The terms 'rock' and 'rocky' are used by the authors to indicate that the subject of their books is coastlines of erosion and not coastlines of deposition. They justify their books on the grounds that most works on coastal geomorphology are devoted to the study of coasts of deposition even though 80% of the world's coasts are formed of cliffs produced by erosion.
The books are not concerned with landforms as such. What, in fact, they are almost entirely devoted to are the processes of erosion producing coastlines composed of cliff-shore platform pairs at present sea level in easily eroded rocks. The rocky coasts they describe are composed of rocks such as tills, soft sandstones, shalesindeed, anything soft enough to have been significantly eroded in the last 6000 years of relative sea-level stillstand. Thus the 'rocky coasts' are those of Norfolk, Holderness and equivalent coasts elsewhere, particularly in Japan and Australia. They are not those of, say, the west coast of the British Isles, which are what most British readers would expect. Although 80% of the world's coastline may be cliffed, a much smaller percentage is formed by cliff-shore platform pairs currently being produced by marine erosion. Much is formed by cliffs composed of rocks a good deal harder than till or shale, which plunge below the sea with little or, more often, no sign at all of any erosion having taken place at sea level. Both books almost completely ignore such coasts to concentrate on the cliff-shore platform pair coasts.
A third of each book is devoted to the agents and processes of erosion. Sunamura emphasizes the importance of laboratory experiments and he substitutes symbols and functions for descriptions of erosion at work in the field, even though he is unable to quantify many of his symbols. He makes great use of FR (resisting force of rocks) and Fw (assailing force of breaking waves). Both of these are clearly complex functions of a variety of variables which he is unable to specify. Trenhaile tends to make more use of field descriptions of processes at work and their results. Both authors confine themselves to a 6000 year period of erosion, this being their estimate of the length of time the sea has been at its present level eroding the coasts they study. Consequently neither author gives any consideration to the processes or results of erosion by rising sea level.
Sunamura distinguishes three types of cliffed coastline profile, but recognizes no gradation between them. The three types of profile are those with horizontal shore platforms, those with gently sloping shore platforms and those with plunging cliffs. He states that if FR > Fw (as defined above) then no erosion takes place, no shore platform is produced and a drowned cliff of unchanging slope (vertical in his figures) results. If FR<Fw, however, then erosion takes place and either a horizontal or a gently sloping shore platform is produced. He presents three measured profiles taken from plunging cliffs. However, these profiles continue no more than 100 m seaward and to depths of no more than 20 m and he does admit to the present inadequate state of investigation of plunging cliffs. He presents five profiles of horizontal 0 1994 by John Wiley & Sons, Ltd.