
sufficient answer in itself.

It is as well to point out that it is just possible that
other causes might bring about a more rapid solution of the
calcareous matter, and that a radiolarian ooze might accumu-
late in much shallower water than is possible now, but, if we
couple the fact with the other reasons given, we cannot avoid

lO

The History of Deyoiislxire Scenery*

the conclusion that the Ordovician ocean at the time of its
maximum was a great expanse comparable with the Atlantic,
and that its waves rolled freely across the site of the Devon-
shire which was yet to be. The volcanic islands of Wales,
Cumberland, and other spots lifted their summits above the
water off the south-eastern shore of a great continent much

Unconformability.

V^V

Overlap,
as the Canary Isles or even the Azores now lie in the open
ocean oflf the western coast of Africa.

The living things of Ordovician days were far more
various than before. Around the shores and in the shallower
parts of the sea floor banks and beds of shells accumulated and
here and there where the conditions were suitable corals grew
into reef-like masses which have been left to us as beds of lime-
stone which tell the tale of their origin by their fossil contents.

Towards the close of the period the quiet and slow subsi-
dence was converted into a movement of upheaval which was
irregularly manifested. Here and there the sea bottom was

Fofmation of Mountam Chains* ii

raised within reach of the wear and tear of waves or
currents, or even into the open air. The old sediments were
eroded and the muds and sands which marked the beginning
of Silurian time therefore lie in such spots on the wasted
edges of the older rocks. To use the orthodox term the
Silurian beds are sometimes unconformable to the underlying
Ordovician or even older rocks which had been laid bare by
the complete removal of all Ordovician deposits. A consider-
able geographical change is here indicated. In the Welsh
area sandstones, shales, and grits of evidently land derived
material were followed by finer muds and extensive beds of
limestone whose presence indicates periods of clearer water
during which coral reefs could grow and piles of shells and
coral fragments be heaped against them by the waves, where
they have been solidified and now form beds of limestone
like the crest of Wenlock Edge.

The evidence of the Siluriah rocks points to a shallowing
sea, to a steady advance of the coast line towards the south-
east and finally to a great alteration of the map whereby the
coast line was brought southwards to the middle of Scotland
and Ireland. The stupendous forces which co-operate to
make a mountain chain had set in.

As we shall meet with other examples of this vast opera-
tion it may be well to discuss its usual phases in a general
way before dealing with the actual examples.

The chief cause of terrestrial convulsion is undoubtedly
the slow cooling and consequent shrinkage of the internal
portion of the globe. As the store of heat is diminished the
interior shrinks, thereby throwing a tremendous strain upon
the colder crust which has to fit itself to a smaller and smaJler
sphere. At first the strain is borne by the rigidity of the
crust or partially relieved by a general subsidence during
which its deeper seated portions are compressed and hardened.
The result is the formation of a hollow which becomes the
receptacle of material removed from the neighbouring lands,
and the crust is steadily thickened. This deep covering of
the older crust causes its temperature to rise and, owing partly
to irregular loading, fissures are formed which become the
outlets for volcanic action, the results of which are to fill the

12 The History of Devonshifc Sceoery*

cracks with solid wedges and to add to the loading of the
crust.

As the internal shrinkage proceeds the overlying crust
becomes more and more strained, until relief is found by some
part of it giving way and either breaking into numberless
slices which slide over one another or, more frequently, folding
up into a complicated series of folds. It is evident that such
relief will necessarily follow a series of lines at right angles to
the direction of the greatest pressure, and will be more likely
to take place where a great thickness of new soft rock has
accumulated and the underlying old rock has been softened
or weakened by heat, than in those places where the solid old
rocks have been undisturbed.

Ideal Scctimis from tfie centre to the edge of a, BAbontaiii Cbaiiu
A Rocks altered, original bedding destroyed.
B Rocks slig-htly altered, bedding* obscure.
C Rocks unaltered, beds much bent.
C Rocks unaltered, beds much broken.
D Marginal gentle folds.

The result of the folding and puckering of the rocks or of
their being piled up into a heap of fragments is to thicken
them immensely. They cannot project downwards, therefore
they bulge upwards, and the repeated folds make up a series
of roughly parallel ranges traversing great distances.

If we study the detailed structure of such a region we find
the folds broad and gentle on the flank, narrower and sharper
as we proceed further until in the axis of the chain the con-
fusion of the strata, once broad sheets of sediment on the

The Scandinavian Cliain* 13

floor of the sea, is almost inconceivable to anyone who has
not seen it.

At the close of the Silurian period this comer of the world
experienced the first great mountain building throes of which
we have any certain knowledge. The floor of the sea was
raised into dry land, the Silurian, Ordovician, Cambrian, and
Pre-Cambrian rocks were folded and crumpled, in some
places so profoundly crushed and changed that they can no
longer be identified, and a system of hill and mountain ranges
brought into being. They extended through the Scandina-
vian peninsula, across the North Sea and Scotland, passed
along the north-western shores of Ireland, and so away to
some unknown distance along the southern shore of the
North Atlantic Continent.

The Grampians, the mountains of Donegal and the
southern uplands of Scotland are the ruined foundations of
some of these ancient ranges, which have thus formed pro-
minent features in British geography, as the Scandinavian
range has formed a great feature of Europe, ever since the
end of Protozoic time.

The building of modem Europe had begun and we reach
the date when the history of Devon begins to be readable from
its own records, when we can assign to it a place and
character among its surroundings, not merely by induction,
but from positive evidence supplied by things which may be
seen by all who care to see.

CHAPTER II.
The Devonian Rocks of N. Devon.

The great movements which closed the Protozoic cycle
resulted in a land surface which presented some very remark-
able features in that part of the British area north of the
Bristol Channel. Over extensive districts we meet with a
great series of conglomerates, sandstones, and very impure
limestones, nearly all of which are stained deeply with red
oxide of iron, but here and there coloured less deeply in
shades of yellow and even grey. These beds have long been
known as the Old Red Sandstone.

Where the base of the system can be seen it is usually
found that the upper part of the Silurian rocks are red
in colour and that the bottom layers of the sandstone lie
conformably upon them without any marked break in the
succession. In other places the bottom beds lie on the
denuded edges of older rocks and are obviously made up of
the broken fragments of whatever underlies them.

The change from the finer materials of Silurian time is
the result of the geographical change. The upheaval des-
cribed in the last chapter ridged up the floor of the Silurian
sea, shutting off portions into more or less land-locked lakes,
or gulfs, into which were swept the debris of the intervening
ridges.

The Old Red Sandstone everywhere abounds in proofs
that its beds were accumulated close to shore, in shallow
water and in reach of violent and variable currents. The
thin beds or laminae composing the strata are very irregular,
showing frequent examples of what is known as "false
bedding" a structure always found in modern sands which
have been deposited under such circumstances.

The pebbles which make up the conglomerates are often
very large and very slightly waterworn as if they had formed
parts of great sloping piles of rubbish fallen from the cliffs
which had been rearranged roughly by the waves, or as if

Old Red Sandstone. 15

they had been slowly accumulated in steep mountain valleys
by the action of the weather and then hurriedly swept down
by a violent torrent and piled in confusion over the floor of a
lake or arm of the sea.

Here and there remains of plants have been found, especi-
ally in the south of Ireland where the slabs of sandstone are
in certain places covered with the prints of magnificent fern
fronds which cannot have drifted far from the spot on which
they grew. In other cases sedge-like and grass-like markings
have been found covering the surfaces as if the plants had
grown not far away.

No shell fish of orders such as inhabit the open sea have
been found in the Old Red Sandstone except in its topmost
beds in the Welsh district, but in Ireland and other places a
shell* has been found which strongly resembles the great
freshwater mussel of our modern lakes and streams.

By far the most important fossils are the remains of great
Crustacea called Eurypterids, some of which were like cray
fish, five and six feet long, and numerous fish of remarkable
types which had their heads and bodies armoured with bony
plates. These fish remains are unevenly scattered throughout
the series. Sometimes a level is found at which the remains
are thickly strewn over the rock surfaces as if some great
catastrophe had caused the death of thousands and had then
buried them before decomposition had set in.

Now the areas where Old Red Sandstone rocks are found
are definitely marked and are separated by broad regions
which we know from their rock structures were just those
along which the Silurian sea floor was ridged up into ranges.
The arrangement and nature of the coarser materials points
to these ridges as their source, so that we should be prepared
to learn that the basins were really distinct. If we bear in
mind the indications of a freshwater origin, we at once begin
to suspect that the basins were really great lakes.

The fish remains form an almost conclusive proof. If we
form a set of collections from the diflerent basins and compare
the fish of one with those from another it is at once seen that

* Amnigenia (^Anodonta) Jukesiu

i6 The Histoty of Devotulilfc Sceneiy^

these basins cannot have been parts of an open sea. The dittat*
ences are too great, and can only be satisfactorily explained
by the theory of great lakes more or less completely
separated.

We have already compared the Caledonian and Scandina-
vian chain with the Rocky Mountains or the Alps. We have
here another point of similarity, for both these modem chains
have passed through a stage when the hollows between their
ranges were filled by sheets of water far larger than the
present, which are but trifling pools on the floors of the
ancient lakes.

So positive does the conclusion seem that Sir A. Geikie
has given definite names to the diflierent lakes. The most
northern basin extends from the North Sea in a south-westerly
direction on both sides of the Moray Firth. This he calls
Lake Orcadie* South of the Grampian ridge came a long
narrow sheet of water which reached across the central
valley of Scotland and extended far into the north of Ireland.
It is known as Lake Caledonia, and must have been a sheet
of water comparable with the great lakes of Africa or America.
Further south a large basin lay over the site of Hereford
and extended from Shropshire in the north to Pembroke and
the Mendip Hills in the south. It seems to have been less
completely isolated than the northern basins and is known
sometimes as the Welsh lake, or, from its possibly marine
relations, the Welsh Gulf.

Kerry and Cork were the site of another freshwater lake
called Lake Munster. A smaller region in the Cheviot Hills
is called Lake Cheviot, and a smaller still, in Argyllshire, is
known as Lake Lome.

The sands and conglomerates of Lake Caledonia are
interstratified with great flows of lava and coarse volcanic
fragments which show that its shores were fringed with active
volcanoes whose broken cones were washed by its waves and
their materials spread out on the lake bottom. The volcanic
phase appears to have been temporary only, and marked a
time of earth movement when the lake basins experienced a
further tilt so that the upper beds of the Old Red Sandstone
series do not rest evenly on the lower.

Ideal restoration of Old Red Sandstone and Devonian Geography*

The Great Lake Basins* 17

We are thus enabled to draw with considerable confidence
a map of the British area north of the Bristol Channel and
west of a line from Bristol to Berwick. East of this line the
older rocks are hidden from view by much younger strata, and
it is only where the Pre-Cambrian hills of Charnwood Forest
peep up above the covering that we get a glimpse of an old
land surface.

We can do more than mark the approximate boundaries
of land and water. We can trace the lines along which the
principal ranges lay and can even form a rough estimate of
their importance by studying the amount of folding and com-
pression their component rocks have undergone. The south-
eastern ranges were of moderate extent when compared with
those further north. Beyond Lake Caledonia the changes
have gone far beyond mere crumpling. The rocks have been
metamorphosed. Crystalline minerals have been produced,
and structures are met with clearly indicative of the core of a
considerable mountain mass. Beyond Lake Orcadie up in
the north-western corner of Scotland the rocks, which include
some of certainly Cambrian and Pre-Cambrian age, have been
intersected by innumerable planes of fracture sloping gently
to the south and east, and whole mountains have been made
to slide up these planes for miles until the structures are prob-
ably the most complicated which have ever been unravelled.*

We shall certainly, then, be in small danger of error if we
suppose the main chain lay over this north-western corner,
and reached up to heights above the sea quite comparable with
those attained by the great mountains of to-day. Lower and
lower ranges lay between it and the sea, much like the way
in which the Sierra Nevada and the coast ranges of California
lie between the Rocky Mountains and the Pacific, while the
dry basin of Utah is the equivalent of the area covered by
the waters of Lake Caledonia.

In the map, the arrangement of land and water must
be taken to be purely diagrammatic. We cannot at this
distant date pretend to trace the shore lines with any
detailed accuracy. Moreover, if we could do so for any

• See Quart Jour. Gcol. Soc, 1888, page 378.

i8 TIic Histoff of Dcfoo^bitc Scenery*

particular moment during the vast lapse of time covered by the
period, it 'would be incorrect for even the next year. It is
equally impossible to locate individual mountains or any
valleys accept the large ones, and quite beyond our power to
trace the rivers* It is true that the outlets from which some
cf the lavas flowed can be identified, but no volcanic crater,
no ridge or hollow of the time, can possibly have survived
the wear and tear of the countless ages which have elapsed
since they were first exposed to the wasting action of the aic

So fax nothing has been said of Devon. Attention has been
restricted to the country lying north of the Bristol Channel.
The reason is simple — that the Old Red Sandstone extends no
further south; its place in the geological sequence is there
occupied by a totally difiierent set of deposits which were most
certainly marine.

Deposits of the same age as the Old Red Sandstone are
found in two districts withm the limits of Devonshire. The
ziorthem area extends southwards from the Bristol Channel
to a line almost coincident with the railway from Taunton to
Barnstaple, but generally a few hundred yards further souths
At this boundary the beds of rock disappear under a newer
series and do not reach the surface again until they rise up on
bath sides of Dartmoor, at Tavistock on the west and
Chudleigh on the east From these places to the English
Channel by far the greater part of the country is coveted by

In both districts the racks have been greatly crushed and
broken, so that it is comparatively seldom that we are able
to find any fossils which are not more or less distorted, and in
some places the original structure of the rock itself has been
almost entirely destroyed by events which occurred consider-
ably later on. In the extreme south of the county we have
already said there are some crystalline metamorphic rocks
making up the district round Ssdcombe and the Start which
may be older, but which are just as probably of the same date
as those immediately next to them.

The two series of deposits di£Eer considerably, but the
difference is not greater than we should expect to find in
places whose distance from the shore of the old continent

TIic North Devm GoMts. 19

varied by a space equal to the thirty miles which lie between
them.

There are no similar rodcs anywhere in the British Islands
except in Cornwall, which is largely covered by a continuation
of the southern series, and in the hills of West Somerset,
whose structure resembles that of North Devon.

Having been first studied in Devon they received the
name of Devonian Rocks and the period is therefore known
all the world over as Devonian. We have already said that
there is sufficient evidence to show that the Old Red Sand-
stone deposits were formed in lakes or land-locked basins,
while the Devonian deposits were undoubtedly marine. Now
when the structure of other parts of the world came to be
explored it was found that the Devonian was really the
world-wide, and that the Old Red is the local and excep-
tional variation.

The best way to examine these rocks and endeavour to
interpret them is to confine attention to one of the two regions.
To begin, then, with the northern exposure we will start at
Lynmouth, where the great ch£fs give us magnificent sections,
and the deep gorges and rocky valleys enable us to see a great
deal of the inland structure. Here there is a marked di£Ferenoe
between the red beds of the Foreland and Countisbury and
the grey and purple grey cliffs to the west of the harbour.
The red rocks can be well studied at low water by walking
along the beach and there are several sections in the roadside
cuttings on the road to Watersmeet. The resemblance to the
Old Red Sandstone deposits of the Welsh basin is so strong
as to strike anyone who has seen both, but the colour is not
as a rule so deep, the grey beds are much more numerous, the
texture of the rock is generally much finer and here and
there where small bands of fossils occur they are the remains
of marine organisms.

At first sight the beds look as if they were very regularly
stratified, though the strata have been greatly tilted and folded
but a closer inspection reveals the {act that in many places the
planes of division which look Uke bedding are really the result
of pressure. In making the coach road to Watersmeet there
are several places where the rock had to be removed by blasting

20 The History of Deyonshire Scenery*

and these sections are well worth a careful scrutiny. The
rock as a whole is very barren of fossils, but here and there
rather wavy lines of irregular holes are to be found in the
hard sandy stone. These lines run obliquely across the
planes of division. A vigorous use of a hammer will soon
show that the lines of holes are really little patches of
fossils. The shells themselves have disappeared, and the
cavities they once occupied have been more or less filled in
with a red brown powder which crumbles at a touch.

Now if we walk over a sandy shore at low water everyone
knows how usual it is to come upon little patches of shells
left by the tide. We may walk for many yards without
seeing one and then suddenly there are dozens in a square
yard or so. Sometimes these patches lie in lines marking
some pause in the tidal ebb or some local hollow in the sands.
If we could clear away all that lies above one of the fossil
bands we have been discussing there is no doubt we should
lay bare just such a patch of shells, only they would be shells
of Devonian time, and we should be looking on what
was once the sea shore or the sea bottom close to shore.

As a rule the fossils are squeezed out of shape and the
bands in which they lie do not coincide with the present
planes of division. This, however, is a structure impressed
at a later date and does not afifect our interpretation of the
conditions under which they were first formed.

The coarse grain of some of the beds, the irregularity of
their internal structure here and there, and the mode of
occurrence of the fossil shells all point to a shallow sea near
shore, and the conclusion that these are the seaward continua-
tion of the sands of the Welsh basin becomes irresistible.

If we turn from Lynmouth and go westwards either along
the cliff paths or along the beach we find much finer grained
materials and grey grits and sandstones which lie not much
inclined from the horizontal. The grey grits are admirably
shown in the Castle Rock and along the Valley of Rocks,
while at the back of Lynton, in the Station Hill, there are a
number of little quarries such as one in a lane known as
Mount Sinai Lane where the beds are a very fine-grained
shaly material of a dirty yellowish grey. These must have

Lynmotttli and the Castle Rock* 21

been a finer mud settling to the bottom of the sea further
from their source and not unlike the slimy muddy sand
revealed at low water every here and there along the modem
Bristol Channel. In the grey grits of the Castle Rock
marine fossils are not rare, but they cannot very easily be
found. A curious point about them is that they stand out on
the surfaces which have been long exposed to the weather,
and for a little distance into the stone they can be traced with
sufficient care, but well within the interior the rock splits
under the hammer and chisel without any regard to the
fossils which may be there.

In the little quarry at Mount Sinai Lane the blocks of
shale are easily split and the surfaces are often found to be
covered with the traces of a marine hydrozoon Fenestella
and with fragments of crinoids.

The curious castellated look of the Castle Rock and others
in its vicinity is due solely to the facts that the beds lie nearly
horizontal and the rock is naturally divided by cracks known
as joint planes into roughly cubic blocks, and the blocks them-
selves vary a good deal in their power of resisting the wear
and waste of time. The hills therefore tend to become rough
piles of cubic blocks calling to mind the idea of ruined
Cyclopean masonry.

As we pass along the coast we find the beds of rock
dipping down towards the west in Wooda Bay where they
exhibit a great variety of texture. Some of these beds are
fossiliferous, but the greater part are very barren. The rapid
changes of texture point to variations in the power of the
currents which brought down the material, such as might well
be produced by changes in the ebb and flow of currents or an
irregular sequence of rainy and drier seasons over the neigh-
bouring land.

When we come to the great heights and magnificent cli£f
slopes of Trentishoe and the Great and Little Hangman hills
we find another series of sandstones and grits strongly
resembling those of the country east of Lynmouth. Are they
another part of the same series of rocks, or does it mean that
the conditions which gave rise to the Foreland deposits had
been re-established ? This is the first of the countless difficult

22 The History of Devonshire Scenery*

problems which we encounter. As we proceed we shall find
many others, and it will be wisest to postpone any attempts to
answer them imtil we are able to take a comprehensive view
of them all. The cli£f sections seem to indicate the return of
the okl conditions, but the proof is by no means conclusive.

After crossing Combmartin Bay we come to a series of
rocks more like those we have already seen in Wooda Bay, a
great series of shales which split into wavy flakes interspersed
with thin bands of fine-grained sandstone, thicker layers of
a soft slate-like rock, and here and there thin beds of lime-
stone which thin out rapidly in all directions as if they had
originally been lenticular patches on the sea floor. In most
of these beds fossils are few and far between, but the lime-
stones are in places made up of corals, crinoids, shells, and
other organic remains. But here, as at the Castle Rock, the
fossils can only be detected with difficulty in the interior of
the stone. The difierence of texture is so small that nothing
but the slow and gentle solvent action of the weather can
show them up properly. Almost all of them are more or less
distorted.

To anyone who cares to try to unravel a greatly disturbed
district, Ilfracombe and its neighbourhood is a paradise.
Along the western face of Rillage Point the beds have been
little crushed. They are tilted up at a high angle and near
low water time, with a falling tide, they can be studied well.
The paths to the beach are not very easy to find from above,
but the section is well worth the trouble of scrambling down.
When visiting the beach it is a wise precaution to have a
companion who is not a keen geologist, but who may keep an
eye upon the tide, as it comes in very rapidly and might easily
pen an enthusiast in some recess from which there would be
no escape without a swim.

Hillsborough again has a comparatively simple structure,
though the great features of the clifi' are due to the joint
planes rather than the stratification. The Lantern Rock tells
us a very diffierent story. Viewed from the beach on its
western side it is at first sight made up of a series of beds of
rock rather highly inclined and dipping towards the south.
But a closer inspection shows us that some of the apparent

Under the Torrf^ Ilfracombf*

Key showiog original bedding of Rock shown above.

Under the Tom, Ilfracombe*

Key showing original bedding of Rock shown above.

Tbc Hfracombe District* as

beds are nothing of the kind. The original stratification has
been almost destroyed. The soft shales have been crumpled
up into a confused mass which has been sheared across by
crack upon crack and it is these cracks which simulate the
bedding.

The Capstone hill a£fords another example of subsequent
disturbance. On its western £Eice the original strata are boldly
shown by the thin sandstone beds which are interspersed
among the shales. The latter split up along planes more
highly inclined, and, if it were not for the sandstones, these
cleavage planes would almost certainly have been taken to
represent the planes of deposit instead of a totally different
structure, namely cleavage induced by pressure.

Perhaps the best examples of these changes are to be
found in the neighbourhood of the Torrs Walks, on the beach
beneath them and in the road cuttings behind.

Some distance along the Walks there is a path which leads
down some steps to the beach. These steps are cut down a
low cliff in which the bedding is at first sight very plainly
shown, but careful study shows that the surfaces of the rock
are traversed by wavy bands in shades of grey and brownish
grey. These are the original beds, and the other apparent
beds are only planes of division caused by a shearing action.

The correctness of this view is very plainly shown in a
large rock on the opposite side of the cove, where the true
bedding is betrayed by a thin band of sandstone, the hardness
of which has enabled it to resist deforming forces which pro-
foundly affected the softer shales.

The same thing is shown again in the road behind the
Torrs. There a cutting shows dark grey shales apparently
inclined in one direction. But some height above the road
they are crossed obliquely by a series of whitish bands greatly
puckered and copying each other's folds in such a manner
that they can only be the old rock bedding.

Similar structures are found here and there as we go on
towards Lee Valley and Morthoe, but the materials of which
the rocks are made become finer and finer. Sandstones
disappear, limestones are fewer and further between, until at
Morte Point and along a belt of country extending eastwards

24 The History of Devonshire Scenery*

through the Station Hill at Ilfracombe we find pale grey slates
which must have been originally fine clay mud very much like
some of the grey muds of the Silurian Sea. The forces which
distorted the Lynton fossils, and which obscured the bedding
of the rocks round Ilfracombe, have here acted with far
greater intensity, and the original bedding has been almost
entirely destroyed and its place taken by a slaty cleavage
which causes the rock to split along almost vertical planes.
For a long time these slates were supposed to contain no
fossils, but Dr. Hicks in the year 1890 found a considerable
number in various spots. One of the most prolific is a small
quarry at MuUacott, on the road which leads inland past
Ilfracombe Station. Some distance up the long hill there are
two little quarries ; the southern one now contains the town
dust destructor and the smaller northern excavation is partly
filled in with old scrap iron, lobster tins, and similar un-
savoury waste which is presumably incombustible. Up in
the western corner of this unlikely looking spot the planes of
cleavage happen to coincide with the bedding, and fossils will
almost certainly reward an hour's industry. The slates have
to be split open with the sharp edge of a hammer. They
themselves are sharp and fairly hard, so that thick gloves are
very desirable.

In another quarry across the valley the slates are covered
with curious markings which Dr. Hicks claimed to be grap-
tolites, but the general belief is that they are only markings
produced by the infiltration and deposit of mineral substances
between the slates.

The original bedding can be detected with difficulty here
and there. The best way to see it is to choose a time when
it is low water at spring tides and walk out on the sands by
the water's edge just below the newer part of Morthoe. Then
if the light is favourable the contorted beddfng may be seen
as bands of shading cutting most irregularly across the edges
of the slates. The beds have been folded over and over again
so that the tangle is impossible to unravel. It is best seen
when the sun is in the west so that there are little or no
shadows since the jagged slates stand out as a series of great
saws projecting westwards.

Mofte Slates showing traces of stratificatioo.

Wtii face of the Lantern Rock, Ilfracombe*

Baggy Point and Braunton* 25

We have seen that the Ilfracombe beds are, on the whole,
made of finer materials than those previously described, finer
than the shales of Lynton and Wooda Bay, and much finer than
the Hangman and Foreland grits. This should mean greater
distance firom the shore, or from the source of the sediments, or
the arise of some obstacle so that the finer material came to
rest after the coarser had fallen to the bottom. The original
mud must have been deposited in moderately deep water, and
the limestone patches point to rather long periods during
which the water was clear enough for corals to begin to grow
on shell banks, but before they had built up any considerable
reefs an influx of muddy water overwhelmed them time after
time.

Continuing our exploration of the coast we cross the long
stretch of Woolacombe Sands where the low cliflf is composed
of a series of sandy rocks called the Pickwell Down Sand-
stone, but it is unfortunately buried under a pile of blown sand
heaped up against it by the western gales. On reaching the
bold slopes of Baggy point, we find purple and red coarse-
grained sands known as the Marwood beds. Beds of fossils
occur and there is every indication of shallow water and either
a near shore or strong currents. Indeed the conditions indi-
cated by the Hangman and Lynton beds are to a large extent
repeated. If we follow the shore round into Croyde Bay
and on to Braunton we find a sequence of rocks very like that
of Wooda Bay and Lynmouth, sandstones and hardened
shales interspersed with bands crowded with fossils re-
sembling in their general appearance those from the northern
rocks, but of different species. These are known as the
Marwood and Pilton beds. This last series is not so much
disturbed as the Morte slates or the Ilfracombe rocks, but
the evidences of compression are again more like those seen
at Lynton. The fossils are almost always distorted. The
beds are often highly inclined, dipping southwards at a high
angle and their surfaces where laid bare along the coast are
often marked with a waved structure which may be ripple
marks like those upon a modern sandy bottom, or on the
other hand may with equal probability be a pucker structure
resulting from great pressure.

a6 The Hiflory of Devooshxte Scenery*

We have, so £ar, avoided the question of the order in
which these different groups of rocks were deposited, the order
of superposition. Unfortunately the coast section is not
complete. It is broken here and there so that we cannot be
certain whether one group is the true continuation of another
or whether the groups owe their apparent succession to a
series of great fractures, or faults, between which the groups
stand at different levels.

There are, in fact, two totally diverse views of the North
Devon succession. It was formerly supposed that the Fore-
land grits were the oldest, and that they were overlaid in turn
by the Lynton beds. Hangman grits, Ilfracombe beds, Morte
slates, Pickwell Down sands, Marwood beds and Pilton beds.
According to this view we can explain the sequence of rocks
by supposing that the Foreland grits were the seaward ex-
tension of the Lower Old Red Sandstone of the Welsh basin,
that the sea then deepened, or that the currents slackened for
a time, or that a barrier arose shutting off the Welsh basin,
and that the original conditions were soon re-established.
Again the sea deepened and the coast line retreated or the
currents slackened more and more until the fairly deep sea indi-
cated by the Morte slates was attained. Then, rather suddenly,
the old arrangements were once more produced and the sands
of Baggy Point laid down. But the lapse of time had been
considerable and the species of shells had been changed, so
that the newer sands had different inhabitants. There is no
impossibility in these suppositions, but it is not easy to
account for the much greater symptoms of compression in
the Ilfracombe and Morte beds than in the rocks on either
side, and such considerable changes in geographical conditions
seem rather improbable. Moreover it seems certain that
the earlier investigators to whom this explanation is due
did not fully understand how profoundly the structure of
some of these districts had been altered. It seems that they
probably mistook for true stratification some of the planes of
division which have been pointed out to be really planes
of shearing, the result of great earth pressures, and almost
obliterating the original stratification.

The Morto Slates* 27

So strongly were these difficulties felt, coupled with
another which will be described further on, that in 1896
Dr. Hicks published an entirely different theory.'*'

It has been mentioned that he found fossils in the Morte
slates which had previously been supposed to be barren. We
have also referred to the resemblance between these rocks and
some Silurian beds. He annoimced his belief that they were
actually of Silurian age and that the sequence in the district
was really — Morte slates of Silurian age, and then the
Ilfracombe beds of lower Old Red Sandstone time, while the
sands and grits of Lynton and the Hangman Hills were of the
same age as the sands and grits of the more southern district.
He believed that the divisions between the groups were prob-
ably faults.

The identification of the Morte slates as Silurian appears
to rest on insufficient data. The fossils found seem to be of
peculiar species, and none have been certainly shown to agree
with those from undoubted Silurian rocks. But, however this
may be, it is quite possible that his view may be correct in so
far as the relative age of the groups is concerned. If he is,
the sequence of geographical events would be as follows : —
The Morte slates and Ilfracombe beds would be the marine
deposits forming in a sea separated from the Welsh Lake
by some barrier which prevented the coarse detritus from
the land from spreading beyond its boundaries. The lake
may have acted as a great settling tank, keeping the neigh-
bouring sea comparatively clear, so that only the finest^mud
could reach the deeper water. As time went on the great basin
became partly filled and probably the barrier became wasted
by erosion until at length it was destroyed or overwhelmed,
or the lake filled up and the sand-laden rushing rivers carried
their burden freely into the open sea where it was spread
further and further. The difference in the shells of the two
districts is no more than might fairly be expected on a shel-
ving bottom in a distance of fifteen or twenty miles.

This is a simpler hypothesis than the other, and one more
in accordance with our experience of such phenomena at

• Quart. Jour, Geol, Soc^ 1896, p. 254.

28 The History of Devonshife Sceacry*

other times and in other places. The changes required are
progressive, and indeed they are such as we know must most
probably have occurred in the absence of earth movements
such as would have been almost certain to have left their traces
in the Old Red Sandstone region on the other shore of the
Bristol Channel.

The structures due to pressure were created at a later
date and do not affect the question in hand.

It can only be settled by further work. It may be
possible on the one hand to correlate the North Devon beds
more positively with those of South Devon and the Continent
by means of their included fossils, and local geologists by
diligently recording every section in careful detail may bridge
over the gaps in the succession and show that the apparent
order of superposition is the true sequence. On the other
hand a greater number of better fossils may result in proving
that the northern sands and grits are really represented by
the southern, and the great faults which Dr. Hicks suggests
may be found to be actual fact. Finally it may be shown
that the whole North Devon structure is that of a single
folded ridge, folded so strongly as to crumple and fracture all
the beds and produce the structures we see, but essentially
consisting of a single or repeated arch with the system of
grits the newest and the fine grained slates of Morte the
oldest.

CHAPTER III.

The South Devon Rocks.

The rocks of South Devon are much more diversified than
the northern rocks which we have just described. They lie
in much greater confusion than even the Ilfracombe beds,
though it is doubtful whether there is anything in South
Devon quite comparable with some of the structures already
mentioned as affecting the district of Morthoe. The beds
are almost always highly inclined and in many places they
have been actually overturned, so that the apparent order of
superposition is the reverse of the true succession. Sharp
curves and acute folds are quite common, and as we move
further and further south these symptoms of intense com-
pression become more and more pronounced.

The great bulk of the strata consist of soft slates and shales
with sandy beds of harder rock, all of which resemble strongly
the deposits already seen at Wooda Bay and Ilfracombe.
They are made of sands, grits and muds which can only be
the results of weather action on some land mass, and on the
whole they represent types of sediments which would prob-
ably come to rest further away from the source of origin than
the corresponding rocks of the Exmoor area. They are,
however, mixed with very important masses of material which
had a local origin, namely, the limestones which form almost
the most conspicuous feature in the scenery, and a great
series of volcanic formations which are spread as a string of
patches from Newton Abbot southwards to Totnes. South of
this town they swell out into a wider expanse, which seems to
mark one of the chief centres of activity. The village of
Ashprington lies south of its centre, hence when they were
described in detail by Mr. Champemowne he named them the
Ashprington Volcanic Series.* The valley of the Dart from
Totnes to Dittisham is cut through a complicated pile of

* Quart, your. Gcol. Soc., 1889, p. 369.

32 The History of Deronshite Sceaery*

The volcanic rock thus contains its own certificate of the
conditions under which it solidifiedi and an injected sheet is
known technically as a sill.

There are other tests which can be applied if there is any
ambiguity about the rock itself. When a lava stream flows
over some other rock, this underlying material is baked and
more or less hardened and altered by the great heat. As the
lava cools, great cracks are formed in its rough and irregular
upper surface, and when the subsequent deposits fall upon it
they penetrate these cracks and, of course, show no signs of
baking or alteration.

An injected sill, on the contrary, bakes and alters both the
beds below it and the beds above it, and, so far from being
penetrated by either, it commonly sends o£f branches of its
own substance into them, or even breaks irregularly across
them wherever they chance to have been fractured.

Injected volcanic material is by no means always confined,
even in part of its course, to the planes dividing one stratum
from another. Sills are the exception rather than the rule.
Far more frequently the molten material breaks quite irreg-
ularly across bed after bed, paying little or no regard to the
original divisional planes. It is then said simply to be
intrusive.

All these phenomena are exemplified again and again in
South Devon. Some of the volcanic rocks are clearly inter-
stratified with the slates and limestones. These at least must
have been the products of eruptions which took place from
time to time during the same period. They must, as we say,
have been contemporaneous with those slates and limestones.

Where they are intrusive, either as sills, or as filling cross
and branching fractures, we cannot be certain of their exact
age, except that the eruptive forces which injected them
were exerted at some date later than that at which the
slates [and limestones were laid down. It is possible, then,
that some of the volcanic rocks intrusive into the southern
Devonian formations may really belong to a later date, and,
as we shall see in the sequel, this is fully probable.

There are hundreds of examples of volcanic rock in Devon,
and, of the whole, only a minor fraction have yet been studied

Alteration of Rocks* 33

in full detail. When all have passed under the careful scrutiny
of experts it may be possible to identify those of Devonian age
and separate out those (probably fewer) which really belong
to a later period. In a given volcanic region it is usually
found that the products of the earlier eruptions di£fer in
chemical composition, and therefore in the minerals they
contain, from those of the later phases of activity. We know
well that the Devonian volcanoes were continued into a much
later time, and it is possible that some sequence of composi-
tion may be revealed which will give us the clue by which
the newer rocks may be distinguished from the older.

If the sedimentary rocks, the grits, shales, slates and lime-
stones were spread out in widely extended sheets and contained
numerous well preserved fossils it would be easy enough
to write the history of the time. But the facts are far
otherwise. Great earth movements have broken up the
district and piled the parts irregularly together, crushing,
distorting and even destroying the fossils, so that there are
considerable areas whose proper place in Devonian time
can only be guessed quite roughly by the general colour and
texture of the deposit.

It has been said that the results of compression become
more marked as we pass southward. As we do so, the wavy
surfaces of the flakes and slabs into which the shales and
slates weather become dotted with glistening flakes of various
minerals. At first the original character of the rock can be
plainly seen, and the new minerals only appear as spots and
streaks upon the planes of cleavage. But the folding and
signs of pressure increase southward, till, when we pass a
line running east and west from Tor Cross through Kings-
bridge to the mouth of the Avon we meet with beds of quite
uncertain age, which extend over a belt of country about
two miles wide and reaching from sea to sea. On the
southern limit of this belt the strata suddenly become true
crystalline schists, or rocks more or less completely crystalline
and composed of wavy layers of different minerals. Some of
them were almost certainly originally shales or slates, others
were either sills or lavas, but their minerals have been
rearranged so as to assume the same structure in wavy layers.

D

34 The History of Devooihlfe Scenery.

These are the rocks which some consider to be altered
representatives of deposits formed in Protozoic or even Pre-
Cambrian time. Others consider that they are only Devonian
rocks much more highly altered than their neighbours It is
quite certain that they could have been produced bymeta-
morphic action on a series of Devonian strata, but if such
they are, we should have expected to find the metamorphic
changes shading gradually upwards from those shown to the
north of the line until they reached their full intensity, and
not suddenly jumping from a quite early stage in the re-
crystallization to the fully developed crystalline schist. The
boundary may well be a fault, and these enigmatical rocks
may be only a deeper seated part of the Devonian S3rstem
brought up along the line of fissure, just as we know the lower
beds lie in juxtaposition with the upper in the neigbour-
hood of Torquay and Paignton. The metamorphism dis-
played in them is exactly such as would be produced by
lateral compression under a sufficient vertical pressure, and
such as we find produced in rocks of all ages which have
been exposed to adequate causes.

Some of these schistose rocks, which were originally
volcanic, are coloured a vivid green, especally striking when
they are wetted by the waves. Others are various shades of
grey, and fresh surfaces glitter with spangles of mica and
crystals of quartz. They are all of them often penetrated
with branching veins of white quartz.

They can be well studied along the coast from Hallsands
to the Start, and around the Bolt Head. In the latter
district they are cut up by a series of contortions which help
to determine the features of the cli£f.

So far, although we have had occasion to refer to differ-
ences in age within the Devonian rocks of South Devon, we
have avoided any attempt to describe their succession in time.
North Devon presented a difficult problem, but the much
greater complexity of the structure of the southern area
makes the problem at first sight far more hard to solve.
Indeed as long as geologists had only local evidences to rely
upon the task was impossible. Fifty years had elapsed
since the Devonian system had been made known to science

The Sotfth Devon Sequence* 35

by the work of Englishmen in Devon, before it became
possible to unravel the tangle. De la Beche, Godwin-Austen^
HoU and Champemowne each attempted the task in vain,
though each contributed something, especially the last named.
It was reserved for Mr. W. A. E. Ussher to find the true
key and apply it successfully, and even his work is not yet
complete.

It has been pointed out, in the last chapter, that the
Devonian type is widespread. As a matter of fact rocks
of this age and character are found in France, Belgium,
Germany, Russia, and in North America, over all of which
the waves of the Devonian ocean rolled. In these regions
the sediments formed on the sea floor have been compara-
tively little disturbed. Their fossils are well preserved and
the true order of superposition of the strata can be easily
read.

By studying these deposits it becomes a simple matter
to arrange the fossils in the order in which they appeared,
and it is seen that certain organisms were widely disseminated
and followed each other in the same order wherever they
were found.

When this test is applied to the rocks of Devon we
find that the local fossils are frequently abundant enough to
justify definite conclusions as to whether they belong to
the lower, middle, or upper beds of the system, and if we
can so locate one bed, that gives us a clue to the position
of many others with which it happens to be associated.
There are wide areas over which no fossils have yet been
found sufficiently well preserved to admit of identification, so
that we can there only rely on the general character of the
beds by comparing them with other similar rocks whose
approximate age we can determine more certainly.

Broadly speaking, the lower division is characterised by
the occurrence of sandstones and grits and the absence
of volcanic constituents. Though this is generally true, the
coarse sediments shade upwards irregularly into finer
grained shales and slates which merge quite insensibly into
the lower strata of the middle division. It is thus evident
the coast line from which the coarse material came must

36 The History of Devonsliife Sceooy.

have receded, or that the rivers must have slackened. The
process was not sudden, but steadily progressive during
lower Devonian time, and the same conditions continued
into the earlier part of the period in which the middle
Devonian beds were laid down.

These middle beds consist at first of grey and bluish slates
with occasional thin patches of fossils. They are overlaid by
shaly limestones, generally dark grey in colour from the
contained impurities, which are in turn covered by more
massive limestones, paler in colour, and in some places
practically built up of corals.

The massive beds lead up to the upper Devonian
division. This consists of thinner bedded limestones which
are often coloured red or purple red, and these alternate
with chocolate coloured slates and mudstones which become
pale lilac in tint after exposure to the weather. The
limestones are generally very compact, and often of lumpy
or concretionary structure. They are overlaid by red and
greenish slates which pass upwards into deposits belonging
to the next great geological epoch.

