an indefinite period with no material change of surface. But, should
they be upraised, the elevation, by increasing the slope of the
streams, augments their erosive power, and enables them once more to
deepen their channels. Hence, plains like that of the New Forest,
which have been trenched by the water-courses that traverse them, may
with probability be assigned to a time when the land stood at a lower
level than it occupies at present. In this connection the successive
river-terraces of the country deserve attention. They may be due not
to the mere unaided work of the rivers, but to the cooperation of
successive uplifts. It would be an interesting inquiry to correlate
the various river-terraces throughout the country, for the purpose of
discovering whether they throw any light on the conditions under which
the most recent uprise of the country took place. That the elevation
proceeded intermittently, with long pauses between the movements,
is shown by the succession of raised beaches. It may be possible to
establish a somewhat similar proof among our river-terraces.
The submarine plains are by far the most extensive within the British
area. The tendency of tidal scour and deposit must modify the form
of the bottom. In the case of the North Sea, for example, this great
basin of water is obviously being slowly filled up by the deposit of
sediment over its floor. A vast amount of mud and silt is borne into
it by the rivers of western continental Europe, and of the eastern
coast of Britain; while at the same time the waves are cutting away
the land on both sides of this sea and swallowing up the waste. We
have only to contrast the colour of the Atlantic on the west of Ireland
or of Scotland with that of the North Sea, to be assured of the wide
diffusion of fine mud in the water of the latter. There is practically
no outlet for the detritus that is thus poured into the basin of the
North Sea. From the north a vast body of tidal water enters between
Scotland and Norway, and travelling southward, aided by the strong
northerly winds, sweeps the detritus in the same direction. On the
other hand, another narrower and shallower tidal stream enters from
the Strait of Dover, and, aided by the south-west winds, drives the
sediment northward. Yet, making every allowance for the banks and
shoals which this accumulating deposit has already formed, we can
still, without much difficulty, recognise the broader features of
the old land-surface that now lies submerged beneath the North Sea.
As already mentioned (p. 131), it presents two plains or platforms,
of which the southern has an average level of perhaps a little more
than 100 feet below the surface of the water. This upper plain ends
northward in a shelving bank, probably the prolongation of the
Jurassic escarpment of Yorkshire, and is succeeded by the far wider
northern plain, which lies from 100 to 150 feet lower, and gradually
slopes northward until it is trenched by the great south Scandinavian
submerged fjord. The drainage-lines of the united Rhine, Thames, etc.,
on the one side, and the Elbe, Weser, etc., on the other can still
be partially traced on that sea-floor. The site of the Irish Sea was
probably once a terrestrial plain dotted with lakes. This land-surface
appears to have been submerged before the whole of the present fauna
and flora had reached Ireland.
THE COAST-LINE.
Some of the most characteristic and charming scenery of the British
Islands is to be found along their varied seaboard. Coast scenery
appears to depend for its distinctive features upon (1) the form of the
ground at the time when by emergence or submergence the present level
was established; (2) the composition and structure of the shore-rocks;
(3) the direction of the prevalent winds, and the relative potency of
subaërial and marine denudation.
The British coast-line presents three distinct phases: in many places
it is retreating; in others it is advancing; while in a few it may be
regarded as practically stationary. As examples of retreat, the shores
of a large part of the east of England may be cited. In Holderness,
for instance, a strip of land more than a mile broad has been carried
away during the last eight centuries. Even since the Ordnance Survey
maps were published in 1851, more than 500 feet have in some places
been removed, the rate of demolition being here and there as much as
five yards in a year. The advance of the coast takes place chiefly
in sheltered bays, or behind or in front of projecting headlands and
piers, and is due in large measure to the deposit of material which
has been removed by the sea from adjoining shores. The amount of land
thus added does not compensate for the quantity carried away, so that
the total result is a perceptible annual loss. The best examples of
a stationary coast-line, where there is no appreciable erosion by
the waves and little visible accumulation of detritus, are to be
found among the land-locked fjords or sea-inlets of the west coast of
Scotland. In these sheltered recesses the smooth striated rocks of
the Ice-Age slip under the sea, with their characteristic glaciated
surfaces still so fresh that it is hard to believe that a long lapse of
ages has passed away since the glaciers left them.
The remarkable contrast between the scenery of the eastern and western
coast-line of the British Islands arises partly from the preponderance
of harder rocks on the west side, but probably in large measure upon
the greater extent of the submergence of the western seaboard, whereby
the sea has been allowed to penetrate far inland by fjords which were
formerly glens and open straths.
The details of coast-scenery vary with the rock in which they are
developed. Nowhere can the effects of each leading type of rock upon
landscape be more instructively studied than along the sea-margin. As
distinct types of coast-scenery, reference may be made to sea-cliffs
and rocky shores of granite, gneiss, basalt, massive sandstone and
flagstone, limestone, alternations of sandstone shale or other strata,
and boulder-clay, and to the forms assumed by detrital accumulations
such as sand-dunes, shingle-banks, and flats of sand or mud.
