_Dinas_, four miles from Fishguard, affords another, where a natural crevasse has been carefully scarped in order to separate a headland from the mainland. The examples given have been taken from South Wales and the Cornish peninsula, where for obvious reasons less probability of disturbance during later periods has occurred. Ideal spots like Portland are to be found in the British Isles, but the operations of man in quarrying, building, etc. have probably destroyed all traces of defences erected by the primitive inhabitants. _Clifton Camps_, three in number, lying on either side of the Avon, afford us examples of cliff castles remote from the sea. The projecting land jutting out into the loops of the winding river has in each case been protected by lines of trenches. It can hardly be supposed that cliff castles generally were continuously occupied, because as a rule the area is limited, and could not afford sustenance for flocks and herds. Neither do they boast the possession of the indispensable well or spring in the majority of cases. Simplicity in plan is their chief feature, and generally the fosse defending them is single, rarely double, and practically never treble. They probably afforded the last resort when hard pressed by the enemy; abandoning flocks and herds and thinking only of life and limb, the refugees could make a last stand within them, and, if fortune still proved adverse, could lower themselves down the steep faces of the cliffs, and trust to the mercy of the waters. (_b_) Another class of fortresses falling under the same heading are those which depended upon woods, marshes, rivers, and similar natural defences for their efficiency. The _Dyke Hills_ at Dorchester, in Oxfordshire, undoubtedly formed at one time a safe haven of refuge, being almost surrounded by swamps forming a most effective defence. At the present time, however, these have disappeared owing to the general lowering of the water-level throughout England, by drainage, locks, weirs, etc., and they consequently give no indication of former efficiency. Two great fosses may be traced reaching from the Thame to the Thames, thus cutting off a piece of land and entirely defending it by means of water. The _Isle of Avalon_, near Glastonbury, is essentially a peninsula, rising from the midst of a marsh with a series of aggers and accompanying dykes carried across the isthmus. [Illustration: COMB MOSS, DERBYSHIRE.]