Lower Devonian rocks form the sands, slates, and grits
of the Torquay peninsula, where they may be easily studied
in the neighbourhood of Meadfoot sands and Warberry
Hill. They also cover a considerable area to the north
and west of Paignton, where they crop out from under
the much newer deposits on which the town is built.
Passing on along the coast, they form Southdown Cli£f and
extend thence in a series of bands of variable breadth
across to Plymouth Sound.

According to Mr. Ussher the Middle Devonian strata
comprise, first, the Eifelian slates and shaly limestones,
so-called from their representatives in the district of the
Eifel. Secondly, the Ashprington volcanic series which is
partly, at least, contemporaneous with the massive grey
Middle Devonian limestones. The volcanic rocks can be
found in numerous places. The widest expanse is between
Totnes and Ashprington on either side of the Dart. Here
is a district of between nine and ten square miles entirely
composed of consolidated tu£fs, and penetrated by lavas and

Volcanoes and Coral Islands* 37

injected igneous materials. But they are by no means
restricted to this region. Pipes, veins, and sheets of molten
rock have penetrated the shaly and slaty beds west and
south-west of Newton Abbot in numberless places. Indeed
this volcanic district extends from Kingsteignton through
Newton Abbot in a great sweep round the south-eastern
corner of Dartmoor, by way of Totnes and Ashprington,
whence it is continued westwards as a band of variable
width, bounded by Eifelian slates, till it reaches Plymouth
Sound, whence it spreads far into Cornwall. Throughout
this extensive area the volcanic rocks are predominant,
but they come up as sheets, sills, and intrusive veins in
many other places, such as the cli£fs of Babbacombe, the
shore of Anstey's small Cove, and the neighbourhood of
Dartmouth and Stoke Fleming.

The limestones are a connecting link between Middle
and Upper Devonian time. In the survey map no dis-
tinction is made between those which belong to each
division. In many cases well preserved corals are abundant
in them, and here and there, as at Barton, Lummaton,
and Petit Tor, the rock is composed of corals having a
structure well shown in some of the so-called Devonshire
Marbles whose *' figure " is due to the coralline composi-
tion.

From bottom to top of the whole series we have clear
evidence of marine conditions. We also find that if we
except the volcanic accumulations the materials are fine,
such as would have come to rest on the sea bottom some
distance from shore. The individual beds of sediment are
also thin, a fact which again indicates slow accumulation.

The tuffs and volcanic ashes are often regularly
stratified and their materials constant for some distance,
which indicates the settlement of dust through the water
rather than the actual building up of a volcanic island.
Other sections, however, indicate a different structure, and
we cannot be far wrong in concluding that a chain of
volcanic islets and submarine volcanoes extended in long
lines from the Ashprington patch northwards and west-
wards.

33 The History of Deronshire Sccaery.

The limestones are of two kinds, those where the beds
of calcareous material are thin and are interspersed with
shales. In this case we most regard them as having been
formed during times when there was little mud either
from the distant land or from the neighbouring volcanic
shores, by the accumulation of organic debris from the
creatures living in the water or on these islands. Next,
there are the massive beds made up here and there of
corals. These we cannot hesitate to identify as coral reefs
which grew up around the shores, or on the shoals around
the volcanic cones which must have been thickly strewn
over the district.

Coral reefs, whether fringing reefs, or any other type
have been shown to contain but little indications of their
coralline origin. From the interior of a modem coral
island, limestone is raised which contains no more numer-
ous traces of its origin than any of the South Devon stone.
The narrow crevices of the reef building corals get filled
in with calcareous fragments and mud, and, in time, the
whole becomes thoroughly welded together. Here and
there the structure is preserved, and it is beautifully
shown in many parts of Devon.

The history, then, of Devonian time, as it may be read
from the rocks of South Devon, is briefly thus: —

We begin with an open sea extending from the North
Devon district to Brittany, reaching to an unknown distance
westwards, and extending eastwards through the centre of
what is now Europe.

It will be remembered that the south of Wales was
the site of one great lake, separated from North Devon by
an imperfect barrier, while another large sheet of water,
which was almost undoubtedly fresh, lay over the extreme
South of Ireland. This was most probably cut ofi" com-
pletely from the sea. The rocks of Cornwall on the
other hand are of the same type as those we have been
describing, except that they do not contain the same great
development of limestone. It seems, then, that the near-
est coast line of the north-western continent must have
lain somewhere along the middle of St. George's Channel.

Section of Devonian Limestone.

Wavy structure and shear plane^ near Kingsbridge.

Volcanic Islands^ 39

Rivers, no doubt, flowed into the sea, and brought with
them from the land detritus, which was strewn far and
wide over the sea floor. Hence the grits and gritty slates
of Lower Devonian time. But, as the slope of the rivers
decreased as the land became worn away, they carried
finer mud, and after a time it was only occasionally that
any large quantity of it was borne so far as the district
we have described.

Beds of limestone now began to form, at first thin and
inextensive like those of Ilfracombe, but later on more and
more massive.

But simultaneously with the clearing of the water
from the muds of the continent, a chain of volcanic centres
began to show symptoms of activity. It. began with the
formation of shallows on the sea floor, which grew into
islands, while, in the periods of repose, corals took root
upon them and built up fringing reefs and barrier ree£5
extending outwards into deeper water on the top of piles
of broken coral torn from their own upper portions.

Again and again, new floods of lavas were erupted, and
the molten rock in seeking an outlet forced its way
through the slates and limestones, forming the veins and
pipes and sills of igneous rock so often seen.

The volcanoes, however, like most of our modern
volcanoes situated on islets, frequently gave rise to explo-
sive outbursts, when clouds of steam carried with them
vast quantities of volcanic dust and debris which fell to the
bottom of the sea, killing the corals and entombing many of
the creatures which crawled over the muddy bottom.

As the volcanoes grew, rain falling on their sides
carried down mud and sand into the sea, and the luxuriant
growth of corals came to an end, their ancient homes being
covered with mud, which is now solidified into the slates
which are generally regarded as forming the latest of all
the long series of deposits, which are grouped under the
name of the Devonian Rocks.

We can thus close our attempt to reconstruct the geo-
graphy of Old Red Sandstone and Devonian times by
picturing a coast line roughly coincident with the Bristol

f

40 The History of Deronshire Scenery.

Channel and extending far westwards some distance south
of Ireland. North of this line a vast continent, fringed on
its south-east border by a great mountain chain whose
parallel ridges cut up the region into a number of basins,
some of which were occupied by great freshwater lakes.
One of these on the borders of Wales was shut o£f from
the open ocean by a chain of islands like the Zuyder Zee,
or as the Sea of Japan, at present, is cut off from the Pacific.

0£f the shores of this continent was the sea dotted with
an archipelago of volcanic islets, fringed with reefs and
banks of coral over the site of Devon, but curiously
enough we cannot say exactly where either the islands or
the coast line were. It has been repeatedly said that all
the Devonshire rocks show proofs of enormous crushing,
crumpling and folding. We must allow for this in our
attempted reconstruction, and imagine these deposits spread
out in some such layers as they were when first formed.
We shall then find that the North and South Devon beds
must have been many miles further apart than we find
them to-day. If it were possible to trace out all the folds
and contortions, and if it were possible to measure the
distances along which each block of rocks has been pushed
over its neighbours, we might construct a map showing the
ancient reefs, and locating some of the chief centres of
eruption. In the absence of the necessary knowledge, we
must be content with the general facts, and r^ard the
coral islets as having stood where we now find their ruins.
The general dimensions also of the archipelago must not
be estimated from what we see to-day. We must remember
that they may have extended a long way further east and
south where now lie the waters of the English Channel.

It is possible also that where the lower Devonian beds
now come to the surface, they may have been covered with
deposits like those of Brixham or Ashprington, so that the
same conditions may have extended further south and west.
This we can never know, so that however much the rocks
of Devon may be studied, and however much we may add
to our own present knowledge of them, we can never hope
to know all their story.

CHAPTER IV.

The Culm of Devon-

At length the great continent began to subside, and
the water of the open sea flowed up the valleys, filling the
basins of the great lakes as far as the Grampian ridge and
spreading over the lower lying parts of the former land.
The disappearance of the ancient Pre-Cambrian country
was repeated once more, but this second sinking was less
complete.

Everywhere where the top of the Old Red Sandstone
or Devonian rocks can be seen their topmost beds are seen
to shade upwards into a series of sands and shales containing
some of the same organisms mixed with a number of new
forms which are undoubtedly marine. There was no sudden
break either in the life of the region or in the geography,
but the change in the distribution of land and water was
progressive, and a similar alteration was produced in their
inhabitants.

The lower beds of the new series are composed of
land derived material, and, as the thickness of a group
of deposits of a given kind is a rough indication of the
length of time during which they were formed, it seems
that the sinking of the old land must have been rapid.
The sands and shales are seldom more than a couple of
himdred feet in thickness, over all the great district from
the old coast line south of Bristol across the central parts of
England and Ireland until we approach the basin of Lake
Caledonia and the neighbourhood of the Cheviot and
Cumbrian Mountains in the north.

Over all the central parts of England and Ireland the
basement beds are covered with a vast deposit of limestone
which contains numberless traces of its organic origin.
Corals, shells, crinoids and other creatures have contributed
largely to its production. It has long been known as the
Carboniferous or Mountain Limestone. It is a fairly pure

42 Tlie History of Deronsliifc Scenery*

carbonate of lime containing very little earthy impurity such
as might have been borne from a distant shore, and must
have taken an immense time to form. In places it is more
than 3000 feet in thickness, the maximum being reached
in the Mendip Hills, which form almost its most southern
outcrop. It is interspersed with layers and patches of chert
formed chiefly from the siliceous sponges and organisms
originally mixed with the calcareous mud, but subsquently
gathered together by the obscure process called segregation.
The whole deposit must certainly have been formed in a
sea singularly free from land derived material, so that if
any shore lines came nearer than a hundred miles, those
shores must have been made of hard rocks and cannot have
had any rivers or streams bearing mud into the sea.

As we pass northwards we find the limestone somewhat
thinner, and in the North of England it becomes more
and more broken up by the interposition of beds of sand
and shales and even coal, until in Northumberland the
whole series indicates that shores of some extent were
not far away. The limestone still exists, but the periods
when it was allowed to form were frequently interrupted
by times when the sea had a sandy bottom.

On crossing the border and entering the basin of
Lake Caledonia we find the whole deposit from bottom to
top indicative of shallow water and abundant influx of land
derived debris. The limestones are only thin lenticular
beds, while every here and there occur coal seams and
layers of ironstone.

We cannot here enter into a discussion as to the origin
of coal. It is the general belief that most of our coal
seams are an accumulation of vegetable matter formed
firom plants which grew where the coal now lies, at a time
when the clay, so often found beneath, was the soil of a
swampy forest. The coal plants were mainly analogous
to our mares' tails, club mosses, and other spore pro-
ducing plants, and it is believed that the regions where
they flourished in greatest luxuriance were level plains,
sometimes partly occupied by firesh water lagoons, some-
times intersected by sluggish rivers, and all liable from

Catbonfferocfs Geogfaphy* 43

time to time, as subsidence progressed, to be overwhelmed
by an influx of the sea.

Here and there the coal was probably formed from
vegetable matter drifted from a distance, and some seams
may have been locally produced from deposits of resinous
spores.

On the whole it is safe to say that the occurrence of coal
seams points to shore lagoon swamps, and a succession of
seams with their interveining sandstones we shall speak
of as the shore lagoon type of strata.

In Ireland the changes are similar in character, and
the shore lagoon type shows signs of setting in as we
approach the site of the southern end of the great lake.

There is another peculiarity in the South of Ireland.
Here there are many indications of shores lying not much
further south or west, a point which will be seen to have
an importance in the history of Devon.

Jukes-Brown has shewn* that there is reason to think that
a large island lay over part of the English Midlands, and
extended through Wales to the Wicklow Mountains and
the Mourne Mountains.

It is not easy to reconcile this with the purity of the
Carboniferous Limestone all round it except on its northern
side. It seems more likely that as the continent subsided
the Cumbrian and Cambrian Mountains and the Wick-
low and Mourne heights, all of which were, in Devonian
times, certainly far more prominent heights than they are to-
day, remained above water as islands; and another island
may well have existed as a relic of the high ground on the
east of the Welsh Lake with a ridge connecting it to the
western group.

The higher parts of these ridges would have been exposed
to atmospheric waste during all Old Red Sandstone time.
They would probably have been denuded of their softer
parts and would stand out as peaks of hard reck such as
would yield but little debris. The small size of the islands,
coupled with their texture, would account for the absence

Building of the British Isl^s^ page 86.

44 The History of Devonshire Scenery*

of land derived material. If, moreover, we assume that these
islands drained towards the region of the Irish Sea or St.
George's Channel we have a full explanation.

The rapid change in moving from the Northumbrian
district to the central valley of Scotland was no doubt due
to a chain of long islands lying along the line of the Cheviots
and the southern uplands, the tops of the long ridge which
had previously formed the southern shore of the great lake.

The forests and lagoons of the Caledonian region were
devastated from time to time by the outbursts of neighbour-
ing volcanoes. Great floods of lava were poured out, and
now lie as successive sheets intercalated among the other
beds, and interspersed with layers of volcanic ash. There
are numerous places in Ayrshire, and still more in Fife
and on the southern shore of the Firth of Forth, where
some of the ancient hills from which eruptions came
have been preserved almost uninjured. The ruined cones
have been buried under other deposits, and in recent times
these newer rocks have been cleared away, leaving us sections
which show many of the details of volcanic action in wonder-
ful perfection.

The Carboniferous Limestone is everywhere covered
with a great sandstone foundation known as the Millstone
Grit, which changes its character as we go northward, much
as the limestone does. It probably indicates a general
shallowing of the sea and an accompanying upheaval of
the neighbouring lands. It is thick around the district of
the Midland Island, or Island group, and is especially thick
between this district and the Cumbrian Island. This sug-
gests that a large part of its materials may have come from
the shores of these spots.

It is overlaid throughout by the productive coal
measures, which make up our coal fields, the total thickness of
which has been estimated* at 6,500 feet in Somerset, 8,000
feet in South Lancashire and 2,900 feet in Scotland.

The coal measures are, throughout, deposits of the
shore lagoon type. They indicate a slow and prolonged

*Geikie Text Book, p. 1048.

The Coal Measores« 45

subsidence accompanied by irregular movements which here
let in the sea with its marine creatures, and there upheaved a
district so that it underwent erosion.

It is difficult to picture the exact physical geography of the
time. In these days there does not appear to be any part
of the earth where similar conditions present themselves.
Indeed, although productive coals do occur in rocks of
widely different dates, the richest coal fields of Europe,
Asia, America and Australasia are all of about the same age.
The only conclusion possible is that the terrestrial conditions
of the time favoured the accumulation of vegetable matter
more fully than ever before or ever since. The conditions
seem to have been slow oscillating movements interrupted by
long pauses, but on the whole a subsidence. This must
have been accompanied by abundant rainfall and sufficient
warmth. It has been suggested that the atmosphere was
more highly charged with that essential food of plants,
carbonic acid gas, than it is at present. This is quite
possible, but there is no evidence. It has also been sug-
gested that the earth enjoyed a widespread tropical climate,
but this is negatived by the occurrence of undoubted glacial
deposits in India, Australia, and South Africa. These are
questions of great general interest, but for our present pur-
poses it is enough to picture the country north of the Bristol
Channel and the Somerset flats as an extensive swampy
forest interrupted by the hill region of Wales and the
Midlands; then more swamps till we reach the slopes of
the Grampians and the Donegal Mountains, which still
formed part of a diminished mountain chain flanking a large
North- Western Continent.

It has been said that the Old Red Sandstone passes up
quite comformably into the basement sands and shales
below the Carboniferous Limestone.

If we now turn to Devonshire we find, in the few places
where the passage can be traced, that the topmost Devonian
rocks shade off quite gradually into others of Carboniferous
age which are known as the Culm Measures. The boundary
between the two systems is often obscured, and in many
places the division is a line of fault, but in North Devon

46 The History of Devonshire Scenery*

it is fairly well defined by the valley along the line followed
by the Railway from Taunton to Barnstaple. The earliest
beds of the carboniferous period are a series of thin shales,
often very dark in colour, and which are overlaid by im-
persistent beds of Limestone of peculiar character, and these
are in turn covered by thin even bedded cherts. These beds,
known as the basement beds, have been greatly broken,
folded, and in places crumpled so that it is very di£Gicult
to be certain of the exact order in which they succeed each
other. But taking all the exposures together there is no
doubt as to the true sequence.

The question at once arises whether these black and dark
grey shales and overlying limestones and cherts are the
local representatives of the basement shales and the Mountain
Limestone of the Mendips, South Wales and the Midlands. It
is answered by the fossils found in the two series. The shaly
partings between the limestone beds of Devon, and the shaly
beds themselves, contain adundant traces of plants of car-
boniferous genera. The limestones contain other fossils,
some of which are peculiar to the district, while some
are identical with species found in the Carboniferous Lime-
stone. Moreover the position of the beds on top of the
Devonian strata necessarily implies their identity in time
with the rocks immediately above the Old Red Sandstone.

These basement beds may be seen in many places, since
both the limestone and the chert have a commercial value,
and therefore quarries are opened wherever they occur.
The limestone is used for building, for making lime, and
in some districts for road metal. The cherts lie in thin beds,
generally only an inch or two in thickness, and they are
naturally broken up by joint planes, or cracks, which cut
up the beds into such small pieces that they need very
little additional breaking to fit them for mending roads.

Let us first consider the limestones and their relation
to the vast calcareous deposits of the rest of the country.

We lost sight of the Carboniferous Limestone after we
had seen it at its maximum thickness in the Mendip Hills.
On their southern edge the beds dip down under the modem
alluvial flats of Somerset. About twelve miles away towards

Tbc Westldgfi Limestone* 47

the south-west we find an isolated patch of similar rock
rising up between the Parret and the Quantocks in Canning-
ton Hill, but it is surrounded on all sides by newer deposits,
and we can only identify it and note that it proves that the
conditions remained unchanged, or not materially altered,
so much further south.

Crossing a belt of country about seventeen miles in width,
which consists partly of Devonian rocks and partly of
much younger deposits, we reach the neighbourhood of
Burlescombe Station, about half a mile to the west of
which a number of abrupt, but low, hiUs rise from the
new rocks by which they are surrounded, as a group of
limestone patches, where there are very large quarries.
The rock is here considerably darker in general tone
than the Mountain Limestone. It contains fossils of
carboniferous date, but they are few and far between, and
principally exist in the thin red shaly layers which sep-
arate the beds. The fossils are restricted to a narrow
band which does not seem to be opened in all the
quarries. A small one, a little south-west of Westleigh, is the
most prolific. Here certain beds are crowded with fossils,
mostly such as might have lived on the floor of a fairly
deep sea or have moved freely in its waters. They are
nearly all flattened out, so that they appear only as mark-
ings, or very thin films on the surfaces of the shales or
limestones. But mixed with the animal remains there
are abundant traces of plants of early carboniferous age.

The limestones are frequently banded with cherty lay-
ers which are specially firequent in the upper beds, and
according to Messrs. C. J. Hinde & Howard Fox* some
of the limestone beds are of foraminiferal origin.

Among the fossils there are several species of Gonia-
tites, the creatures which were the precursors of the
Ammonites which became so abundant later on, and shells
of bivalves known as Posidonomya Becheri^ and Posidonomya
LaUraUSf both of which are extremely abundant in
certain beds. Crinoidal remains are numerous, and on one

*Quart. Jour. GcoL Soc.^ 1895, p. 620.

48 The History of Devonshire Scenery*

occasion a large one was uncovered lying almost complete
as if it had been entombed where it had lived.*

Similar beds can be traced through Holcombe Rogus
and Ashbrittle. There is then a gap until the great
quarries of Bampton are reached.

Here the Posidonomya beds occur again, and some of
the Goniatites are found, but fossils are less numerous,
the limestone is much darker in colour, and the total
thickness of the series is certainly less.

From Bampton it can be traced every here and there
along a line lying south of Barnstaple, and as it goes
the change in the character of the stone and its dimin-
ution in thickness progresses, until we get the coal black
rodk of Venn.

It will be remembered that the limestones at Westleigh
were 1>anded with chert. At Bampton similar cherts are
seen, and at both places it is possible to get blocks of
solid stone streaked across with several cherty zones, show-
ing that there was no pause between the two deposits, but
only a somewhat gradual change in its character.

If we now cross over to the line where the basement
beds lie on the southern Devonians, we find similar
broken exposures of limestone running round the north-
em limit of Dartmoor, as at Drewsteignton, Okehampton,
and Bridestowe. In all these places it resembles the
black rock of Venn, and it is evidently of the same age, as
it contains the same fossils.

Now the black limestone owes its colour mainly to the
presence of finely divided carbon, and on ignition this can
be burnt away and a white or very pale lime is the result.
Moreover, according to analyses of the Drewsteignton lime-
stonet it contains actually 62 per cent, of silica with only
30 per cent, of carbonate of lime and nearly i per cent,
of carbon.

Before considering the interpretation of these facts let
us examine the overlying chert beds. They have long been

•Found by the members of the R.A.M. College Field Club.

fKindly made by Mr. F. Southerden, B.Sc, F.I.C, Lecturer in Chemistry

at the R.A.M. College, Exeter.

C ^.

Thin bedded Bbck Limestone^ DrewstdKnton.

Thick bedded Grey Limestone, Westleigh.

The Coddon Hill Chert. 49

known as the Coddon Hill beds, from a conspicuous hill
about a mile south of Barnstaple, and forming the southern
side of the valley in which the black limestones of Venn
were formerly worked. In a quarry, on the north-west
of the hill, the beds are admirably shown. There are some
of them almost as hard as porcelain, and of various dark
or mottled shades of colour, but some are streaked with
white, like a porcelainized flint, while some of the interven-
ing beds are a powdery pale grey shale which can be
crumbled between the fingers.

Precisely similar beds form a line of bold hills stretching
eastwards to near Ashbrittle. Here they are lost, and are
apparently represented by the chert bands so intimately
associated with the limestones of Westleigh and Holcombe
Rogus.

The same beds crop out above the southern limestones
and have been traced from the Cornish coast past Laun-
ceston, round the northern edge of Dartmoor, to the neigh-
bourhood of Chudleigh.

When, in 1893, Dr. Teall and Mr. Howard Fox
discovered the Radiolarian origin of the chert at MuUion
Island, the idea suggested itself to many that the Coddon
Hill and other chert beds might possibly have been formed
in a similar way, so that when in 1895 an exhaustive paper
on these beds was read before the Geological Society by
Mr. Fox and Dr. G. J. Hinde, Devonshire geologists
were not surprised to learn that it was proved that these
basement beds of the Culm repeated the deep sea phe-
nomenon of the earlier date.

We are now in a position to attempt a reconstruction.
We may regard the massive limestones of the Midlands
as the solidified ooze of a moderately deep sea. It will
be remembered that while there was land where the Carbon-
iferous Limestone was subsequently deposited there was
open sea over Devon. If now, as we have pointed out
was possibly the case, the rather rapid subsidence was
general over a wide district, a lowering enough to convert
the land into a deep sea would necessarily convert the
neighbouring seas into very deep ones.

B

50 The History of Devonshire Scenery.

Let it be granted that this occurred. Then as we
pass from the old shore lines we should find the bottom
rapidly sinking. At first the foraminiferal mud would be
able to accumulate, but the water being deep the cal-
careous matter in the ooze would bear a smaller propor-
tion to the whole, and the greater the depth the larger
the relative amount of silica would become. Throughout
the district the total thickness of sediment accumulated in
a given time would be less than in the neighbouring
shallower sea, and the greater the depth the thinner and
more siliceous the deposit. If, then, we consider the
Westleigh cherty limestones to have been formed in deeper
water than the lower part of the Mountain Limestone
we easily explain its differences. If also we suppose that
the sea deepened westwards and south-westwards we
account for the high percentage of silica at Drewsteignton
and the much smaller thickness of th^ limestone as a
whole. But the subsidence was not limited to the brief
time between the top of the Old Red Sandstone and the
bottom of the Mountain Limestone. It must have con-
tinued long after the formation of the latter had begun.
In Devon, therefore, the deep sea of the early part of
the period would grow deeper and deeper. In the Mid-
lands it is quite possible that accumulation kept pace
with subsidence, so that the sea maintained a nearly
constant depth. If so, and if Devon shared in the down-
ward movement, the slower accumulation would fail to keep
pace with the subsidence, and the sea would steadily
deepen. At last the conditions would be such that all
the calcareous matter was dissolved before reaching the
bottom, and the result would be a Radiolarian ooze such
as Messrs Fox & Hinde have traced wherever the Coddon
Hill beds can be found and even into the cherty bands
of Westleigh and Ashbrittle.

The argument seems sound, and indeed the conclusions
may very possibly be true. But there are four difficulties.

In the first place the Devonian rocks in both North
and South Devon which immediately underlie these base-
ment beds of the Carboniferous do not indicate deep

Abundance of Plant Remains* 51

water. It seems therefore unlikely that the difference in
depth between Devon and the Mendip region would have
been great enough. Still less probable does this seem when
we think of the coral islands and volcanoes of South Devon.

Next, the series of rocks which lie above the cherts
do not indicate deep water at all. We must, therefore,
suppose a very rapid subsidence at first, and at the close
of the deep water period an equally sudden great upheaval.
True, the sudden incoming of the millstone grit above the
Mountain Limestone does point to rapid change of the kind
we need, but the change from a Radiolarian abyss seems
too great to be very likely.

Again, how are we to account for the abundance of
organic matter in the black limestones and black shales, so
closely related to each other and to the cherts. From
the bodies of the Radiolaria and other organisms ? This is
possible, of course, but hardly likely.

Lastly, we have the occurrence in great abundance of
traces of vegetation. At Westleigh plant remains are more
abundant than other fossils, and in most of the quarries
where basement beds are exposed we find similar fossils,
often excellently preserved.

Now plant remains are always regarded as an indication
of nearness to some shore, and of a shallow sea. How is
it possible to reconcile such a conclusion with the abysmal
theory ? It seems most unlikely that so many, and in some
cases such well preserved plant fragments could ever
reach a great enough depth to be interstratified with
abysmal deposits.

It will be remembered that the solution of the cal-
careous matter and consequent formation of a purely
siliceous deposit is not, as a matter of fact, directly due
to depth, but only indirectly. The water at great depths
is more highly charged with carbonic acid, and it is this
which effects the solution.

If, then, we can find some other reason for thinking
that the water over Devon was more highly charged with
the solvent gas we shall have a cause quite adequate to
explain the facts observed.

52 The History of Devooshire Scenery*

This we have in the organic matter, and particularly
the plant remains.

It is well-known that dead vegetation in the process
of decomposition forms a number of organic acids such
as the bodies known as humic acid and ulmic acid,
which soon break up, and in turn give rise to carbonic
acid. When water is loaded with rotting leaves or other
vegetable matter it becomes a powerful solvent of carbon-
ate of lime, and very much of the dissolving action of
rivers, lakes and ponds, and of rain water which has
percolated through the soil, is known to be due to the
presence of these products of decomposition.

If now we suppose that the subsidence, so even and
regular over most of the British Area, did not extend
much further south than, let us say, the English Channel,
but left dry land not far away, on the south or east
or west, we should account satisfactorily for the plants
which can hardly have been drifted from the central
island across the Carboniferous Limestone sea ; and we
also discover a source from which the other abundant
organic matter came. We should then regard the Devonshire
sea not as one of unusual depth, but as being more or
less girdled by low lying land thickly clothed with plants
descended from those which spread over the old continent,
and drained by sluggish rivers heavily laden with vegetable
products which they poured into the land locked sea. If
we imagine this sea little disturbed by tidal or other
currents, we have all the conditions which we want.

These two views are the complete opposites of each
other, and time may show that the abysmal theory is the
correct one, but in the meantime the sequel will give yet
other reasons for inclining to the idea of a stagnant sea
laden with vegetable matter.

The basement beds shade upwards into dark shales and
slates interspersed with occasional thin beds of grit. The
two groups are so closely related that Mr. Ussher has re-
garded some of the lower shales as actually having been
formed in some spots while the Coddon Hill cherts were
growing not far away. They all consist of land derived

The Exeter Type of Culm* 53

material, and on the abysm theory must mark a consider-
able upheaval, su£Bcient to bring the shores much nearer
to Devon, or to greatly increase the carrying power of the
rivers. This series of beds he caUs the Exeter type of
Culm measures, from the fact that they are admirably dis-
played in numberless sections on the northern side of the
city. Every roadside cutting shows them more or less, and
they can be well studied along the road to Cowley Bridge and
on towards Stoke Canon. They are singularly devoid of
recognizable fossils, but some of the shales show markings
which suggest that they were made by shells which have since
been removed. Their general colour is grey, but there are
purple stains which have probably been caused by subsequent
events. Here and there the colour is a pale drab, a tint
shown repeatedly where the beds are more gritty.

The grain is alwa} s fine, even in the thickest grit beds,
so that the land from which the material came was probably
some distance, say twenty or thirty miles away. It is
hardly likely that it was much further ofF, as the whole series
is interspersed with beds which are full of obscure evidences
of vegetation. In the neighbourhood of Exeter, although
there can be no doubt that the remains are those of land
plants rather than seaweeds, they suggest the idea that the
leaves and stems were rotten when entombed.

Generally speaking, the basement beds of black shales,
limestones and cherts are over-laid by a series of the Exeter
type. But the district around Chudleigh offers an excep-
tion which is very significant.

So long ago as 1840 Sedgwick and Murchison pointed
out, in their Report on the Physical Structure of Devon,
that in Ugbrooke Park there occurred coarse sands and con-
glomerates. De la Beche pointed out that these beds con-
tained pebbles apparently derived from "Carbonaceous"
deposits, by which he meant the Culm basement beds.
Mr. Ussher has pointed out that in fact they do lie on top
of the baseAient beds, replacing the normal succession strata
of the Exeter type.

They contain numerous fossil plants in a state of good
preservation, such as to indicate very plainly that they were

54 The History of Devonsliirc Sceacfy,

formed in shallow water certainly not many miles away
from shore.

There are similar beds on the west of Dartmoor, but
their position is not so easy to determine in consequence of
the greater complexity of the present structure of the district.

Now there is no doubt that the series of deposits which
succeed the basement beds are the southern marine represen-
tatives of the shore lagoon swamp beds or coal measures
of Glamorgan and the Midlands. These we have already
attributed to a change which resulted in a considerable
shallowing of the Carboniferous Limestone sea. Slow and
intermittent subsidence followed, but it is evident that the
period of maximum submergence had passed and the time had
been reached when earth pressure had again set in. It
will be remembered that the upheaval which closed the
Protozoic cycle and created the Caledonian-Scandinavian
chain was prefaced by local upheavals of the floor of the
Silurian Sea. Here at the close of Deutozoic time we find
the same sequence of events, and it is evident that the
Ugbrooke Park beds mean one of two things — either that
the sea bottom was suddenly upheaved from a depth perhaps
of 2,500 to 3,000 fathoms until part of its floor was subjected
to surface erosion, or that the southern low islands, whose
existence we have supposed, were lifted higher, so that the
rivers no longer flowed into the Devonian Sea loaded with
the refuse of vegetable swamps, but that they rushed swiftly
down, carrying sand and pebbles to the shore, and spreading
ordinary mud, more or less mixed with plant fragments,
wherever the Exeter rocks are now found.

Lying above the rocks of the Exeter type we find a series
in which the fine shales are still numerous, but, instead of
being separated by thin fine grained grits at rather wide
intervals, the grit bands are much thicker and coarser,
many of them being actual sand and resembling strongly
the sandstones of Ugbrooke Park. These Mr. Ussher
describes as Culm measures of the Morchard type. They
are well displayed in numerous quarries almost anywhere
on the northern side of the long tongue of newer red
rocks which runs past Credition.

The Bidefofd Anthracite* 55

These in turn are overlaid in the eastern part of the
Culm area by a series of massive grits and sandstones
among which the shales are only represented by thin
layers which serve to separate the coarser beds. These
are well shown around Eggesford, and are therefore named
by Mr. Ussher the Eggesford Grits.

The Devon Culm Measures, then, from the top of the
basement beds upwards through the whole series are
indicative of shore Unes not far away and approaching
nearer and nearer. From bottom to top they contain
numerous remains of plants which have been identified as
belonging to the same period as those which make up our
English coal. This has been particularly emphasised in
recent years by the labours of Mr. Inkerman Rogers, who
has found in the Culm beds near Bideford, not far removed
from the so called anthracite bands, numerous well pre-
served plants and a mollusc known as Carbonicola which
has long been known as an inhabitant of the coal lagoons.
These fossils have been described by Mr. Arber, and
it seems that they form a strong argument against the
abysmal theory of the underlying basement beds.

The " Anthracite " is an impure coal which is found in
seams interstratified with the Culm, and there is no doubt
it has been formed from vegetable mud drifted from the
coal swamps of Glamorganshire.

So far we have said nothing of volcanic action in Devon
during the deposition of the Culm series, nor have we
reached in time beyond the first indications of the great
transformation of the map which closed the Deutozoic
cycle. The two sets of phenomena are closely related
to each other, and must form the subjects of another
chapter.

CHAPTER V.
The Great Upheaval.

We have, so far, seen the Devonshire area only as one
over which more and more materials had been accumulating;
a region in which bed after bed of rock had been laid down,
some as sheets of gravel and sand and mud, the waste of
neighbouring lands — some as floods of lava or showers of
volcanic ash, and some as the debris of vanished forms of
life. The same general sequence of events had been
going on over a broad belt of the European area
stretching from our own south-western counties far to
the eastward. It had gone on without intermission during
a vast lapse of time which had witnessed stupendous
changes. The Cambrian shores had been converted into
the Ordovician Ocean, this into the lakes and mountains
of Old Red Sandstone days, and these again into the seas
and forest swamps of the Carboniferous period.

A deep broad band of soft and uncrushed material had
thus been built up in the earth's crust, forming a district
which was certain, sooner or later, to feel the effects of ter-
restrial shrinkage. Moreover, this weak region was bounded
on its northern side by one in which the upheaval of Proto-
zoic age had already compressed and hardened the rocks, and
which was therefore specially rigid. Indeed, the conditions
which we have seen resulted in the crushing up of the earlier
sea floor against the relics of a north-western land area
were reproduced again with but minor differences. The old
Caledonian-Scandinavian chain ran approximately from
N.W. to S.W., since the earth pressures acted from the
sea towards the ancient coast. Here, at the end of Deu-
tozoic time, the pressures acted from the south, and the
accumulated sediments were folded against a northern land,
rising into a series of ranges which lay in a general east
and west direction. They stretched from our most western
coasts through the northern part of France, the forest of
the Ardennes, and the coal fields of Belgium away into the

Hercynian and Pennine Systems* 57

centre of Europe and beyond. This was the second great
mountain chain of the European area, and in its prime it
must have been fully as important as its predecessor. Its
parallel ranges extended from the Mendips almost to the
Loire ; and the hills and mountains of Killamey, Devon and
Cornwall, Brittany, the Ardennes and the Hartz have been
carved by the wear and tear of time out of its framework,
just as the Grampians and the Southern Uplands of the
Scottish border are relics of the earlier chain. Two names
have been given to it, the Hercynian chain, from the region
of the old Hercynian forest through which it runs, and the
Armorican chain, from the old name for Brittany.

The foldings due to the southern pressures were com-
plicated in a peculiar way over the British area. If we refer
to the map showing Old Red Sandstone geography we see
the Caledonian system of ranges would join the newer set
somewhere a little south of Killarney. The bulk of the
British area was thus pinched up in the angle between the
two converging lines of uplift, so that a smaller system of
folds and fractures was produced in which the ridges and
troughs ran approximately north and south. One very
prominent range thus formed still stands as the prin-
cipal feature in the scenery of Northern England — the
Pennine range — hence this minor set is known as the
Pennine system.

The effect of the double system of foldings was to distturb
the structure of the country in an extraordinary way, which
is probably best understood by reference to the behaviour
of waves. Anyone who has watched a rough sea with long
rollers sweeping in obliquely against a sea wall, such as the
walls which guard the Great Western Railway at Teign-
mouth and Dawlish, is familiar with the behaviour of two
sets of waves crossing one another. As the incoming rollers-
sweep landward they are crossed by a smaller set reflected
from the wall and moving seaward. Where the crest of one
wave coincides with the crest of the other the water is thrown
up into a dome or point, and where the crest of one happens
to fall on the trough of the other the surface may stand
almost at its normal level.

SS The History of Devonshire Scenery*

The folds of the earth's crust are similar. The hard,
firmly welded base of the Caledonian-Scandinavian chain
may be likened to the sea wall, the grand folds of the
Herc3mian system to the incoming rollers, and the Pennine
folds and fractures to the reflected waves. The two alter-
nately reinforce and neutralize each other and sometimes
deflect each other from their normal line.

Just as is the case with reflected waves, the Pennine dis-
turbances are greatest where they abut upon the wall, and
diminish in intensity as they recede. They join the Cale-
donian system in the Lake district, and as we trace them
southward they become less and less marked until in the
Devonshire area they have only a minor importance.

The main ranges of the Hercynian chain lay where the
English Channel now exists, or even further south, and as
we go northwards the folds become smaller and less abrupt.
In the North of England they take the form of broad and
rather gentle curves, which tend to throw our coal fields
into a series of shallow troughs running east and west.
But the troughs narrow and the folds get sharper as we
move southwards.

When we reach the Mendip Hills we see the flrst con-
spicuous existing feature due to Hercynian folds. They
form part of a ridge which rises up at its^eastern end on the
borders of Wiltshire, and runs through Somerset and across
the Bristol Channel, and is continued as the southern lip of
the Glamorganshire coal fleld to the coast of Pembroke. It
is a sharp anticline in which the Carboniferous limestone is
thrown into a prominent arch which, in the Mendips them-
selves, dips northwards under the coal basins of Bristol and
Radstock, and southwards plunges under the recent alluvium
of the Somerset flats. It is probably somewhere under this
district that the productive coal measures change into the
unproductive Culm of Devon, but the presence or absence
of coal on the southern side of the ridge awaits decision until
some adventurous capitalist will put down a trial boring.

On the southern side of the Severn sea and the Bridg-
water flats, the Devonian rocks rise up as the wreck of a much
larger range. Much larger it must have been, because the

The Exmoor Mountains* 59

signs of compression are very much more intense. We have
no need to quote details again. We have already described
them when considering the North Devon rocks. How much
larger the ridge may have been it is difficult to say. If the
succession of the beds is as Dr. Hicks supposed, that is to
say, if the Foreland grits, the Hangman grits, and the sands
and grits near Barnstaple are only different parts of the
same series of beds and are of approximately the same age,
then we have only to imagine these beds continuous over
the intervening high ground, with the Carboniferous (Culm)
rocks on top of all, to get some notion of the magnitude of
this Exmoor ridge. On a very rough estimate for the
thickening due to folding it may well have reached three or
four thousand feet above the present summits of Dunkery
Beacon and the Brendon Hills. In such a case its northern
slopes probably lay only a few miles nearer to the coast
of Wales than the present cliflfs of Lynton.

On the other hand, if the more orthodox theory of the
North Devon structure is the truth, the Lynton and Fore-
land beds are the actual core of the ridge, and we must
imagine at least twice as much material piled above the
modern hills, bringing the summit to eight or nine thousand
feet, and throwing the northern face of the ridge so many
miles further north that it will leave very little room for
the trough which must have lain between this range and
the Mendip ridge beyond.

We shall find later on an excellent reason for believing
that these northern slopes were, in fact, not very far from
the line of the present hills, and although the argument
is not one which could be pressed very far in itself, it
goes at least a little way to strengthen the reasoning set
out by Dr. Hicks.

In either case it is evident that the Exmoor range,
continued eastward by the Quantocks, must in Post Car-
boniferous time have been a far more important feature in
the local scenery than the great hills so familiar to us
to-day

As we step from the Devonian rocks on to the base-
ment beds of the Culm we pass from arch to trough. A

6o The History of Deronshire Scenery*

great shallow syncline extends southwards until we draw
near to the margin of Dartmoor, where the rocks rise up^
again as the abutment of another arch. Throughout this
broad syncline the Culm beds are so crumpled and dis-
torted that it is impossible to make any accurate estimate
of the compression that they have undergone. It is certain
that if they could be laid out flat and the broken blocks
fitted into their proper places they would cover a country
at least twice as wide as that which they now occupy.
Indeed since block has been pushed over block it is
quite possible that they might require a district four or
five times as wide. But the minimum is large enough to
show the enormous nature of the forces which have been at
work. At the present time the beds occupy a district from
twenty to thirty miles in width, and that is only at most a
bare half of what they once covered. Apply the same scale
to all Devon — ^and there is good reason to believe the
crushing and compression was far greater in South Devon
— and we find that the rocks of the Foreland and the Start
are at least sixty or seventy miles nearer to each other now
than they were before the mountain building throes began.