The concluding portion of the last lecture was devoted to an indication
of the connection between the scenery of a country and the history
and temperament of the people. This subject was considered from four
points of view, the influence of landscape and geological structure
being traced in the distribution of races, in national history, in
industrial and commercial progress, and in national temperament and
literature.[68]
FOOTNOTES:
[55] An abstract of five lectures given at the Royal Institution in
January, February, and March, 1884. _Nature_, vol. xxix. pp. 325, 347,
396, 419, 442. The notes here inserted are now added for the first time.
[56] See postea p. 154.
[57] To these east-and-west foldings of the terrestrial crust we owe
the plication of our Cretaceous and older Tertiary strata which have
given us the ranges of the North and South Downs. They were accompanied
by powerful horizontal thrusts of portions of the crust. The successive
plications of the terrestrial crust in the European area have since
been discussed by Prof. Suess in his _Antlitz der Erde_.
[58] See note on p. 146.
[59] A pre-Cambrian group of mountains has been exposed by denudation
in the west of Ross-shire. See p. 72.
[60] Since these lectures were given the remarkably complex structure
of the North-West Highlands has been made known. It has been
ascertained that gigantic horizontal displacements of rock have
occurred in that region, and that similar 'thrusts' have more or less
affected the rest of the Highlands.
[61] A striking instance of one of these fragments is to be seen on the
summit of Slieve League in Donegal. See p. 61.
[62] See pp. 161, 193.
[63] Other periods of prolonged denudation might be mentioned. Thus in
pre-Cambrian times the Lewisian Gneiss was stupendously eroded before
the deposition of the Torridon Sandstone, which in turn was enormously
worn down before the Cambrian sediments were spread unconformably
over it. The deposition of the Old Red Sandstone was preceded and
accompanied by a vast degradation of the pre-existing rocks.
[64] That the Secondary formations once extended far beyond the limits
within which they are now confined has been impressively demonstrated
by the discovery of large masses of Rhaetic, Liassic, and Cretaceous
strata in a great volcanic vent of Tertiary age in the Isle of Arran
(see Messrs. Peach, Gunn, and Newton, _Quart. Journ. Geol. Soc._,
lvii., 1901). It may consequently be inferred that the present drainage
system and topographical features of much, if not most, of the country
have been established since the time of the Chalk (see the 'Geology of
Eastern Fife' in _Memoirs of the Geological Survey_, 1902, p. 281).
The stupendous erosion of the Tertiary lava-plateaux of the west of
Scotland and the north of Ireland shows, in the most impressive way,
how greatly the topography has been carved out since older Tertiary
time.
[65] I have shown that some of the wildest glens of the Highlands
and the deepest dales of the southern Uplands of Scotland have been
hollowed out since early Tertiary time by the various streams that
still flow in them. _Scenery of Scotland_, 3rd ed., pp. 162, 339, 361.
[66] The Scottish Lakes have in recent years been made the subject of
detailed study by Sir John Murray and Mr. F. Pullar. The results of
their investigations have appeared in the _Geographical Journal_.
[67] Lough Neagh has been produced by subsidence, probably since the
Glacial Period. See _Ancient Volcanoes of Great Britain_, vol. ii. p.
448.
[68] Some of these subjects were subsequently more fully treated in the
three foregoing essays of the present volume.
V
The Centenary of Hutton's 'Theory of the Earth'[69]
In its beneficent progress through these islands the British
Association for the Advancement of Science now for the fourth time
receives a welcome in this ancient capital. Once again, under the
shadow of these antique towers, crowded memories of a romantic past
fill our thoughts. The stormy annals of Scotland seem to move in
procession before our eyes as we walk these streets, whose names and
traditions have been made familiar to the civilised world by the
genius of literature. At every turn, too, we are reminded, by the
monuments which a grateful city has erected, that for many generations
the pursuits which we are now assembled to foster have had here their
congenial home. Literature, philosophy, science, have each in turn been
guided by the influence of the great masters who have lived here, and
whose renown is the brightest gem in the chaplet around the brow of
this 'Queen of the North.'
