LITMIR.BIZ

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but the general slope of the surface above the part directly attacked by the sea may well leave a stronger impression on one’s mind than does the lower part of the cliff, which is likely to be steep. If the strata are inclined away from the coast the cliff slope is as a rule moderate. These simple cases can easily be visualised. In nature the form and structure of cliffs are very variable. Chalk Cliffs (see here) are often nearly vertical independently of their structure. This is presumably the outcome of the effects of marine and subaerial erosion on a rock of great homogeneity, good jointing, and often marked bedding. The profile of the cliffs of north Devon varies a good deal, but is locally steep—immediately north of Hartland Quay there is a range of high and almost vertical cliffs which are made up of sharply folded beds. On the other hand, soft rocks often form steep cliffs. The boulder clay cliffs of Holderness and of north Norfolk, or again around Criccieth and Afon Wen are soft and easily eroded by the waves. For this reason they are undercut and steepened. But local composition and height play their parts. The glacial cliffs near Sheringham are c. 100 feet high and steep, often tumbled, and composed not only of boulder clay, but sand and gravels. The natural angle of slope of these materials, even if partly consolidated, will not allow of verticality. Farther north the lower and, on the whole, more homogeneous Holderness cliffs sometimes approach the vertical.

In parts of north Devon and Somerset the slope of the land to the sea is decidedly steep. It is not in any sense a cliff of marine erosion, and the effect of the action of the sea can be noted at the bottom of the slope, which has been cut back into a low cliff. Comparisons between various parts of the Cornish coast bring out differences of this sort clearly. The relatively sheltered parts of the southern coast are fringed by low cliffs, whereas on the exposed parts of the northern coast there are fine and bold ones. But here again it is worth pausing to consider their origin. It looks as if these cliffs are entirely of modern formation, i.e. since the present levels of land and sea existed. But is this so? In order to illustrate this point turn for a moment to the Gower Peninsula, where there are some fine limestone cliffs at the foot of which are many traces of raised beaches. These remnants, whilst commonest in sheltered spots, are not only found in such places. A similar raised beach platform may have existed along north Cornwall; the remains of beaches in the Camel estuary and on the south coast are suggestive. Thus, it may be that the existing Cornish cliffs are far from being wholly produced under modern conditions. It is more than probable that they are but the slightly modified forms of much earlier formed cliffs, just as are those in the Gower peninsula. The same is true of the magnificent Old Red Sandstone cliffs near Duncansby Head in Caithness. The Geological Survey Memoir notes that the stacks seem to rise from a low platform, part of which may be found at the cliff foot. These are merely examples; many others could be given. They serve to show that our knowledge of cliff form and evolution is still in an elementary condition. More studies, such as that by Miss Arber¹ on the cliff profiles of Devon and Cornwall, are wanted before we can make any real advance in our knowledge of cliff scenery.

Before leaving this question, consider the western coast and islands of Scotland. In Chapter 8 it is shown that much of this area is all that remains of a former great plateau of lava. The disposition of the lavas and sills in Skye, Eigg, Mull, and other islands shows that these rocks once covered far greater areas. In Skye the cliffs are often largely or wholly formed of lavas and sills. No part of the island is fully exposed to the Atlantic, but nevertheless severe storms attack its shores. On its more exposed south-westerly facing side, there are some magnificent cliffs near Talisker Bay and Loch Brittle. Waterstein Head, farther north, is an imposing cliff of lavas and sills. At the foot of the major cliff is a low projection which is eroded by the waves; it does not follow that the major cliff above is similarly formed. In the comparatively calm waters of Loch Bracadale there are several instances of vertical cliffs to which it is impossible to ascribe an entirely marine origin. The east coast of Skye facing the island of Raasay is steep, and the cliffs are for the most part made of lava flows and sills resting on Mesozoic rocks, and fringed by a boulder beach. Raasay Sound is narrow and protected: it is difficult to suppose that cliffs along it are simply formed by wave action—in fact the green, steep slopes of the Mesozoic rocks of Skye imply that marine erosion is negligible. Judd many years ago showed that a fault probably runs along this Sound. It is known that faulting and foundering have broken up all this former volcanic area. Thus many lines of steep cliffs in lavas and sills are primarily fault-formed, and only secondarily modified by wave action. Since it is not for a moment supposed that the sides of sea lochs are the product of wave erosion, there is no reason for thinking that in places like the Sound of Sleat or the Sound of Mull, marine erosion has accomplished serious cliff erosion. The steep cliffs fringing so many parts of Skye and other islands, in relatively protected waters, are probably no more than the slightly (often very slightly) wave-modified slopes produced in some other way, in western Scotland sometimes by faulting.¹

Another feature which throws light on this problem is often seen in Scotland. As shown in Chapter 9 the present coast may be fringed for miles by raised beaches, usually by the 25-foot beach. This bench, which may be two or three hundred yards or more wide, forms almost a promenade attached to the land, and is backed by the old grass-grown cliffs. It is being eroded by the waves today; only where it is poorly developed have the waves cut through it and are now attacking the cliff behind, which is in those places clearly a composite cliff. How long this raised beach platform took to form is not known; it has not been greatly worn away in recent times and the cliffs cut in it are merely low crags and quite unlike the old cliff behind the beach, or the often numerous stacks on the beach platform. It is true that the coastline of most of England and Wales fails to show raised beach remains like those in Scotland, but the evidence in Scotland, Cumberland, Gower, Cornwall and elsewhere, makes one hesitate in ascribing many other English cliffs wholly and automatically to modern conditions.²

      Cliff scenery varies greatly from place to place. In Chapter 5 an analysis is given of certain lines of cliffs. Here there is only need to emphasise the importance of major structural lines. If a series of gentle folds runs more or less parallel with the coast, cliffs may be eroded along them, whilst at some other locality they cut across the folds (see here). The form of cliffs also depends largely on the structure and nature of the land in which they are being cut. Much of the beauty of a cliffed coast depends not merely upon the details of marine erosion in various rock types, but on the occurrence of rivers debouching into the sea. In Lyme Bay there are a number of small streams which reach the sea by percolating through the shingle. The valleys have been cut down to, or even below, sea level, but the present streams are not powerful enough to keep their mouths clear. The streams at Chideock, Charmouth, and Burton Bradstock are examples. On the other hand powerful rivers usually have wide open mouths. There are, however, other factors to consider. The Stour and Orwell in Essex, the Ouse and Arun in Sussex, the Tamar and Fal in Cornwall possess many similarities, but also exhibit important differences. It is true to say of all that the existing streams and conditions could not have produced the present features. In each case there has been a drowning of the lower part of the river, and since the river mouths may separate lines of cliff, they add enormously to the beauty of the coast. A walk along any cliffed coast may be made rather more strenuous by these breaks, but it is unquestionably more interesting.

If, however, the streams are small or if for some other reason their downward erosion has not been able to keep pace with either the change of level or with the inward erosion of the sea, the valley will have its mouth part way up the cliff face, and the stream in it will fall into the sea by one or more cascades. Coastal waterfalls are often extremely beautiful. The finest examples in England and Wales are between Boscastle and Westward Ho!¹ The watershed along this coast runs close to the sea, so that all the streams are short. The nature of a fall depends mainly upon whether the stream

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