The effects of compression are not always the same.
Sometimes we find the rocks, even the hardest of them,
bent into most complicated folds, through which each
particular bed can be traced for a long distance. This is
the case when the beds are of uniform texture, and when
the folding has been effected under the weight of a heavy
superincumbent load.

The Culm beds, on the contrary, are so much broken
that it is quite impossible to follow the fortunes of any
stratum. The hard beds have been broken to pieces at the
bends, and the fragments have been forced irregularly into-
the intervening softer shales. This is especially obvious
in the Exeter type of Culm, but it is to be traced also here
and there among the younger beds of the Morchard and
Eggesford types. The most remarkable illustration in point
is shown in the contorted exposures of the basement lime-
stones and cherts. These hard, resistant, rocks have been
broken into great pieces which have been bent and buckled

Results of Small Vertical Pfessuse* 6i

^nd pushed into the softer beds, so that they stand up in a
most irregular manner along the margins of the trough,
instead of forming a continuous lip on either side. Thus
it comes about that the Burlescombe limestones cannot be
traced up to those of Bampton, and these again are dis-
connected from those further west. They repeat on a large
scale the structures shown in miniature wherever a good
exposure of Exeter type Culm can be seen. They are a
necessary consequence of very great lateral compression
acting on a mixture of hard and soft strata which are not
at the same time exposed to great vertical pressure.* The
Culm beds had only their own weight acting downwards
4ipon them, and the highly broken structure of the basement
beds is an indication that the total thickness of the middle
and upper Culm was never very great.

This structural indication of vertical pressure has many
applications, and we may remark that of all the North
Devon beds the Ilfracombe and Morte rocks indicate the
heaviest pressure, and should, therefore, be older than those
which appear to have been compressed under a lighter
load.

It is illustrated again in part of South Devon. Here
the confusion of the strata is extreme. The irregular mixture
of soft shales and sands and beds of ash, with hard lavas,
•crystalline volcanic plugs, and massive limestones, has yielded
to the lateral compression in the characteristic way. In
the district round Torquay it seems certain that the vertical
pressure was small, a piece of evidence which fits in well
with that of the Ugbrooke Park beds as indicating an incom-
plete local deposit of culm. Over the whole district it is quite
impossible to unravel the confusion and say where any troughs
and ridges were. All we do know for cer^in is that, like all
other Hercynian folds, they ran approximately east and
west. Indications of vertical pressure increase southwards
until we reach the metamorphosed rocks of the Start and
Bolt Head. These must probably have lain not far from
the core of a range much larger and loftier than the heights of

♦ Lord Avcbury, Quart your. Geol, Soc, 1905, p. 34S

62 The History of Devonshire Scenery*

Exmoor. Just as North Devon, on any hypothesis, is the
stump of an arch, or anticline, and the Culm of Mid-Devon
is a trough, or syncline, so South Devon is the northern
half of a great and complicated anticline, whose southern
abutment must have lain far out in the English Channel.

We have no means of estimating the probable height of
this ridge from the rocks we see, except by comparing the
structures with those of more modern mountains. In Europe
the Belgian geologists have estimated that their local
representatives of the chain probably rivalled Mont Blanc
in stature, and the Devonshire structures compare with those
of some of the lower Alpine ranges, so that a height of ten
thousand feet or so above the basin of Mid- Devon is by no
means an unlikely altitude for our southern range. There
can, at any rate, be little risk of error if we picture the
Channel as land traversed by parallel ranges of Alpine size,
one of which crossed the extremities of South Devon and
Cornwall.

The main features of Devonian folding we see are
determined by Hercynian folds. But they are not wholly
so. The Pennine system, though comparatively insignificant,
has left its mark. In the North of England it consists of a
series of fractures which cut up the country into terraced
steps rising abruptly on the west and sloping gently towards
the east. Crossing, as it does, the gentle Hercynian folds,
it divides the coal fields into two rows of basins which, in
the north, are generally longer from north to south than
in the transverse direction.

As we pass southwards the Pennine disturbances diminish
and the Hercynian increase, so that the coal fields tend to
lie in basins elongated from east to west. Pennine dis-
turbances are not very obvious in Devon, but there is
certainly a north and south ridge of Devonian rocks rising
up under the newer covering of the Haldon hills, and the
basement beds of the Culm are brought up in the Perridge
tunnel of the Exeter railway. The Devonian rocks form
the base of the slopes on the east of the valley of the
Teign to some distance north of Chudleigh. Indications
of a northward continuation of this ridge are afforded by

Ideal restoration of Post-Carboniferoui Geography.

Origin of the Granite Domes* 65

the Culm masses of Stoke Hill and Ash Clyst forest,
and by the trend of the limestones of Westleigh.

The Culm shales and cherts also rise up on both flanks
of Dartmoor, and a similar arrangement is shown by the
Devonian rocks on the eastern and western sides of the
granite bosses across the Cornish border. It has been
explained by supposing that the granite existed before the
Devonian rocks, or, at least, before the Culm measures
were laid down ; but the granite shows no sign of having
been subjected to the forces which folded the Culm, and
the surrounding rocks show no indication of change of
composition or texture such as we should expect on approach-
ing a great mass of solid rock. It seems far more probable,
and we shall see later on, almost certain, that the granite
rose to its present positions in a fluid state after the earth
pressures had done their work, and that those positions
were determined by the folds, and did not in any way
determine them.

If we bear in mind what was said earlier about two
sets of waves crossing each other, and remember that there
must have been many points where the Pennine undulations
reinforced the Hercynian, it is easy to understand that
Devonian and Culm may have been thrown up into a
number of dome-like structures above the subterranean
lava reservoirs which had fed the volcanoes which were
so active throughout both periods. This we believe to have
been the case, and that the molten material rose up into
these domes and ultimately became the granite bosses. The
exact age of the granite and its connection with the volcanic
rocks have been the subjects of much discussion, and many
theories have been advanced. Their consideration will
come more profitably later on. It is enough to point out
that the structures shown by the surrounding rocks can
be easily explained as due to the crossing of the two sets
of folds which we know existed all over the south and west
of England. We must, then, in our attempt to reconstruct
the geography of the time, picture the heights of Dartmoor
and Bodmin moor as replaced by elevated districts composed
of folded Devonian and Carboniferous rocks, piled up>

^4 The History of Devonsliire Scenery*

above the present contours to heights of which we can
form no confident guess.

Nor is this all. In this description of the Great
Upheaval we have said nothing of the manifestations of
volcanic activity which seem to be the invariable accom-
paniments of all great earth movements, and which were
so intense in Devon that they have left as large a mark
on the present scenery of the county as anything we have
described. It will be shown in the next chapter that the
Dartmoor dome must have been more or less covered with
volcanic products, either arranged as Mr. Worth has sug-
gested'^' in a great composite volcano, or in a number of
smaller cones and craters high above the present contours
of the moor.

• Quart Jour, GcoU Soc,^ Vol. xlvi^ p. 69.

1

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I

I

I

I

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<5

CHAPTER VI.
Volcanic Rocks.

The story of the volcanoes of Devon is one over which
there has been much dispute, and about which there are
differences of expert opinion, even greater than those to
which repeated reference has been made about the North
Devon succession. In order to weigh the evidence accessible,
it will be necessary to briefly consider some of the general
principles which seem to govern volcanic action.

All volcanic rocks are the result of the cooling of material
which has been brought up from a depth within the crust
in a fluid state. This fluid, spoken of as the magmas
appears to collect in vast underground reservoirs, especially
on the flanks of a rising mountain chain, and finds its way
to the surface in obedience to some impulse which Dana
has called the ascensive force.

When part of the magma appears on the surface, it is
always found to contain more or less water, which is given
off as steam ; but whether this water is a necessary part of
every magma, or whether it is derived from the passage of
the fluid rock through wet surface strata, is a point which
is quite unsettled.

If now, a part of some magma cools and solidifies
slowly, as it will do at a depth within the crust, its different
elements group themselves into definite mineral compounds
which crystallize one after the other until the whole is a
closely packed mass of crystals. As we should expect, the
minerals which crystallize first form well developed crystals,
while those which come later have to fill up the irregular
interstices, until the last to solidify may seldom have an
opportunity of assuming its proper external form.

If another part of the same magma solidifies in a
smaller mass, such as an intrusive vein or thin sill, much
nearer to the surface, cooling will be more rapid. Before
the earlier crystals have had time to grow large, others
will form, and these in turn will be surrounded by yet

F

66 Hie History of Devonsliife Scenery*

another set. The whole mass will thus be crystalline, but
the texture will be finer. It is possible that some minerals
may have developed and grown to some size before the
mass was forced to its final position, and this will produce
a rock consisting of large crystals of the minerals which
form early, surrounded by a matrix of finer crystals.

Next, suppose the fluid material erupted actually on to
the surface. The contained water will flash into steam and
form bubbles which will tend to rise up to the surface.
If the quantity of water is large the rock may be reduced to
the state of an open sponge, or even a kind of froth. There
will be all grades, from a rock containing but few bubbles
to the familiar pumice, the texture being dependent upon the
fluidity of the molten rock, and on the proportion of water.

Where the lava is poured out in a semi-fluid state in a
small quantity, it will cool rapidly, so rapidly in fact, that
much of its material will set in the form of a dark glass.
If, on the other hand it is emitted at a very high temper-
ature in a limpid form, and forms deep floods or streams,
the steam bubbles will be mainly restricted to its surface,
and the interior and deeper parts may take so long to cool
that well defined crystals will be formed, which may leave
little or no glass to be detected. Such a lava will be com-
posed of small crystals, and will not always be easy to
distinguish from a vein or sill which has cooled quickly.

Lavas, like sills and veins, very often contain some of the
early forming minerals in large well formed crystals, bedded
in a matrix, which is either made of small crystals, or of
glass, or of a mixture of the two.

The first great distinction, then, to be noticed is the difi"-
erence of texture, which is determined by the conditions
under which solidification took place.

Rock magmas differ also in their chemical composition.
They are usually represented as consisting of silica and a
number of metallic oxides. Silica plays, in nearly all rock
forming minerals, the part which is played by the acid in an
ordinary chemical, while the metallic oxides are called the bases.

A given quantity of silica can enter into combination
with a given quantity of bases to form a particular mineral.

Classifteation of Igneottt Rodu*

67

If there is an excess of either acid or base, it ivill be
left to crystallize by itself, unless the elements can so alter
their grouping as to use up the excess by the formation of
different minerals.

Now a volcanic rock usually contains a large number
of bases, and the possible groupings which may be pro-
duced is often manifold. The same magma by cooling under
certain conditions of temperature and pressure may arrange
its parts in one set of crystalline minerals, while under other
conditions the chemical grouping may be different. One
thing, however, will be unchanged, and that will be the
chemical composition of the whole.

Broadly speaking, volcanic rocks are classified in three
groups. The first, which contain silica in excess of that
taken up by the bases, are called acid rocks. They contain
from 65 to 80 per cent, of silica, and granite is their deep
seated representative.

Next come the intermediate group, in which the propor-
tion of silica is less. A crystalline mass with granite-like
texture but possessing a proportion of only 60 to 65 per
cent of silica would be called syenite, while one in which the
silica formed only 55 to 60 per cent would be known as diorite.

Reduce the silica below 55 per cent, and we come to the basic
rocks, the deep seated examples of which are known as gabbro*

The relations of these crystalline rocks to the lavas,
which could be formed from the same magma, will be most
easily followed by giving them in a table.
Crystalline or Plutonic Rock. Lavas.

Granite
(Elvans, in veins)

Syenite
Diorite

-

Rhyolite.
Obsidian (glassy).
Pitchstone (glassy).
Quartz-felsite.
^Quartz-trachyte.
Trachyte.
Andesite.

Gabbro

•

fDolerite (matrix coarsely
crystalline).
Basalt (matrix finely
I crystalline).

68 TEe History of Devonshire Scenery*

Such are the main divisions used by petrologists. There
are, of course, very many varieties in each division indica-
ting the presence of certain minerals. Thus, an andesite
may contain mica; if so, it will be spoken of as a mica
andesite, or it may contain other minerals instead, in which
case it is necessary to name them before the rock can be
said to be fully described.

In order to follow the stages in the volcanic action in
Devon, it is not really essential that we should go much
further into the question of composition except in one im-
portant point. Crystalline, or Plutonic rocks, and lavas, are
just as liable to alteration after formation as sedimentary
rocks, and the precise changes impressed will, of course,
depend upon the circumstances which produce them. If,
then, one part of a flow, say the material which solidified
in the pipe of a volcano, has been exposed to heat and
pressure underground, while the lava which flowed from it
has been acted on by exposure to the weather, and sub-
sequent burial under newer material, the inevitable result
will be that their chemical composition will grow more and
more divergent as time goes on, and, owing to the difference
in the conditions under which they originally solidified,
their constituent minerals may have differed from the start.
It may thus come about that we may find the two lying
near one another, and yet be unable to say with any cer-
tainty that they really represent two parts of a formerly
continuous rock.

If we examine the lavas which have flowed from the vents
of a volcanic district it is the general rule to find that the
earlier extrusions belong to the intermediate group and consist
of trachytes and andesites, while the later products include
acid rocks such as rhyolite and the basic lavas known as
basalt and dolerite.

There are, however, many apparent exceptions to this typical
cycle. Instances are known in which it has been repeated
with no important break between. In other cases intermediate
lavas have made a brief reappearance in a later phase of the
cycle, or the basic rocks have been erupted in one part of the
area while acid lavas were making their appearance not far away.

The Sequence of Volcanic Rocks* 69

It has already been pointed out that the magma which
supplies a volcanic district appears to collect in vast under-
ground reservoirs which have a definite size more or less
proportioned to the symptoms of activity above them. Years
ago it was the common belief that aU volcanoes were in some
way fed from a molten interior which was supposed to make
up the bulk of the earth, or to form at least a continuous
stratum on which the solid crust floated like ice on water.
This view, however, has been generally abandoned for many
reasons which space will not allow us to describe in these
pages, in favour of the idea of subterranean lakes whose
formation is closely connected with the great earth move-
ments which result in mountain chains.

Changes in the products of activity must mean changes in
the magma which feeds them. There is no escape from this
conclusion unless we may make the improbable supposition
that the changes are produced while the molten material is
finding its way to the surface, an explanation of which there
is no hint, and which implies a far longer journey than appears
generally possible.

The ordinary sequence of changes implies that the usual
composition of the magma is intermediate, but that in time
the diverse constituents separate into an upper acid portion
and a lower or basic part. The solid superincumbent crust
will almost certainly present an irregular roof to the lava
filled reservoir, and wherever this roof rises highest, there the
lighter acid material will collect. Suppose, then, a fissure offers
an opening from above into one of these domes, the lava which
will be erupted will be acid. If, on the other hand, a fissure
formed on the margin of the district reaches down to the side
or lower part of the reservoir some of the basic material
will escape.

Imagine a time when this separation has not gone very
far, and when it is only the topmost domes of the reser-
voir which are filled by acid rock. It is clearly possible
that an eruption may result in an outpouring of acid
pumice, or rhyolite, followed by trachyte of intermediate
composition, and that in turn by basic basalt, as deeper and
deeper parts of the magma are drawn upon. Still more, a

70 The History of Devooshire Sceaery*

series of violent eruptions may stir up the whole contents
of the reservoir and the cycle will be repeated.

At last the piles of erupted material will become so
extensive that unless aided by fresh earth movements, the
tendency of the melted rock to force its way to the surface
will be counterbalanced. The separation of the acid and
basic components will then go on steadily until cooling and
and final solidification set in, and spread gradually down-
wards through the whole mass.

If, after crystallization has spread downwards for some
little way, the region is disturbed by fresh movements, the
solid top of the magma may be cracked in numerous
places, and some of the underlying still fluid material
injected into the fissures, or even on to the surface.

The differentiation of the contents of the reservoir
appears to be brought about in two ways, and it is a
matter for discussion as to how far each cause may be the
chief.

We have already said that the minerals cystallize in a
definite order. We can now go further, and without going
into minute particulars, say that the more basic minerals
are those which crystallize out first. These are also the
heaviest, and some of them are separated while the lava is
quite limpid. If this is so they must obviously sink down.

Now it must be remembered that cooling of the contents
of a lava reservoir must begin at the top and spread down-
wards, very little of the process beginning at the sides and
spreading laterally. It follows that at a particular level we
shall have the temperature about the same, with only slight
diminution as we reach the sides.

Very little is known about the exact influences exerted
by temperature and pressure upon the crystallization of
rocks, but it is almost certain that the separation of a given
mineral is strictly analagous to the crystallization of an
ordinary chemical from solution. There are two ways in
which this may take place. The crystals may be formed
on the walls of the vessel, particles of the substance appar-
ently travelling from the interior of the solution to the
sides, or to any foreign bodies or already solidified crystals.

Changes in a Lava Reservoir* 7^

This tendency for marginal crystallization is little shown
in cooled igneous masses, though Mr Marker and others
have pointed to cases in which something of the sort may
possibly have happened. The second method of separa-
tion is by the formation of crystals throughout the whole
mass as soon as its temperature reaches a certain critical
value, which depends on the substances concerned and the
strength of the solution. It is well illustrated by an ex-
tremely pretty experiment. Take a little nitrate of lead, or
acetate of lead, dissolve in water, so as to form a solution
of moderate strength, and add a few drops of solution of
iodide of potassium, when a bright yellow precipitate
is formed. Then boil the liquid, and if necessary add a little
water and boil again, until the yellow powder is entirely
dissolved. Now allow the almost colourless liquid to cool.
When the right temperature is reached glittering golden
spangles suddenly make their appearance throughout the
mass and settle rapidly downwards.

Such, then, is one way in which differences of composi-
tion may be brought about. It has been objected that it
would be impossible to have cool molten rock floating on a
hotter substratum, as the hotter rock must be the lighter.
So it would be if the composition were the same, but it
would be quite possible to have comparatively cool melted
granite floating on hotter molten basalt, just as cool oil
might float on hot water. So we may safely dismiss the
objection.

There is a second way in which change may be effected,
and one which certainly seems to be very important. Sup-
pose the contents of the reservoir to be at a temperature
well above their melting point — they will melt off and
dissolve some of the rocks which bound it, that is to say,
those within which the space has been formed. Next, if we
consider the crust above the reservoir, its surface tempera-
ture will be that of the locality, its lower surface that of
the lava, the rate of fall as we ascend from the melting
and dissolving base being determined by the conducting
power of the rocks. Suppose, now, the reservoir roof is
only just at its melting or dissolving temperature but that

7^ The History of Devonshire Scenery*

the igneous material at a short depth lower is still hotter^
eruptions on to the surface will check the escape of heat
by thickening the crust, and will draw ofif some of the
colder upper parts of the magma. Either cause will increase
the temperature of the melted material in contact with the
roof, and the result must be that the magma will work
upwards through the crust, gradually eating away the
over-lying rocks and incorporating their materials with its
own. If these materials consist largely of sand and grit,
as they will if they are sedimentary rocks, the result will be ta
add to the acidity of the magma in which they are dissolved.

In the previous chapter it was shown that the folding
of the Devonian and Culm strata indicated a series of
mountain ridges crossing Devon and Cornwall, and that
these were intersected by minor disturbances of Pennine
character, which threw up some of the Hercynian ridges
into detached domes.

We now see that we may consider the abundant volcanic
rocks of middle and upper Devonian time as having been
supplied from a lava reservoir which underlay most of Devon
and all Cornwall, and extended further westward at least
to the Scilly Isles. The same reservoir persisted through
Carboniferous times, and may even have been connected
with the one which supplied the more extensive eruptions
which took place at about the same time in Brittany.

Then came the earth pressures. The first upheaval
took place over Devon at the close of the Culm basement
beds epoch, and this was followed by the great uplift and
stupendous folding already described, at the end of Car-
boniferous time. Then it was, according to the view already
sketched, that the molten material rose up into the domes
and their connecting arches, and most of the pipes and sills
which we find injected into the Culm were forced into
their present position. How long afterwards the activity
persisted we have no means of knowing, but the time was
considerable, for we find lava streams of great size occupying
such positions that it is clear the earth's movements must
not only have ceased, but denudation must have gone on
for ages before they flowed down the slopes and solidified*

Carbonifefous Volcanic Rocks* 7S

The next step is to describe the volcanic components
of the Carboniferous rocks of Devon, and see how far they
bear out this view.

They are abundantly displayed on both sides of Dart-
moor. The crumpled Culm basement beds upon its eastern
flank contain numerous interbedded sheets of undoubted
lava, and a few beds of interstratified tufif. Both have been
greatly altered. In the case of the lavas the steam holes
have been filled with mineral deposits, some of the original
minerals have been completely changed, so that we find
one mineral filling a series of spaces which present the exact
outlines characteristic of another; others have been partly
changed, and new minerals have been developed from the
decomposition of the first set. This alteration makes it
hard enough to trace out the full history of the rocks^
but it is complicated by another difficulty even more
serious.

Devon and Cornwall show no signs of having been ex-
posed to the grinding action attributed to the ice sheet of
the great Ice Age. North of the Thames the ancient pre-
glacial land surface has all been ground up and pushed away
in the form of boulder clay. South of that line the soils
we see have been forming since a much earlier age, and the
slow rotting of the rocks and their contained minerals has,
in the south-western counties, reached depths so great as
to render it difficult to get specimens which do not show
changes due to surface actions. The same deep soil and
moist climate give rise to the rich growth of vegetation,
and the three combine to make minute exactness in mapping
the underlying rocks often impossible.

However, in spite of these peculiar local difficulties a
great deal is known, and the evidence all points in one
general direction.

If we take the two sheets of the new Survey Map^
numbered 325 and 339, we find that the Culm exposures
between Haldon and the granite of Dartmoor are chequered
with patches of volcanic rocks. It may almost certainly
be taken that those which appear as elongated streaks and
ovals are either lavas or tuffs erupted during the deposition

74 The History of Devonshire Scenery*

of the Culm, or sills injected during the progress of the
earth movements. Some of them, Mr. Ussher has shown,
share the disturbances with the culm. But many of the
exposures give rounded sections on the map, not much
elongated either way, and some at least of these can
be shown to be intrusive. An intrusive rock must
have taken up its present position after the deposit of
the rocks through which it passes, and which are baked
and altered where they come in contact with it. These
intrusive pipes of rock cut across the bedding of the sur-
rounding culm, so that they are almost certainly later in
date than the folding.

South of the Culm area, the northern part of the
district mainly occupied by Devonian rocks is similarly
riddled by intrusive volcanic materials, and there is a
high probability that these also, or at least many of them^
belong to Carboniferous times.

Now, the study of these rocks is not easy. They are
all classed together as "greenstones,** which is a compre-
hensive term applicable to all sorts of basic rocks and
the more basic of the intermediate group. A more pre-
cise term is *' diabase, " which further implies that they
have been considerably altered. In order to write their
history we want to know what they were when they
cooled from fusion.

There is no doubt about the Teign Valley lavas. They
were originally dolerite, basalt, or the more basic varieties
of andesites, but principally dolerites. The intrusive rocks
range, so far as is known, from an intermediate rock
resembling syenite to a fairly coarse grained gabbro.
There are many quarries in which these rocks have been
worked for road metal, and a walk for a few miles along
the road which follows the Teign will show numerous good
sections. The stone is exceedingly tough, and requires a
heavy hammer and vigorous work if good specimens are
to be got. Other sections are shown in the railway cuttings,
while the pile of rocks known as Bottor, near Hennock,
is the largest block of dolerite, and is so coarsely crys-
talline that it is a question whether it should not be

Layas of the Teign Valley* 75

regarded as a gabbro. Reference to the table in the early
part of this chapter will show that the difference between
the two rocks is only one of degree, the latter term applying
to a rock which has cooled deep down, and the former
to the same mass if it has cooled in the throat of a volcano
or on the surface.

Although we have said many of these crystalline plugs
and bosses are certainly intrusive, there is not one which
has yet been shown to have any connection with a lava
stream, nor can we, by studying the lavas and tuffs, make
any progress towards locating the centres from which they
came. Those which were erupted before the folding have
been so crushed, broken, and crumpled that we cannot
trace them home. Those which are subsequent to the
earth movements, and which probably fed eruptive cones
above, are only the pipes which led up to a sur&ce which
has long since been removed by denudation. The only
definite conclusions we can make from these rocks are that
the eruption of basic and intermediate materials began
before the earth movements, were continued during their
progress, and did not cease until after they were completed.
We must, however, note one more point. If thin sections
of these rocks are examined under the microscope the
crystals, many of which are large and well defined, are
found to be cracked, broken, and even crushed; an
indication of exposure to powerful stresses which will be
referred to further on.

If we turn to the western side of the Moor we come
to ground which has been thoroughly studied by Mr.
Rutley* and more recently by General McMahon.f

Their investigations have led to important results. Mr.
Rutley showed that De la Beche was right in supposing that
Brentor was actually the remnant of a carboniferous volcano,
and he indicated clearly the site of the vent from which its
beds of ash and lavas had been ejected. The original
memoir should be consulted, as our space is far too limited

* Memoir Geol. Survey on Brentor, 1878.
i Quart, your, Geol, Soc, 1894, p. 338.

76 The History of Devonshire Sceaery*

to give even a respectable abstract. In its prime Brentor
must have been a volcano of considerable size, but not a
great mountain in itself. Its rocks have taken part in the
earth movements, so that the date of its activity was prior
to the main upheaval.

All along the western flank of the Moor the sedimentary
rocks are mixed with igneous. Most of them are con-
temporaneous, but some appear to be intrusive.

General McMahon's paper describes a large number of
most interesting rocks, among which there are many beds
of more or less altered ash and agglomerate, while some
seem to have been lavas which had flowed over loose ash,
so that the two became intimately mixed. Some of the
ash beds have been re-crystallized, as, for instance, those
of Cocks Tor, near Tavistock. Sourton Tors and their
neighbourhood are formed of hardened ash, inter-bedded
with acid felsites and trachytes, while the little hill of
Was Tor, close to Lydford Station, contains an altered
basalt and a rhyolite. The beds of agglomerate, he also-
showed, have been made up from the fragments of a
great variety of lavas ranging from Acid to Basic, so that
acid lavas must have existed in abundance in cones which
were subsequently blown to pieces by violent paroxysmal
eruptions analogous to that which destroyed Pompeii and
Herculaneum, and to the more recent explosive eruptions
in the West Indies.

Where were these volcanoes situated ? Can we find
their craters, or the pipes which supplied their lavas, or
is it possible that all traces of the ancient cones have been
swept away, the abrading influences of time having planed
them down to the very base from which they came, namely,,
the lava reservoir itself?

These are the questions which lead to the next chapter.

CHAPTER VII.
The Dartmoor Granite and Exeter Lavas.

There are two ways in which a given proposition can
l>e proved. The first is by what is called direct evidence,
which means the announcement of a fact or facts which
cannot be explained on any other hypothesis than the one.
The second is by so-called circumstantial evidence, which
usually consists of a number of facts, any one of which can be
explained also by some .other hypothesis, but all of which
find their common explanation in the proposition in
question. The larger the number of these circumstantial
points the more convincing is the proof, until it becomes
every bit as conclusive as the most direct evidence we can
imagine.

At the end of the last chapter some questions were asked
which we shall now attempt to answer, not by any proof
of the first order, but by an amount of circumstantial
evidence which seems to the writer to be fully conclusive.
It is the fashion in mathematics to preface the proof of
any proposition by a concise statement of the theorem
which will be shown to be correct. We shall follow this
method here, and as we go on shall consider the main
objections and rival explanations.

We shall attempt, then, to show that the granite mass of
Dartmoor is really the solidified upper part of the cooled
lava reservoir from which the Carboniferous and Post-Car-
boniferous volcanoes of Devon were fed. That it was at
one time crowned not only by a great mass of Culm strata,
but also by extensive volcanic cones from which acid lavas
were outpoured, and from which explosive eruptions built
up layers of volcanic ash. Simultaneous with these acid
extrusions others of a very different character were taking
place, outflows of basic and intermediate lavas of peculiar
character issuing from other vents, which presumably com-
municated with deeper-seated portions of the same magma.
Finally, that some at least of these lavas were derived

7^ The History of Devonshire Scenery*

either from the Teign Valley basic pipes or from similar
rocks further west, which were dissolved away by the
granite as it worked its way upwards or removed by
denudation.

The first point in the chain of evidence is the direction
and nature of the folds produced during the great upheaval.
This is so obviously related to the granite that there can
be no doubt of some connection. Mr. Ussher* has explained
this by assuming that the granite was actually in position
and cool before the upheaval, and that the uprise of the
Culm basement beds around it was the result of their having
been squeezed up against it. But closely related to the
main granite mass are the elvans or granite veins, which are
certainly more recent than the great upheaval, as they cut
right though the beds, though the majority follow lines
parallel with those of the folds. There must, therefore,
have been melted granite under the whole region at this
period. If, then, the granite had been solid before the
upheaval it must have been fused by the compression, or
an entirely new eruption of exactly similar material must
have invaded the district. General McMahon,t in an
interesting paper, has pointed out the extreme improbability
of this view, and very pertinently asks how we can suppose
the pressures could have remelted so large a mass, when it
produced so small an effect upon surrounding rocks. It is
far simpler, and more in accordance with all we know from
the study of other districts, to suppose, as we have done,
that the granite existed in a fused condition below the
sur£su:e prior to the upheaval, and that its rise into some-
thing like its present position was determined by the
particular conditions of the folding. That the main mass
of the granite was not solid at the time of the folding,
unless indeed fused in the process, is sufficiently evident
from two things. We remarked that the crystals of the
Teign Valley lavas and those of some of the intrusive rocks
were greatly crushed and broken. This can only be due

* Proc. Somerset Archctological and Nat, Hist, Soc., 1892.
t Quart, Jour. Geol» Soc,, 1893, p. 385.

Age of the Dartmoor Granite* 79

to the strains produced during the upheaval. Now, the
crystals of the granite show nothing of the kind. They
are sometimes a little distorted, but we know of no instance
in which they show such symptoms of rough usage as those
shown by the Teign Valley dolerites.

These dolerites and those of the Brentor region were
erupted before and during the upheaval. They must have
risen from a subterranean reservoir, and from their
similarity with each other and with many other rocks
beyond the Cornish border, it is impossible to resist the
conclusion that a reservoir of the same composition
underlay the whole district. Such a deduction is evidently
incompatible with the separate existence of the granites in
a fused condition, and cannot be reconciled with it in a
solid state, unless we suppose either great pillars of solid
granite penetrating the basic reservoir, or that the acid
rock consisted of quite thin cakes of solid stone above
the denser molten mass. No instance of either conditions
is known. It is more reasonable, then, to suppose that,
at the date of the basement beds, the granite had no
separate existence, but that it formed only the upper part
of a reservoir which had begun to divide itself into an
acid and a basic part. The dome in which this lighter
portion collected formed the land from the detritus of which
the Ugbrooke Park beds were formed.

Now the extrusions on either side must be supposed
to have come from the deeper parts of the reservoir. If
any were simultaneously taking place above the granite
dome, they must have assumed the shape of rhy elites^
felsites, or trachytes, such as those of Sourton Tors. Such
lavas are not erupted in a very limpid form, and would
not flow far from the vents. They would quickly build up
steep-sided cones, from which the processes of denudation
would rapidly remove material, thereby affording much of
the sandy substance which went to make up the middle
and upper Culm.

It should be borne in mind that all which applies to
Dartmoor applies with nearly equal force to the neighbour-
ing mass of Brown Willy.

So The History of Devonshire Sceaery^

We should thus have two districts made up of materials
of granitic composition, amply sufficient to account for the
undoubted fact that the Culm of Bude is composed of
granitic particles, without assuming that the actual granite
was laid bare.

The domes of granite may very probably have been the
seat of eruptions from the magma before its parts had
begun to separate- Indeed, this is what we should expect
to find if subsequent denudation had not done its work so
thoroughly. If so, the same districts ought to have sup-
plied a certain amount of debris of trachyte or even ande-
site, both of which are represented in the Sourton Tors
Agglomerates. We should then picture the Devonshire
area as resembling the Lipari Islands of to-day, where the
ruined central volcano is made of intermediate lavas, while
the islands of Lipari and Vulcano are built of rhyolites,
and Stromboli and Vucanello of basalts.'^

The great upheaval would necessarily squeeze up the
domes into a series of elongated bubbles, and the crossing
of the two sets of flexures would, with equal certainty
cause these bubbles to rise much higher in certain spots
where the waves of flexure crossed. Meanwhile, eruptions
on both sides of the domes would continue to be fed from
the deeper seated magma, while those above the lava filled
bubbles would be supplied with acid materials. We should
thus expect the elevated districts to be crowned by cones.
It is possible that each granite mass represents the base of
a single cone comparable with the great mountains of other
countries. But it has been said that acid extrusions do not
generally flow far. They are viscid, and soon seem to block
up their vents with solid rock. This is equivalent to tying
down the safety valve, and the result is either the out-
break of new vents near by, or violent explosions which blow
away much of the old cone. It is more likely, therefore,
that each granite mass represents the base of a district
which was thickly dotted over with ruined cones of inter-
mediate composition, and smaller craters and hills built up

*Juddy VolcanoeSy p. 200.

Stages in the Consolidation* 8i

from the later rhyolites, volcanic glasses, and beds of
ash.

As long as the vents remained open, the cooled parts
in the upper portion of the reservoir would be drawn off
from time to time, and the molten mass would remain hot
enough to go on dissolving the over-lying solid crust.

The word dissolving is used instead of melting, because
it is found that in some cases a lava which is fairly easy
to fuse, has eaten its way through materials which have a
much higher melting point, just as the very infusible lining
of a Bessemer converter, or a blast furnace, is corroded by
the molten slag, unless its composition is properly adjusted.
Moreover, there are many places around Dartmoor where
hand specimens can be found in which the contact between
the granite and the Culm is clearly seen. There can be
no doubt from an inspection of such specimens that the
granite has reached its present position by dissolving the
Culm rather than by simply melting it.

If we suppose the dome of molten material to have
been originally covered by Devonian rocks as well as Culm,
and that these were largely mixed with, or covered by, the
earlier intermediate extrusions, this process of solution
would bring the granite through each in turn until it at-
tained to a level so near the surface that the rate of
cooling exceeded any possible gains of temperature from below.

Solidification of its upper parts would then begin, and
would gradually spread downwards.

But earth movements of great magnitude are generally
followed by minor disturbances something Hke those which
precede them. It is therefore probable that the cooling
of the whole reservoir would not proceed uninterruptedly.
The portions earliest solidified would be cracked open;
and fluid material from beneath would be injected into the
cracks. Hence the elvans, or granite veins, which are
found in great numbers penetrating not only the sur-
rounding sedimentary rocks, but even the granite itself^
or at least its marginal parts.

Some of these injections of a granitic magma have a
peculiar structure. There is a part of one which may be

G

82 The History of Devonshire Scenery*

seen intersecting the granite blocks of Heltor, above
Dunsford Bridge. It differs from ordinary granite by con-
taining large lumps of crystalline quartz embedded in a
finer grained granite matrix. Careful inspection shows that
it is not a case in which the quartz had crystallized first,
but one in which the crystals had been somehow mixed
up with the ascending granite. There seems no way of
explaining it except by supposing that the uprising hotter
molten rock had re-melted all the more fusible minerals of
some granite which had already solidified, and the quartz being
least fusible, had been left to be carried on in suspension.

Exactly similar rock is to be found in other places, and
if we suppose it to have reached the surface, it would have
cooled as a lava containing large lumps of Quartz in a much
finer grained, or even glassy matrix. We shall see presently
what evidence we have of such lavas.

Long after the upper parts of the reservoir have solidified,
we may still have eruptions fed from its deeper parts, and
these will be most likely to occur by the formation of
fissures not through the granite, but on its flanks, especially
where the surface has been depressed by a synclinal fold.
Exactly such a place is the Teign Valley district which
lies between the Dartmoor dome and the Pennine ridge,
which we have referred to as running under Haldon and
away in a north-easterly direction.

The next points to be considered are as follows : — What
evidence have we of the presence of such cones as we have
suggested over Dartmoor after the upheaval — ^and what
evidence is there of lava flows from the depths of the
reservoir on the flanks of the moor. There will then be
a final query as to whether there is any fact which is
contradictory to our hypothesis.

The first is capable of an abundant answer in the
affirmative. It is supplied by the beds of rock which were
laid down all over the east of Devon after the upheaval
was practically ended, and long after all movements excepting
possibly a few insignificant disturbances.

These are the deep red rocks which form the coast line
from Paignton to Torquay, and from a little north of

The New Red Breccias* 83

Babbicombe to beyond Exmouth. They cover the country
from Haldon to the foot of the Woodbury Common ridge,
send a long tongue up the valley of the Creedy, another
shorter tongue from Tiverton to Loxbeare ; and then, after
lapping round the limestone hills at Westleigh, sweep up
the valley between the Brendon Hills and the Quantocks
to the northern slopes of Exmoor above Williton and
Watchet.

The first point to notice is that these rocks lie uncon-
formably on the upturned edges of the older strata. Near
Paignton they may be seen lying almost horizontal on the
upturned edges of slates of Devonian age, which are almost
vertical. In places along the western face of Haldon similar
relations are shown. Close to Exeter there are spots where
they may be seen resting in a similar way on the Culm.
One very good section was uncovered some years ago at the
eastern end of the tunnel between Exmouth Junction and
Queen Street Station, where the red rocks lay with a gentle
slope towards the south on highly inclined Culm shales.

But there is no need to look for sections in whieh the
actual junction can be seen. Thanks to the deep lanes
and roadside cuttings so universal in the county, we seldom
need go far in order to see something of the geological
structure; and everywhere where we pass from the red
rocks to Culm or Devonian, we step from beds which are
little disturbed, and which have evidently been unaffected
by the forces we have described, to others which have borne
the full strength of the consequent earth movements. Not
only have the red rocks been formed later than the upheaval,
but the lapse of time between the first of them and the
compressing movements was so long that a large amount
of denudation had taken place, so large that in some places
the Culm has been removed, and the red rocks now rest
directly on those of Devonian age.

We have here a blank in Devonshire history, and,
unfortunately, we have no means whatever of gauging its
length. It is commonly believed that the red rocks in
question belong to part of the Permian period, which was
the one immediately following the Carboniferous, but real

84 The History of Devonslifre Scenery*

proof is wanting. They consist of mixtures of boulders,
pebbles only slightly rounded by water action, sharp angular
fragments of many kinds of rock, sand, and marly sand,
all rather deeply stained by red oxide of iron. Geologically
they are described as breccias, sandstones and marly sand-
stones, and they form the base, so far as Devon is concerned,
of the great series of sandy rocks which followed the Post
Carboniferous disturbances. As these are rather like the
Old Red Sandstone, but are much younger, they were originally
grouped together under the name New Red Sandstone. In
the Midland Counties and in Germany, where rocks of this
time are largely developed, they can be clearly separated
into a lower series, called Permian, which is taken as the
last period in the Palaeozoic era and an upper series, known
as the Trias, which forms the first period of the secondary
era.

In Devon there is no clear line of division, and it is quite
uncertain where it should be drawn, so it is usual to beg
the question by adhering to the old term, the " New Red."

The base, then, of the New Red series consists of
a great thickness of breccias and sands. The former are
admirably displayed in the cliffs by Teignmouth and Dawlish,
and in numerous quarries, where they have long been worked
for building stone. Most of the old churches of Exeter
have been built of it, and in more recent times the great
wall which protects the station road at Torquay has been
built of similar material.

The fragments of which the rock is composed are largest
at Teignmouth and its neighbourhood, and there we find
them comparatively little intermixed with sand. But as we
move northwards the fragments become rather smaller, and
sand is more abundant. Close around the Brendon Hills
the texture is coarse, and as we recede from Dartmoor,
or from the Exmoor Hills, the diminution in the average
size of the fragments is very evident. This alone is almost
enough to prove that the two high districts were the
localities from which the d6bris was distributed. But
it is not the only evidence. Even more conclusive is a
careful examination of the fragments. Near the Brendoo

Origin of the Breccias* 85

Hills and Quantocks these are broken and slightly water-
worn local rocks, mixed with fragments of Culm grit.
Exactly such as must have been worn away by denudation
from the Exmoor and Quantock ridges we have described,
and their presence south of Watchet on the northern slope
of the range shows that here, at least, that northern slope is
not far from its original position.

