Once a Week (magazine)/Series 1/Volume 8/The transformations of our southern coast
THE TRANSFORMATIONS OF OUR SOUTHERN COAST.
It is a frequent complaint with geologists, that without travelling there are few opportunities of examining any great convulsions of nature. We have no volcanoes; we lie out of the region of earthquakes; even avalanches and landslips must be sought in Switzerland. In many parts of Great Britain, indeed, we may discover their effects, but then it is rarely possible to meet with any historic evidence of the convulsion. That these complaints, however, are not always well founded, we were glad to acknowledge on a late excursion to the West of England, while studying the phenomena of geological disintegration.
Few coasts are more favourable for this study than that which lies between the oolite of Portland and the granitic and trappean headlands of Cornwall. Off Portland, for instance, rolls the Chesil travelling beach, each pebble carrying a long history in every scratch upon its surface. Passing by the Dorset oolite, we enter upon the lias some way east of Lyme Regis. Its dark-blue flakes are falling from the cliffs with every change of temperature, disclosing wonderful saurians and ammonites, and trampled into thick slime on the beach. Then come the greensand and new red sandstone, so characteristic of the Devon coast, on to Teignmouth. Curious are the transformations visible down this coast from disintegration. Often gigantic columns and huge masses of rock and marl are left standing in the sea, like champions from whom the main line of cliff, which does battle against the waves, has retired. “The Parson and Clerk Rock,” familiar to travellers on the South Devon Line, is an instance of this.
In the case of maritime cliffs, the chief agents in the work of disintegration are the sea below and atmospheric changes above. Constantly beating on their base, the waves sap them, and then their own weight brings down the overhanging masses. Again, frost, heat, and rain are great disintegrants: the latter, insinuating itself into chinks, washes out argillaceous or calcareous veins, thus frequently dislocating large masses of rock. Sometimes these stand in fantastic forms; sometimes their débris raises a regular breakwater against further marine encroachments. Other and deeper causes must be sought for such phenomena as the continuous sinking of the entire continent of South America. Constant rains will frequently wash down the whole face of a cliff. Such catastrophes alter the character of the ground so completely that a stranger would often affirm what is really the work of a night to have sprung from the gradual effects of ages.
We came upon two very characteristic landslips of this kind, which we will describe as illustrative of the preceding remarks. Skirting the coast from the west the traveller passes from the Sidmouth greensand into the chalk region of Beer. The beach all at once fails him; the huge white cliff-walls trend back for a quarter of a mile, enclosing within their arms a tract of from seven to ten acres broken into hillocks and dips of every shape and size, and pierced here and there near the sea by precipitous, tower-like masses crowned with verdure. Heaps of barren flints diversify one hollow; a second is full to profusion of rare orchises, and of every other kind of flower dear to Devon skies; bushes tenanted by active colonies of rabbits close in round a third. It is a wild, lonely spot, falling away from varying heights into the sea, with huge chalk blocks glittering under the waves like the cherished hopes of a summer dream; and from the distant shelves of Beer Head you may catch the faint croaking of a raven warning you against putting too much trust in your bright visions. A path leads up the face of the cliff, conducting the sure-footed to a view unsurpassed by any other Devon headland, prodigal of grand scenery as they are.
Naturally the question arises, How came this convulsive rent in a line of coast so uniform in its high cliff beached with a narrow pebbly strand? Does it date back to unknown ages when the cave bear and elephant roamed over our land? The neighbouring villagers will tell a different tale. One fine night in March, 1789, this tract suddenly sank from 200 to 260 feet. The fishermen at sea heard crashings proceed from the site, and the impingement of such an enormous weight produced a rise of submarine rocks in front. Crab-pots, placed in the evening in 20 feet of water, were found next morning, high and dry, 15 feet above the sea level, the rocks having risen 35 feet from their old position.
Before examining the causes which led to this freak of nature, let us pass some four miles further on, hard by the commencement of the Lyme Regis lias. Here is another and more extensive landslip, which took place on Christmas Day, 1839. The whole line of cliffs at this point, instead of presenting a continuous front of sea-wall, is broken up into an undercliff extending inland more than a furlong. It is even more picturesque than the Beer landslip, partly owing to the causes which resulted in this “rougement” (as the natives call it) having been similarly at work in its neighbourhood for centuries, and partly because the ground displaced was originally wooded. Now it is a wild scene of dingles, clumps, and terraces, covered thickly with trees and bushes.