Lingering for a moment over these local associations, we shall find
a peculiar appropriateness in the time of this renewed visit of the
Association to Edinburgh. A hundred years ago a remarkable group
of men was discussing here the great problem of the history of the
earth. James Hutton, after many years of travel and reflection, had
communicated to the Royal Society of this city, in the year 1785, the
first outlines of his famous _Theory of the Earth_. Among those with
whom he took counsel in the elaboration of his doctrines were Black,
the illustrious discoverer of 'fixed air' and 'latent heat'; Clerk,
the sagacious inventor of the system of breaking the enemy's line in
naval tactics; Hall, whose fertile ingenuity devised the first system
of experiments in illustration of the structure and origin of rocks;
and Playfair, through whose sympathetic enthusiasm and literary skill
Hutton's views came ultimately to be understood and appreciated by the
world at large. With these friends, so well able to comprehend and
criticise his efforts to pierce the veil that shrouded the history
of this globe, he paced the streets amid which we are now gathered
together; with them he sought the crags and ravines around us, wherein
Nature has laid open so many impressive records of her past; with
them he sallied forth on those memorable expeditions to distant parts
of Scotland, whence he returned laden with treasures from a field of
observation which, though now so familiar, was then almost untrodden.
The centenary of Hutton's _Theory of the Earth_ is an event in the
annals of science which seems most fittingly celebrated by a meeting
of the British Association in Edinburgh.
In choosing from among the many subjects which might properly engage
your attention on the present occasion, I have thought that it would
not be inappropriate nor uninteresting to consider the more salient
features of that 'Theory,' and to mark how much in certain departments
of inquiry has sprung from the fruitful teaching of its author and his
associates.
It was a fundamental doctrine of Hutton and his school that this globe
has not always worn the aspect which it bears at present; that, on the
contrary, proofs may everywhere be culled that the land which we now
see has been formed out of the wreck of an older land. Among these
proofs, the most obvious are supplied by some of the more familiar
kinds of rock, which teach us that, though they are now portions of
the dry land, they were originally sheets of gravel, sand, and mud,
which had been worn from the face of long-vanished continents, and
after being spread out over the floor of the sea were consolidated
into compact stone, and were finally broken up and raised once more
to form part of the dry land. This cycle of change involved two great
systems of natural processes. On the one hand, men were taught that
by the action of running water the materials of the solid land are in
a state of continual decay and transport to the ocean. On the other
hand, the ocean-floor is liable from time to time to be upheaved by
some stupendous internal force akin to that which gives rise to the
volcano and the earthquake. Hutton further perceived that not only had
the consolidated sediments been disrupted and elevated, but that masses
of molten rock had been thrust upward among them, and had cooled and
crystallised in large bodies of granite and other eruptive materials,
which form so prominent a feature on the earth's surface.
As a further special characteristic, this philosophical system sought,
in the changes now in progress on the earth's surface, an explanation
of those which occurred in older times. Its founder refused to invent
causes or modes of operation, for those with which he was familiar
seemed to him adequate to solve the problems with which he attempted
to deal. Nowhere was the profoundness of his insight more astonishing
than in the clear, definite way in which he proclaimed and reiterated
his doctrine, that every part of the surface of the continents, from
mountain-top to seashore, is continually undergoing decay, and is thus
slowly travelling to the sea. He saw that no sooner will the sea-floor
be elevated into new land than it must necessarily become a prey to
this universal and unceasing degradation. He perceived that, as the
transport of disintegrated material is carried on chiefly by running
water, rivers must slowly dig out for themselves the channels in which
they flow, and thus that a system of valleys, radiating from the
water-parting of a country, must necessarily result from the descent
of the streams from the mountain crests to the sea. He discerned that
this ceaseless and widespread decay would eventually lead to the entire
demolition of the dry land, but he contended that from time to time
this catastrophe is prevented by the operation of the underground
forces, whereby new continents are upheaved from the bed of the ocean.
And thus in his system a due proportion is maintained between land and
water, and the condition of the earth as a habitable globe is preserved.
A theory of the earth so simple in outline, so bold in conception,
so full of suggestion, and resting on so broad a base of observation
and reflection, ought, we might think, to have commanded at once the
attention of men of science, even if it did not immediately awaken the
interest of the outside world; but, as Playfair sorrowfully admitted,
it attracted notice only very slowly, and several years elapsed before
anyone showed himself publicly concerned about it, either as an enemy
or a friend. Some of its earliest critics assailed it for what they
asserted to be its irreligious tendency--an accusation which Hutton
repudiated with much warmth. The sneer levelled by Cowper a few years
earlier at all inquiries into the history of the universe was perfectly
natural and intelligible from that poet's point of view (p. 128).
There was then a widespread belief that this world came into existence
some six thousand years ago, and that any attempt greatly to increase
that antiquity was meant as a blow to the authority of Holy Writ. So
far, however, from aiming at the overthrow of orthodox beliefs, Hutton
evidently regarded his 'Theory' as an important contribution in aid of
natural religion. He dwelt with unfeigned pleasure on the multitude of
proofs which he was able to accumulate of an orderly design in the
operations of nature, decay and renovation being so nicely balanced
as to maintain the habitable condition of the planet. But as he
refused to admit the predominance of violent action in terrestrial
changes, and on the contrary contended for the efficacy of the quiet,
continuous processes which we can even now see at work around us, he
was constrained to require an unlimited duration of past time for the
production of those revolutions of which he perceived such clear and
abundant proofs in the crust of the earth. The general public, however,
failed to comprehend that the doctrine of the high antiquity of the
globe was not inconsistent with the comparatively recent appearance of
man--a distinction which seems so obvious now.