In South Devon, near Paignton and Torquay, fragments
of Devonian and Culm rocks are abundant, especially the
former, and as we go northward the Devonian constituents
diminish and the Culm increase That the breccias were
made by the accumulation of debris of local rocks is thus
.assured. In every case the sedimentary fragments can be
precisely matched by rock which is in situ not far away in
the direction of the existing high ground.

The majority of the fragments moreover show little signs
of having travelled far. Waterworn boulders and pebbles
do occur, but they are only a very small minority and are
rarely rounded to such an extent as to mean a lengthy
journey on the bed of a stream. Judging from the analogy
of modern rocks it seems that the fragments must have
accumulated in steep mountain valleys which were now
and then the courses of violent torrents, caused by heavy
rains or the melting of snows, which occurred only at long
intervals. In many parts of the Egyptian Soudan, in the
arid regions of the United States, and especially in the
dessicated parts of Turkestan exactly similar deposits are
now being produced. During the dry season, or dry years,
changes of temperature, oxidation, and the impact of wind-
driven particles, act on the rocks flanking the mountain
valleys, and the debris falls down the slopes and lies in the
valley bottom. At length heavy rains descend, such rains
as do fall at long intervals in such countries, and each
valley is occupied by a raging torrent which in a few hours
clears away the accumulation of months or even years.
The streams with their burdens of d6bris debouch upon
the gentler slopes or on the plains, their speed becomes less
and their burden is dropped, gradually building up great
fan-shaped piles of new deposit. It makes little difference

86 The History of Devonshire Scenery*

whether the new beds are deposited in a lake or on land.
The waves of a large lake may round ofF many of the stones
before a new influx covers them up, and the finer mud and
sand will be spread further than the coarser fragments and
will settle down in more evenly grained beds. But the
arrangement of the coarse materials will be much the
same in both cases. Such fan -like deposits are known as
alluvial fans, and are characterised all the world over by
the admixture of coarse and fine material and the scanty
signs of wear shown by the fragments.

It seems, then, that the breccias and, therefore, pre-
sumably the sands and finer marly beds must have come
(in Devon) from mountain valleys further west and from
the high ground towards Exmoor.

The New Red deposits north of Exeter afford another
piece of evidence which is well worth mention. It will be
seen, on reference to the Survey Map, that the two hills
called Stoke Hill and Ashclyst Forest are folded Culm and
that the latter is surrounded on all sides by the red beds
which in one or two places may be seen actually
resting on the Culm. There is no doubt that the hills
existed in something very much like their present form
before the red beds were deposited.

If we examine any rocks which underlie the New Red
we find these rocks. Culm or Devonian as the case may be,
deeply stained by infiltration of red oxide of iron. The
phenomenon has long been known locally as the " raddling "
of the rocks, and explains the beautiful red veining of some
of the ancient coralline limestones. To take Stoke Hill as
an example. When we ascend and step off from the red
rocks on to the Culm we see raddling in full force. When
we get a little way up the steeper slopes the red hue
becomes less marked and presently disappears. As, how-
ever, we approach the summit it b^ins again, and on the
top is so strong that we begin to look for patches of still
existing New Red. Now, these facts might have been
brought about by an upheaval of the hill after the deposit
of the red rocks, but in such a case the red beds around
would show symptoms of disturbance which are entirely

Origin of the Breccias* 87

absent. They can only be due to the hill having existed
with rather steeper sides before the red beds were formed.
If we imagine layer after layer of red beds to have accumu-
lated around it until they ultimately overwhelmed even
its highest point, and then after long ages conceive the
wearing away of this ruddy mantle, we have a full explana-
tion. Erosion necessarily follows the valleys and is most
rapid on the steepest slopes. On the top of a flat-topped
hill wear and tear is at a minimum. Hence a capping of
red rocks would remain on the top long after it had been
wholly removed from the slopes, and after the valleys had
been deeply scoured. Stoke Hill was certainly carved into
much like its present shape by the very denudation which
produced the breccias and sands. The absence of raddling
on the slopes simply means that the reddened layer has
been removed, and that the hill is not so steep as it was in
the days of its youth, at the end of Palaeozoic time.

If, now, we note the position of this hill upon the map
and imagine breccia material being derived from the
^lirection of Dartmoor, we should expect that the deposits
would be coarser on the side of the obstructing hill which
faced their source than in its lee. It is actually found that
while the south-western slopes are fringed by breccias they
are represented by sands upon the north-eastern side.

Similar arguments show beyond question that the long
tongue of red land which runs up the valley of the Creedy
fills the bottom of a deeper valley which dates back to the
time following the great upheaval. Indeed all along the
margin of the red rocks we see the old land surface, which
was preserved by burial beneath them, and is only now
emerging to the light of day, as the covering is removed
by the wear and tear of time. The main structure of the
county and many even of its minor features are older than
the red rocks.

The breccias, however, are not only made of Culm and
Devonian sedimentary rocks. They are filled with volcanic
d6bris. So full, indeed, that there are not a few who
believe that they are, in fact, the d6bris of volcanic cones,
or even the far spreading base of a volcanic pile. There is

88 The History of Devonshire Scenery*

much to be said for this view, and it is in no way incom-
patible with our presefnt argument.

These volcanic fragments are full of significance. Mr.
R. N. Worth* has made a careful investigation of them
in two papers, of which the second is the more important.
He shows that they are also mainly of local origin, most
of them bits of rock we can still see in situ, but others
of exactly the acid and intermediate varieties which ought
to be there if our view of the Dartmoor problem is correct,
and if the volcanic fragments came from the direction of the
Moor. So conclusive does the evidence appear to be that
it would probably have been long since generally accepted
as proof had it not been for two apparent contradictions —
the presence of Dartmoor granite, and even bits of elvans,
in the breccias, and the peculiar nature of the lava streams
interstratified with them in the neighbourhood of Exeter.

The granite, it has been argued, cannot have risen to-
its present position after the upheaval and folding, because
its solidification must have taken place deep down, and it
cannot, therefore, have been exposed on the surface so that
fragments could be broken off so soon after that upheaval
as the date of the breccias. It will at once be seen that
this objection is based upon an estimate of time — the time
between the Post Carboniferous folding and the deposit of
the breccias. Surely the facts may be equally held to show
that the time was long. It has been pointed out that an
enormous amount of wear and tear had been effected in
the interval, and we must remember that this wear and
tear would act most rapidly on the steeper slopes.

A few years ago a boring was put down at Lyme Regist
in a vain quest for coal. It went down 1,300 feet without
reaching beds which are known to lie far above the breccias.
If, then, the highest land lay where we have supposed it
to be, and if the accumulation of d6bris followed the usual
law, and began in the neighbouring hollows, it must have
taken a very long time indeed for the pile of deposits to reach

• Quart, Jour, Geol. Soc^ 1889, p. 398, and op. cit., 1890, p. 69.
t Quart, Jour, Gcol, Soc., 1902, p. 279.

Origin of Granite in the Breccias* 8^

so high up the slopes as the places where we now see them
resting. They are supposed by many to be of Permian
age. This may be correct, and yet they may belong to
its closing years. If so, the lapse of time would be ample
for the purpose.

Moreover, we have supposed that the top of the lava
reservoir began to solidify soon after the earth movements
had almost run their course, but that the injection of the
elvans, or granite veins, from the still fluid parts beneath,
marked some closing throes. These elvans would, some
of them, reach the surface, where they would cool, and a
trifling lapse of a few centuries would be enough to lay
some of them bare.

In other cases the opening of fissures would be almost
certain to give rise to violent paroxysmal outbursts during
which not only pre-existing cones, penetrated maybe by
elvans, would be blown to bits, but portions of the under-
lying rock, including the coarse grained granite itself^
would be torn off and ejected. Granting, then, that the
granite was in position, there is no difficulty in accounting
for the fragments even without any great lapse of time,
and we have no real evidence that the time was not ample
for the earlier solidified granite to be uncovered by simple
denudation.

It has also been argued that the granite, when it con-
solidated, must have been deep down. There is no such
necessity. It must have cooled slowly, therefore it must
have had a considerable thickness of material above it. It
has been pointed out that the breccias require for their
formation steep and deep valleys, down which occasional
torrents must have rushed with great violence. Some of
the partly rounded blocks near Teignmouth weigh tons,
and even larger blocks are found near Ide in deposits which
are later than most of the breccias. In order to get the
slopes we need, we must imagine the valleys of the Teign
and its tributaries had no existence, being filled in by the
local eruptions, and that over Dartmoor the granite rose
above its present surface, and on top there lay the crumpled
and hardened Culm, crowned by the volcanic cones built

90 The History of Devonshire Scenery*

by eruptions from the lava reservoir before solidification.
This will give sufficient thickness of overlying material.
Moreover, the size of the crystals and rate of cooling will
be affected as much by the volume of the cooling body as by
the thickness of the covering, so that there is no necessity
to assume a thickness which might not have been penetrated
by the joint action of subsequent (elvan) explosions and
torrential denudation.

The next difficulty is the Exeter lava streams. They are
of very peculiar types, which have been described by the
Director of the Geological Survey, Dr. Teall, while their
geographical position has been given in detail by Mr. Ussher
in the Survey report on the Exeter district. They have
also been carefully studied by Mr. B. Hobson.* They
may be classed under four types. The first and most basic
is represented by the dark chocolate-coloured rock well seen
at Ide and Dunchideock, and which lies in a huge mass
just under the Belvidere on top of Haldon, where it
dips sharply towards the east. It is a basalt, but is
peculiar in containing numerous grains and crystals of
quartz and felspar, which appear as glassy spots in the rock.
Under the microscope it is seen that each of them has a clear
interior, but its superficial portion is corroded and looks as if
it had been heated to its softening point without melting.

The second type is the paler stone, more the colour of
cocoa, which is largely quarried in many places, among
which we may mention Pocombe and Posbury. The same
kind of rock makes the hill of Rougemont, in Exeter, and
crops out again at Raddon, near Thorverton, Silverton,
Budlake, Poltimore, and Broadclyst. Sometimes it is
massive, with its cracks filled in with deposits of subsequent
minerals, giving the stone its veined appearance ; some-
times it is as full of steam holes as a modem lava. A line
of it crosses Killerton Park through Columjohn Wood to
Budlake. It was originally a basic rock, but contains the
wrong kind of felspar, the kind which is usually associated
with acid rocks.

• Quart, your. GeoL Soc., 1892, p. 496,

Lava Quarry at Pocombe.

Pocombe Lava resting on upturned culm.

The g^rassy ledge shows the top ot the culm.

Types of the Exeter Lavas* 91

The third type is represented by the grey mica-spangled
rock of Killerton Park. The lava at the Belvidere on
Haldon is separated from the upturned edges of the denuded
Culm only by an impersistent band of sand. The Pocombe
stone may be seen in the roadside cutting to be actually
resting on the Culm. At Killerton the grey lavas rest on,
and are separated by, breccia and sand. It has, therefore,
been supposed that the Killerton rock is newer than that
of Pocombe. But it is quite possible that breccias may
have existed at Killerton long before they had reached so
much nearer to their source as Pocombe or even Exeter.
Indeed, this view is strengthened by the fact that a thin
layer of Pocombe type lava actually overlies the grey
rocks peculiar to Killerton.

The grey rocks are trachytes, but are peculiar in the
quantity of mica spangles they contain.

A fourth type is shown in the large quarries at Knowle
Hill near Crediton, and at Marshfield, Loxbeare, and
possibly Holmead, near Tiverton. These are intermediate
between the lavas of Killerton and Pocombe. They are a
kind of trachyte, but it is abnormally basic.

For our present purpose it is not necessary to say more
about the composition of these rocks, though they open up
many avenues of research. The point is that they are all
peculiar, and it might be thought that the vents from which
they came might have been identified by a similarity of
chemical composition. Nothing of the kind has yet been
possible. Geikie* gets over the difficulty by supposing
that they flowed from vents which are now buried under
later New Red deposits, and that the slopes on which some
of them rest are the consequence of earth movements sub-
sequent to their eruption.

But they are intimately associated with the breccias.
We have shown that these have most certainly come from
the Dartmoor direction, and that some at least of the hill
slopes were much as we find them to-day. The breccias must
have come down hill, and this is equally certain of the lavas.

* Ancient Volcanoes of Great Britain^ vol. ii, p« 99.

gi The History of Devonshire Scenery*

This direction of origin is well indicated by the distribu-
tion of some of the beds which lie very little above the lavas.

It has long been known that the deep red rocks of the
hills between Ide and Dunchideock are made of a kind of
marly material in which are found many large fragments of
a decomposed volcanic rock containing clear lumps and
crystals of quartz, quartz porphyry it is called. Fortu-
nately the making of the Exeter Railway involved two long
and fairly deep cuttings through these deposits. Before
the sides of these were smoothed down they presented an
extraordinary sight, being stuffed full of blocks, some
well rounded, and varying in size up to huge massed
weighing many tons, which had to be reduced by blasting*
Some were blocks of hard breccia, some may have been
derived from the dolerites and diorites of the Teign Valley,,
some from the waste of the Ide type lavas. But the
quartz porphyry blocks were most frequent, and apart from
the red colour of the matrix they might well have been
derived from the vein of quartz-containing granite pre-
viously mentioned, as dividing the coarse-grained granite
of Heltor, which is the nearest point of Dartmoor.

Similar, but smaller blocks, are to be traced here and
there towards Exeter, and in the brickfields on the north-
eastern side of the city the fragments are very numerous.
In Hancock's great pit, for example, we have a deep series
of marls marked by irregular horizontal bands of green, and
quite a large variety of decomposed volcanic boulders, which
are sometimes as large /as a man's head. Among them the
quartz porphyry is easily recognizable, and so are numerous
fragments which must have come from distant parts of the
stream of lava which forms Northemhay. Most of these
boulders have been much altered. The Northemhay, or
Pocombe type specimens, vary from bits whose origin
cannot be questioned, through a gradation of changes until
we get sometimes a chocolate-coloured block spotted with
white (the steam holes originally), which has been altered
into a smooth-grained stone as soft as prepared chalk. The
writer once marked a seJL of. examinations with a bit of this
in lieu of a. coloured pencil.

Photo by F.J. Collins.

Ide ctftting in cotsfse of construction, showing Quarts Porphyry Blocks.

Brccdat near Dawlish, showing sharp* angular fragments.
The lar^ block is about 9 inches cube.

Origin of the Exeter Lavas. 93

But the decomposition of the material is less important
than the identity of the quartz porphyry blocks, and their
diminution in size as we pass away from Dartmoor towards
the north-east, which clearly indicates this as the direction
in which they travelled. The stream of blocks also follows
the same line as the lava, which suggests that they were
swept down the same valley as that along which the lava
had previously flowed.

The Posbury stone is in places full of steam bubbles,
and in part of the quarry these may be seen to lie in strings
pointing away from the moor.

The trachytic types may either have come from a
similar point, or they may have flowed down the opposite
side of the deep Creedy valley from some point near
Tiverton or further north, as, for instance, the intrusive
dykes at Rose Ash.

In any case there is nothing in the least degree
unreasonable in supposing that the cones from which these
lavas came should have long since disappeared. The lavas
themselves have only been preserved by their burial under
later deposits, and the parts we see have not long been
exposed to view. Unless the cones should have been
similarly buried they could not have survived, and all we
could hope to find would be the pipes which fed them.

In the Teign Valley we have a number of intrusive
pipes. Some approximate to syenite, some to gabbro,
but, so far as is yet known, none of them reproduce the
peculiar characters of the lavas we are discussing.

It must, however, be borne in mind that the lavas have
undergone many chemical changes in consequence of exposure
to the weather, burial under other rocks, infiltration of water,
and so on. The Teign Valley pipes have been altered
also, but by a difiierent series of actions going on deep
under ground. Such intrusive pipes as there are must have
solidified far below the surface, and the originally formed
minerals may have difiered considerably from those in the
lavas they supplied.

The lavas of Pocombe and Ide must have been erupted
in a limpid condition, and on steep slopes such as we have

94 The History of Devonshif e Scenery*

supposed would have flowed many miles from their source,
just as the fluid lavas of Hawaii and of the Icelandic
volcanoes have been known to flow for distances of upwards
of 50 miles. It is possible, therefore, that the pipes we
want may really be some of those in the Teign Valley,
or we may find them further away in some of the intrusive
rocks of the Newton Abbot district.

Finally, it is even possible that the lavas may have
originated on Dartmoor itself. It is not at all unlikely
that an eruption of the elvan phase may have been attended
by the extrusion of quantities of acid lava, which would
not flow far, followed by fluid drawn from deeper zones
in the magma which would be less viscous, and therefore
flow to greater distances. If the present surface of the
granite at the spot where this occurred is below the part
then solid, no trace of cone or pipe could now be left.

However this may be, it is clear that the absence of
recognizable pipes is no contradiction to the proposition
we set out to prove, and the supposed absence of the
acid eruptive rocks is a false premise. On the other hand
we have a general accumulation of evidence all tending
to justify the view that Dartmoor is, in fact, the upper
part of the cooled lava reservoir which fed our Devonshire
volcanoes, that it rose to its present place in consequence
of the Post Carboniferous earth movements, and that it
was then and for some time after crowned, or fringed^
by active eruptive craters.

Fossil Salt Ciystals from the Red Marls*

Spongy Lava from under Southemhayt Exeter*

The large steam holes are filled with black manganese, the small ones

with a white mineral.

CHAPTER VIII.
The Salt Lake Period.

The Post Carboniferous breccias are not limited to Devon
and Somerset. They are found in several places in the
Midland district, from the Lickey Hills near Birmingham,
through North Staffordshire and North Worcestershire to
Shropshire and the borders of the coalfield of Flint. They
also occur on the coast of Cumberland and all along the
vale of Eden and on the northern side of the Solway Firth.
Generally they consist of fragments of local rocks which can
be identified, but the fragments have sometimes been carried
such long distances — up to 30 miles — that Ramsay and others
have supposed that they must have been carried by ice. But
torrential action such as we have described would be ample
for the purpose if we suppose that the hills from which they
came were then high enough to have their upper valleys
filled by glaciers ; and this same supposition also accounts
for all indications of ice action, without supposing a glacial
period.

These beds, as a whole, rest on the denuded edges of
carboniferous and older rocks just as they do in Devonshire,
and this is equally true of a different set of deposits which
lies on either side of the Pennine ridge. On the west, in
Lancashire, we find breccias and sandstones and a thin band
of magnesian limestone from 10 to 25 feet in thickness. On
the eastern side the breccias and sands and marls are thin,
and the magnesian limestone forms a massive deposit
reaching through the counties of Nottingham, Yorkshire
and Durham to the coast of the North Sea near Simderland.
In Durham it is from 500 to 600 feet thick, and often
weathers away in most curious patterns. Sometimes the
wasted surface resembles piles of marbles or cannon balls,
sometimes it looks like branches of elaborate corals. If,
however, one of these objects is broken open, it is seen to
to be built up either of concentric layers or to have a
radiated structure.

9^ The History of Devonshire Scenery*

We have already said that the breccias resemble those
now forming in arid regions where mountains look down on
desert lowlands. We have in the magnesian limestone and
its structure another indication of just such a climate. The
great salt lake of Utah and other saline sheets of water in
the same district are only the shrunken remnants of lakes
of far larger size which belonged to a prehistoric time. The
shores of these former lakes are fringed by deposits which
strongly resemble the magnesian limestone. They have been
formed not by the accumulation of calcareous remains of
animal life, nor indeed by the settlement of calcareous mud,
but by the deposit of material from solution in concentrated
salt water. Layer after layer was thus laid down, sometimes
around solid fragments of stone, sometimes around some
other nucleus, and in time spongy masses were built up
whose pores were subsequently filled in by a similar process.
Rocks of such a kind are said to be concretionary, and so
far as is known, they are only formed in land-locked lakes
or inland basins of drainage of the type seen from the
Caspian to Lake Balkash, or that which lies immediately
west of the Rocky Mountains.

In Germany the great salt deposits of Stassfurt, 1,200 feet
thick, lie among similar strata, and show that there, at
least, the climate must have been so dry as to completely
evaporate a large inland sea, and bring about the crystalli-
zation on a vast scale of other chemicals which on ex-
posure to ordinary damp air absorb so much moisture as to
dissolve.

The Post Carboniferous upheaval had clearly changed
the whole aspect of this part of the globe, by replacing the
abundant moisture and luxuriant forest swamps by an arid
desert. We see that we must picture England as fringed
by the denuded Caledonian mountain system on the north,
by lofty points and steep slopes on the west, where the
Lake district and Wales now lie, and a great new chain of
rugged ridges along the south. Meanwhile the Pennine
ridge projected into the plains, and its slopes on both sides
descended to the waters of a salt inland lake which existed
longest and was largest on the east.

Pcfinian and Ttias* 97

We have no evidence of a similar salt lake in Devon.
The sands and marls so closely related to our local breccias
do certainly appear to have been deposited in water, and
show every sign that the water was shallow and apt to be
disturbed by strong currents such as the torrential rushes
we have supposed. But these waters may have been fresh,
and the Devonshire lake may have drained northwards into
the Midland basin, carrying salt and other substances to
be deposited by evaporation mainly on the east of the
Pennine hills.

A further change followed. The beds we have described
are covered by another set, which in the Midlands consist
of a lower division consisting of red and mottled sandstones
with a central layer of well rolled pebbles, and an upper
division of paler sandstones and thick red and mottled
marls. This series is often found to lie with a distinct,
though slight, unconformity upon the older set. This is
one among many reasons which have led geologists to
separate the two into systems with different names; the
breccias and magnesian limestone series being called Per-
mian and being regarded as the topmost deposits of
Palaeozoic time, while the upper set are named the Trias
and are regarded as the earliest series of the Secondary
Era. A more important reason is afforded by their fossils.
Such as they are, those of the lower series of beds resemble
the forms contained in carboniferous rocks, while those of
the upper set are closely allied to those which follow in the
overlying series. This is a piece of evidence of which we
can see nothing in Devon, since the whole of the New Red
series is remarkably devoid of fossil contents.

The Triassic period is so called from the fact that in
Germany there is a middle division composed of fossiliferous
limestone, but this is completely absent in England, where
there are only two divisions called respectively from their
German representatives Bunter and Keuper.

Attempts have been made from time to time to sub-
divide the Devonshire red rocks in accordance with the
system which is applied to their Midland contemporaries.
But so far no convincing evidence has been adduced. It is

H

93 The History of Devonshire Scenery*

commonly held that the breccia series, with the Exeter
and Tiverton lavas, belongs to Permian time, but there
is no evident unconformity to show where this ends.
Mr. Ussher would draw the line provisionally above the
sandstones which lie immediately above the breccias.
Others place it at the base of the great pebble bed which
makes the ridge of Woodbury Common, which Mr. Ussher
considers to be a probable representative of the missing
limestones of Germany. The discussion is interesting to
the specialist, but is quite unimportant for the purposes
we have in view. The absence of the unconformity so
common in the districts further north is in no way remark-
able, and may be easily explained by supposing that Devon
was too near to the hardened and compressed axis of the
Hercynian chain to be affected by the last disturbances of
the tract which lay between it and the older chain.

Whatever their precise date, there is no doubt that the
red sands shown in the cliffs between Exmouth and Bud-
leigh Salterton were deposited in water. They were
irregularly laid down, and signs of the partial erosion of
one stratum before the next was formed are to be frequently
seen. They are interstratified with beds of red marl, which
show irregular bands of a pale green tint. Now and then,
when the blocks fallen from the cliffs split open along the
original planes of bedding, the surfaces are found to be
covered with markings exactly reproducing the sun cracks
formed on the surfaces of modem muds when dried, while
others show the ripple marks of a sandy beach. Clearly
the lake varied in the level of its waters. Deposits mark
the inflow of the rainy season, ripple marks and irregular
bedding a shallow water time, and sun cracks must mark
a rainless period, during which the lake shrank and left its
shelving shores to dry.

On reaching Budleigh Salterton we meet with a great
bed of well rounded pebbles, which can be traced from the
coast all along the Woodbury Common ridge and far inland.
It is admirably exposed in many places, where deep pits
have been excavated in order to get the pebbles. They are
used as a rough building stone to some extent, but their

The Bttdldgh Pebble Bed, 99

chief industrial use is for road metal. At Budleigh and
along the ridge for a dozen miles the pebbles are chiefly
of different kinds of hard quartzite, which is a greatly
hardened sandstone. Some of these, which have a lilac
tint, when broken open are found to contain numerous
fossils, and neither stone nor fossils can be matched in
Devon or Cornwall, or indeed anywhere on this side of
the Channel. Many of them, however, can be matched
from the hard grits of Brittany.

It seems, therefore, that these pebbles must have been
brought by a large river or by the action of waves either
from Brittany itself, or at least from some ridge of the old
Hercynian ranges which have already been shown to have
occupied the channel. Many of the pebbles are as large
as a man*s head, so the current which carried them must
have been one of considerable velocity, and must, at least
in the rainy season or when the mountain snows were
thawing, have been of great volume. It seems almost im-
possible that they should have actually crossed the Channel,
but pebbles of hard rock are carried long distances under
the conditions we have mentioned. They afford, therefore,
one more link in the chain of evidence which points to
mountains like the giants of the Alps lying not very far
south of our present coast. They indicate also that the
drainage of the chain was from south to north, a point
which is further shown by the facts that the stones are
largest at Budleigh and dwindle in size as we go north-
wards, and that the fossil bearing stones become fewer and
fewer in the same direction.

Reference has already been made to the division of the
Bunter series of the Midlands by a bed of pebbles. This
is made of equally well-worn stones, most of which can be
matched by rocks which lie to the west and north, the
same direction as that from which the materials of the local
Permian breccias came. The general contour of the coun-
try was therefore, similar, but the greater roundness of the
Bunter pebbles means, not necessarily a longer journey in
miles, but one which involved more knocking about on the
way, such as would result from a gentler slope. The breccia

TOO The History of Devonshire Scenery*

material must have been swept out of the valleys with
such force that all except the largest boulders were carried
almost in suspension, while the Bunter pebbles must have
been trundled along the bed of a fairly rapid river, or one
which became so in flood time. The reduction of cliflfs and
precipices to less abrupt slopes by the progress of denuda-
tion will explain the change.

But between the breccias and the pebble beds lie great
deposits of sand and marl, a fact which looks as if the two
coarse deposits mark two periods of violent floods, separ-
ated by a long interval, during which the torrents and
streams had been small and unable to carry anything coarser
than sand or mud.

It follows from this that the Budleigh pebble bed and
those of the Midlands must have been simultaneously formed.
They indicate a geographical change of such importance
that, unless each can be shown to be due to a local up-
heaval or some such cause, they can only be attributed to
climatic change such as would affect a wide district.

From this time onwards to the close of the Trias, a
great lake covered the whole region of the red rocks, and
from Budleigh Salterton eastwards, as far as the beds can
be traced, they abound in evidences of the saline character
of its waters, and the barren aspect of its shores.

From Budleigh Salterton there is a splendid coast walk
past Ladrum Bay to Sidmouth. The footpath follows the
cliffs most of the way, and although there are not many
spots where it is possible to climb down to the beach, many
fine sections can be seen from above. In Ladrum Bay itself
the sandstones are greatly false bedded, and calcareous con-
cretions of irregular form are common, though this feature
is better seen nearer to Sidmouth. At low water of spring
tides much of the coast can be visited, but it is a wise pre-
caution to have a boat within call, as there are many small
bays in which the water rises to the perpendicular cliffs.
Not far beyond High Peak there is a path down to the shore
which gives an excellent section of the marls which lie above
the sands. On reaching the beach, if we turn westwards and
examine the dark red sandstone rocks which form the point.

Base of Budkigh Pebble Bed resting on uneven stiHace of marL

Strings and veins of Gypsum in the Red Marls near Watchet.

The Red Cliffs of SidmoutIi« loi

we find they are in places almost breccias. The surfaces
are covered by a network of concretions of calcareous
material. Exactly similar things are to be seen at Otter-
ton Point on the eastern side of the mouth of the Otter.
Indeed, this section has even greater interest, being the
spot where Mr. Johnston Lavis found remains of an amphi-
bious animal known, from the structure of its teeth, as
Lahyrinthodon, and Dr. Carter noticed many traces of bones.

Moving on eastward the 500 feet of cliflf under Peak
Hill show the marls and sands to perfection. As we go, it
is well to break open some of the rounded nodules of red
or pale-green stone which lie here and there among the
rocks at the foot of the beach. Some of them are hollow,
and are found to be concretions lined with calcareous crys-
tals, generally gypsum.

Beyond Sidmouth, a few yards beyond the mouth of the
Sid, the sandstones end abruptly against a fault, and the
marls descend to the beach itself. It is a heavy pull to
walk over the pebbles along the coast to Branscombe, and
the section has a sameness which robs it of much of its
interest. All the way the cliffs are made of the same red
marl, streaked and spotted with pale green. The different
beds vary in texture, but, as a whole, the materials are
fine, and the bedding indicates fairly tranquil deposit.
Strings and layers of nodules of gypsum occur every here
and there, while the marls now and then show a curious
marking on the original surfaces of deposit. When split
open the surface shows a number of square pits, varying in
size, but averaging about a quarter, or a third, of an inch
across.

If the pits had been round, as they are in some instances
from the red marls of the Midlands, they would have been
formed by a shower of rain pattering down on the half -dry
mud. But square holes 1

Now in arid regions, such as we have compared with
Britain in Triassic time, we can see the explanation. Cubic
crystals of salt separate out from the wet mud as it dries
up, and when an influx of fresh water comes they are dis-
solved and the new mud fills the holes. The markings are

I02 The History of Devonshifc Scenery,

then fossil crystals of salt, and prove completely that the
waters were salt.

From Peak Hill eastward the red marls are seen to be
capped with beds of pale green grey sandstone and other
strata of a buff tint. As we go from Sidmouth to Brans-
combe these beds come lower and lower until at the land-
slip of Hooken Cliff they hide the red rocks completely.

These, however, reappear at the bathing cove of Seaton,
and form the shore line on to the greater landslip at Rousdon.
The pale beds which overlie them belong to a date far later
than the red marls and to conditions utterly different, which
will be described in their proper place. To confine our atten-
tion for the present, then, to the red marls, we can follow
them along under the Haven and Bindon Cliffs east of the
Axe. It is well to note that this piece of coast has been
in a very dangerous condition for several years. The pale
beds are porous, the red marls impervious, so a line of
springs issues along the junction, and the result is frequent
slips and falls of material, which build up sloping screes.
The stones which lie upon the beach are chiefly fragments
of the pale beds, but among them lie numerous concretions
of the same character as may be seen further west. They
are often filled with beautiful glittering crystals of gypsum.

The cliffs themselves show frequent little faults, and the
division of the deposit into distinct beds is clearly shown.
Some whole beds are green in colour, and as we near Culver-
hole, where the landslip reaches the sea, we find this pale
green hue becomes more and more frequent until we get
bed after bed of the same tint. These are known as the
tea green marls, and they are just the colour of the pale
green tea which used to be mixed with the ordinary black
variety.

They are overlaid by a thin black stratum which is not
easy to find. Its dark grains and particles fill up the cracked
surface of the underlying marl, and indicate a complete
change of conditions. The red and green marls may be
searched for years without yielding a fragment of a fossil,
but this thin black bed is full of little bright black points
which a pocket lens reveals to be the teeth and spines of

Blown Sands of the Midlands* 103

fish. Diligent search usually results in the discovery of
fragments of bones, and even unbroken specimens. This is
the famous bone bed, and it marks the beginning of the
end of the great salt lake.

The beds which lie above it alternate in colour, white,
grey, and buff beds, chiefly calcareous, are interspersed
among black shales, and the thin greenish marls rapidly dis-
appear. The whole series is full of fossils, and shows that
while the inhospitable character of the waters made a few
temporary returns, the region had now changed from an
almost lifeless waste to one teeming with living things.

In the Midlands and the North of England similar
rocks characterise the time, but the sands of the Bunter
division contain some beds in which the grains are like
fine round shot. Now this is not seen in modem sands
except where they have been blown about on the surface of a
desert. They are known as the Millet seed beds, and are
regarded as indicating a local drying up of part of the
great lake so that the sands were blown over its basin. It
is worth noting that some of the sandy beds which lie
just above the Heavitree breccias show a similar structure.

The water formed sandstones are often false bedded, and
their surfaces are frequently rippled. Here and there they
are indented by the footmarks of three-toed animals, tracks
of the labyrinthodon and reptiles of the time.

The marls show sun-cracks, rain pittings, and the fossil
salt crystals such as have been mentioned as occurring now
and then in the marls of Sidmouth.

The series of marls, known as the Keuper, contain
layers and nodules of gypsum far more extensive than any-
thing which can be seen in Devon. Indeed, we have only
to go to Watchet to see the same marls literally riddled
with layers and veins of gypsum, which is quarried from
the cliffs. Not fax from Cardiff it occurs in large blocks
of solid white or mottled crystalline stone, and the same
thing may be seen near Bristol.

Near Nottingham the gypsum deposits are thick enough
to yield large slabs of beautifully veined stone which is
then called Alabaster.

I04 The History of Drronsliife Scencir*

In Cheshire not only do we find gypsum in abundance,
but even beds of rock salt, which have been famous for
ages.

The Mendip Hills are surrounded by the red rocks.
They run up the present valleys showing that those
valleys, like some of the hills and vales of Devon, date
back to this distant time. But the Mendip red beds are
peculiar. They are coarse conglomerates in which many
of the pebbles are very little worn. They consist of pieces
of the Carboniferous limestone, and evidently at one time
they formed the beach and broken piles of fragments, fallen
from the limestone cliffs which stood up above the waters
in which the red deposit was formed. But this is not all.
Although there is no doubt that the fragments of stone
were Carboniferous limestone they have a different com-
position. They are now Dolomite, which is carbonate of
lime and magnesium. How is this to be explained? By
supposing that the waters, like those of the Dead Sea and
other salt lakes, contained a large quantity of compounds
of magnesium in solution. The same substances mixed
with salt will also explain the abundant deposits of gypsum,
for all river water contains carbonate and sulphate of lime
in solution. If, then, such water enters a salt lake of such
a character, the whole of the lime is precipitated in the
form of gypsum.

The proofs of the existence of the salt lake are then
conclusive enough to satisfy the most sceptical, and there
are probably few passages in the whole of geological history
which can be supported by so complete a chain of
evidence, or on which there is more perfect agreement
among geologists.

The next step is to ask whether we can explain a
state of physical geography so totally different from that
of the Carboniferous forests, and equally contrasted with
the times which followed.

The desert regions of to-day all owe their dryness to
one, or both, of two causes. Either they are surrounded by
lofty ranges of mountains, so that moisture-laden winds
have to cross these barriers before they can reach the

The Red Mark near Seaton ihowing green bands.

Cttlverhole, where the Sea Green Maris and Bone Bed reach the shore*

Causes of the Desert Climate* 105

inland basin, or they lie in a region where the winds are
persistent and blow from a cool sea on to a hotter land.

Suppose a country fenced in by heights. As the air
rises to surmount the obstacle it ascends into regions of
diminished pressure, with the result that clouds and rain
are produced. The air, deprived of this moisture, may be
further cooled by contact with the cold moors and glaciers
on the summits, so that it loses still more moisture. It then
descends, comes under greater pressure, is compressed and
heated in the process, and sweeps over the lowlands as a
hot and parching blast. So dry may such a wind be,
that the ancient Peruvians used to make mummies of their
dead by simply leaving the bodies to be dried by the winds
from the Cordilleras of the Andes.

An example of the second type of desert is afforded by
the Sahara. The prevailing wind blows from over the
comparatively cool waters of the Mediterranean on to the
warm soil of North Africa. It is, therefore, heated in the
process, and, unless this is counteracted by a rise over high
land, the air only becomes able to take up more moisture,
and so grows drier and drier, since the dryness of the air
does not depend on the quantity of moisture it contains, but
upon what fraction that is of the greatest quantity it could
contain at its particular temperature.

Now the great lake basin, which has been described, lay
in the angle between two mountain chains, by which it
was sheltered from all directions except the north-east, and
it is quite possible that other ranges parallel to the Pennine
ridge existed where the North Sea now lies. The lower
and older chajn in the north-west was probably still backed
by an extensive area of land, but however that may have
been, the ranges themselves would have been enough to
rob winds from that direction of much of their moisture.

The southern chain would be an effective barrier on the
south, and the two must have met somewhere south of
Ireland.

The region thus penned in was open, if open at all,
only towards a direction from which the winds would be
cool, and from which they would have travelled far over

io6 The History of Devonshire Scenery*

a continental land which extended northwards from the
Hart2 Mountains.

All this part of the world lies in a latitude where the
normal winds are more or less from the west. They may
have been varied by a seasonal change like the winds of
Manchuria and Southern Asia, but any rain-bearing wind
must come from the ocean, and at the time of the desert
climate this lay far away on the southern side of the
Hercynian chain.

It seems, then, that the dryness of Permian and
Triassic time was a necessary consequence of the geography.
The rainy seasons were produced by a seasonal occurrence
of warm winds from the southern sea, which brought brief
heavy rains, not only on the seaward slopes of the mountains,
but even on to their northern sides, just as the south-
west monsoon brings snow and rain on to the northern
slopes of the Himalayas.

During Permian and Bunter time these rains and snows
varied in frequency and amount. Some years they hardly
came at aU, while at other times the rivers descending
into the inland basin were large and swift.

But as time went on the mountain barrier was worn lower
and lower, and subsidence helped to make breaches in the
southern heights. The volume of the rivers increased and
the great lake spread further and further over the plains.

A large district comprising the British Islands, and a large
part of Western Europe must have slowly subsided until it
formed a region lower than the level of the ocean. The
desert conditions seem to have extended from Great Britain
to the Hartz, and from Sweden to the north of Spain,
but Western Germany, and the British area apparently
formed a single depression whose deepest hollows held the
salt lakes.

The great ocean lay over Switzerland and Eastern Europe,
and occupied a large part of what is now Asia.

Finally the breach opened wide, and in some time of
storm and high tide the waters of the sea broke through
the neck of land and rushed into the inland basin, carrying,
with them the living things with WHich the ocean swarmed.

The Ifniption of the Sea* 107

Now our Keuper Lake was so large that although it
was on the whole far Salter than the open sea, it is quite
possible that the saltness of its different gulfs varied as
much as is the case in the modern Caspian. This is
indicated by the occurrence of a few species of shells
and fish in the red marls of Warwickshire, which are
associated with remains of plants. Probably they lived
near the mouth of a large river which entered the lake from
the north-east, and were unable to spread into the Salter
waters elsewhere.

The bone bed is found not only in Britain, but also in
a similar position on top of the sediments of the salt lakes
of Hanover and Western Germany. There seems no rea-
sonable doubt that it marks the first irruption of the sea;
and it is usually explained as composed of the remains of the
animals which inhabited the lake, and which were unable
to survive in the fresher sea water. But it seems much
more reasonable to assume that the fish and other creatures,
which must have been killed in millions, were really those
brought in with the ocean water and poisoned by the salt
and bitter fluid with which it mixed. This is indicated
very plainly by the fact that the remains are almost en-
tirely those of animals which would swim freely in the
water, or which might have been swept from the shores by
the invading flood.

The first irruption would be brief, but, as subsidence
went on another and another would follow, until at last
the salt lake of Keuper times became only a great arm
of the sea like the Baltic or the Persian Gulf, and the
silent shores of the great Dead Sea awoke to a new world
and new forms of life.

CHAPTER IX.
The Age of Reptiles-

The geographical revolution ivhich closed the Triassic
period was hardly less important than the great upheaval
of early Permian times. Although the earth movements
which produced it were comparatively trifling, their effect
was to bring about a complete change of climate, and so
to utterly alter the aspect of the country. Instead of an
arid desert, with salt and bitter lakes, in which few creatures
lived, the land was covered with forests ; rivers and streams
came tumbling down the slopes ; and the long sheet of
water which covered a considerable part of the British area
had become a great arm of the ocean, swarming with living
things.