On the morning of the 24th December, 1839, slight fissures were observed in the cliffs. That night, however, they appeared in the fields above, and on Christmas night an immense tract of a mile in length, about 80 yards in width, and between 100 and 200 feet deep, sank into a vast ravine. About 100 acres of cultivated land were thus depressed, and all broken up and dislocated into patches, with huge chinks intervening, and soil from above constantly precipitated into the abyss. At the same time the ground between this “rougement” and the sea was riven afresh with, the wildest confusion. Some labourers who were dwelling on the depressed tract luckily escaped by flight. But a still more curious phenomenon occurred on that night. “One of the coast-guard men,” says the pamphlet we mentioned, “whilst on duty near the Undercliff, observed the sea to be in an extraordinary state of agitation. The beach on which he stood rose and fell. Amidst the breakers near the shore something vast and dark appeared to be rising from the bottom of the sea, amidst the deafening noise of crashing rocks and flashing lights, attended with an intolerable stench. He fled to the cliffs above. These also were trembling round him, but he gained the firmer ground, almost dead with terror.” In the morning a huge reef of lias and broken rock, 40 feet high and more than a mile long, covered with seaweed and shell-fish, was found extended above the sea, doubtless caused by the vast lateral pressure of the ground which had sank parallel to it. Each end terminated in a basin of deep water, and of course the natural features of the coast had undergone an entire change. Strange to say, during the ensuing January this reef gradually sank from 10 to 20 feet, and in two or three months disappeared entirely. Now there remains no trace of it.
As might be expected, thousands of visitors flocked to the spot after the convulsion, and all the wisdom of the neighbourhood was at issue upon the causes which had led to it. The advocates of the marvellous were unanimous in favour of an earthquake. It was useless to tell them that the coast lay quite out of the line of volcanic action that there had been no tremulous motion—that no shock had been felt, even in farmhouses close at hand. They triumphantly appealed to the scared coast-guardsmen, and their depositions are given in the pamphlet to the effect that they felt the beach “rise and fall under them,” heard noises like “distant thunder,” while the reef was “rising out of the sea attended with flashes of fire and a strong smell of sulphur.” Plutonic, certainly! As for the neighbouring farmers, they still persist, spite of the clearest evidence to the contrary (as is generally the way with farmers), in regarding it as a windfall; so that the visitor should provide himself with a ticket to view the cliffs, or they will not be very civil to him.
Those who can be satisfied, however, with reasonable causes, without calling in a needless “deus ex machinâ,” will probably agree with Buckland and Conybeare. Close examination convinced them, that as the mass which slipped (or rather sank) consisted of sandstone and cherty flint resting on more than 100 feet of loose sand (locally termed “foxmould”), which itself rested on a bed of solid lias, the heavy rains which, preceded the catastrophe were the proximate causes of it. The upper strata were saturated, and the water, oozing through and finding vent from the “foxmould” in landsprings, undermined the whole tract. So the superincumbent mass slid onwards over the retentive lias into the gulf. Its pressure forced up the reef, which gradually sank into its old form on the momentum ceasing to act upon it. As to the other landslip at Beer described above, it was found that the spring of 1789 had also been unusually wet. Many other authentic cases of such “landslips" (the generic term even when the land sinks) appear to bear out this theory.
We returned from our investigation convinced that the natural forces in daily operation on the earth will be found, the more they are studied, to account for far more geological changes than are usually placed to their credit. The hypothesis of countless aeons of antiquity is one which (like the earthquake mentioned above), though a very simple and accommodating solvent, should be used, as sparingly as possible in physical inquiries. It has acquired such gigantic though airy proportions, that its very bulk is fatal to it. Like “goodness driven to a plethora,” it often “dies of its own too much.” Reasonable men will always be ready to accept a plain in preference to a marvellous cause, in order to account for much that they see around them.