Hutton died in 1797, beloved and regretted by the circle of friends
who had learnt to appreciate his estimable character and to admire his
genius, but with little recognition from the world at large. Men knew
not then that a great master had passed away from their midst, who had
laid broad and deep the foundations of a new science; that his name
would become a household word in after generations, and that pilgrims
would come from distant lands to visit the scenes from which he drew
his inspiration.
Many years might have elapsed before Hutton's teaching met with wide
acceptance, had its recognition depended solely on the writings of
the philosopher himself. For, despite his firm grasp of general
principles and his mastery of the minutest details, he had acquired a
literary style which, it must be admitted, was singularly unattractive.
Fortunately for his fame, as well as for the cause of science, his
devoted friend and disciple, Playfair, at once set himself to draw
up an exposition of Hutton's views. After five years of labour on
this task there appeared the classic _Illustrations of the Huttonian
Theory_, a work which for luminous treatment and graceful diction
stands still without a rival in English geological literature. Though
professing merely to set forth his friend's doctrines, Playfair's
treatise was in many respects an original contribution to science of
the highest value. It placed for the first time in the clearest light
the whole philosophy of Hutton regarding the history of the earth, and
enforced it with a wealth of reasoning and copiousness of illustration
which obtained for it a wide appreciation. From long converse with
Hutton, and from profound reflection himself, Playfair gained such a
comprehension of the whole subject that, discarding the non-essential
parts of his master's teaching, he was able to give so lucid and
accurate an exposition of the general scheme of Nature's operations
on the surface of the globe, that with only slight corrections and
expansions his treatise may serve as a text-book to-day. In some
respects, indeed, his volume was long in advance of its time. Only, for
example, within the lifetime of the present generation has the truth of
his teaching in regard to the origin of valleys been generally admitted.
Various causes contributed to retard the progress of the Huttonian
doctrines. Especially potent was the influence of the teaching of
Werner, who, though he perceived that a definite order of sequence
could be recognised among the materials of the earth's crust, had
formed singularly narrow conceptions of the great processes whereby
that crust has been built up. His enthusiasm, however, fired his
disciples with the zeal of proselytes, and they spread themselves
over Europe to preach everywhere the artificial system which they had
learnt in Saxony. By a curious fate Edinburgh became one of the great
headquarters of Wernerism. The friends and followers of Hutton found
themselves attacked in their own city by zealots who, proud of superior
mineralogical acquirements, turned their most cherished ideas upside
down and assailed them in the uncouth jargon of Freiberg. Inasmuch
as subterranean heat had been invoked by Hutton as a force largely
instrumental in consolidating and upheaving the ancient sediments that
now form so great a part of the dry land, his followers were nicknamed
Plutonists. On the other hand, as the agency of water was almost alone
admitted by Werner, who believed the rocks of the earth's crust to have
been chiefly chemical precipitates from a primeval universal ocean,
those who adopted his views received the equally descriptive name of
Neptunists. The battle of these two contending schools raged fiercely
here for some years, and though mainly from the youth, zeal, and energy
of Jameson, and the influence which his position as Professor in the
University gave him, the Wernerian doctrines continued to hold their
place, they were eventually abandoned even by Jameson himself, and the
debt due to the memory of Hutton and Playfair was tardily acknowledged.
The pursuits and the quarrels of philosophers have from early times
been a favourite subject of merriment to the outside world. Such a
feud as that between the Plutonists and Neptunists would be sure to
furnish abundant matter for the gratification of this propensity.
Turning over the pages of Kay's _Portraits_, where so much that was
distinctive of Edinburgh society a hundred years ago is embalmed,
we find Hutton's personal peculiarities and pursuits touched off in
good-humoured caricature. In one plate he stands with arms folded and
hammer in hand, meditating on the face of a cliff, from which rocky
prominences in shape of human faces, perhaps grotesque likenesses
of his scientific opponents, grin at him. In another engraving he
sits in conclave with his friend Black, possibly arranging for that
famous banquet of garden-snails which the two worthies had persuaded
themselves to look upon as a strangely neglected form of human food.
More than a generation later, when the Huttonists and Wernerists were
at the height of their antagonism, the humorous side of the controversy
did not escape the notice of the author of _Waverley_, who, you will
remember, when he makes Meg Dods recount the various kinds of wise folk
brought by Lady Penelope Pennfeather from Edinburgh to St. Ronan's
Well, does not forget to include those who 'rin uphill and down dale,
knapping the chucky-stanes to pieces wi' hammers, like sae mony
road-makers run daft, to see how the warld was made.'