The change was not brought about suddenly. When
the sea first entered the inland basin, and the rainfall became
abundant, the whole region must have been covered by
the debris due to desert erosion. If we read a description
of the Sahara, or the great Asiatic desert^ we can form an
idea of the state in which the country must have been.
Accumulations of desert-blown sand and dust must have
filled up many of the valleys, and great screes of broken
rubbish must have strewn the slopes.

When the climate changed, these deposits must have
rapidly crumbled away, filling the streams with a heavy load
of mud. The desert soil, when properly watered, must have
been rapidly covered with luxuriant vegetation, which would
help further disintegration ; and would also, by reducing the
compounds of iron change the colour of the muds to shades
of green or black. Large districts must have been com-
posed of disintegrated coal measures, while many of the
higher hills and peaks were crags of Carboniferous Limestone,
and over the Channel the heights of the western part of
the Hercynian chain were made of Devonian sandstones,
grits;, and limestone.

It is only in the extreme east of Devon that we can
now see anything of the sediments which formed under

CulTcrhok and Cliarton Bay* 109

these new conditions, so, if we would know the story of the
country during the time, we must go to this eastern end,
and must also go much further afield.

The grey green marls which end the deposits of the
Keuper Lake have already been described as showing them-
selves with their bone bed cap at Culverhole, under the
Bindon Cliffs. This is just at the beginning of the great
landslip, and the exact order of the overlying beds is not
clearly seen. But a few yards further east there is a low
cliff of blue black shales, covered by some impure cream-
coloured limestones. Both are fossiliferous, and the black
shales are, in places, almost made up of broken shells, or rather
of layers of mud shewing the impressions of shells which
have themselves disappeared.

A better section is afforded by the cliffs in Charton Bay,
just beyond the spot where the private road from Rousdon
reaches the shore. Here the upper part of the Trias is well
shown in the cliffs. The beds are bent into a low arch, or
anticline, so, as we move eastwards, higher beds come
down to the beach. Above the low cliff the land slopes up,
terrace upon terrace, and if we clamber up them we can
see a fine section of the upper beds. Black and dark grey
shales alternate with thin seams of impure limestone, which
get whiter and more frequent as we get higher in the series,
xmtil we reach a group of pale cream-coloured limestones
which are separated from each other only by thin layers of
white or pale grey marl. These are the White Lias, as
they have long been called, and they mark the end of the
transition period.

From the bone bed to the top of the White Lias we
have the local representatives of a series which is known as
the Rhaetic beds. They form a good example of what are
known as passage beds, which means that they were formed
in a time of rapid geographical change, and are a connecting
link between two much more extensive series formed under
more stable climatic conditions. Below them we have the
Trias, with its record of long continued desert conditions ;
above them we have the Lias, with its tale of the narrow
seas and exuberant life.

no The History of Devooshire Sceoefy*

Still higher up the cli£f slopes, above the bay, vre meet
with the lower part of the Blue Lias, with its beds of blue
grey clay and shale and thin bedded grey limestone.

The name Lias is supposed to have been derived from
the way in which the quarrymen have been in the habit
of pronouncing the word layers, a descriptive name for the
kind of stone. Lias limestone has long been worked, both
as a building stone and for the making of lime. For the
latter purpose it has certain special advantages. It burns
white, giving a white lime which sets into concrete and
plaster almost as well as Portland Cement, and it is a
frequent stipulation in building contracts that no lime but
Lias lime may be used.

There is a disused road track from the Rousdon Water-
works, which slopes gradually down to the shore at Charton
Bay. Here we can see the Lower Lias, and first meet
with abundant traces of its rich variety of fossils. We can
see also, very well, the characteristic arrangement of the
deposits in alternating layers of shaly clay and limestone.

In some places where large blocks of the shale have
partly dried, they split up on exposure to the weather into
thin sheets which suggest the idea of sheets of thick paper
or rotten millboard. They are well-known as the paper
shales, and of course the sheets are the separate laminae^
each plane of division marking a brief pause in deposition.

To see the Lias to the best advantage, we must go just
over the county border into Dorset and descend to the
shore at Pinhay Bay. Here, at low water, we can find
the same black fossiliferous shales laid bare upon the beach»
In the base of the cliff we have the white Lias, and form-
ing the cliff all the way to Lyme Regis there is a splendid
section of the Lower Lias.

Along the shore, embedded in the rocky ledges, we can
see frequent examples of a great Nautilus, Ammonites of
various sizes up to two feet or more in diameter, various
other molluscs, pieces of fossil drift wood, and now and
then the bones and vertebrae of great Saurians.

Beyond Lyme, along the coast towards Charmouth, the
same, and still higher, beds of the same great series may be

The Vett Cliff, Lyme Regit.

The Church Cliffs, Lyme Regis.

Ljtac Regis and its Ammonites m

seen. The Church CliflFs, just east of Lyme, probably give
the most typical section of the limestone layers. Further
east the clays become more and more predominant,
until the limestones are comparatively few and far between.
Indeed, although the limestones are best known from their
commercial value, the Lias as a whole is a great clay for-
mation, and the sea in which it was deposited must have
been generally muddy.

Exactly similar rocks are to be seen on the coasts of
the Bristol Channel, and in some places near Watchet fossils
are much more easily found than they are at Lyme. Be-
ginners in geology who are in the acute fossil hunting stage
are generally disappointed on first visiting the Dorset coast.
The fossils have to be looked for carefully. But here and
there on the coast of the Bristol Channel they are to be
seen by the hundred. Again, the Lyme Regis fossils are
often embedded in the hard limestone, from which it is by
no .means easy to free them, while near Watchet they are
shown on the surfaces of the shales, and may be easily
secured.

It is in the Lias that we first, in Britain, meet with
the order of Ammonites, fossils which are a joy to the be-
ginner from their abundance and beauty, and also to the
specialist, who, revelling in the minute distinctions between
their dilBferent species and genera, changes their names every
few years. This pastime of the specialist is at the same time
the despair of the student, who finds himself face to face with
the necessity of re-learning the generic names periodically.
To the field geologist, who need not trouble himself about
names, they are an invaluable guide to the age of almost
any secondary rock; for it is probable that in the whole
range of marine organisms no other order can compare
with the Ammonites for mutability. Genus after genus, and
species after species, seems to have come into existence,
to have rapidly multiplied, and then to have disappeared
for ever, while its place was taken by some diflferent form.

For instance, while the bottom beds of the Blue Lias
were being formed, the sea swarmed wiih one Ammonite*
whose specific name is Planorbe or Planorbis. Its place

112 The Hiftory of Devonshife Sceoefy*

was then taken by another called Angulaius^ and it in turn
gave way to a third which is known as Bucklandi. We
therefore speak of the Planorbis Zone, the Bucklandi Zone,
and so forth; and when we find Planorbis in Pinhay Bay,
we know that the beds in which it occurs are of the same
age as those between Blue Anchor and Watchet, in which
Planorbis may be seen in thousands.

The whole of the Lias is thus divided up into seventeen
zones, each named after its typical fossil. In later deposits
of the Mesozoic or Secondary Era other orders are pressed
into service for a similar purpose, and we shall meet with
several examples later on.

In Liassic time the dominant forms of life were reptiles,
and, while some were not unlike a modern representative of
the class, there were large numbers of others of the most
extraordinary types. Best known among these is the
Ichthyosaurus, a voracious carnivorous creature, which had
the body of a porpoise, provided with a great vertical tail
and four powerful paddles in place of the ordinary reptilian
limbs. A powerful swimmer, it must have caught its prey
by sheer speed, and its great jaws and teeth showed that it
lived on large animals. Next in order of familiarity was
the Plesiosaurus. It also was adapted for a marine life,
but it had a long thin neck which was probably as stiff as
that of a giraffe, its paddles were of a feebler build, and in
its habits it was probably a vegetable feeder.

But most remarkable of all were the Pterodactyles. Their
front limbs were greatly modified, so that they served to
support long membranous wings, by which the creatures
flew from place to place like birds. Most of them were
small in Liassic time, and they probably fed on the insects,
dragon-flies and beetles, etc., whose remains are often found
entombed along with the bones of the Pterodactyles.

Truly the world must have been a strange place, and
if space allowed it would be easy to write whole chapters
on its Liassic inhabitants, but although these creatures were
some of them Devonians, they were but a passing phase
of life, the population of the country for a time, and they
are briefly mentioned only as indicating the kind of climate.

Ideal Restoration of Liassic Geography.

Liassic Geography* 113

Full descriptions of the fossils and excellent restorations of
their living forms must be sought elsewhere.*

The Liassic Sea, we remember, was formed by the
admission of the open waters to the inland basin by a gentle
subsidence in a south-eastern direction, towards Germany.
The question then presents itself as to how far it extended
over the British area, and what part did the Liassic clays
and limestones play in modifying the pre-existent scenery.

If reference is made to the ideal map of the red breccia
periodt the Permian lakes will be seen occupying the lowest
parts of the inland basin. From the southern lake long
valleys run westward over central Devon, between Exmoor
and the Quantocks, and along the Bristol Channel. Low-
lands are found in the English midlands, over the Irish Sea
and Antrim, and stretching northwards along the North
Channel and the western Isles of Scotland. Here the plains
are part of the basin of Lake Caledonia, and a little further
north they expand again over the basin of Lake Lome.

Now as the waters of the Keuper Lake rose higher, they
spread further and further over these flatter districts, and
the probable margin of the water can be easily traced.
Mr. Jukes-Browne has shownj that the Keuper Lake extended
far beyond the limits of the Permian sheets of water, and
that two detached lakes lay in the northern basin which
were probably fresh. One of these occupied part of the
site of the Old Red Sandstone Lake Orcadie, while the other
lay where the Minch is now.

It has already been said that the influx of ocean water
was to a great extent brought about by a subsidence of
part of the long Hercynian chain. This is shown by the
distribution of Liassic rocks in Europe, and in attempting
a geographical restoration, we must represent this by sup-
posing that the eastern end of the English Channel became
filled with water. It seems likely, however, that some of
the ranges of hills would still project as long narrow islands.

* Extinct Monsters, by Hutchinson, and Dragons of the Air, by
H. G. Seeley.
t Page 62.
t Building of the British Isles, p. 130.

I

114 The History of Devonsfilre Scenerr*

The shore line all along the Eastern counties is exceed-
ingly problematical, and the same is true of the line east of
Yorkshire. There is no doubt however that it was not
very far away, from the frequent occurence of plant remains.

The main arm of the sea extended over Cheshire and
Lancashire, over the basin of the Irish Sea, and far up the
western shores of Scotland. Gulfs extended almost around
the Cumbrian mountains, which stood out as a hilly promon-
tory, others ran up the Clyde far enough to cover the Isle
of Arran, and over the islands of Skye, Mull, and Raasay, and
finally up the Minch, and along the line of the Caledonian
Canal into the basin of Lake Orcadie.

It is interesting to note how the old structural features
dating from the Protozoic upheaval, again asserted them-
selves after so vast a lapse of time. The basin of the
southern Lake Caledonia seems only to have been refilled in
its south-western part : probably because the p)ortion which
extended across Scotland was blocked by the products of the
Volcanic episodes of Carboniferous and Permian time.

The western shore extended along the border counties of
England and Wales, and it is not likely that it ever extended
many miles further west than the Permian breccias. They
were certainly accumulated at the feet of steep slopes and
many of them were most likely mountain screes rising steeply
out of the water of the lakes. When the level rose with the
progress of Triassic time it is not likely that the water made
much advance into the mountain regions of Wales and Devon
except that it would run a little further up the valleys,
forming long narrow lochs. The same must have been
true of the Liassic Sea. Quite a moderate rise of level
might well account for such changes as we have described,
and a change of a hundred feet or so would n6t greatly
alter the coastline of a mountainous shore.

It is certain however that the lower Lias did extend up
the valley of the Bristol Channel, and it is probable,
therefore, that it also extended up the valley of central
Devon, but we have nothing left to suggest its former
presence above the breccias. There is one piece of
evidence which points to a westward extension further

Ofigin of Lias Limestones* 115

south, and that is an observation by Mr. R. N. Worth,
of Liassic fragments in an ancient gravel near Plymouth,*
but if we picture the probable contours of the country it
seems more likely that these fragments came from some
southern fjord of the Liassic Sea than from the north, and
it is thus suggested in our ideal restoration.

The Liassic limestones are themselves rather puzzling,
and their mode of occurrence is especially difficult to under-
stand. The Silurian limestones were evidently due to
organic accumulations in clear water. The Devonian lime-
stones we have also attributed to the agency of corals and
other reef building organisms. The massive limestones of
Carboniferous times were again mainly organic. What
then about the Lias? Does each thin band of limestone
mean clear water, and the growth of calcareous organisms ?
If so, we should expect such beds to dwindle away as we
approach the ancient shores, and should look for evidence
of an organic origin in the stone itself. As a matter of
fact, the limestones become more prominent as we near the old
shore, and the beds give very scanty indication of an organic
origin. We are forced to the conclusion that the Lias lime-
stones are formed from calcareous mud derived from the wide
extent of Carboniferous and Devonian limestone, which was
certainly laid bare upon the hills and mountains around.

But this conclusion by no means ends the difficulty.
If we look at the Church Cliflfs of Lyme, and consider
their regular alternations, we may well ask why the mud
should sometimes have been nearly all calcareous, and why
at other times it should have been ordinary clay; and
again, does the alternation record mere oscillations of weather
according to the seasons, or do the recurrent changes point
to the sun spot cycle, or some other periodic change ?
These are questions which cannot be answered with any
confidence, though we may make suggestions that they are due
to changes of rainfall, and that most likely the limestone
mud came when certain rivers were in flood, the ordinary
muds when others were full.

♦ Qnarl Jour, GcoU Soc, 1889, p. 401.

ii6 The History of Devonshifc Scenery*

Important as the Lias is» it formed only the first phase
in a long series of changes. We find that the great clay
deposits are covered by an equally large and important
series of cream-coloured limestones which abound in proofs
of their organic origin. These are the lower or Bath
Oolites, which may be studied all along the district from
Bath to Cheltenham, and across England to the Yorkshire
coast. For some reason or another the muds were shut oflf
from the greater part of the sea floor, which became covered
with banks of shells and coral reefs, and layers of calca-
reous sand and mud derived from their waste.

The change is so rapid that it looks as if some earth
movements must have come into play, which lessened the
declivities down which the rivers flowed, and probably also
resulted into converting some parts of their valleys into
lakes where their mud could be dropped, leaving the water
as clear as that of the Rhone when it issues from the lake
of Geneva. If we suppose that the great western continent
began to subside at this time, we have the explanation we
want, especially if we remember that there was little or no
change in the coastline of Devon and Wales. The amount
of subsidence necessary would be small, for apart from the
suddeness with which the final change took place we should
expect that the quantity of mud available for deposit
would rapidly lessen as the covering of loose decomposed
materials formed in the desert period was denuded away,
and the harder solid rock brought next the soil.

The northern parts of the Liassic basin became the
sites of estuarine deposits, and in Yorkshire even seams of
coal were formed over swamps, which were probably the
delta of a large river coming from the east, or north-
east.

Somewhat similar evidences of a lessening of the sea are to
be found on the West of Scotland and in the Midlands, while,
on the contrary, under London the Oolites spread over the
Devonian ridges which had stood up above the waves of
the Liassic Sea, and a similar overlap on to older rocks
may be found at the eastern end of the Mendips close to
Frome.

Corals and Clays of the Oolites* 117

At present the most western bits of the lower Oolites
are at Ilminster, Crewkerne, Beaminster, and Bridport, but
although they do not at any of those places bear any signs
of a special approach to land, there is no reason for sup-
posing that they ever extended far into Devon. If they
did they have been totally removed, and the only part they
can have borne in the building of our scenery must have
been a temporary delay in the waste of the underlying
rocks.

Again the sea deepened, the rivers became laden with
mud, and the shell-strewn coral reefs were buried in a great
clay deposit called the Oxford clay, which spread over the
whole region once occupied by the Liassic Sea, except, per-
haps, its south-western borders. It is well shown in the
dark blue clays close to Weymouth, where it may be
easily seen and its fossil contents compared with those
of the Lyme Regis cliffs.

This is again overlaid by massive coral banks which
must have swarmed with sea urchins and shell fish. Evi-
dently the clear water conditions had returned, and the
modified descendants of the sea creatures, which had built
up the Bath Oolites, returned to the haunts of their fore-
fathers. The Corallian series, as it is called from the
multitude of corals, is fairly thick in Dorset, but grows
thinner northwards by Oxford and then thickens again in
Yorkshire, an early indication of the formation of a ridge
which would later on separate the south-eastern sea from
that of the Yorkshire coast. This is another example of
the long persistence of a physical feature, for it really
dates back at least to that partial division of the carboni-
ferous sea by a midland ridge to which we referred in an
earlier chapter.* The clearance, however, was only for a
time. The Corallian series is covered in turn by yet another
great clay deposit known as the Kimeridge clay, which ex-
tends from Dorsetshire to Yorkshire.

This is a formation of great interest, and probably marks
the period at which this part of the world possessed

•Page 43.

ii8 TIic History of Deronshite Scenery*

a richer variety of reptilian life than at any other. Ichthyo-
saursy Plesiosaurs, and Pterodactyles were abundant, and
their remains are mixed with those of Tortoises, Crocodiles,
and many representatives of a group called the Deinosaurs.
This last included some of the most uncanny, and some of
the largest animals which ever trod the earth. Some of
them were herbivorous, others carnivorous. Some went on
all fours, while others used the forelegs only for holding or
fighting, being in the habit of getting about by walking
on the hinder pair.

The oscillations of the whole region which brought the
alternations from clay to coral and back again to clay were
beginning to near their end. The Kimeridge clay does not
cover the whole basin of the Lias Sea, but is very thick
at its eastern end, where a boring put down in Sussex
passed through it for i,ooo feet. The earth movements had
not ceased, they had changed into a general uplift of the
northern and western parts of Britain, accompanied by a
steady shift of the coast-line towards the south-east.

The rivers which had flowed from the north western
continent into the marine gulf of earlier Jurassic time now
had to find their way across the gentle undulating plains
laid bare by the retreat of the sea; and for a time they
discharged themselves into a steadily shrinking region over
the counties of Dorsetshire and Wiltshire.

In the shallow seas a series of sands and limestones were
formed, somewhat resembling the Bath Oolite, but greyer
in colour. Some of them are the excellent building stone
so largely quarried at Portland, while others are entirely
built of shells, or of the calcareous mud in which they were
embedded. One great bed is very curious ; it is known in
Portland as the " Roach," and lies just above the best stone,
so that, although it can only be used for rough building
purposes, it has to be quarried away to get at the under
layer. Evidently a vast accumulation of shells had gathered
on the sea floor, and all the interstices between and within
them had been filled in with calcareous mud. Then, for
some strange reason, the whole of the original shells were
dissolved away, leaving perfect hollow casts of their external

Portland and Ptffbeck Limestones* 119

form, and in each hollow an equally perfect cast of the shell's
interior. The Cobb at Lyme is built of this stone, and its
peculiar structure may be seen there, though, of course,
it can be better studied at Portland.

These shallow water marine beds could not accumulate
greatly without still further diminishing the area of sea. Shell
banks arose above the water, and the river-borne materials
helped to fill in the deeper parts, until the open water was
pushed further and further south and east.

Where the shallows became low lying islands soils were
formed upon them, and the forests spread from the neigh-
bouring shores. In the pools between these islets sands
and mud and beds of limestone composed of freshwater shells
accumulated. Then came a further small subsidence and
inroad of the sea, only to be followed by a second silting
up of the whole district.

Thus it was that the Kimeridge clay was covered by
the Portland series, and it in turn by the mixed freshwater,
estuarine and marine beds of the Purbeck time, so called
from their development in the isle of Purbeck.

Some of these fresh-water limestones are full of the
remains of insects, some of them are entirely composed of
shells of genera whose modern representatives are only
found in fresh water. For instance, the so-called Purbeck
Marble is a hard limestone, wholly made of little snail-shells
of a fresh-water genus Paludina. The stone takes a high
polish, and the "figure" of its markings is due to the
sections of the shells. Excellent examples may be seen in
the slender shafts which make the great pillars of Exeter
Cathedral.

The old soils are particularly interesting. In some of
the Portland quarries one of two of the Purbeck "dirt
beds " lie above the stone, and in the course of the quarry-
ing operations extensive areas of dirt bed are sometimes
uncovered. When this is the case it is possible to walk
on the ancient land surface, to see the stumps of the forest
trees (now completely converted into silica) in the position
of growth, with their roots branching downwards into the
soil. Other broken bits of the fallen trees lie about half

I20 The Ipstoty of Deronshire Scenery*

buried in the soil, and though there is no vestige of woody
material left, the minutest details of its structure are pre-
served in the stony substance by which it has been replaced.

The Purbeck beds give us the last glimpses of the re-
treating sea, and at length it was pushed almost away from
Britain, leaving only a narrow area from Swanage to
Sussex, which formed a hollow which was rapidly silting up.

Here the Purbeck limestone series passes gradually up-
wards into a great mass of sands and clays which are all
of fresh water origin. An important change had taken
place somewhat gradually, and is indicated by the deposit
of the coarser detrital material on top of the locally formed
shell banks. The carrying power of the rivers had been
increased by a further uplift of their upper reaches, where-
by the slopes down which they flowed were made a little
steeper.

A great river discharged itself not far from the position
of the Isle of Wight, and at low water, on the western
coast, the local guides point out a " submerged forest." It
is nothing of the sort, but is a vast raft of tangled tree
trunks which was stranded on the shallows of the river
delta after some violent flood, just as we find similar rafts
borne down the great rivers of to-day.

Sandy beds full of Paludinae occur, and detached bits
of driftwood, fossil ferns, and other plants, and bones of some
of the great Deinosaurs are characteristic of the whole
deposit.

Beds of this character spread over the area of the Weald
of Kent and Sussex, so the period is often spoken of as the
Wealden. The cliffs of Hastings give fine sections of some
of its beds, and at low water, when the original surfaces
of the strata are laid bare, it is no uncommon thing to find
the huge footprints of Deinosaurs, showing the tracks they
made as they wandered over the sandy flats and shallows
in search of food. One footprint, a cast of which shows the
wrinkles on the creature's skin, is preserved in the Hastings
Museum. It measures about twenty inches in length.

It is a question whether the Wealden deposits are a
delta such as that of the Mississippi, or whether they are

Erosion during Jurassic Time* 121

not more probably river-borne deposits collected in a large
lake. But this is a matter which has little bearing on our
main purpose, which is to trace the changes of time in
their bearing on our western shires.

In this brief account of Liassic and Jurassic days we
have seen the coast line pushed far away from the western
hills until they stood up far away in the interior of a great
continent. It is almost certain that the English Channel
was represented between Devon and Brittany only by the
valley of a river or rivers flowing eastwards. Indeed, the
drainage system of the whole region was probably towards
the south-east, though we have no evidence to show how
far further west lay the edge of any possible Atlantic.

Devon had all this time been undergoing the wear and
tear of time. When we consider the vast quantity of sand
and mud which must have been required to make up the
Bunter sands, the Keuper marls, the clays and limestones
of the Lias, and the great deposits of the Oxford and
Kimeridge clay, and then reflect that this had all been
worn away from the neighbouring land, it becomes evident
that a vast amount of erosion must have taken place.

What wonder, then, that we have felt justified in speaking
of Dartmoor in Permian days as lying far above the present
surface. And the whole length of Jurassic time was only
a small step from then to now.

Here, then, we may picture our western hills as moun-
tain summits overlooking a wide plain which stretched east-
wards to the Solent and beyond. Across this plain great
rivers wended their slow courses to the distant swamps,
meandering through jungles and forests something like those
in the best watered parts of tropical Australia, for the vege-
tation of the time and even some of the animals were not
very much unlike those of the great island continent to-day ;
for in spite of the huge reptiles, which have long vanished^
the world was beginning to assume a guise far nearer to its
present state. Many of its simpler organisms, and even some
of its higher plants and animals, were beginning to resemble
those which we now can find pushed away into the far
comers of the world.

CHAPTER .X.
The Return of the Sea.

We have no means by which we can estimate, except
by the roughest comparisons, the lapse of time during any
geological period. We cannot say, therefore, for how many
years the rivers of Southern Britain flowed into the Wealden
Lake. All we can feel certain about is that their number
would be expressed by many figures.

The broad plains left dry, as the waves retreated during
the closing phases of Jurassic time, must have been acted
on, like any other country, by the streams which crossed
them. Wherever the Keuper marls, or any part of the great
clay deposits formed the surface, erosion must have been rapid
and the valleys must have opened wide, forming a landscape
of gentle slopes and level stretches. Where, on the other
hand, the harder limestones came to the surface, the rivers
would have deepened their channels faster than the valley
slopes were worn away, with the result of deep valleys
flanked by steep slopes such as those we find round Bath
and Bristol at the present day.

The western edges of the limestones must then have
formed lines of hills as they do now, but these escarpments,
as they would be called, must have been further west than
the modern hills. Moreover, as the drainage of the whole
country was certainly towards the south and east, we can
picture a great river following the line of the Liassic Sea,
and gathering together as its tributaries those which had
flowed from the western and northern highlands. Others
further south flowed from the mountains of Wales and
Devon, and probably from further west, perhaps even so
far as Ireland, and these, in following up the retreating
shore, must have cut across ridge after ridge.

The fact that the upraised bed of the old inland sea was
thus necessarily converted into an undulating country, with
lines of hills at difierent heights and with varying slopes, is
a point which will have to be remembered later on.

The Lower Greensand* 123

It is also well to point out that nothing which we have
yet mentioned in the history of Jurassic time would have
been likely to alter substantially the lines of mountain and
valley in any part of the western districts. They would still
be those mapped out during the post -carboniferous upheaval,
only slightly modified here and there by volcanic outpourings,
and by the slow changes due to river erosion.

During the continental period the newer sediments were
from time to time shaken by earthquakes, and the rocks were
traversed by lines of fracture accompanied by vertical move-
ments. But such changes do not often result in any marked
alteration in the geography of the country affected. Some-
times they modify some of the minor features of the drainage
system, but their results are soon smoothed away, unless
they are much more considerable than any disturbance which
can be shown to have affected the rocks during Jurassic and
Wealden times. That they did occur can be clearly seen
in the frequent faults which cut through the Jurassic and
earlier strata and do not penetrate those which lie aboVe.
Many of these can be seen in the Keuper marls of the
Devonshire coast. They are probably due to the slow shrink-
ing and consolidation of the underlying materials, and are
quite a different thing from the thrusts and flexures caused
by the throes of mountain building.

However long the continental period may have been, at
length its end was reached, and a wide-spread subsidence set
in, accompanied by a steady return of the open sea. Every-
where where the top of the Wealden can be seen, it passes
upwards into a great series of sands and clays which con-
tain abundant marine organisms. Some of these beds are
dark green in colour, from the presence of large quantities
of a deep green mineral called Glauconite. These green
sands are sometimes so conspicuous that they have given
the name of Lower Greensand to the whole series. The
name is unfortunate, as the bulk of the deposits are
coloured shades of yellow and brown, the distinct green hue
being restricted to a few beds.

The Lower Greensand may be studied very well in the
Isle of Wight, either in the coast southwards from Shanklin,

124 The History of Devonshire Scenery*

or at the south-western comer of the island, by Blackgang
Chine.

Its beds may be seen also all round the Weald of Kent
and Sussex, where they form a line of lofty wooded hills
standing out in front of the smooth rounded heights of the
North and South Downs.

The change having been due to a subsidence, it naturally
follows that the marine Lower Greensand spreads over a
larger area than the underlying Wealden. At present it
does not extend further west than the Isle of Purbeck, and
northwards it reaches into Berkshire, where it assumes a
peculiar shore-like form. Its beds are there filled with
fragments and pebbles of Jurassic rocks, mixed with shells
and fossil sponges in such a way as to show that it
consists partly of the debris of the old land made by the
waves as they advanced.

Step by step the general change of level continued, and
we find the Lower Greensand buried under a formation
which, in the south-east of England is a thick clay, so fine
grained that many of its fossils still show their pearly
lustre, like some of the Ammonites of the Lower Lias clays
of Blue Anchor,

No doubt the old Jurassic clays were being used over
again after yet another process of disintegration and decay.

As this south-eastern clay, called the Gault, is traced
across the country towards the west, its character changes.
Sandy particles become mixed with it. They become more
and more numerous, and when we enter Devon it is all sandy.

High up the terraced slopes of Black Venn, near Lyme
Regis, the Gault clay is represented by a few feet of dark
greenish grey stuff, half sand, half clay, in which badly pre-
served fossils are numerous. The new Survey Map shews
it again in the cutting at the eastern end of the Honiton
tunnel, and exactly similar material, causing a patch of
marshy ground and the outbursts of springs, occurs at
the foot of the White Cliff, by the bathing cove at Seaton,
and in several places in the Axmouth landslip.

• Now the fact that it occurs only here and there over
these western counties is highly suggestive. If present in

The Gault Clay in East Devon* 125

the Honiton cutting why does it not occur in many places
in the neighbourhood. There are miles and miles around
where the underlying and overlying rocks are to be seen,
but, so far, it is only in the one spot that any representative
of the Gault clay has been identified. Everywhere else it
is apparently missed out.

At Black Venn the Gault lies on the eroded surface
of the Lower Lias ; at the Honiton cutting it is on a similarly
worn surface of Triassic Marl. At Seaton the dark sandy
clay also reposes on denuded Triassic Marl.

The explanation is doubtless to be found in the fact that
the surface upon which it rests is the old land surface.

We have pointed out that this must have been diversified
by hill and dale, and as the sea advanced, unless that
advance was so exceedingly slow that the waves could
entirely plane away all projections (which is almost out of
the question), it must have flowed up the valleys first. From
them it would rise gradually over the intervening water-
sheds, and when it had finally overtopped them the contour
of its bottom would still preserve a sort of fainter copy of
the contours of the submerged land.

If then we suppose that in such places as the Honiton
tunnel, and possibly the White Cliflf of Seaton, we have
relics of a submerged valley, we have a complete solution
of the mystery, for the Gault clay of one place is but the
deeper water representative of the sandy clay of other places
where the depth was less, or of the sands still nearer shore.

The Gault clay is in turn generally overlaid by a series
of sands and Chert beds, which, as a whole, are much paler
in colour than the Lower Greensand, but exhibit a green
tinge in some of the beds. This is commonly known as
the Upper Greensand.

A fine typical section of the whole formation as it is
found in the east of Devon may be seen in the White
Cliff at Seaton.

If we go westwards from the town along the path under
the cliffs we get a fine view of the general structure of
the section. On reaching the corner it is well to follow
the path as it ascends to the road. On reaching this there

126 The History of Dcvoosbitc Scenery*

is a sharp turn to the left, which leads in a few yards to
the cliffy where there is a seat looking down on the bathing
cove. Here we command a splendid view of the details of
the Greensand.

The base of the cliff is a dark sandy clay which makes
a patch of wet ground thickly clothed with reeds, mare's
tails and moss. Above this is a much thicker stratum of
greenish sands which make a moderate slope covered here
and there with small potato fields. The face of the cliff
then becomes vertical, and is formed of greenish sands cut
up into layers of about two or three feet in thickness by
broken lines of harder stone locally known as cowstones.
These stand out from the rest and fall down to the beach
as the softer intervening sand is worn away. In our illus-
tration of Culverhole the great majority of the large flattish
stones with which the beach is covered are wave-worn
cowstones.

Above these there is a stratum of yellow sand capped
by rusty weathered cherts which, when seen from a distance
stand out very conspicuously as a ruddy band. This is
the bottom part of a great series of chert beds separated
by rather thin bands of sand. The part of the cliff where
they form the face is very rough and rugged. The soft
intervening sands are worn away by frost, and rain, and
wind, while the hard cherts stand out as projecting shelves
on which seagulls and jackdaws make their nests.

The Cherts are covered by a thin band of very bright
green sand. It cannot be well distinguished in the main
section of the cliff, but is best identified by clambering over
the rocks below till we get near to the point which forms
the eastern end of Beer Cove. Here the top of the green-
sand comes down to the beach, and its uppermost beds
may be studied in detail.

The green and yellowish sands below the cherts are
commonly known as the Foxmould.

The same strata are exposed in the cliffs all along the
great landslips from the Haven Cliff on the eastern side of
the Axe to Lyme Regis, and they may be examined in the
broken fragments of the underclifF, or on the beach. In the

We&tetn Limit of the Gfeensand* 127

Haven Cliif and along the shore to Culverhole, they may
be seen resting on an eroded surface of the Keuper marls,
which show numbers of small faults and undulations, not
one of which passes up into the Greensand beds above.

At the Landslip the Greensand rests on the Rhaetics
and near Rousdon on the Lias.

If we go westward from Seaton, we find the whole series
dips down out of sight under Beer. But it reappears on
the other side of Beer Head and can be followed in a long
stretch of magnificent sections through the Branscombe
potato fields, under Hooken Cliff, and, resting always on
the Keuper marls, all along the coast to Sidmouth, rising
higher and higher above the beach as we go along the
shore.

After passing Sidmouth we can still trace it forming the
the cap of Peak Hill and High Peak, and underlying the
surface beds of all the greater hills. The Woodbury
Common ridge does not seem to have any Greensand beds
in their original position, but there are extensive patches of
gravels whose lower portions contain Greensand fossils in
such a condition as to show that they cannot have travelled
far, so we may be sure that the formation which they
characterise capped that ridge also, in the days when the
gravel was formed.

If we cross the broad valley of the Exe, and climb up
the slopes of Haldon, we soon come upon the Greensand
beds again. They crop out once more on the western face
of the hill, high on the flank of the valley of the Teign,
but here is the end. The greater heights of Dartmoor
show no vestige of any former coat of Greensand, and it
is impossible to suppose that if the chert beds had ever
extended over it every trace of such an enduring rock
could have been cleared away.

The Greensand sea must have ended over what is now
the valley of the Teign.

The same beds can be traced all along the Haldon
ridge, but with the exception of a few isolated patches far
to the west, which suggest that a long fjord ran westwards
along the line of the Crediton valley, and which we should

128 The History of Devonshife Sccneir*

expect to find there, we have to turn eastward again to
the Blackdown Hills before we can follow them northwards.

All over these hills the Lias and Trias are capped by
a layer of Greensand, and along its western outcrop it as-
sumes a peculiar form.

Some of the sandy beds contained numerous fine grained
concretionary lumps which harden on exposure to the
air and made excellent scythe stones. They were formerly
the object of a considerable industry. Tunnels were driven
in along the right layers, and great heaps of material were
dug out and now lie in white scree-like slopes just below
the crest of the hills.

Quanfities of fossils were thus found, many of them
beautifully preserved, and all marked by the fact that the
calcareous matter has been wholly removed and its place
taken by silica. This is noticeable also in the fossils from
Haldon, and indeed generally from the Greensand of Devon.

The Blackdown beds and their fossils have been well
described by the Rev. W. Downes,* whose collection of
fossils may now be seen in the Museum at Exeter.

It is enough for us here to say that the species of
shells, and the condition in which they are found, all point
to shallow water and to a near approach to land.

Among the cherts and the harder sandstone beds, the
spicules of fiinty sponges are to be seen in immense abun-
dance, so much that it is evident that the chert beds are
to a great extent made up from the fusion together of
such spicules.

The glauconite grains which give the greenish tinge to
some of the beds are worth examining. Under a pocket
lens they seem to be rounded grains of sand, but under the
microscope they are to be recognised as the internal casts
of the shells of foraminifera. It is interesting to know that
precisely similar grains are now being formed oflf the coasts
of Georgia and South Carolina, by the deposition of the
green mineral inside minute calcareous skeletons, and in the
interstices of shells.

* Quart, Jour. Gcol. Soc,, 1882, p. 75.

-I

3
£1

Appfoach of the Atkatk* 129

The Upper Greensand extends all across England from
Haldon to Yorkshire, varying a good deal in its texture and
even in its materials. It has long been a subject for dis-
cussion as to how far it may strictly be regarded as a mere
shallower water representative of the Gault clays. It is now
generally agreed that to a great extent this is the case, at
least in its lower portions, while some of its uppermost
beds may very well represent other deeper water deposits
which we shail meet with later on.

We have already pointed out that the country on the
western shores of the old Liassic sea must still have pre-
served its main features. We have now shown that the Upper
Greensand sea in Devon reached much the same limits. It
is only reasonable therefore to suppose that its coast extended
some way up the valley of the Bristol Channel and then
curved eastward round the border hills and through Mon-
mouth. From this point it crossed the old sea basin in a
north-easterly direction to the eastern flank of the Pennine
range, and thence followed the contours of the country to
the coast of Yorkshire or Northumberland.

Now the Upper Greensand is a very dififerent formation
from the underlying Gault clay and Lower Greensands. Still
more marked is the contrast between the Chert beds and
the Foxmould. The latter is made largely, though not
wholly, of land derived materials, whereas the Chert beds
suggest a fairly clear sea into which no considerable rivers
can have poured the waste of the land.

Here is a problem which evidently needs solution, and
the most probable answer is that it was during Upper
Greensand time that the Atlantic began to make inroads
on the north-western continent, and worked northwards along
our western coasts. This would mean that many of the
rivers which had flowed into the Liassic Sea and had after-
wards found their way to the Wealden Lake, were now
turned westwards and carried their sand and mud into the
western sea, while perhaps others were shortened by the
deflection of their upper waters along the channel of some
western tributary whose slope had been reversed.

K

I30 Tli« History of Devonshifc Sceaery*

When Gault and Greensand are traced eastwards across
England they are found to pass into a red calcareous deposit
called the red chalk. It is well shown in the cliffs of Hun-
stanton in Norfolk. As they are traced towards Dover the
clay gradually forms a larger and larger portion of the
whole, until at Folkestone the sands are represented only
in the bottom beds.

These facts again need explanation, and a fairly satis-
factory one is easily suggested.

When the waves of the sea beat upon a shore they
remove its materials and spread them over the sea floor in
the neighbourhood. The finer mud is carried far out to sea,
while the coarser sand soon settles to the bottom. If there
should happen to be a strong tidal current, or any other
current, along the shore, the mud will be picked up and
carried away by it, and if this mud has a peculiar colour
the drift of the current must be marked out upon the sea
bottom beneath.

It is only necessary to stand on the cliffs near Sidmouth,
or the Church Cliffs at Lyme, when there is a heavy surf
beating against their base, to see the propess in full progress*
The water for some distance out will be seen to be turbid
with mud, forming a red fringe at Sidmouth and a grey one
at Lyme.

Another fact of some importance may be seen at the
Warren at the mouth of the £xe. This is an accumulation
of sand, which extends from the western bank of the estuary
and projects eastwards beyond Exmouth.

Now the source from which this sand is derived is cer-
tainly, in the main, the neighbouring cliffs; and the dimi-
nution of the size of the Warren in recent years is most
probably to be traced to the building of the Great Western
Railway walls along the foot of the cliffs most of the way
to Teignmouth, whereby the supply of sand has been
lessened.

The grains of sand when taken from the cliffs are deep
red in colour and are often sharply angular. But that which
is taken from the Warren is rounder and has very little
red, resembling in colour some of the red cliff sand

Sources of Greensand Materials* 131

which has undergone a long boiling in acid. It seems
that the jostling of the grains upon the shore, and possibly
to some extent the chemical action of the salts in solution,
removes the skin of iron rust which colours them, rounds off
their edges and even extracts the red stain from their cracks.

If, now, we picture the waves advancing over the old
land, we can see that a very large part of the Gault clays
may have come from wave action on the older clays of
Jurassic and Liassic time; that the red chalk of Norfolk
and Lincolnshire owes its redness to a similar erosion of
Triassic Marls; and finally that the sands of the Upper
Greensand are to a large extent the old Bunter and Permian
sands ground down and cleaned, and mixed with the green
ocean-formed grains of glauconite.

When at last the waves had reached the hard rocks
forming the flanks of the ancient mountains, these supplies
would be cut off, and the only fine mud and sand brought
into the sea would have been that brought by the streams ;
a scanty contribution which was often insignificant in com-
parison with the layers of sponge spicules from myriads of
siliceous sponges with which the water swarmed. Then the
chert beds would be produced, but they would only appear
as cherty concretions in places where the river-borne or
wave-brought material was more abundant.

We should thus expect to find the sea floor of the time
covered with red mud in one place, green sand in another,
while chert might be slowly forming as siliceous mud else-
where ; and all might be modified in special places by river
borne detritus. It is easy then to explain the great local
variation of deposit.

In Devon the upper layers of sand must have been derived
partly from the Permian breccias, partly from the red sands
of Exmouth, but also from the debris of the Devonian hills
of North and South Devon and the volcanic piles of the
Dartmoor district. Wave action and rivers must both have
contributed their quota, but during much of the time the
water was clear.

While the Upper Greensand was forming over the British
area a wide open ocean extended eastwards through Europe

13^ Tlic Histofy of Derooshire Scenery*

and Asia, and unless there may have been a land mass
where the Pacific now lies, it must have formed a girdle
round the earth. Our own Upper Greensand sea was a
northern gulf opening towards the east.

Now if we remember that the tidal wave in the ocean
travels from east to west, and that the ebb and flow and
other tidal movements are always greatest in gulfs which
open wide to meet it and narrow towards their extremity, we
see that our local waters must have been the site of consider-
able disturbance. We should expect, therefore, to find
symptoms of local erosion and signs of strong currents
here and there, and feel no surprise, therefore, when they
are pointed out. There are numerous spots where Greensand
or Gault can be shown to have experienced local erosion
or rearrangement of exactly the kind which would be brought
about by strong movements due to the tides. These currents
would also explain the concentration of the fine red chalky
mud in one district, while the sands accumulated not far
away.

We can, then, with confidence picture the Devonshire
area as lying on the eastern coast line of a considerable
extent of land which still comprised the district which lies
south of Ireland, and west of Cornwall, and extended north-
wards and southwards for some hundreds of miles. Dart-
moor was still partly covered with its volcanic mantle, and
the Exmoor heights still raised their heads into lofty points.
The great hills plunged steeply down into the waters of a
clear sea, clearer even than that which washes the coast of
Cornwall now.

Long fjords and gulfs ran westward into the land, flanked
by hard rock and paved with white sand or naked rock, while
the tide ebbed and flowed even more rapidly than it does to-
day on the shores of the Bristol Channel.

Great Saurians still wandered along the shores, and wide-
winged Pterosaurs sailed through the air, some of them
having a width of wing of 20 feet and more. But mixed
with these descendants of the Liassic reptiles were other
creatures which were more direct forerunners of those which
were yet to come.

Life of the Greenland* 133

Strange feathered birds flitted through the forests or
waded in the shallows. Birds with toothed jaws, but other-
wise resembling those we might find to-day. The forests
which clothed the hills had also assumed an aspect not much
unlike the present. Trees like our oaks, willows, and mag-
nolias flourished from Europe to places now bi within the
Arctic circle, a fact which seems to show that the climates
of the world in those distant days must have been con-
siderably warmer than they are at present.

But the Greensand was only the earlier phase of a period
which reached its full development later on, a period marked
off from all others in Britain and France by the formation
of the unique deposit which makes the white cliffs of Albion,
and from which the whole time from the Wealden till the
next great change took place has been named the Cretaceous
period. We mean the chalk.

CHAPTER XL
The Chalk.

Once more let us wend our way to Seaton, and the
beautiful cliff scenery of Eastern Devon. If possible, let it be
early in the year, in April when the primroses are in bloom, or
in May when the cliffs of Beer are purple with the blossoms
of the wild sea stock, at any rate before the sunshine has
reached its full power, for we shall want to clamber about the
slopes of fallen debris, fully exposed to the noonday sun.

Let us start from the White Cliff where we saw the
complete section of our local Greensand topped by the rugged
chert beds and the line of green sand; but this time our
attention must be turned to the upper part of the cliff, which
is formed of the lower portion of the Devonshire Chalk.

Next above the belt of green sand there comes a band,
only a few feet thick, of a cream-coloured limestone, full of
fossils, and containing large numbers of rounded grains of
quartz sand. It is sometimes called the Chalk with quartz
grains, but is now more often known as the Cenomanian
limestone.

Above this is a mass of hard chalk, full of harder lumps
which contain grains of glauconite. It is often stained with
yellow compounds of iron and is not always easy to distinguish
at a distance from the underlying limestone.

This hard nodular chalk is covered by a much thicker and
less massive series of beds, consisting of soft white chalk
divided by lines of flints, and, here and there, narrow seams of
marly chalk which are hollowed out by the weather. It extends
to the loftiest point of the clifi.

Let us now take the footpath along the top of the cliff and
follow it over the hill to Beer. As we go along, if we look
eastwards, we can see the line of cliffs across the bay, with
their base of Keuper marls and Rhaetics, the upper surface of
which rises and falls in gentle curves, while the overlying
Greensand and the Cherts and Chalk which cap the whole lie
smooth and undisturbed. If the day is clear we can make out
Culverhole and the great landslip, while Golden Cap and the

I

The Chalk of Beet Cliffs* 135

Dorset coast may be seen on the horizon stretching eastwards
to the faint grey line of Portland.

As we move downward into Beer we pass close by a great
buttress of chalk called Annis' Knob. It is worth careful
study. The rock is stufifed full of harder nodules which stand
out on the surfaces exposed to the weather; but it is white
chalk, very different from that which lies next above t^
Cenomanian limestone, and it is distinguished alsp by the
presence of innumerable flints, often arranged in lines. ,

If we follow the path to the shelter just above the C^ove,
where the main path turns to the right towards the village, we
find a track leading eastwards down to the beach. A few yards
down this slope we come again upon the soft white <^alk with
its lines of flints, and as we look along the face of the cliff we
cannot help noticing that some of them lie in regularly spaced
black layers.

Low down the cliff there is an almost continuous layer of
flint which lies at the base of a white band of flintless chalk, as
if all its proper share of flinty matter had been concentrated at
its base. This band is about 2 feet thick. Higher up are two
equally conspicuous lines about 3^ feet apart, and just above
them is a similar band free from flints which is about 4 feet
thick. Dr. Arthur Rowe and Mr. C. Davies Sherborne, who
have made an exhaustive study of the Chalk, make use of
these bands in their paper on the district,"' and we shall have
occasion to refer to them later on as the 2 ft. and 4 ft. bands.

By walking along the beach, still towards the eastern point,
we see the flint lines rising higher and higher, while stratum
after stratum comes into view above the pebbles, until, when
we get within a few yards of the point, the hard nodular chalk
without flints makes it appearance.

The point itself is made of this hard chalk, and it forms the
lower projection, which in turn is continued seaward by
a reef, which is the top of the Greensand with a capping of
Cenomanian limestone.

If the tide is low enough the top of the Cherts is laid bare
below the pebbles, and we can see that its beds dip gently down

""Froc, Geol. Ass.^ Vol. XVIII, p. i., et seq.

136 The History of Devooslufe Sceaery*

towards the sea and to the centre of the Cove. It. is possible
also to walk through a low natural arch drilled through the top
of the Greensand and covered by the limestone and its
superincumbent hard chalk, and on emerging on the eastern
side we find ourselves at the foot of a vertical clifif which gives
a most perfect section of the different beds. The chert layers,
black and brown in colour, rise up gently^ and they, and their
related sands, can be studied in detail.

Returning to Beer Cove, and crossing to its western side, we
find the same flooring of cherts rising out of the sea and again
covered by the same beds in the same order. There is, however,
one difference. The Cenomanian limestone does not rest on
a greem sand, but on a brown layer. Moreover, in the corner of
the Cove, on each side of a pile of fallen blocks of nodular
chalk, the Greensand forms the base of the cliff, and it is seen
to be either false bedded on rather a large scale, or else the
Cenomanian limestone lies on an eroded surface. There is one
place where the limestone projects a foot or so beyond the
crumbling surface of the sand, and its under side can be seen to
be full of fossils. Indeed it is evidently mainly composed of
the shells of ammonites and other organisms, mixed up with
calcareous mud, and grains of quartz sand; while it rests upon
what look like the eroded edges of layers of ruddy brown sand,
with numbers of green glauconite grains throughout their
mass.

All along the line of cli£fis which run out towards Beer
Head we can trace the same divisions. There is a shelf of
waveworn Greensand projecting firom the base of the cliff, and
above it lie the limestone, flintless chalk, and white chalk, in
their proper order, and the same lines of flints can be followed
winding as parallel markings from point to point.

On the western side of Beer Head the same divisions are
to be traced, but if measurements are taken of the thickness
of each they will be found to differ considerably from those
taken at the White Cliff. But more important changes soon
become evident. The great cliff under the Coastguard station
on Beer Common gives another fine section. It is known as
Hooken Cliff, while the slipped portion which broke away from
the main mass in the year 1789 is called Under Hooken.

Beer Cove: Cenomanian Limestone on Greensand.

Beer Cove: Cenomanian Limestone on eroded Greensand.

Hooken Cliff and Under Hooken.

Hooken Cliff and Under Hooken. 137

There is a beautiful walk here along the sloping undercliff
through the little fields where early young potatoes are raised
in quantities. Tall pinnacles of fallen blocks stand out above
the greensward of Under Hooken, and in these we can
examine the different beds at our leisure, while Hooken Cliff
itself gives a diagram of the whole. All the beds shown at
Beer are to be made out eadly. There is the Cenomanian
limestone lying just below the black entrance to some old
quarry workings which have been cut into the hard flintless
chalk, and above these are the same strong lines of flint with
their bands of marly chalk. The 2 foot band is rather more
than half way up the cliff, while the 4 foot band frequently
disappears under the grass of the slopes which come down
from the top.

If we follow the path which leads westwards through Under
Hooken, it brings us down almost to the beach. Here we
come to a stile, and just beyond is a short sloping track to the
shingle. But the main path keeps on by the top of the low cliff
winding along by the potato fields. About a hundred yards
brings us to a large mass of rock perched on the edge above
the shore, and the path winds on its landward side. This is
Martin's Rock and if we turn and look at the inland cliff, which
towers above us, we can make out an important change. The
2 foot band of flintless chalk rests almost immediately upon
the Greensand.

The Cenomanian limestone, then the hard nodular chalk,
and then the lower part of the flinty chalk have thinned out and
disappeared. We have before us a sandbank of the sea in
which those beds were laid down. We say a sandbank, for the
disappearance is only local, as the missing beds reappear on the
other side of the Branscombe Valley, capping the loftier hills
for some miles further.

In the last chapter the Greensand was followed past Sid-
mouth and Woodbury Common to its end on the Haldon Hills.
Did the Chalk ever extend so far 7 None can be seen, but in its
stead these western heights are covered with a thick sheet of
flinty rubble, and every road round Exeter shows great heaps of
flints which have been brought from Haldon. Some of them
are more or less rounded as if they had been rolled about, either

138 The History of Deronsiiife Scenery^

by the waves upon a coast, or by a river, but many of them
are as sharply rough and angular as if they had just fallen from
the cliffs of Beer, or the Hooken. Evidently the Chalk, as we
see it in these places, once reached wherever the Greensand
extended, but in the times which followed it has been removed,
and only the hard enduring flints remain. There will be more
to be said about these deposits later on.

Flint debris is also known here and there up the Crediton
fjotdy pebbles of it are found on the Cornish coast, and it is
said that angular flints may be dredged from the sea bottom
off" the Lizard Point.

The whole of the Blackdown Hills are capped by deposits
like those on Haldon, and flint pebbles are common in the
valley gravels by the Culm, but according to the Rev. W.
Downes they are wholly absent from the gravels of the Exe
above its junction with its eastern tributary.

If we travel eastwards from Devon we find the Chalk
extending, through Dorset and the Isle of Wight, all the
way to the coast of Kent ; forming the expanse of Salisbury
Plain, the long lines of the Berkshire Downs, the North and
South Downs on either side of the Weald, and extending
northwards by the Chiltern and Gog Magog Hills to the
white cliff's of Flamborough Head in the north, and to Nor-
wich in the east.

This is not its limit. There is a kind of chalk in Antrim,
where it rests on eroded surfaces of Liassic and Rhaetic
beds ; and other patches are found in the Isles of Mull and
Arran, and elsewhere on the west coast of Scotland. These
outlying bits are particularly interesting, as they show that the
Chalk once reached at least as far as the distant shore lines of
the Liassic Sea. From the intervening districts it has been
removed, but in Antrim and Mull bits of it have been pre-
served under some floods of lava poured out at a later date,
while in Arran we ascertain its former presence from a
number of great fragments which fell with the underlying
Jurassic rocks into an ancient volcano of the same age as
the lava flows.

The Chalk sea evidently extended further than the Green-
sand, and marks a greater submergence, so great in fact that

Zones of the Lower Chalk* 139

all the south-eastern part of England was submerged, and the
water penetrated far into the western and northern land.

In the south-eastern parts of England it is divided into
three sections, Lower, Middle and Upper. The Lower Chalk
contains a considerable quantity of marl. Its bottom beds
contain glauconite, and are called the Chloritic Marl. These
are followed by the Chalk Marl, as it is called, which contains
a considerable proportion of muddy material, and this again
by a grey chalk, the total thickness shown in the cliffs of
Kent being about 200 feet.

Now the whole of this Lower Chalk is rich in fossils,
ammonites, sea urchins, and others. Each sub-division has
its own particular assemblage, but throughout the greater
part certain ammonites are frequently found. Two of these
may be named here which belong to the genus Acanthoceras,
namely, Manielli and Rothomagense^ and another which rejoices
in the name of Schlombachia varians. These beds are therefore
known as the zone of these ammonites, and they are covered by
another zone in which a belemnite called Actinocamax plmus
occurs. All these zones are grouped together in Devon into
the few feet of the Cenomanian limestone, a fact which shows
how slowly it must have formed.

Indeed if we couple this fact with the eroded Greensand
surface upon which it lies we cannot avoid the conclusion that
while the sea was deep and still over Kent, it was shallower,
and disturbed by rapid currents or other movements further
west, so that fine mud, whether calcareous or otherwise, could
only collect where sheltered in banks of shells which were
themselves too heavy to be carried away to the deeper water
in the east. The result was that deposits 200 feet thick in the
neighbourhood of Folkestone are only 2 feet 6 inches in
Pinhay Cliffs, about 14 feet at Beer Head and 24 feet at
Hooken Cliff.

It is, however, to be noticed that the chert beds of the
Greensand show an entirely opposite change. They become
thicker and thicker as we move westward, and it becomes a
question whether they do not, at least in part, represent the
shallower water deposits contemporaneous with some of the
Lower Chalk. We ought, if this were the case, to find at

I40 The Hlstonr cf DewoDMbixe Scenery*

least some of the ammonites, which were free swimming
creatures, entombed among the Cherts. But so far no
identity of zone has been made out, while the fossils are so
crowded in parts of the Cenomanian limestone that the
writer once extracted from a single block of a few cubic feet
from an exposure at the Seaton Golf Links, a nautilus, four
different ammonites, and several other fossils. Almost equal
richness may be seen in some of the blocks which lie on the
beach under Hooken Cliff.

These geographical changes in the Lower Chalk are clearly
given in a paper by Messrs. Jukes Browne and W. Hill* which
is called a " Delimitation of the Cenomanian." It deserves to
be carefully studied.

Passing upwards in the Kentish series the lower and impure
beds are followed by a massive formation of fairly pure chalk.
Its lowest bed is hard and gritty, and is made up of minute
fragments of shells. This rests upon a surface which often
looks as if it had been slightly eroded, and either a considerable
lapse of time, or some important geographical change, is shown
by a complete disappearance of most of the fossils, so abundant
in the lower series, and the incoming of a different assemblage.

Above this basement bed comes a deposit, not far short of
200 feet in thickness,of soft white flintless rock made of crumbled
fragments of shells and especially vast quantities of the skeletons
of Foraminifera. It shades upwards into a similar deposit,
which is cut up by lines of black flints much like the lines
we can see at Beer. The whole series, including its gritty
basement bed was formerly known as the '* Chalk without
flints," but it is now recognised as the Middle Chalk.

It, in turn, is covered by a still thicker soft white powdery
deposit containing numerous flints, which are generally arranged
along the lines of deposit. This Upper Chalk was formerly
described as the '' Chalk with flints" and was supposed to be a
tolerably continuous deposit. Mr Whitaker, however, has
shown that it contains certain layers which have distinctive
features, and MM. H6bert and Barrels, as the result of their
study of the similar strata round Paris, showed that it can be

• Quart. Jour. Geol, Soc.^ 1896, p. 99, et seq.

Beef Qiffs: Looking Ea&tward.

ICey showing Zones, &c.
A. Annis' Knob. P. Path from Seaton. PP. Path from Beer.

1. Top of Cherts.

2. Cenomanian Limestone.

3. Zone of R. Cuvieri,

a, 2 ft. band.

4. Zone of T. Lata.

5. Zone of H. Planus.

6. Zone of M. Cor-test.

b, 4 ft band.

Zones of the Middle Chatb 141

divided up into zones by its fossil contents, and that its beds
show traces of temporary erosion every here and there. One
of these is seen in the I^e of Thanet, and in other places, as a
hardened surface with rolled nodules of chalk coated with
glauconite particles. It marks the limit between one assemblage
of fossils and another.

This description of the Chalk in the south-eastern counties,
where it is best developed, is enough to show that the task of
determining which portions are represented by our Devonshire
deposits is by no means an easy one. Indeed, as long as the
subdivisions were based on the character of the rock itself the
feat could not be performed at all satisfactorily. Thanks,
however, to the divisions into zones, we can now go a long
way towards solving the problem.

It has already been said that the thin stratum we have
called the Cenomanian limestone actually represents a group
of beds which in Kent measure about 200 feet.

The Middle Chalk of the south-east has been divided into
three zones. The lowest is characterised by the frequent
occurrence of a small brachiopod shell called Rhynconclla
Cuvieri. This zone has been identified at Beer by Dr. Rowe
and Mr. Sherborne* as the hard nodular stratum between the
top of the Cenomanian limestone and the first flint line above.
It is 100 feet thick in Sussex, but near Seaton it rapidly
thins away to 20 feet at Beer, and disappears altogether just
beyond Hooken Cliff, to re-appear about a mile further west.
The next zone is characterised by another brachiopod, a
beautiful little shell, less than a quarter of an inch across,
which may be found in thousands at Beer and the Hooken
Cliff. In Dr. Rowe's paper, and all but the very latest literature
of the subject, it figures as Terebrainlina gracilis^ but the
powers which determine such things now say it should be
called Terebraiulina lata. This stratum measures 170 feet
in Sussex, 89 feet at Beer, and then thickens to 156 feet so
close as Hooken Cliff. It will be remembered that all the
cliff above the lowest zone is full of flints at Beer, but in

* "The Zones of the White Chalk." Proc GeoL Ass., Vol. XVIII.,
p.l,ctscq.

14^ The History of Devonsliire Scenery*

Sussex the flints do not come in until the next zone is
reached.

The top of the Middle Chalk consists of the zone of HclasUr
planus^ a particular species of sea-urchin which makes its
appearance in some abundance. This zone is about 60 feet
thick at Beer, and extends from the top of the main cliff,
along the eastern part of the cove to a line about half-
way up Annis' Knob. In Sussex this zone is only 48 feet
thick.

The upper part of Annis' Knob shows a part of the zone of
another sea urchin called Micraster cor-Ustudinarium^ and is
the local equivalent of a zone which measures over 100 feet in
Sussex. The same zone forms about 50 feet of the top of
the Pinhay Chalk Cliffs, and these are the only representa-
tives in Devon of the whole of the Upper Chalk.

Now the Sussex cliffs show a thickness of nearly 550 feet
of chalk higher up than the top of Pinhay Cliff'; and an
interesting problem at once presents itself.

We can see that all over Devonshire, wherever there is
Chalk or Greeensand, these deposits are covered with flint
gravels and rubble, much like that which has been described
as lying on the Greensand of Haldon. It has also been
pointed out that these rubble deposits consist partly of sharp
angular flints which cannot have been brought from a dis-
tance, but which must have been simply dropped into
position by the removal of the Chalk.

Similar removal is even now going on all over the Chalk
districts. Rain water percolates through the soil and dis-
solves some of the products of vegetable decomposition, such
as carbonic acid and humic acid. When it comes into
contact with the Chalk, it dissolves a little and then
Alters away. The soil thus steadily descends, slowly and
irregularly. But the insoluble flints remain.

Now is it possible that a sheet of Chalk more than 500 feet
in thickness once extended over Devon, and that the whole of
this has been removed except its flints ? We have no means
by which we can answer this with absolute certainty, but we
have one clue which throws at least some light upon it. The
fossils of the Chalk are not restricted to its calcareous portions.

*^^gjl^ w

Zone Fossils from Beer and Seaton.

A. Schloenbachia Varians

B. Acanthoceras Mantelli

C. Rhynconella Cuvieri

D. Terebratulina Lata

E. Micraster Cor-te«:tiidinariuni

F. Holaster Planus

% natural size.

%

Zones of the Upper Chalk* 143

The flints are often formed around some organism such as a
sea-urchin, a shell, or a sponge, and in such a case the fossil
consists, not of carbonate of lime, but of flint, as hard and
enduring as its matrix.

The Haldon flints contain numbers of such relics. The
stone breakers know them well as cockles, gipsies' crowns, and
such fancy names, and a little use of the silver hammer will
easily secure them.

The missing zones, in ascending order, are the zone of
Micraster cor-anguinuMy an urchin much like cor-iestudinariutn
the zone of MarsupiUs UstudinariuSy a creature something
like the feather stars of to-day; and finally the zone of
Actinocatnax qiiadratus a particular species of the family of
Belemnites, which were not very different from our
modem squids and cuttle fishes. Of these zone fossils the
Micraster is abundant in the flints, and a few plates of the
Marsupites have been found. The Exeter Museum has several
specimens from Haldon and another was found by Mr. F. G.
Collins on Beer Common.

It is evident, therefore that these two zones did once extend
over Devon, but there does not appear to be any record of the
Belemnite, or any of the fossils associated with it in the
Norwich Chalk, which is the highest known in England. This
is, of course, only negative evidence ; but, as the sequel will
show, the Chalk period was ended by an upheaval of much the
same character as the submergence. It is likely, therefore, that
the western districts would first emerge from the waters, and
that the upper zones should be either absent, or thin, or
represented by shore materials.

This leads us to a consideration of the conditions under
which the Chalk was formed.

We have nothing exactly like it now collecting. The
nearest resemblance is the Globigerina ooze of the North
Atlantic, which dries into a pale grey deposit not unlike the
grey chalk, or some of the marly seams which have been
mentioned. The Atlantic ooze contains a percentage of silica
which is absent from pure Chalk ; but that absence is fully
accounted for if we suppose that the siliceous matter is
concentrated into the flints. The great point of resemblance

144 The Hbtorr of Deroosbife Scenery*

is the fact that both are composed very largely of the skeletons
and fragments of skeletons of Foraminifera.

The Globigerina ooze is a deep-sea deposit, and it has
been generally concluded that the Chalk must have been
formed under similar conditions. But the accumulation of
Foraminiferal skeletons is not due to depth at alL Indeed the
depth is rather a preventative, because it helps the solution
and corrosion of the calcareous shells. The essentials for the
rapid gathering of such a deposit are a warm surface
temperature, so that the tiny organisms can flourish freely,
and an absence of land derived material to obscure their remains.

The Lower Chalk contains many signs of contemporaneous
erosion, and the Cenomanian deposits of Somerset and Devon
are studded not only with well rounded grains of sand, but
contain even rounded quartz pebbles. These facts both point
to shallows, sandbanks, or even shingle, so near that the
pebbles could be rolled along, either by powerful tidal
currents or by the disturbance due to waves.

The disappearance of the lower beds at Hooken Cliff is the
strongest argument of the kind. Here is a spot which must
have been a sandbank while Chalk was forming close by.

Rapid changes in the thickness of the different zones, such
as are recorded in Dr. Rowe's paper on the Devon coast, are
also quite inconsistent with the idea of a deep sea, but fit in
admirably with the notion of a comparatively shallow one, into
which scarcely any land derived mud could ever come, and
whose floor, every here and there, rose near enough to the
surface to be affected by its movements.

When dealing with the chert beds of the Greensand they
were explained as pointing to clear water in which siliceous
sponges flourished in prodigious abundance, till the sea was
paved with a mud formed of their spicules. Into this sea from
time to time came an influx of sand. Sometimes the sandy
layer was thick enough to wholly hide the sponge deposits.
At other times the two became mixed, and material was formed
such as we find at Blackdown, where sandy layers occur
which contain pockets filled up with a fine yellowish powder
which is a tangled mass of spicules easy to see with a
pocket lens.

Formation of Chalk* 145

Remove the shores a little further, and perhaps thereby
open up a wider access for warm currents from the ocean, and
the waters will swarm with calcareous Foraminifera and with
the sea creatures which prey upon them, and on each other.
Then the deposit forming on the sea bottom will be an impure
chalk. Sand grains will wash from the Greensand where it
stands high enough and, in the shallows around, the shells of
larger organisms will collect, while the smaller Foraminifera
will be washed by tides and waves away to greater depths,
except where sheltered by the shells. Hence the sandy
Cenomanian of Devon and the thicker masses of the Lower
Chalk of the south-east.

Still further push back the shore lines, or lessen the distant
river slopes, and even the finest mud will oVily reach the sea
floor after times of unusual flood or storm. Then the
accumulation of Foraminiferal ooze, mixed with the flinty tests
of Radiolaria and the spicules of sponges, will go on uninter-
rupted, while one after another difiierent species of creatures
enter the region from other parts, or are evolved within it,
only to be replaced in turn by others.

Now and then, at long intervals, we must suppose the
sea floor rose within reach of surface movements, to sink
again, each oscillation being accompanied by some geo-
graphical change, which would slightly vary the environ-
ment, and so tend to make some change in the life of the
whole district so aflected. Thus it comes about that we
find bed after bed of the chalk regularly deposited over a
wide district and then we come to some horizon at the
junction of two zones where there are symptoms of surface
waste.

There is no need whatever to assume great depth, in any
part of the Chalk, but on the contrary, every here and there
are signs which can only be accounted for by a shallow sea
perhaps less than 100 fathoms deep.

If this is so, then in attempting to reconstruct the map of
this part of the globe, we do not need to follow the example of
the older geologists and regard our district as reduced to a
trifling archipelago whose islets were the summits of our
mountains. The waters certainly spread over the whole of

L

146 The HistxMT of Devonshire Scenery*

the region once covered by the Lias Sea, and overlapped its
shores, running far up the valleys and overflowing the
low lying districts. Meanwhile if we suppose the Atlantic
(as we did in accounting for the chert beds), to have drawn
nearer, it is possible that the two seas may even have joined,
and strong currents may have ebbed and flowed through the
straits.

But the general slope of the district was still from north-
west to south-east, and it is not probable that any such
connection was formed in the neighbourhood of Devon and
Cornwall ; and the improbability is heightened by the sequel.

We have no evidence of the Chalk having spread in Devon
much further than the Greensand, and all we know of such
western relics as the flints already mentioned, would be the
natural consequence of a small extension of the old Liassic
fjords.

The approach of the Atlantic can be entirely accounted for
by a sinking of the country which formerly lay on the western
side of the Caledonian Ranges, but the ranges themselves, and
above all the district where they joined on to the Hercynian,
would be least likely of all to become submerged.

It seems then that South- Western England was most likely
part of a rock-shored land which extended from Ireland and
Wales to Britanny, and which may or may not have been
separated from the Northern Continent which still existed
from Iceland and Scotland to Scandinavia, and which still
bridged the North Atlantic ; a country clothed with forests
somewhat resembling those of Southern Europe to-day,
through which the descendants of the Jurassic Deinosaurs
wandered, while the empire of the air was disputed between
the strange toothed birds and long-winged representatives
of the vanishing Pterodactyles.

The Secondary, or Mesozoic, Era was hastening to its
close, and the strange beasts which characterised it were
nearing their end. A new map of the world was coming*
a new set of conditions, and higher forms of life.

CHAPTER XIL
Tbe Plateau Gravels.

With the beginning of Tertiary time we reach an im-
portant stage in the modelling of the county. The
materials of its structure had been almost entirely accumu-
lated; they had been placed in something very much like
the relative positions in which we find them now; and
the main lines of the county architecture had been
determined. The changes which had still to be carried
out were some trifling rearrangements of the superficial
materia], and the final sculpturing of the hills and valleys
by the action of rain and rivers, sun and frost.

The Era was ushered in by a widespread upheaval
which almost exactly reversed the long subsidence traced
in the preceding chapters. So far as the British region
is concerned the movement was not, at first, complicated
by any considerable flexures of the crust. It was a
general uplift which step by step restored an eastward
sloping country, stretching from the high lands of the
west to the sea shores in the south-east.

During the long submergence the parts of the old
Jurassic land which were overflowed must have been buried
under a deep mantle of new deposits — Greensands and Chalk
— a mantle thin and unimportant in the extreme west, and
growing thicker and thicker towards the east.

Now it has been pointed out that the burial of a land
surface beneath such a cloak of new sediment does not
necessarily obhterate its features. The contours of the old
land tend to persist. Their asperities will be rounded off*,
and the amount of such softening will be roughly propor-
tional to the thickness of sediment. Hence, in the east it
is probable that if we could compare the buried land of
Wealden days and the newly emerged surface of Tertiary
time the contours of the latter would show little of the
former, except a few shallow hollows above what had been
the principal valleys, and a few gentle swellings above the
main lines of hills.

14^ The History of Devonshifc Scenenr*

On moving westward, where the Cretaceous mantle be-
comes thinner, the new surface will approximate more and
more to the old; becoming a smoothed and softened copy
of the buried surface when we reach the neighbourhood
of the Cretaceous shore.

Those parts of the continent which had not been sub-
merged will, of course, show the same features as of old,
modified only by further erosion due to surface agencies.

When, then, the upheaval began, the streams falling
from the heights will have found their ancient channels
still marked out for them on the upraised sea floor, and,
as the shore retreated eastwards, step by step the old
map will have been re-established. In the west even the
minor streams would be thus resuscitated. Further east,
as in Dorset, only the major features would emerge, and
still further east only the largest and boldest.

It is important to realize this fact clearly, for it will
need to be remembered further on.

In the process of emergence, as the shore retreated east-
wards the waves would beat on the rising land, strewing
its surface with sand and shingle, and, if no other agents
had been at work the new country would have been left
with a stratum of littoral deposits covering the whole,
from the western limit of the Chalk sea to the most
eastern end of its retreat. But other agents must at once
have come into operation. Rain, rivers, and all those many
agencies which are grouped under the general head of sub-
aerial denudation, would come into play. The sands and
shingles of the shore would be re-arranged as gravels and
river sands, and ground down into fine mud; while in flood
time fine clayey detritus would be borne from the western
heights, to settle in any hollows, and to be spread over
the floor of the shrinking sea, mixed with river-rolled
pebbles and with the wave-worn detritus of the beach.

Such should be the geological record of the time. Let
us see what it is.

If we climb to the top of any of the great hills which
command wide views of Eastern Devon, such as Haldon,
Cadbury, Hembury Fort, or even the ancient battlefield

The Post-Cretaceous Peneplain* 149

between Pinhoe and Poltimore, we cannot help noticing
how all the eastern heights reach up to about the same
altitude and are capped by a fairly level plain. The idea
is at once suggested that the whole country was once at
that height, forming a gently undulating surface into which
the modem rivers have dug their way. The view from
Peak Hill looking inland, or that from the hills south of
Honiton looking northward, is so striking that no one can
help feeling that the modern scenery has been chiselled out
of an ancient plain.

This conviction grows stronger with further investiga-
tion. All round the Blackdown Hills similar valleys
exist, trenching the sides of a flat tableland. If we move
into Dorsetshire by Lyme Regis and Hardown we find
the same features again and again, and can thus trace
the fragments of a plateau from Haldon all the way to
the heaths and moors which stretch round Studland and
Poole Harbour.

American geologists have invented an expressive term
for such a common level attributable to some definite
epoch. In England it used to be called a plain of denu-
dation, but in the States they call it a peneplain, which
expresses no idea except that it is almost flat.

We find, then, that the Cretaceous rocks of Devon and
Dorset rest on the eroded surface of the old Jurassic land,
which may be called the Jurassic peneplain, and that they
are capped by another surface of erosion which might be
called the Post-Cretaceous peneplain. The first was made
by the advance of the sea modifying a land surface, the
second by the retreat of the sea and the advance of land
conditions over a sea bottom.

The Tertiary Era is subdivided into a number of
periods, which in order of time are known as Eocene,
Oligocene, Miocene and Pliocene, terms which refer to
the proportion of existing shells which are found in their
respective deposits. Thus Eocene means the " dawn of the
recent,'* and beds of this age contain a great assemblage of
shells of which, according to Geikie, about three and a half
per cent, are those of still existing species.

ISO The Histonr of Deronshire Scenery.

If, now, we are right in believing that the Post-
Cretaceous peneplain, which forms almost the dominant
feature of the scenery of East Devon, was formed during
the retreat of the sea, this must have been in Eocene times.
We should have expected therefore to find some of the
materials left behind by the retreating waves dated beyond
question by their fossil contents. Unfortunately this is not
the case. The beds which cap the hills contain nothing
organic, except fossils which have been clearly derived from
the underlying Greensand or Chalk. Their place in Tertiary
time has only been established in recent years by Mr.
Clement Reid* by working westwards from more eastern
deposits whose date is much more clearly shown.

There are two districts in the east where Eocene beds
are well developed. One is the south of Hampshire and
northern half of the Isle of Wight. The other is the dis-
trict around London. The beds of these two areas may
be tabulated thus —

Hampshire London

^Ml^^^ } Upper Bagshot sands

Middle I Bracklesham beds and \ Middle and Lower
1 Leaf bedsof Alum Bay,&c. J Bagshot Sands

Lower Bagshot Sands
London Clay
Blackheath beds
Woolwich & Reading

beds.
Thanet Sands

The Thanet Sands seem only to have formed in the
London basin. They contsun about 70 species of marine
shells and a few plants.

The Woolwich and Reading beds consist of irregular
patches of clay, loam, sand, and gravel, well water-worn
and sometimes containing marine shells. But, as we work
westward, the fossils disappear, the gravels become

* Quart, your, Geol, Soc.^ 1896, p. 490 ; 1898, p. 234.

Lower

London Clay

Woolwich & Reading beds

Age of the Platcati Grayels* 151

subangular or much less worn, and fragments of Greensand
chert and sponge spicules appear.

The London Clay also, which is highly fossiliferous
near Bognor, becomes more sandy towards its western
limits and loses its organic contents.

The Bagshot Sands point still more strongly towards
a western origin. At the eastern end of the Isle of Wight
they are 150 feet thick, but expand to 600 feet at the
western end, where they contain lenticular patches of white
pipe clay, with plant remains.

In the cliffs of Bournemouth the same sands and pipe
clays occur, but coarser grains are more abundant, frag-
ments of Greensand chert and splinters of flint occur, and
more significant still, there are fragments of black radio-
larian chert.

Beyond Wareham, in the interior of Dorset, the sands
are much coarser and become gravelly; unworn flints and
little worn chert become abundant, together with pebbles
of vein quartz, hard quartzites and other western materials.
Pipe clay is abundant, and while the radiolarian chert,
black grit pebbles, and white quartz pebbles all indicate an
origin in the Culm and Devonian rocks, the pipe clay is
exactly like that which is found everywhere around the
fringe of Dartmoor.

From the moorland and heaths of Dorset the gravels
stretch westward on top of the Chalk, and then on to the
flint rubble. The railway cuttings on the Lyme Regis
branch show some excellent examples. In one cutting there
is nothing to be seen except angular flints mixed up with
rounded and subangular pebbles of flint, chert, and other
western rocks, in a matrix of sand and pipe clay most
irregularly mixed.

In another exposure layers of sand are interspersed among
the other substances in such a manner as to suggest
rearranged Greensand.

The flat-topped hills of Blackdown, Honiton, and Haldon
show similar gravels resting on, and to some extent mixed
up with, the rubble of unworn flints which we have al-
ready attributed to the solution of the Chalk. On Haldon,

15^ The History of Deyonsliire Scenery*

just north of the road from Exeter to Chudleigh, these deposits
are extensively worked for road metal. There the Greensand
is covered by the unworn flints, among and above which lie
the worn pebbles and layers and pockets of sand and pipe clay.

There can be no doubt, then, that these plateau gravels,
as they are sometimes called, are of Eocene age, or that
the finer and more water-worn gravels of Dorset are the
representatives of the coarser and more angular beds of
the Exeter district. But we want to know much more
about them than a rather vague determination of geological
date. Do the whole of these gravels coincide in age with
the Bagshot Sands, or are parts of them coaeval with the
London clay or still earlier deposits ?

Again, by what agencies were they produced?

Mr. Clement Reid answers these questions by regarding
them as the gravels spread over the wide valley of a large
river which flowed eastwards. But they difiier in many
ways from ordinary river gravels, and they spread over so
wide a district that if they were wholly due to a stream
it must have been very large and very rapid. A river
capable of carrying the unworn or slightly rounded frag-
ments would have been far more likely to have scooped
out a narrow steep-sided valley ; and one which could
build up a plain of such width would almost certainly
have built it with a much larger proportion of fine
material mixed with a smaller part of well rounded gravel.
In Dorset, Mr. Reid has pointed out that the London Clay
which is undoubtedly marine, seems to have been eroded,
so that the gravelly Bagshot Sands lie on the eroded surface
and overlap it, resting then directly on the Chalk. In the
same district there are pebbles of Purbeck stone*
which prove that at the time the gravels were formed, not
only Greensand, but even some of the underlying Purbeck
beds must have been exposed. Even in Devon fragments
of Greensand chert appear with the flints, so that we must
suppose it was uncovered, and from their abundance the
area exposed must have been considerable.

•op. cit

Origin of the Plateau Gravels* 153

In a previous chapter it has been shown that in all
probability the coast line of the Chalk sea was not much
farther westward than that of Greensand times, and that
neither of them were more than a few miles west of the
present limits of the formations. How comes it, then, that
the gravels lying immediately upon the renmants of Chalk
should be full of fragments of a rock which lies properly
beneath the Chalk?

It is possible that the western Greensand fjords were
never filled with true Chalk, but that in the narrow waters
close to shore the deposits coaeval with the Chalk of the
more open sea were identical with Greensand. But even
if this were not the case, it is tolerably certain that the
shore deposits of Chalk were thin and sandy, such as
would be easily removed by the waves of the retreating
sea, or by the streams, which would necessarily return to
their old valleys as soon as those were raised above sea
level.

The only interpretation which seems to meet all the
difficulties is the one which has been foreshadowed, namely
that these gravels and sands are primarily marine, created in
the first instance as shore and shallow water deposits due to
the retreating sea, and that they have been rearranged, sorted
and distributed eastwards by the various streams. The steps
by which this was done would not be restricted to any narrow
limits of time. They would begin directly a part of the sea
floor came near enough to the surface to undergo erosion.
The fine unconsolidated mud would soon be washed away
into deeper water, and as this would be mixed with land-
derived muds, the resulting deposits would be quite different
from Chalk. Flinty nodules would be left on the surface
to be thrown up on the beach, and more or less rounded
like the flints on a modern shore.

Meanwhile the streams which were reoccupying their
temporarily submerged valleys would soon cut down through
the remaining Chalk and lay bare the Greensand and its
cherts, pebbles and fragments of which would be washed
shorewards, to be there mixed with the wave-formed
material.

154 '^^^ History of Devonshire Scenery*

Suppose that at this period the beach line lay along
the Haldon ridge. The deposit would rest upon a stratum
of Chalk covering the underlying Greensand and would be
arranged much like a modern beach.

But as the upheaval progressed, the beach line would
retreat eastwards, and as it did so the older deposits on
Haldon would in turn become subject to other actions.
Soil would form upon them, percolating water charged
with humus woidd begin its work of corrosion. Streams
would flow over them cutting channels through them, re-
arranging their components and carrying some to the newer
shore.

Meanwhile the fine mud, whether originating on the
western heights, or on the beach strewn slopes, would be
carried off in flood time to the distant sea, where it would
settle down as a deposit of clay.

So the process would go on, the minor streams carry-
ing their materials into the larger ones, trundling the stones
along and carrying the finer fragments in suspension.
But unless these minor streams flowed down much steeper
slopes, their carrying power would be far less than that of
the main rivers, and the slopes of the plateau on which
we find most of these gravels now can never have been
very much greater than they are to-day. It is to the
larger rivers then that we must look as the chief agents
in the bodily transfer of pebbles any considerable distance
towards the east, though their tributaries would be amply
competent to effect substantial changes locally.

The result would be that in any given place the
materials of the deposit would consist chiefly of local rocks,
and that as the shore retreated eastwards the pebbles of
western origin would get gradually smaller and more
rounded, and that the accumulations beneath the sea would
be finer still: clay in the deeper parts, sands and fine
gravels nearer shore.

While the coarse shingle was being thus spread over
Devonshire, finer gravels and sand must have formed in
Dorset and probably clay still further east. When at
last the shore reached Dorset the waves ard streams would

Origin of Pipe Clay Seams* 155

have to remove the new accumulations before they could
attack the underlying Chalk. If the progress of the
upheaval was rapid, this would only be partially effected,
and we should find finer western gravels or sands intermixed
with coarser locally formed stones. But if there should
be, as indeed would almost certainly be the case, any
considerable pause in the shift of the shore line, the gravels
or sands or clay would be eroded, and locally formed beach
deposits would be built up from their remains and those
of the underlying local rocks. It seems that the erosion
of the London Clay beneath the gravels and sands of
Dorset can be easily explained as due to a pause of such
a nature.

The seams and pockets of pipe clay would be a natural
consequence of the eastward slope of the land. The rivers
which were capable of rolling pebbles from Devonshire
would be a still more efficient means for the carriage
of the finer mud from the great granite masses of the
west. Some of the white clay bands in the Chalk may
well have come from the same source, and i^ in the process
of erosion, these clayey bands were exposed, the solution
of their chalk would leave a pipe clay indistinguishable
from that which comes direct from granite*

So far we have made no reference to three other
important features presented by these deposits, the
abundance of unworn chips of chert and flint, the absence
of fossils, and the exceedingly confused arrangement of
the materials.

Now the pipe clays of Alum Bay, in the Isle of Wight,
and those of Bournemouth have yielded a large number
of leaves of plants which are of such kinds as to imply
a tropical climate. There is no doubt that as the land
emerged above the sea it became quickly clothed with a
dense forest — a forest resembling that of the Malay
Peninsula of the present day. The great carrying power
of the streams also implies a humid climate, and indicates
heavy and frequent floods.

Under such circumstances trees and bushes are torn
from the banks of rivers and carried far down stream,

156 The History of Devonshire Scenery*

dropping the subsoil and splintered surface rock entangled
in their roots as these are washed and torn.

A dense covering of vegetation also gives rise to a deep
surface soil rich in humus. Rain falling on such a soil
becomes highly charged with acid bodies, which corrode
many rocks, and have a special power of dissolving chalk.
Over most of the districts where these gravels are found
they rested on chalk. This must have been dissolved
away, solution taking place upon its surface, but acting
always most irregularly. In some places deep hollows
would be eaten out — ^hollows into which the overlying
gravels, and subsoil, would descend. We have only to
visit some large chalk pit, such as are common in a chalk
country, to see how even our modem soil sinks down
irregularly into the Chalk, forming what are called sand
pipes. They may be seen everywhere where the Chalk
is laid bare, cliffs, railway cuttings, house foundations, all
exhibit the phenomenon, and neither rainfall nor humus
is anything like so abundant now as was probably the
case during the earlier part of the Tertiary Era.

As the Chalk was thus eroded under the soil, the flints
were comparatively little changed. At least they would
neither be rounded nor bodily removed. They would there-
fore remain to be irregularly mixed with the gravel and
subsoil as it slowly sank.

Again the clayey particles of the marl bands so abun-
dant in the Chalk would not be removed. They would
remain as streaks and lumps of white pipe clay.

It is possible to form a rough, but approximate, estimate
of the thickness of chalk which has thus disappeared. We
have pointed out that many of the Chalk fossils are com-
posed of flint, and are really part of the flints, and
that these fossils are largely extracted from the Haldon
flints when broken up for mending the roads. We thus
find that the flints of Haldon represent all the zones of
the Chalk which are found at Beer, and one higher zone
at least. If, therefore, we estimate the thickness of chalk
which has been dissolved away from Haldon underneath
the originally marine gravels, at one or two hundred feet.

Early Tertiaiy Erosion* i57

we are almost certainly far within the mark. But the
irregular removal of only one hundred feet of rock from
under a layer of gravel, letting down a bit here and a bit
there, would inevitably leave the whole mixed in the
greatest confusion with the insoluble residues.

The structure of the deposit is therefore easily ex-
plained, and the absence of fossils, except those derived
from the older rocks, would be a consequence of the same
causes. The solvents which have removed the Chalk would
also remove any calcareous shells, and no hollow casts of
them could possibly survive the confused and irregular
movements accompanying the descent of the deposit as the
chalk was dissolved.

It may be objected that the very causes to which we
have attributed the transfer of material to the east would
surely have long since removed the whole of any such
littoral deposits as we have supposed. The answer is that
they have been thus removed wherever the carrying power
of the streams has been sufficient. If we examine a map,
such as the new sheets issued by the Geological Survey
for Exeter, Teignmouth and Lyme Regis, we see the
Eocene deposits capping the fiat-topped hills, but as a
general rule entirely removed from the lower ground. A
glance is enough to show that the portion which remains
is far less than that which has gone.

Where would the removal take place most quickly?
And where would it be slowest ?

In the first place the deposits, even before any con-
siderable removal of the Chalk, must have been eminently
porous, so that the greater part of the rainfall must have
soaked straight in, to percolate underground until it emerged
as springs along the sides of the valleys occupied by the
streams. These streams must have originally marked out
certain courses over the rising land, and it does not matter
whether these courses were determined (as we have said
they probably were) by the contours of the older land.
However they were determined they would be quickly
deepened, and the rate at which each valley would be en-
larged would depend upon the steepness of its slope, and

15^ The History- of Deronshire Scenery.

the volume of water flowing down. On the flat grounds
between would be the places where erosion would be at a
minimum, since the slope is little or none, and with so
porous a subsoil the quantity of water flowing over the
surface would be also nil. The only way, then, in which we
can satisfactorily account for the survival of the plateau
gravels is to suppose that they emerged from the sea with
only a gentle eastern slope, that the early rivers flowed
in courses somewhere above the modem valleys, and that,
in point of fact, the Eocene emergence was the time at
which our present system of hills and valleys was initiated.

We use the word initiated advisedly, for it must not
be supposed that there have been no changes since. The
sequel will show that changes have been numerous and
important, and there are instances in which the modem
streams most likely flow in the opposite direction to that
in which they went in Eocene days.

The early Tertiary Era was a time in which stupendous
changes took place in other parts of the world. Among
them was the upheaval of the Alps and Himalayas, just
as the British chains had arisen in earlier times, and although
the main lines of disturbance had now shifted far from our
neighbourhood, the terrestrial swell from those convulsions
gave the finishing touches to English geography.

The Eocene emergence however witnessed the general
marking out of hill and vale over a large part of southern
England, and so far as Devonshire is concerned this must
certainly have been the case. If we could slip in a hundred
feet or so of chalk under our plateau gravels we should
restore something like our Eocene hills, and to complete
the restoration we must imagine the valleys very much
shallower and narrower. Moreover the English Channel
had no existence, rivers must as a whole have drained
eastward, and those eastward flowing streams would be
flanked by tributaries flowing from Exmoor on the one
hand, and on the other from Dartmoor and the southern
ridges which still bridged the channel southwards, and
linked the hills of Cornwall and Devon with those of
Normandy and Brittany.

CAAPTER XIIL

The Bovey Lake.

South-west of the Haldon Hills, occupying the surface
of a broad basin surrounded by heights, there is a peculiar
district which stretches from within a mile of Lustleigh to
Kingskerswell, and from Blackpool almost to Ideford. It
thus measures some ten miles in length by four miles in
breadth. About a mile below Chudleigh Bridge the Teign
enters this tract about a mile and a half above its junction
with the Bovey, which flows in from the north-west. The
district is low lying as a whole, but its margins climb a
long way up the slopes of the surrounding hills. The
Bovey at Bovey Tracey is less than 90 feet above sea
level and the Teign at Chudleigh Knighton is less than
eighty. The deposits which characterise the district are at
Heathfield only about 100 feet above the sea, but at
Blackpool they touch the 300 foot contour line, near
Lustleigh they reach 445 feet, near Ideford 400 feet, while
on Milber Down they climb up to the 500 foot line.

The peculiar character of this part of Devon is not
only shown by its distinct type of vegetation, its industries
are also unique. Great open clay pits are dotted over its
surface, and the tall chimneys of several flourishing potteries
stand up above the pines ; clay of excellent quality is raised
in very large quantities, and the result has been the
opening of a number of sections of the greatest interest.

On visiting one of these pits, the first thing that strikes
the eye is the fact that the deposits are somewhat irregu-
larly stratified, and are of all shades of brown and cream
colour, while some are white and others actually black.
Some of the beds are mere lines of colour on the section,
some of them are several feet in thickness.

It has long been known that the brown and black
colouring matter is of vegetable origin, and many of the
beds are good lignite which can be used as fuel. Indeed
in former days it was mined at Bovey under the name of
Bovey Coal, and was used in the local cottages as well

i6o The History of Devonshire Scenery*

as the Bovey Potteries. But the combustible matter always
contains enough iron pyrites to produce an unpleasant
sulphurous smell, so that it is seldom used for domestic
purposes, and the heating power of a ton of lignite is so
much less than that of a ton of coal that its use has been
discontinued in the potteries. It is, however, still in use
for driving the engines used for hauling purposes in some
of the pits.

The whole deposit lies in a hollow of the older rocks.
North of Newton Abbot this basin has been eroded in
Culm and Devonian strata, and south of the town its base
is partly Devonian, but chiefly Permian breccia.

There does not seem to be any place where the actual
depth of the hollow has been proved, but at the Bovey
potteries Mr. Pengelly showed, in his classic memoir on the
Lignite Formation of Bovey Tracey,* that the peculiar
beds extended to a depth of 215 feet below the present level
of the sea. More recently a boring put down by Messrs.
Candy & Co., at the Great Western Potteries, close to
Heathfield Station, passed through 520 feet of sands, clays
and lignites, without reaching their base. As the ground
is here less than 100 feet above sea level, the basin must
now descend fully 400 feet below the sea, and its depth
may really be much greater.

There are three great open pits. The great so-called
"coal" pit at the Bovey Potteries was the scene of the
careful labours of Pengelly and Heer,t but the bottom is
all covered with a sheet of water and the sides of the pit
are crumbling away, so that very little of the actual bedding
or of the seams of lignite can now be seen. A mile and
a half south-east comes the more modern excavation of
the Heathfield Pottery. Here it is easy to see how the
surface layer consists of gravel, known locally as " head/'
which rests on an eroded surface of the underlying sands,
clays and lignites. But the lignites are here only represented
by thin seams, and are not easily recognised. In the
Bovey pit Pengelly described 72 distinct beds in a thickness

• PhU. Trans., 1862. t Op ciU

Bovcy CUyi and Lignites: The Plantation Pit*

r v

^-^-^-,

Heatbiield Clay Pit.

The BoYcy Clays and Lignites i6i

of 125 feet exposed, and of these the first consisted of
7 feet 6 inches of gravelly " head."

This surface coating will be referred to later on. It is
quite different in character from the underlying series, and
belongs to a much later period.

The Bovey beds in the section consist of an upper
series of alternating sands, clays and lignites, then 11 feet
of quartzose coarse sand and 9 feet of clay, and below
this a second series of 23 beds of clay and 22 lignites. It
it a noticeable fact that the lignites of each series become
thicker as they are lower. Thus the bottom bed of the
upper series was about 6 feet thick, the lowest reached in
the second series measured 4 feet.

Thoughout the whole of these sections the dip of the
beds was fairly regular, and to the south-east, but it is
probable that this is only a local feature. At Woolborough
a seam of lignite some feet thick has been observed dipping
north-east, and other directions have been observed else-
where.

The best section now open is a very fine one in a
large pit east of the road from Chudleigh to Kingsteignton,
about half a mile north of the milestone which marks
three miles to Chudleigh. To see the section to the best
advantage the cart track should be followed through the
wood right round the margin of the pit, which is on the
right, and hidden by a mound of refuse. On reaching the
northern end the track suddenly turns eastwards to some
huts used as offices. Here is a fine view of the workings,
and of the sections shown on the terraced end of the pit,
where clay and lignite are being dug.

It will be at once noticed that the principal beds lie
in a basin, rising sharply on each side. The curve of the
lower beds is smooth and regular, but an important fact
is immediately obvious, namely, that the upper beds show
folds and even crumples which are not shown by those
they rest upon. It looks almost as if these upper beds
had slipped down in the cup formed by the lower, and
had puckered themselves in the process. To some extent
this may have happened, but some of the disturbances are

M

i62 The History of Devonshire Scenery*

still more suggestive of a sinking of the upper beds dur-
ing the rotting and consolidation of the lower — an action
much like that described in the last chapter, but due to
the uneven shrinkage of the substratum rather than any
removal of its substance by percolating water.*

The base of the section, which can be best seen from
the floor of the pit, consists of a thick bed of good clay,
over which lies a seam of lignite which is used as fuel in
the engine-house to do the hauling throughout the works.

Along the eastern margin of these Bovey beds, every
here and there they are seen to be flanked by deposits of
coarse sands and gravels, with layers of white clay and
coloured sands and containing well rounded Chalk flints
and Greensand chert, together with radiolarian chert and
other pebbles derived from the older rocks. There is an
exposure described by Mr. Clement Reidt not far from
Combe Hill Cross.

At Milber Down, Woolborough Church, and, turning
westwards along the southern edge of the basin, again at
Staple Hill precisely similar beds are shown.

In every case these gravelly strata dip as if they formed
the floor of the Bovey deposit, and were continued, at
least some distance, beneath the clays and lignites. That
they have not hitherto been traced is doubtless due to the
fact that all borings which are put down are effected with
the object of finding good beds of clay, and would be dis-
continued on coming into the increasingly sandy beds
which form the gradation into the gravels. It is noticeable
that these basement beds, if such they are, have not been
found along the northern edge of the basin, where the
clays apparently end up abruptly on the Culm.

These marginal gravels have been much discussed.
They have been thought to belong to the same period as
the "head," but there is nothing to connect the two.

* I am indebted to Messrs. Watts, Blake and Beam, the proprie-
tors of this pit, for permission to secure the illustration and to
examine the workings.

t Quart, Jour. Geol. Soc., 1898, p. 235.

Age of the Bovey Beds* 163

Mr. Clement Reid* has shown pretty conclusively that
they are really of the same age as the gravels of the
Haldon plateau, that is to say they are Eocene, and there-
fore belong to the same or an earlier time than the clays
and lignites. They may be shore deposits of the same age
as the lignites, or they may be what they seem to be, the
basement beds of the whole series.

The age of the clays and lignites has also been much
discussed. Mr. Pengelly, in i862,t came to the conclu-
sion that they were of Miocene age. This determination
was based upon an investigation by Dr. Heer, of the
numerous plant remains and solitary beetle's wing case,
which were found during his researches at Bovey. No
shells, no bones of animals have ever been found in the
Bovey beds — a fact which must be attributed to the water
being highly charged with humic acid, which would rapidly
dissolve any calcareous shells or bones. But the plant
remains, though rarely well preserved, are abundant enough.
Ferns of the osmunda kind, oaks, cinnamons, laurels, coni-
fers, figs and palms have been found, and were identified
by Dr. Heer as resembling the fossil flora of certain
continental beds which belong to a date formerly regarded
as Lower Miocene, but now known as Oligocene.

More recently, Mr. Starkie Gardner]; points out that
these same plants, some of which can be positively identi-
fied as the same species, are to be found in the white pipe
clay seams of the Bournemouth cliffs, which are of undoubted
Bagshot age.

It seems then that the whole of these Bovey deposits,
except the ''head," are of the same general age as the
gravels of the plateau of Eastern Devon, and must there-
fore be a local variation of those deposits whose peculiar
characters are due to local circumstances which modified
the conditions under which they were formed. What, then,
were these local circumstances?

There is a general agreement that the basin was originally
a lake. No other hypothesis will account for the fairly

*Op. ciL tOp. cit. t Quart, your. Geo. Soc, 1879, p. 227.

i64 The History of Devonshifc Scenery*

regular stratification of the various beds. Where the gravels
lie the incoming streams must have been fairly rapid, and
it is not at all unlikely that these gravels really mark the
positions where the feeding streams entered the land-locked
sheet of water. The coarser sediment would soon settle,
the finer, particularly the fine mud which was to make the
clays, would be evenly strewn nearly all over the basin.
At intervals there must have been long periods during which
nothing entered the lake except vegetable matter, and that
must have been brought abundantly. Hence the streams
must, as a rule, have been too sluggish or too small to have
much carrying power. Slowly their carrying power increased.
Floods capable of strewing clay, or even sand, over the lake
bottom increased in frequency, and the lignites became
thinner and less pure. But after an interval the old con-
ditions were re-established and the upper series of lignites
and clays laid down.

The Bovey basin, however, lies some hundreds of feet
below the top of Haldon, and the bottom of the hollow in
the Palaeozoic rocks must be at least 500 feet lower still.
How, then, can we account for the fact that Haldon was
capped by Greensand, and that by Chalk, while neither of
them are to be found among the Bovey beds, though relics
of both are abundant in the marginal gravels ?

Had the Bovey beds been of Oligocene age it would be
easy to suppose that the whole basin was formed after the
plateau gravels had been produced. But the identification
of both as Eocene puts an entirely different complexion on
the matter. The Bovey beds ought to be underlain by
Greensand and by flint rubble like that of Haldon. But
they are not. There may be some portions of both buried
away under the clays of Heathfield, but neither Greensand
nor Chalk peeps out on either side.

It has been explained in a previous chapter that the
erosion of the rising sea floor would begin nearest the old
shore, would be most rapid along the streams and on the
steeper slopes, and least of all on elevated flat tracts.

Now the base of the Eocenes on Haldon at present
reaches dovm to the 600 feet contour. If we add on» say

Formation of the Lake Basin* 165

200 feet for the chalk which has been removed by solution,
we can then calculate the difference in level between the
base of the Eocene on the plateau and the base of the
Bovey beds. Put it for the sake of argument at 1500 feet.
If now we suppose that when the land began to rise, and
the Haldon gravels were the beach line, the general east-
ward slope was about five degrees steeper than it is now,
we bring the two to a common level. Five degrees is only
a small angle, and the difference may well have been greater,
and the sequel will show that there are good and sufficient
reasons for thinking that; as a matter of fact, there was a
substantial decrease in the slope at a later date.

If we now bear in mind that all the surrounding heights
must have been much loftier, we get at first, steep slopes,
and therefore great erosive power, for the streams flowing
down from Dartmoor and from the southern hills between
Newton Abbot and Ashburton. Moreover, the western land
extended far beyond the present limits of Devon, and it is
almost certain that the rivers coming into the Bovey region
from the west were far more important than the Bovey at
the present day. It has been shown by Mr. Jukes-Browne*
that the Dart probably did not turn aside from its eastward
course, as it now does, but wended its way by Bickington
to join the Bovey in the old lake basin. But this is not
material to our argument, it would only strengthen the
erosive actions and so help their work.

The valleys down which these rivers flowed would be
rapidly cleared of all remnants of any beach material left by
the retreating sea, and by the time the waves were ebbing
and flowing over Haldon, much of the Chalk and possibly
also the Greensand, both of which must have spread some
distance westwards, would have been cleared away.

This erosion would go on until the bottom of the valley
reached down either to the shore level, or to the level of
any barrier which existed lower down the stream. The
valley drains at present across the ridge of Permian breccias
through the gap occupied now by the estuary of the Teign.

*QtMrt. Jour. GeoU Soc,, 1904, p. 333.

i66 The History of Devonshitc Scenery.

Probably this was the course then followed, and the valley
was eroded to the level of the hard resisting ridge. This
was the first stage in the process, and it is a necessary step
to account for the removal of the Cretaceous rocks ; but it
should not be forgotten that we suppose the base of the
Bovey valley to be level with the top of the obstructing
ridge, which might itself be nearly level with the top of
Haldon.

As the upheaval progressed further east it is most likely
that the general slope of the country decreased. Indeed, it
is believed on excellent grounds that a large part of the
Bagshot Sands, and of the sands and gravels of Dorset were
formed in shallow shore lagoons rather than the shore of a
rapidly deepening sea. Hence we must not suppose that
Southern England arose at the same vertical rate from
Devon to Hampshire. The records suggest rather that the
movement resulted in a greater uplift in the east than in the
west, with the result of a distinct and gradual dimunution
of eastward slope.

The result would be to raise the hard barrier which lay
further down across the Bovey river above the bottom of
the Bovey valley, thereby converting it into a lake, and
lifting the Haldon gravels above their continuation, a move-
ment which would also lessen the slope of the streams
above the lake, reducing their carrying power and so chang-
ing their load from sand and gravel to fine clay and
lignite.

If this really represents the course of events, the Bovey
gravels might be the true contemporaries of the Haldon
deposits and really coaeval with the London Clay or still
earlier Eocene deposits, while the clays and lignites of the
old lake were the local representatives of the Bagshot
beds of Bournemouth and the Isle of Wight.

It may well be asked why we should attribute the
erosion to the Bovey, possibly aided by the Dart, when
we have the Teign coming in from the north. The answer
is that in those days the Teign followed a di£Ferent direction,
and the north and south portion of its course was occupied

Formation of the Lake Basku 167

only by a comparatively trifling stream,* This accounts
for the absence or insignificance of the marginal gravels
on the north, to which attention has been already drawn.

There is no question that the Bovey beds are lacustrine,
and there is no other way in which a lake in such a position
can be accounted for at such a time. Lakes are formed
in other ways than that which we have supposed. They
may be formed by a local subsidence. If this had been the
case the Cretaceous rocks, or at least the Greensand, should
have been preserved, and indeed marine Eocene deposits
should have covered and protected them.

Ice action in any form is out of the question, as it is
incompatible with the undoubtedly warm climate; and the
only other way of accounting for the formation of a lake
basin would be to call in an imaginary earthquake or other
agent to produce a huge landslip further down the valley
whereby the course of the river might be blocked. Of such
a catastrophe we have no evidence whatever, and it is
indeed most improbable.

On the other hand we have conclusive evidence of a
difierence in the rate of upheaval not much later on, when
the movements in the west were actually converted into a
subsidence, and the southern and eastern counties were con-
siderably affected. A beginning of these movements is
indicated by an oscillation from estuarine conditions to
marine, and by the occurrence of Purbeck pebbles in the
gravels of Dorset. This must mean that Greensand and
Chalk had been eroded away, and Purbeck beds laid bare,
at the time when those gravels were produced, and that
time, we already know, was the date at which the Bovey
beds were accumulating in Devon. The Purbeck beds
could not be eroded without a considerable upheaval, and
this was probably the earlier stages of an earth movement
which assumed much greater importance later on, and which
was accompanied by very important changes in the far west.

If the alteration in the slope was not a continuous change,
and it is most unlikely that it should have been unvaried,

* Jukes-Browne, Op cit

i68 THe History of Devooshifc Scenery*

bat was brought about by somewhat rapid movements
followed by a long pause, and so on, we have an explanation
of the division of the lignites into the upper and lower series
first recognized by Pengelly.

It must be pointed out that the identification of the
Bovey plants as Eocene is not unquestioned. Thus Geikie
says,* "one cannot say that the botanical evidence is con-
clusive, for the species are few and greatly need re-examina-
tion ; " and again, '' In the meantime, however, these various
plant-bearing deposits are retained here in the Oligocene
series, as possible equivalents of the brown-coal and molasse
of the Continent."

If we put the botanical argument entirely aside, and
consider only the physical reasoning and deductions based
on the mineral compositions of the gravels, it would seem
that the first deposit of the rolled gravels of Haldon and the
erosion of the lake basin must both have been early Eocene,
while the subsequent deposit of the Bovey clays and lignites
must represent a later date. Whether this later date was
Middle or Upper Eocene, or whether deposition was still
taking place in Oligocene time is a matter of little moment.

The Haldon deposits themselves are difficult to date.
There is no doubt that Mr. Clement Reid is right in fixing
the age of the rounded gravels as Eocene, but. those gravels
then rested on Chalk. The solution and removal of this
substratum must have taken a vast time, and it is more than
probable that the Eocene gravels did not attain their present
position on the Greensand, or their present confused admixture
with unworn flints, until a much later date. In Dorset the
underlying Chalk still survives, and renmants of it are
to be found at 0£Fwell, Brice Moor, Membury and Salcombe
Regis. Its final disappearance from Peak Hill and much
of the Blackdown Hills must be regarded as only recently
complete.

*Texi Book of Geology^ p. 1251, Ed. IV.

CHAPTER XIV.
The Rivers of Devon.

If we examine a map of Devonshire on which the rivers
are clearly shown, we notice in the £rst place that streams
radiate in all directions from Dartmoor, or rather from the
western edge of Dartmoor; and that another set arise
near the northern coast line and wend their way south-
wards. We should have expected that the dome of the
Moor, to which reference has been repeatedly made, would
give rise to a radiating water system, and the Exmoor
ridge should similarly be a watershed, and both features
should be older than Cretaceous days. But we soon find
other things which we should not expect.

The Torridge behaves in a most eccentric manner.
The sources of some of its head feeders are only a couple
of miles south of Clovelly, and it then flows south-east as
if it were making for the strip of red land which ends up
at Hatherleigh, but just before reaching that town it turns
sharply to the north-east, and then north, and follows a
tortuous course to Torrington and Bideford. Its whole
course measures about fifty miles, but at Torrington it is
only seven miles from a point more than thirty miles
higher up the stream. The Taw also presents some anoma-
lies. Rising on Dartmoor, it flows nearly due north past
North Tawton. Near Brushford it turns to the east, and
then sweeps round at its junction with the Yeo to flow
north-west. At South Molton Road Station it meets the
Bray, a stream which has flowed almost due south from its
source on Exmoor. The Taw pursues its north-western
journey, twisting through its deep, wooded valley until it
turns sharply to the east on reaching its estuary at Barn-
staple. It is noticeable that the valley of the Torridge is
continued by the gully up which the railway runs from
Braunton to Morthoe and that of the Taw is similarly
matched by the course of Bradiford water and the Colom
stream to Bittadon.

lyo The Hktory of Devooshbe Scenery*

If the courses of these two rivers and their tributaries
are traced on a sheet of paper without any indication of
the direction of flow, or of the present coast line, they
suggest irresistibly the idea that they are streams rising in
the north and flowing south-eastward in the direction of
Crediton.

The Barle and the Exe flow south-eastwards until their
junction near Dulverton, and then instead of taking the broad
hollow followed by the Great Western Railway to Wivelis-
combe and Taunton, the river plunges into the gorge which
sweeps round through the hard Culm hills as if it meant
to go round by Bampton. On meeting the little stream
of the Bathem, it turns sharp round to the south and west
through the deepest part of its gorge and thence wends its
way southwards to Tiverton. Here again is a mystery.
Why does it not flow eastwards along the broad valley to
Tiverton Junction or CuUompton ? Instead, it has cut its
way through the harder Culm past Cadeleigh. But its
strange behaviour is not ended. On reaching the neigh-
bourhood of Brampford Speke, why does it not turn east-
ward by way of Rewe, Broadclyst and Clyst Honlton,
instead of making an equal turn in the opposite direction to
cut its deep valley from Stoke Canon to Cowley Bridge and
Exeter ?

Similar questions may be asked about the Teign and the
Dart, and we have already referred to the probability that
both these streams have been deflected from their ancient
courses.

Still another problem is presented by the vast size of
some of the valleys now occupied by insignificant streams,
while much larger rivers flow through comparatively trifling
hollows. Either they cannot belong to the same date, or
the relative powers of the streams have changed.

It has been pointed out that as the floor of the Creta-
ceous sea rose and became the early Eocene land, the
streams still flowing over the unsubmerged part of the
ancient continent would tend on the whole to resume
possession of their former channels. This they would
necessarily do, unless those old valleys were entirely

Rivers of the Plateau* 171

obliterated, or the general slope of the emerging country
was different from what it had been before submersion.

In the Devonshire area it has been shown that in all
probability neither event would have taken place. The
main valleys would still be hollows, and the slope of the
country would be towards the east. North of the Exmoor
ridge, which must have extended beyond Lundy, lay a
broad valley occupied most likely by a large river which
flowed eastward south of the Mendips on its way to the
eastern sea. In the English Channel, some distance south
of the Start, another great river followed a somewhat parallel
course*

Throughout Devonshire, except for the dome of Dart-
moor, the rivers must have wended their way, on the whole,
eastwards; either to join one or the other of these two
great streams, or they may have gathered together to form
a third which ultimately debouched not far from
Dorchester.

Consider now the small rivers which drain the eastern
plateau, the Axe and the Otter. At the present time the
plateau has a certain slope towards the channel, but the
rivers do not follow this. They run obliquely across it.
Moreover there are good reasons for believing that the
southward slope was the result of the considerable earth
movements which came later on and gave the channel its
present westward inclination. When the plateau emerged
therefore, it must have sloped eastward, and the streams
crossing it must have flowed down hill, which means in the
opposite direction to that they follow now. If either of
these streams is followed to its source it will be found to
end in a dry valley, well below the plateau level, which is
continued through the dividing ridge into the valley of an-
other stream flowing the opposite way. There cannot be
much question that this represents what in Eocene and
following times was the actual course pursued. The Otter
may thus be regarded as a former tributary of the Tone or
of a magnified Parret flowing towards the south-east, while
the Axe may have flowed direct into the head waters of the
Dorset Frome.

172

The History of Dnronshire Scenery*

The Taw and the Torridge present a more difficult case.
If we examine the course of the Torridge where the Okement
joins it at its south-eastern bend, we find the Okement
comes in from the south-east Let us go a short way up
this stream. About half a mile before reaching Monk Oke-
hampton a broad valley, now occupied by a little brook,
comes in from the east. If this valley be followed it leads

TIm RivefB of Devootfufc*

us to a low gap in the divide near Winkleigh, which is only
about a couple of hundred feet above the present level of
the Torridge where we left it. The gap leads to the source
of a tiny tributary of the Taw, which it joins about two
miles above the junction of the latter with the Yeo. In the
angle between the Taw and the Yeo there are several
channels cutting through the hills. Through any of these

Probable Eocene Rhrer System*

173

the river may easily have found its way and may then have
continued its south-eastward journey, first up the Yeo, then
by Morchard Road Station almost along the line now
followed by the South Western Railway into the head waters
of the Creedy.

Now it must not be understood that there is any absolute
proof that the course traced out was in point of fact the

FtehMt River System in Em I7 Tertiary Times.

actual track of the Eocene and Post-Eocene river. There
are two or three other routes by which the connecting
links may have passed, but the one described fits best
with what we know of the previous structure of the country
and follows the line where most erosion was efiected before
the drainage system was changed. We can be certain that
if it were possible to fill in all these channels to a depth

174 The History of Devonshire Scenery^

proportionate to the erosion which the present rivers can
perform, and were then to restore the general eastward
slope of the whole county, such would be the direction of
flow. The estuary of the Taw, of course, would not exist,
and the two portions of the Torridge, the Taw and its
tributaries, would only be the upper feeders of the Creedy,
and they would present a map of a perfectly normal river such
as we should have expected to find at the date we are con-
sidering. A comparison of the two maps shows the difference.

The greater Greedy thus supplied would flow down its
present valley to St. Cyres, but where it most likely went
next is again a difficult problem. Bearing in mind what
we have said as to the general eastward slope and the
certainty that the high plateau was continued far over the
present English Channel, it seems unlikely that it turned
southwards. Neither can it well have flowed over the
plateau. We should look for its ancient valley where
the removal of material has been greatest, that is to say
along the north-eastern face of the Blackdown Hills.

Along the valleys of the Culm and Tone an amount of
erosion has been effected which seems far too great for the
existing streams and out of all proportion to their size.
Not only have miles and miles of Eocene and Cretaceous
rocks been cleared away, but the Permian sands and even
the Budleigh pebble bed have been deeply trenched.

Along this track then it seems most likely that the
drainage of northern Devon went, flowing along the course
of the Tone to join the river of the Bristol Channel and
turn with it south-eastward past Yeovil and Yetminster, also
to join the Frome.

Again we find we can thus construct a normal river
map such as would be likely to be marked out on a new
land. The principal channels would lie approximately where
we have other reasons for thinking they would be, and we
supply the great carrying power which can alone account
for the distant travel to the Dorset estuary of the heavy
debris of northern Devon.

The Exe and Barle would most likely turn off before
reaching Tiverton to join the main stream near Sampford

The Eocene Riret System* 175

Peverell, and the Cadeleigh Dart, sweeping round by Silverton,
would be another tributary from the north. The estuary
of the Exe and the Clyst would be marked out by two
southern tributaries, and it is probable that the overflow of
the Bovey lake curved northwards and formed the con-
tinuation of either the Otter or the Axe.

Mr. Jukes-Browne has given reasons'^ for believing that
the Teign continued its course from Clifford Bridge across
the ridge near Holcombe Bumell into the valley of the
Alphin brook and so joined the Exe. It seems, however,
at least equally likely that it diverged from its present track
near Dunsford Bridge and following a more northerly
direction entered the present valley of the Exe at Exeter
or Cowley Bridge, and then swept on by Stoke Canon to
the great river of North Devon. If so it would have been
the Teign which first began what is now a part of the
valley of the Exe. Truly a strange result, but one which
is far from improbable.

It may be asked why we suppose always that the rivers
must have followed existing valleys. The reason is that
a valley once formed tends to remain a valley, and can
only be obliterated by means which do not seem to have
been brought into operation in Devon since the Cretaceous
submergence. The streams which excavated them may be
diverted, the direction of their slope may be reversed, but
unless some agent is set to work capable of levelling the
hills, or of filling the valleys with material as hard and
resistant as the hills, they will necessarily remain as a
record of the past.

The exact course these streams followed can only be
traced, if traced at all, by a laborious research on the valley
gravels more recent than those of the plateau. This has
not yet been done, so that the course traced in the fore-
going pages must be regarded as a hypothesis backed up
at present only by general arguments, and as the alterna-
tive which seems to be least at variance with the
facts at present known. It will be remembered that in

* Quart, four, Geol. Soc,, 1904, p. 319, ct seq.

176 The Hiitory of Devonshifc Scenery*

order to account for the erosion of the Bovey basin so as
to form a lake, we found it necessary to assume an east-
ward slope, perhaps five degrees or more steeper than at
present. It is significant that if a similar tilt were given
to the whole of North and Eastern Devon, together with a
northern inclination of the southern portion, many of the
changes we have imagined would be actual facts, even
without any filling in of the channels such as we supposed
when dealing with the Taw and Torridge.

Such, then, is a probable restoration of the couaty
itself. But through Eocene and Oligocene times into the
Miocene age it was far from any shore, being part of the
high ground of a continent which included almost the
whole of the British Isles and Western France, and which
was linked to Greenland and America by way of Iceland.
The climate through all that long time was tropical, and
all sorts of strange warm-blooded animals roamed the
luxuriant forests and sheltered in the caves. In Kocene
times these animals bore little resemblance to those of to-
day, but as the centuries rolled by the likeness became
stronger and stronger, until in Miocene days we find
elephants, rhinoceros, anteaters, hogs, otters, antelopes, great
tigers, and even manlike apes.

The early Tertiary periods witnessed some of the most
important geographical changes which the world had seen.
The great chain of mountains which dominates Europe and
Asia received its principal uplift. In Eocene time a broad
deep sea had extended through Europe and Asia to the
Pacific, a sea which swarmed with Foraminifera in such
abundance that their remains have built up massive lime-
stones, called the Nummulite limestone, which is sometimes
thousands of feet thick. Upheaval of this tract began in
the Oligocene period, leaving a strip of sea extending
through the heart of Europe to the Black Sea and the
Caspian. A further and greater movement, of Miocene date,
raised the young ranges higher still, leaving the Black Sea
and Caspian as remnants of the Eocene Mediterranean,
while the Nummulite limestone rose up to heights of
10,000 feet in the Alps and 16,000 feet in the Himalayas.

Changes in the General SIope« 177

Movements oq such a scale have far reaching con-
, sequences. The old arrangements of land and water were
finally destroyed, and the modern distribution was begun.
Volcanoes broke out in new directions, one line being
marked by outbursts in the Auvergne, the Eifel and east-
wards on the northern side of the rising chain, while a still
more northern group made its appearance, either in Eocene
or Oligocene time, on what had been the floor of the north-
em end of the Lias sea. Over large districts in northern
England and Ireland and along the western coast of Scot-
land, innumerable fissures were formed, up which the molten
material rose, to be poured out in flood after flood until
the successive sheets of basalt reached a total thickness of
at least 3,500 feet.*

These sheets of lava are interbedded here and there with
layers of tuff, old soils, beds of lignite and so forth, show-
ing that they were erupted on land ; and the plant remains
are similar to those of Bournemouth and Bovey.

The Eocene upheaval had apparently left the eastward
slope of the British area unimpaired, but towards its close
the sea was pushed southwards from the district round
London and the Weald, a process which was probably
synchronous with the beginning of the great fold which
throws the Chalk into a broad trough beneath London and
a great arch over Kent, Surrey, and Sussex. An arm of the
central European sea still reached into the Hampshire
basin, but during most of the Oligocene period the deposits
which accumulated these were either freshwater or estuarine
in character. Indeed the Solent, Spithead and the country
near, were the broad estuary of the great river we have sup-
posed to have received the drainage of northern Devon.

This differential movement in the south-east of England
indicates that change of slope which we needed to explain
the Bovey lake, and so far as it goes it shows that Geikie
is right in retaining the Bovey beds as Oligocene.

The greater Alpine movements of Miocene time resulted
in a still greater change. Hitherto the British area as a

^GeikiCf "Ancient Volcanoes\of Great Britain^" Vol. II, p.2ix.

N

178 The History of Deronshife Scenery.

whole had drained south eastward, but the eastern sea had
disappeared and the present Atlantic had drawn nearer.
Considerable earth movements took place along our southern
shores. The old Solent Estuary was compressed from the
south, so that the Bagshot beds of Alum Bay and Studland
now stand vertical, and a sharp anticline extended through
the Isle of Wight and along the Dorset Coast. The Chalk
in Dorset was even cleaved by a considerable thrust plane,
while the Purbeck rocks near Lulworth Cove were crumpled
and puckered. South of this anticline the beds in the Isle
of Wight slope gently to the channel. One result of these
changes was to cause the drainage of the channel to flow
westwards. The south western part of Britain was tilted
westwards, while its southern portions were also inclined
towards the south. The Bristol Channel and St. George's
Channel were also converted into broad valleys draining into
the Atlantic, and a broad arm of the North Atlantic pushed
its way between the Faroe Islands and Norway until it
overflowed even parts of our eastern counties and
Belgium.

Such changes were, of course, not suddenly produced.
They must have been going on for some time and may not
have been completed until the close of the Pliocene period,
or even later.

But such reversals of the direction of the great rivers
cannot be effected without considerable alterations among
their tributaries, and it is to some part of Miocene or early
Pliocene times that we must attribute the changes in the
drainage of Devon. The westward subsidence of the Bristol
channel drew off the Taw and Torridge, breaking their con-
nection near Winkleigh, and severing the Creedy from the
Taw, while a southward tilt of the rest of the county, due
to the alteration in the drainage of the channel, formed a
dividing ridge along the northern edge of the eastern plateau.
This last movement, which may be regarded as the con-
tinuation of the Isle of Wight and Purbeck anticline, would
separate the Culm from the Tone, and reverse the flow of
all the rivers of Eastern Devon. At the same time the Exe
and Barle would be affected by both movements. To

Consequences of the Altered Slope* 179

account for their present course we must suppose some
minor tributaries had partly formed the channel south of
Tiverton, and when the earth movements came the main
stream was turned aside into the nearest possible approach
to a south-western course.

The deflection of the Teign and the formation of the
Exe estuary may have been brought about in a similar
way, which would also account for the turning of the
Dart away from the iilled-in Bovey lake to something like
its present course.

It will be noticed that nothing has been said of the
Tamar and its tributaries. The reason is that we have
no reason to suppose that any part of its basin, unless it
be a small district in the immediate neighbourhood of Ply-
mouth, had ever been submerged beneath the sea since the
great upheaval in Permian time. If so, it is a much older
river and would have cut so deep a valley through the
hard rocks which form its banks that the changes in the
slope of the land would be too small to afifect it.

Alterations in the geography of the world, such as we
have described, would naturally have a profound effect
upon its climates. We are not surprised, therefore, to note
that the animals and plants whose remains we find in
Pliocene deposits show that the period was a time of
decreasing warmth, until, at its end, the climate was some-
what similar to what we have at the present day.

Throughout the whole, Devonshire remained well above
the sea, but during the later part of Pliocene time it cannot
have stood very far above its present level. Marine Pliocene
beds are found at heights of 500 feet, capping some of the
Kentish Downs, which shows that there must have been
a considerable westward expansion of the North Sea. The
fact that they are now found only on the summits of the
hills is an illustration of that principle to which reference
was made when dealing with the gravels of the Devonshire
plateau, namely that it is on the hilltops that denudation
proceeds most slowly.

On the other hand, filling a cup-shaped hollow in the
older rocks, there is a small isolated patch of similar beds

i8o The History of Devofuhire Scenery*

at St. Erth, in Cornwall, thereby indicating a small overlap
from the Atlantic.

But the carving of the surface of Devon went on with-
out interruption. Its structure in all except the smallest
details was complete, and its history from the close of the
Pliocene age until the present is merely the story of its
outer garb.

As the Pliocene period drew to its close, glaciers began
to form on all the northern mountains and in ^Vales.
Slowly they grew in thickness and spread further and further,
and insensibly the world passed from the Tertiary Era into
the Pleistocene period, with the great age of Ice.

The Glacial period, as it is called, is one of the greatest
puzzles in the whole oi the geological record. Books and
papers too numerous to count have been written upon it,
without arriving at any satisfactory solution of its cause.
Some attribute it to a cosmic origin, others regard it as an
astronomical event due to exceptional ellipticity in the
earth's orbit, while others argue that changes in the distri-
bution of land and sea, by modiifying the winds and currents,
would be enough to account for all the facts. But whatever
theory is advanced, and however well it may seem to meet
the case when applied to any particular district, none has
been yet devised which meets with general approbation or
against which strong arguments cannot be found. The
cooling seems to have been world wide, and to have ended
not very many thousands of years ago.

Some indications of ice action on a large scale have been
detected in the Permian or Late Carboniferous rocks of India,
and some geologists have thought that the British Permian
breccias indicate the effects of glaciers. But neither of them
seem to point to an age of cold in any way comparable with
that of Pleistocene times, which stands out as an unique
and unexplained epoch in the development of the world.

One thing it did for us. It prepared the world for
habitation of early man by exterminating a large proportion
of the great beasts of Tertiary time. Both in the Old World
and the New the animals of Miocene and Early Pliocene
time were larger and fiercer than those of India and Africa

Absence of Glactatbn from Devon* iSi

to-day, and some of those whose bones are unearthed from
the Tertiary beds of America, Africa and Asia must have
been far more dangerous antagonists than any Uving beast.

At the culminating period of the cold, a vast glacier
covered the whole of Britain down to the Bristol Channel
and the Valley of the Thames. A great sheet of ice flowed
down from the highlands grinding its way across the
lower country, smoothing away its hills, and churning its
soil into a great sheet of clay filled with ice-scratched and
rounded boulders. As it flowed under the mountain crags
great fragments fell on its surface to be carried far and wide,
and dropped many miles from their source.

In our eastern counties the hills were thus almost planed
away, and the old river valleys were filled in with debris,
so that the face of the country was profoundly ctemged.

Not so in Devon. We have here no indication of
glacial action. No ice-scratched boulders, no ancient moraines
like those of Wales and Cumberland, no undoubted ice
borne blocks, unless we count as such a few great boulders
stranded on the shore, as may be seen at Braunton and
Croyde. In the east and north of England, beneath the
soil, we come in a foot or so to the actual rock but little
altered. In Devon the rocks are often rotted and weathered
for depths of 20 to 50 feet and more. The deep soils,
formed by the water percolating downwards from above
through countless years, show plainly that no ice sheet
has ever crossed the hills and vales of Devon.

While Northern Britain was thus buried deep under
its frozen coat the climate of Devon must have been very
severe. The snowfall of the winter must have gathered
deep on Dartmoor and Exmoor, then more lofty than they
are to-day, and in the early summer when the thaws came,
floods of water bearing a heavy burden of detritus must
have rushed seawards down all the valleys, scooping them
deeper, and spreading half worn gravels widely over the
lower ground. Hence came much of the gravels of the
lower Exe and those which cap the cliffs at Exmouth and
Dawlish — ^the valley gravels as they are called on the
survey maps.

i82 Tlie History of Devonshire Scenenr*

We do not know for certain at what height the country
stood, but it is sure that some of the raised beaches around
our shores contain shells which point to a colder cli-
mate than the present, and the agency of the ice foot or
shelf of ice which forms around an arctic shore has been
appealed to in order to explain the peculiar features of some
of these beaches* and to explain the transport and sub-
sequent stranding of the erratic blocks of Braunton and
Croyde.t

On the other hand it has been suggested by some geolo-
gists that the glaciation was, in the main, due to great
elevation of the whole of Great Britain so that all its
higher grounds were above the snow-line. But others have
expressed the contrary belief that the marks of ice action,
generally attributed to a glacier moving over the land, are
really due to fleets of icebergs gnnding their way over the
shallows as they drifted with the currents of an arctic sea.

Strewn over the hill sides we find the numerous patches
of little worn rubbly gravel which may be attributed to
the summer thaws acting on the surface of a soil frozen
to a depth of several feet. But these again have been
otherwise explained. Murchison, for instance, regarded them
as having been produced by a terrible cataclysm in the form
of a great wave-like rush of water all over the country.
Prestwich believed that they were due to a quiet but rapid
submergence, too quick for the waves to erode the loose
surface rock as they rose, and too slow for the advance of
the water to produce a similar effect, and that this was
almost immediately followed by a sudden upheaval, so
sudden that the retreating water roared seawards on every
side like water off the back of a whale. The rapid thaw of
a heavy snowfall, and a deeply frozen ground, would soon
produce the same effect if repeated year by year, and we
prefer an explanation which depends on events which we
know occurred, rather than any which demand exceptional
causes not otherwise indicated.

* Pidgeon, Quart. y<mr. Geol. Soc„ 1890, p. 438.

t McKentiy Hughes, Quart, Jour, Geol. Soc,, 1887, p. 657.

'V

Changes in the Level of Devon* 183

The great Ice Age waxed and waned, and as the climate
improved the country rose again, until a broad bridge must
have extended from England to France, a bridge over which
the European animals returned to populate the forests and
leave records of their presence in caverns like those of
Brixham and Kent's Hole, or buried in the river gravels.
Once more the forests spread far over the floor of the
Bristol Channel and around the shores of Cornwall,
stretching we know not how far westward towards the
Scilly Isles.

At dead low water of spring tides there are numerous
places where tree stumps have been found in the position of
growth with their roots spreading out in a soil, with
fragments of trees like those now native on the shore. Beds
of peat have been found in a similar situation. Moreover
the actual channels of the Dart and the Tamar and its
tributaries and other rivers lie deep below the present
bottom of the sea which fills them. No tidal scour, no
action of the present streams could ever have scooped
out those valleys to such a depth beneath the sea. They
must have been excavated when the land stood at a high
enough level for the rock bottom to be at least within the
reach of surface movements. This may have been before the
Glacial period, but the sides of the submerged valleys conform
to those now seen above the mud and sand which All the
lower part, so that it seems almost certain that the valleys
and the forests are both Post-Glacial, and belong to the
period when the mammoth, rhinoceros and hippopotamus
wallowed in the Exe, and when lions, bears, hyaenas, and
wolves prayed on the bison, reindeer and Irish elk around
Torquay,

The heavy snowfall of the glacial age was followed by a
time of much greater rainfall than the present. Gravels and
sands were swept headlong from the hills and spread out
over the plains, as is seen in the " head " which covers the
Bovey clay. The deposits of glacial time, which probably
existed in hollows and flatter ground, were scoured away,
and the deep river valleys of Pliocene days cut deeper still.
But, as a whole, the county presented much the same features

i84 The Histofy of Deronsliire Scenety*

as we see to-day, save that its shores lay far beyond the
present coast line.

Among the remains of the post-glacial beasts we find, for
the first time in geological history, the implements and
handiwork of man. It seems, then, that the vanished land of
Lyonesse is not an empty legend, the creation of some ancient
poet's brain, but is far more likely a tradition handed down
by word of mouth through the ages of human history from
men and women who had hunted in its forests and sheltered
in its caves. The earliest men of Britain, long-armed and
narrow-headed, uncouth in form and primitive in all their
ways, but undoubted men, who by their advent marked the
beginning of another Era.

Valley of the Otter: Honiton.

Bindon Landslip: The Great Chasm*

CHAPTER XV.

The Modern Scenery.

The ultimate result of the events which have been out-
lined in the foregoing pages has been to produce a greater
variety of contrasted types of scenery than can be found
in any equal area within our shores.

In the east of Devon we have the plateau district,
carved out of the Eocene peneplain. It is characterised by
flat topped hills covered with a shallow stony soil, which
has often been left untilled, and is covered with ling and
heather, chequered with groves of firs and pines.

From these breezy uplands we look down into the deep
valleys whose sides show steep slopes near the summit,
where the Eocene and Cretaceous rocks form the subsoil.
These precipitous walls are also generally clothed with trees
and heath, and are fringed below by a line of springs and
boggy ground which marks the top of the Lias, or the
red marls — that is, the buried peneplain of Jurassic days.

Below this line the slopes are generally more gentle, and
the rest of the valley is occupied by undulating country, most
of which is covered with verdant meadows and tall
deciduous trees.

The southward inclination of the strata has caused the
coast from Pinhay Bay to the Haven Clifif to be fringed
with landslips. Most of these are prehistoric, but some
are quite modern. Thus on Christmas Day, 1839, nearly
forty acres of land broke loose at Bindon Farm and slowly
moved seawards. The Chalk and Greensand here rest on a
surface of impervious Rhaetic clays, and after an unusually
wet year the fox mould was reduced to the condition of a
quicksand, and collapsed under the weight of the overlying
rocks. A great block of nearly fifteen acres slid seaward,
while more than twenty acres either subsided into a great
chasm behind the block, or broke up into tall pinnacles and
stacks. This great slip was followed in February, 1840, by
a smaller one a mile further east where the Blue Lias forms
the base.

i86 The History of Deronshife Scnery*

This is the youngest part of the county, and dates, as has
been shown, only from the Eocene upheaval. Indeed the
present direction of its drainage is more recent still, since
it must be traced to that southward tilt in the middle of
Tertiary time which was the last great modifying factor in
the history of the district. Nevertheless it should not be
forgotten that at least some of the lines of drainage were
originally mapped out by irregularities of the emerging sur-
face, caused by the remnants of the hills and valleys which
must have marked the underlying Jurassic land surface.

The Great and Little Haldon are, of course, outlying
fragments of this eastern plateau. With their exception
we find its edge looks down on country of a totally
different type.

The ridge which runs through Woodbury Common,
Aylesbeare and Whimple up to Burlescombe, marks the out-
crop of the Budleigh pebble bed. Until within compara-
tively recent days it also must have been crowned by a
patch of greensand and a strip of the plateau. But this
has entirely disappeared, and had it not been for the
coarse and porous texture of the pebble bed, and the en-
during nature of its component parts the ridge would have
been reduced to an undulating country like that on its
western side. The stony soil and exposed position fits it
for the growth of heaths and firs, and such are its
characteristic clothing until, further north, its texture
becomes less coarse. Along its base, where the underlying
marls crop out, we have the inevitable springs and bogs.

All across the red land until we near its limits, we find
the scenery is the result of the varying texture of the red
rocks; and on the whole it may be regarded as a larger
instance of what we find in the valleys of the plateau.

But this is modified, as we near Exeter, by the irregular
appearance of low hills marking the outcrop of the Permian
lavas, and by hills of Culm which rise through the red
sands and marls.

The Culm hills, as we have shown, must have been there
before the red rocks were formed, and in them we have,
uncovered to our view after two whole eras of geological

UncoTcred Pennian Scenety* 187

time have passed, the hills and valleys of Permian time.
Their slopes have been smoothed and rounded, and the
bottoms of the intervening valleys are still buried out of
sight. The hard and contorted Culm has resisted the wear
and tear of time, the rush of glacial floods and the action
of rain and frost, better than the more friable breccias and
sands; and so, little by little, the red cloak has been worn
away and the hills have grown more and more prominent
as they have been uncovered.

Now this difference in the resisting power of the rocks
is much less marked where the wear and tear is produced
by the grinding and rubbing of gravel upon the bottom of
a stream, than it is when the agents of destruction are more
gentle.

This is how the channels of the Creedy and the Exe
came to be cut through the Permian ridge of Culm which
extends across them both near Cowley Bridge. We can only
suppose that the courses of both rivers were marked out
on the Eocene peneplain above the hills, and that when
the streams came down to the Culm ridge it was more easy to
cut right across it than to clear another course around the
barrier. We have already attributed the beginning of these
gorges to some southern tributaries of the Eocene river,
perchance the Teign, but they may not have reached the
Culm ridge when the southward movement came, and both
Exe and Creedy were poured southwards. Those gorges
then are not of Permian date, but far later, more likely
Miocene or Pliocene, and the floods of the great Ice Age
probably had much to do with their excavation.

The limestone hills of Westleigh and the neighbourhood
are again partly uncovered Permian, and, if so, those which
lie not much further west must be quite uncovered relics of
the same distant age. Indeed all the broad region between
Dartmoor and Exmoor to the sea at Bude must, as we go
westward, differ gradually more and more from that of
Permian days, by the increasing amount of wear and tear
it has undergone, as it has been longer exposed on the
surface. We have no reason to suppose that the greater
part of North Devon, including Exmoor, has ever been

i88 The Hiftory of Devonshifc Scenery.

covered with newer deposits. The strip of red land which
extends by Crediton, and the smaller tongue at Tiverton
were both fjords on the side of the Permian lake, and in
the former there were probably ! Cretaceous deposits. No
trace of these has been left in the Tiverton district, and
it is unlikely that there ever were any if Mr. Downes is right
in stating that there are no flints in the gravels of the
upper Exe. The Crediton fjord however was certainly
occupied by the waters of the Cretaceous sea, for relics of
its presence have been traced to Orleigh Court, not far
from Torrington, a few miles from the small patch of red rock
in the comer of Bideford Bay. The work of the great North
Devon river was to clear this away and lay bare the pre>
Cretaceous surface, which must in turn have been modified
pre-Permian.

This ancient country is extremely uneven. Its rounded
hills, many of which are crowned by bleak and rather
desolate moors, are intersected by steep sided and richly
wooded valleys, whose slopes and turns have been determined
by the varying texture and irregular structure of their
crumpled rocks.

Close to the northern margin of the Culm district there
rises up a long line of high dome shaped hills which all
mark outcrops of the Culm basement beds of radiolarian
chert and dark limestone.

North of this line we reach the Exmoor range, the
surviving stump of the mountain ridge of the Post-Carboni-
ferous upheaval. The hardened Devonian rocks of which
it is built have produced scenery of quite a different t3rpe.
The great round-topped hills are intersected by deep, narrow,
valleys filled with luxuriant woods, still the home of the
wild red deer. The great boulders which fill the beds of
the tumbling streams are those which are just too big for
the winter floods to bear away, but after a stormy day it
is easy to hear the smaller pebbles rumbling and grating
on the bottom as the work of erosion goes on. So it has
gone on, at one time more rapidly, at others slower, ever since
the range was formed. Put hundreds of feet of rock into the
valleys, and pile hundreds upon the hills, and we should

Lydford Gorge: Pot-holes.

Lydford Gorge: The Deep Cleft.

Types of Rhrer Etosion« 189

restore the features of Eocene times. Make those hundreds
thousands and we have the mountains from which occasional
torrents swept into the Keuper Lake. In many cases we
should have the actual courses of those torrents, for none
of the movements we have described as having taken
place in the Secondary and Tertiary eras were abrupt
enough to change the courses of streams with so steep a
slope.

Southward across the Culm country we come to Dart-
moor, and again the scenery changes. The granite is
surrounded by a ring of basement Culm and Devonian
rocks which have been more or less baked and hardened
by the heat from the molton mass. This altered Culm
produces a margin not unlike Exmoor. On the west there
is the splendid valley of the Tavy, on the north and east
the gorges of the Teign. Further south are the similar scenes
of Bickleigh Vale and Holne Chase.

In these valleys, carved out of hard rock, some of
the work can be seen to be effected by what is known as
pot-hole action. A shallow hollow is formed on the bed
of the stream, or a few large boulders happen to lodge so
as to form a kind of cup into which the water pours in
such a way as to produce a swirling movement. If, now,
some stone is swept into the cup small enough to be
pushed round and round, but too large to be easily carried
away, it slowly abrades the rock, forming a rounded basin
which is gradually deepened. Two neighbouring pot-holes
enlarge until they join ; then the division clears away and
in time the process begins again.

Lydford Gorge, where the little Lyd crosses the aureole
of altered rock, has been almost entirely made by this
process. The narrowest and most sombre part of the gorge
shows innumerable smooth rounded sections of such holes,
some of which are far better than any diagram. The
stream falls and rushes along the bottom of a chasm from
seventy to eighty feet deep, and in places not more than
fifteen feet wide. Truly an awe-inspiring place if visited
when the snow is thawing quickly on the moor, or after
some days of heavy rain when the swollen waters fill the

igo The History of Devonshifc Scenenr*

great crevasse with a thunderous roar, and the black walls
are dripping wet with a mist of spray.

Lower down, where the ring of altered rock is crossed,
the valley opens out, but narrows again where it nears a
patch of volcanic rock, and then gradually opens wider
and wider as the rocks become more distant from the granite.

The granite area of the moor itself is bleak and bare.
It contains none of the deep wooded vales such as abound
among the northern heights, and the summits of its hills
are often crowned by rugged piles of naked rock called tors.

The sandstones of Exmoor, the grits of the Culm, and,
indeed, most rocks, when exposed to the weather, or to
water which has percolated through the soil, break up into
small pieces which are soon rounded into pebbles. With
granite this is the exception and not the general rule. Again,
granite does not yield to abrasion much more easily than
sandstone, but when exposed to the weather it has nothing
like the same power of resistance. The contrast is well
seen in the ruins of Okehampton Castle. The weather of
some centuries has beaten on these old walls, and blocks
of granite in them are deeply corroded, so that they can be
crumbled away and bits can be rubbed out of them with
the fingers, but other stones of red sand from Hather-
leigh seem quite unchanged, and still show the marks
of the mason's chisel.

Soft rocks like the unaltered Culm or Devonian shales
are very easily removed, either by flowing water, or by
exposure to the weather. But if such beds are intermixed
with grit and sandstone, the coarser debris these produce
is not easily removed by the weather ; it requires the action
of running water. If sufficient water power is available the
hard fragments make hard pebbles which are exactly the
tools for digging away the river bed. Thus, in a Culm or
Devonian country the rivers abrade their beds rapidly, but
the valleys do not open wide. The coarse fragments of
the harder beds must lie on steep slopes before they can
be moved.

If the shales also are hardened by heat they resist the
weather almost as well as the grit, but both yield hard

The Weathering of Granite. 191

pebbles, and the result is deep valleys with precipitous
sides, like Fingle Gorge upon the Teign, or in an extreme
case the narrow fissure made by the Lyd.

The peculiar properties of granite, whereby the unde-
composed stone is hard and well able to resist abrasion,
but the stone itself is somewhat easily rotted by the
weather, results as a rule in shallow, wide open, valleys with
comparatively gentle slopes.

This weathering of the granite is worthy of more
consideration. If the face of the rock on one of the projecting
tors is examined it will be seen that the feldspar has
become opaque, and that its larger crystals with the larger
grains of quartz project on the sur&ce. The finer matrix
in which these were embedded has crumbled away.
Beneath the soil it is no uncommon thing to find this
crumbling has penetrated far below the surface, so that the
rotten rock can be dug out with a spade, but the process
is uneven. The granite mass is naturally split up by joints
into great more or less cubic blocks, all of which are
large and heavy, some very large indeed. Some of these
blocks seem able to resist the action of weathering agents,
and remain practically unchanged, while their neighbours
have been reduced to the consistency of a coarse sandy clay.
Two very different types of debris are thus produced, a fine
kind easily removed from a slope and requiring only a
gentle stream to sweep it away, and an exceedingly coarse
kind, too large to be moved by anything short of a rushing
torrent in heavy flood. There is hardly any of that
medium sized hard debris which is the principal product
of sandstones, grits, cherts or flints — material small enough
to be fairly easily moved, and yet coarse enough to act
as efficient abrading tools, such as was the chief agent
in carving the deep valleys of other districts.

Dartmoor streams are therefore thickly cumbered with
these great boulders, and the surface of the moor is strewn
with them, where the removal of overlying and surrounding
crumbled rock has left them lying.

The tops of the hills are at first rounded, showing a
convex contour which becomes concave lower down, and

19^ The History of Devombkc Scenery.

the steepest part is where the character of the curve
changes. Now with such a mixture of very coarse and
fine debris the sides of the hill will be wasted more
rapidly than the top, and the concave slopes will draw
gradually together and extend higher up the hill, until
they reach the summit, and then the hill becomes pointed,
with slopes which get steeper as they near the top.

At the top of such a hill the fierce gales of winter
drive the heavy rains with great violence, and soon remove
the finer products of decay, leaving nothing but a pile of
the unrotted blocks. A pile of blocks once formed protects
the granite beneath it both by directly shading it from
rain, and still more by the absence of soil. It is the
products of vegetable decay which are the most powerful
agents of destruction, and rain which has not soaked
through any soil is far less potent. The result is that the
ground around the tor continues its general descent, but
the erosion of the tor itself is far more slow.

Exactly the same processes account for the crags that
often mark the outcrop of the crystalline rocks or lavas of
the Teign Valley and round Brentor, but the rocks which
form those summits are not naturally divided into great
semi-cubic masses like those of granite. Hence we may
have other tors such as Bottor, but they have not the
same features.

The barrenness of the Moor is due partly to the bleak
winds of winter, but also to a large extent to the nature
of its soil. The decomposition of the rock resulting in a
mixture of sand and clay, the subsoil is too frequently
water logged, and the surface consists of peaty bogs.
Properly tilled and drained, even the higher parts may be
brought under cultivation.

The average surface of the Moor is high above the
surrounding country, because its general rate of waste is
less than that of even the hardened Culm and Devonian
rocks. This seems at first sight almost a contradiction to
what has been said of the rate at which granite rots; it
is not really so. The rate at which a country is planed
away depends far more on the speed with which its rivers

The Cfown of the Moor: Yci Tor.

The Edge of the Moort Valley of the W. Okemcnt.

Scenery of Dartoiooff* 193

can dig their channels deeper. For the reasons given, the
streams on the granite deepen their channels very slowly,
and the surrounding rocks may rot, but the materials can-
not get away ; on the other hand in a district which yields
abundant debris of the right size the valleys deepen quickly,
and when any of the intervening rock does give way to the
action of the weather, it is soon removed and a fresh
surface exposed.

The granite, as a whole, then forms a projecting
highland and its edge is thus frequently trenched by the
streams where they rush down to the lower ground, but
these valleys suddenly narrow when the granite is left.

The greatest heights are on the northern and western
edge, and a broad hollow extends from the line of the
Bovey basin to Chagford. This has been attributed to a
shallow synclinal sinking during Tertiary time. It may be
so, and may therefore be due to a part of the change
which altered the river system.

But it must not be forgotton that the Moor has been
a land surface ever since its superincumbent volcanic peaks
first arose above the waves of the Devonian Sea. Those
peaks must have mapped out a drainage system among
themselves while they were still active volcanoes, and such
a drainage system must on the whole have persisted long
after they had become extinct. The valley bottoms dug
deeper and deeper into the mass of lavas and tuffs and
possible Culm rocks, until some of them reached the granite
and portions of it were carried down to be strewn in the
Permian breccias.

The contours of the granite would thus tend to retain
some slight resemblance to those which had gone before,
and it is more than possible that in the valleys and basins
of the present Moor we have a fainter copy of its surface
long ago.

Three thousand five hundred feet of basalt have been
removed from the west of Scotland, according to Geikie,
since early Tertiary time. Many thousands must then be
piled on the surface of modern Dartmoor, if we would re-
store it to what it was when the great flood of lava rushed

194 The History of DcYonshire Scenery*

from some vanished cone to pour down past Posbury,
Pocombe, Exeter and Poltimore.

Still one more type of scenery is found in southern
Devon, from Newton Abbot to Plymouth. It is a smoothed
and softened copy of the north, but varied by the irregular
distribution and variety of its component rocks. Lime-
stones and volcanic bosses diversify the landscape, caus-
ing the slopes to change abruptly and irregularly. The
deep valleys are varied by bold bluffs and gently sweeping
curves, while they are continued seaward by long branching
fjords. These are no sea-wrought inlets, but only drowned
portions of the valleys, and the beds of the streams which
made them now lie buried far beneath the mud which
paves the present channels. The broad alluvial plains
which in recent times have filled up the estuaries of the
Exe and Axe are made of gravels lodged in broader valleys
which were similarly submerged, and the process is still
going on. We know that in Roman times and later, the
estuary of the Axe was an important harbour, and indeed
it was in use so recently that the harbour quay is still in
good repair.

Such minor changes however have made little alteration
in the whole, but are enough to show that the making of
scenery is still progressing. The same agents of erosion and
reconstruction are busy as of old, and it is by watching
them at work that we can learn how they have worked
before.

A new factor has been added to the great physical
forces of Nature in the restless energy and enterprise of
man. Men hew the forests, drain the marshes, dam the
rivers, and obstruct the waves. But great as is the effect
they can produce upon the landscape, all their efforts do
little more than modify the surface. They cannot yet
control the floods, nor stay the storm. Volcanoes and
earthquakes still exist, but we have no means of knowing
whether the greater earth movements might or might not
still occur. It may be that the world has reached a stable
state, that its frame work has attained its final condition,
like the bones of a full grown man; but it is equally

The Story not Ended Yet* 195

likely that the vanished continents may again arise, and new
mountain chains grow from the ocean floor.

However this may be, many of the processes which have
made our county what it is are still at work, changing and
modelling anew its ancient frame. But some traces of its
present form must always be, for it is just as true of the
making of scenery as it is of human history or human
character, that the past has made the present, and the
present shapes the future.

ERRATA.

Page 49, line 27, for learn read hear,

„ 80, „ 17, „ Vucanello, „ Vtdcanello.

9> i43f It i9f >9 Beer Common „ White Cliff Fall.

Illustration dicing p. 104, for Sea Green read Tea Green.

INDEX-

ACID ROCKS, 67, 80

Actinocamax plenus, 139

Agglomerates, volcanic, 80

Alabaster, 103

Alps, upheaval of, 158, 176

Alain Bay, plants, 155

Ammonites, iii

„ Angulatus, 112

„ Bucklandi, 112

„ Planorbis, ill

„ Rothomagense, 139

„ Varians, 139

Andesite, 67, 80

Annis* Knob, 135

Anstey*s Cove, 37

Ash burton, 165

Ashbrittle, 48, 49

Ashclyst forest, 86

Ashprington, 37

„ Volcanic serieSi 29

Archaean rocks, 3

Armorican chain, 57

Atlantic, approach of, 146
„ ooze, 8

Axe, 171
„ Estuary of, 194

Aylesbeare, 186

Azoic era, 3

BABBACOMBE, 37
Baggy Point, 25
Bagshot Sands, 151
Bampton, 48, 170
Barle, 170
Barnstaple, 48, 169
Barton, 37
Basalt, 67

„ Exeter, 90
Bathem, 170
Bath Oolites, 116
Beaminster, 117
Beer, 127, 135
„ Common, 136
„ Cove, 126, 136

Beer Head, 127, 136
Belvidere, 90
Berry Head, 30
Bickleigh Vale, 189
Bideford, 55, 169
Bindon Cliffs, 102, 109

„ Farm, 185
Bittadon, 169
Bodmin Moor, 30
Bolt tail rocks, 4
Bone bed, 103
Bottor, 74, 192
Bournemouth, 151, 166

„ plants, 155

Bovey beds, 159 to 177

„ lake basin, 165

„ lignite, 159 to 177
Blackdown Greensand, 128

„ Hills, 128, 138, 168

Blackgang Chine, 124
Blackpool, 159
Black Venn, 125
Blue Anchor, 112
Blue Lias, no
Bradiford water, 169
Brampford Speke, 170
Branscomt>e, loi, 102, 127, 137
BrauDton, 25, 169
Bray, 169

Breccias, Permian, 83, 85
Brendon Hills, 85
Brentor, 75, 192
Brice Moor, 168
Bridestowe, 48
Bristol Channel, formation of,

178
Brixham limestone, 30
Broad Clyst, 90, 170
Brown Willy, 30, 79
Bmshford, 169
Budlake, 90
Bndleigh pebbles, 99, 186

„ Salterton, 98
Banter, 97
Borlescombe, 186

198

Index,

CADBURY, 148
Cadeleigh, 170
Caledonian Chain, 16

,, volcanoes, 44
Caledonia, lake, 16
Callington, 30
Cambrian rocks, 3, 5

„ geography, 5

„ volcanoes, 6
Cannington Hill, 47
Capstone Hill, 23
Carbonicola, 55
Carboniferous geography, 49
„ limestone, 41-44

„ sea floor, 50

„ Sea, extent, 53

Carter, loi
Castle Rock, 20, 21
Cenomanian limestone, 135, 140,

145
Chagford, 193
Chalk, 134* 138. I39, MS. ^47

„ marl, 139

„ with quartz grains, 134
Champernowne, 29, 35
Charmouth, no
Charnwood Forest, 17
Charton Bay, 109
Cherts, abysmal theory of, 50
Cheviot, lake, 16
Chloritic marl, 139
Chudleigh, 49, 53, 161

„ Knighton, 159

Church Cliffs, in, 115
Clifford Bridge, 175
Clovelly, 169
Clyst Honiton, 170
Coal measures, ^-45
Cock's Tor. 76
Coddon Hill, 49

„ Cherts, 52
Colom stream, 169
Columjohn wood, 90
Combe Hill Cross, 162
Combmartin Bay, 22
Concretionary limestone, 96
Corallian oolite, 117
Coral reefs, 38

„ limestone, 37
Cornwall, 30
Countisbury, 19
Cowley Bridge, 170, 187
Crediton, 127, 170, 188
Crecdy, 87, 173, 174
Cretaceous fauna, 146
Crewkerne, 117

Croyde Bay, 25
Culm, 41

„ measures, 45-48

„ types of, 53-55

„ greenstones, 74

„ scenery, 188
Cullompton, 170
Culverhole, 102, 109

DART, 29, 165, 183

„ (Cadeleigh), 175
Dartmoor, 49, 63, 78, 79, 80, 127.

193
Dartmouth, 37
Detnosaurs, 118
De la Beche, 35, 53
Denudation, amount of, 193
Deserts, types of, 105
Deutozoic time, 4
Devonian geography, 38

„ limestone, 39

rocks, 18, 19, 35, 40

„ volcanoes, 39
Devonshire lavas, 73

„ . rivers, 178

„ rocks, compression

of, 60
Distribution of sea sediments, 8
Dolerite, 67, 74
Dolomitic Conglomerate, 104
Dorset, Frome, 171
Downes, Rev. W., 128
Drewsteignton, 48
Dulverton, 170
Dunchideock, 90
Dunsford Bridge, 175

EGGESFORD, 55

grits, 55
Elvans, 81

„ with quartz grains, 82
English Channel, formation, 178
Eozoic era, 3
Eocene beds, 150

♦. geography, 158

„ gravels, 150, 151, 154, iS7

„ river, 173

„ surface, 147

„ upheaval, 166
Erosion of valleys, 189
Eurypterids, 15
Exe, 127, 170, 175, 194
Exeter, 83, 170

„ lavas, 90, 91, 94
Exmoor range, 59

Index*

199

Ezmoor scenery, 188
Exmouth, rocks of, 98

FELSITES, 67. 79
Fingle Gorge, 191
Flint rubble, 137, 156
Folding of rocks, 12, 60
Foraminifera, 9, 145
Foreland, 19
Fox, Howard, 7, 47, 49
Fox mould, 120
Frome, 174

GAULT, 124, 125
Geikie, i6, 177, 193
Glacial period, 180
Glaciation, absence of, 181
Glauconite, 123, 128
Godwin-Austen, 35
Goniatites, 47
Grampians, 13

Granite dome of Dartmoor, 63
„ in breccias, 89 ,
„ scenery, 190
Graptolites, 7

Greensand, 126, 129, 131, 136, 137,
153

HALDON, 83, 127, 148
Hangman grits, 21
Hatherleigh, 169
Haven Cliff, 102, 126
" Head/* 160
Heathfield, 159, 164
Heavitree breccia, 103
Heer, Dr., 160, 163
Heltor, 82
Hembury Fort 148
Hennock, 74
Hercynian chain, 57, 58
Hicks, Dr., 24, 59
High Peak, 100, 127
Hinde, 47, 49
Hobson, 90
Holcombe Burnell, 175

„ Rogus, 48, 49
Holmead, 91
Holl, 35

Holne Chase, 189
Honiton, 149

Hooken Cli£F, 102, 127, 136
Hunstanton, red chalk, 130

ICHTHYOSAURUS, H2
Ide,89
Ideford, 159
Ilminster, 117
Ilfracombe, 22, 23
Intrusive lavas, 32, 75
Isle of Wight, 120, 123

JUKES-BROWNE, 43, 113, 165
Jurassic erosion, 121

„ geography, 121

„ rocks, 116

KEUPER, 97

„ geography, 105

„ lake, end of, 107

„ marls, 103

Killerton trachytes, 90, 91
Kimeridge clay, 117

„ „ reptiles, 118

Kingskerswell, 159
Kingsteignton, 37, 161
Knowle Hill, Crediton, 91

LABYRINTHODON, loi

Ladrum Bay, 100

Lakes, Old Red Sandstone, 16

Landslip, Azmouth, 185

Lantern Rock, 22

Lapworth, 5

Launceston, 49

Lavas, 32

Lava reservoir, 72

Lavas in breccias, 92

Lavis, J., loi

Lias, 109, no

Liassic geography, 113, 114

Lias limestone, 115

Limestones, Devonian, 30

„ black, 48

Linton beds, 20
Liskeard, 30
London Clay, 151, 155
Lower Greensand, 123, 124
Loxbeare, 83, 91
Lummaton, 37
Lustleigh, 159
Lydford Gorge, 189
Lyme Cobb, 119
Lyme Regis, no

„ „ deep boring, 88
Lynmouth, 19
Lyonesse, 184

200

Index^

MAGNESIAN LIMESTONE, 95
Man, appearance, 184

„ influence, 194
Marshfield, 91
Martin's Rock, 137
Marwood beds, 25
McMahon, 75, 78
Meadfoot Sands, 36
Membury, 168
Mendip Hills, 58
Metamorphic rocks, 4
Midland pebble bed, 99
Milber Down, 159, 162
Millet seed bed, 103
Millstone grit, 44
Miocene changes, 178
Modbury, 30
Monk Okehampton, 173
Morte Point, 23

„ slates, 24
Morthoe, 23 169
Mountain building, 11, 12, 57

„ limestone, 41
Mullion Island, 7, 8
Murchison, 53

NEW RED ROCKS. 84. 86, 88, 95
Newton Abbot, 37, 160, 165, 194
Nomenclature, geological, 2
North Devon fossils, 20, 22, 25

„ „ range, 59

„ „ rocks, 19, 25

„ „ succession, 26, 28, 59

„ „ syncline, 60
Northernhay, 92
North Tawton, 169

OPFWELL, 168

Okehampton, 48

Okement, 172

Old Red Sandstone, 14-18

Ooze, globigerina, 9

Ordovidan geography, 10
„ rocks, 5
„ subsidence, 10

Otter, 171

Otterton Point, loi

Overlap, 11

Oxford Clay, 117

Paignton, 36, 82
Palaeozoic Era, 4
Paludina, 120

Paper shales, no

Parret, 171

Peak Hill, loi, 127, 149, 168

Pebble beds indicative of change,

100
Peneplain, 149
Pengelly, 160, 163, 168
Pennine folds, 62

„ range, 57
Permian climate, 106

„ geography, 96

„ period. 83, 98

„ scenery, 187
Petit Tor, 37

Pickwell Down sands, 25
Pinhay Bay, no
Pinhoe. battleaeld, 149
Pipeclays, 151,155,156
Plateau gravels, 147, 153

„ scenery, 185
Plesiosaurus. 112
Pliocene climate, 179

„ strata, 179
Plymouth. 30. 194

„ gravels, 115

„ Hoe, 30

., Sound, 36, 37
Pocombe, 90
Peltimore, 90
Portland beds, 118
Posbury stone, 93
Posidonomya, 47, 48
Post-Carboniferous geography, 63
Post-glacial animals, 183
„ erosion, 182

Pre-Cambrian rocks, 3
Protozoic time, 5

„ upheaval, 13, 14
Pterodactyles, 112
Purbeck beds, 119

„ pebbles in gravels, 167

QUANTOCKS, 59. 85
Quartz-porphyry, 92

RADDLING, 86

Raddon, 90

Radiolarian Cherts, 8, 9, 49

Rewe, 170

Red chalk, 130

Reid, Clement, 150, 152, 162, 168

Rhaetic beds, 109

Rhyolites, 67, 79. 81,

Rillage Point, 22

Index.

20 1

Rivers of Devon, 169

River valleys, persistence of, 175

Roach, 118

Rogers, Inkerman, 55

Rock salt, 104

Rose Ash, 93

Rougemont, 90

Rousdon, no

Rowe, Dr. A., 135

Rutley, 75

ST. CYRES, 174

St Erth beds, 180

St. Germans, 30

Salcombe, 4

„ Regis, 168

Saltash, 30

Salt crystals, fossil, loi
„ Lake, causes of, 104

Sampford Peverell, 175

Scandinavian Chain, 13, 16

Seaton, 124, 125, 134

Secondary Era, 97

Sedgwick, 53

Shanklin, 123

Sherborne, CD., 135

Sidmouth, 100, loi, 102, 127

Silurian rocks, 5

Silverton, 90, 175

South Devon, difficulties, 33
„ „ pressures, 33
„ „ rocks, 20, 31, 35, 37
„ „ range, 62
„ „ scenery. 194
„ „ volcanic rocks, 30,

31, 32, 37
Southdown Cliff, 36
Southmolton Road, 169
Sourton Tors, 76, 79
Solution of rock by lava, 81
Staple Hill, 162
Starkie Gardner, 163
Stoke Canon, 170

„ Fleming, 37

„ Hill, 86,87

TAUNTON, 170
Tavy, 189
Taw, 169, 172
Teall, Dr., 7, 49, 90
Teign, 127, 167

„ Valley lavas, 74, 82, 93
Teignmouth, 89
Tertiary animals, 176

Tertiary Era, 149

11 geography, 158
„ rivers, 173
„ upheaval, 147
„ volcanoes, 177

Thanet Sands, 150

Thorverton, 90

Tiverton, 83, 170, 188

Tone, 171

Torquay, 82

„ limestone, 30

Torridge, 169, 172

Torrington, 169

Torrs Walks, 23

Tors, origin of, 192

Trachyte, 67, 79, 80

Trentishoe, 21

Triassic period, 97

Trilobites, 7

UGBROOKE PARK, 54
Ugborough, 30
Upper Greensand, 125, 132
Unconformability, 11
Ussher, 35, 36, 52, 53, 54, 74, 78t
90,98

VALLEY GRAVELS, l8i

Venn, 48, 49

Vertical pressure, effect of, 61

Volcanic agglomerate, 76
„ areas in S. Devon, 37
„ magma, 65
„ ,. changes in, 69, 71

„ rocks, 65, 69

„ „ alteration of, 68

„ „ classification, 67

„ „ crystallisation, 31,

65
„ „ cycle, 68, 69

„ „ escape of, 31

„ „ extrusions from

Dartmoor, 78
„ „ solidification, 32

„ „ texture, 31, 66

WARBERRY HILL, 36
Wareham, 151
Warren, the, 130
Was Tor, 76
Watersmeet, 19
Watchet, 85

„ gypsum, 103

202

Index.

Watchet fossils, iii
Wealden, 120

» geographv, 123
Weald, upheaval, 177
Wenlock Edge, 11
Wcstleigh. 47, 48, 49. 51
Weymouth, 117
Whimple, 186

White Cliffi 124, 125, 126, 134
White Lias, 109
Winkleigh, 172
Wiveliscombe. 170
Wooda Bay, 21
Woodbury Common, 98, 127, 186

Woolacombe Sands, 25
Woolborough, 161, 162
Woolwich and Reading beds, 150
Worth, R. N., 64, 88, 115

YEALMPTON, 30
Yeo, 169
Yeovil, 174
Yetminster, 174

ZONES IN CHALK, 139, 141. 143
„ „ Lias, U2

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