A HISTORY OF CORNWALL their modern counterparts, are frequently cemented by oxide of iron, which has so consolidated them, that they have sometimes been utilized as building stone. In this condition they offer great resistance to the action of the waves, as is well seen in Gerrans Bay on the beach of Pendower. In some instances along the coast the ancient caves of the raised beach have been partially preserved by the old beach floor being sufficiently consolidated to form the roof of modern caves, which have been excavated in a lower portion of the same cleft, examples of which are seen in Falmouth Bay. De la Beche has figured such a cave at Porthalla, roofed by a raised beach. This consolidation is interesting as an example of rock building. Even on the coast line where beaches are absent, a tiny fringe of gravel is often visible. It may be observed along some of the steeper cliffs, its preservation being obviously due to the durability of the cement- ing material, which has not only held the particles together, but has firmly bound the gravel to the rock on which it rests. Every gradation is seen between well defined beaches and mere shreds of gravel either cemented or incoherent occurring in isolated strips above the present high water mark ; and the degradation of them causes the commingling on the modern beach of the Pleistocene pebbles with those of recent origin. The beaches of either age contain, in addition to fragmental material representing the detritus of the adjacent rock formations, numerous foreign pebbles, mainly chalk flints and cherts, which in some situations are profusely distributed. At Cape Cornwall Mr. Reid discovered a pebble closely resembling one of the volcanic rocks of Devonshire. These erratics have either been swept around the coast by current action, or have been derived from a deposit more ancient than the raised beach which fringes our coast beneath the level of the sea. The modern beach which lines the shore fronting Loe Pool is thickly strewn with these erratics. In some instances the rock shelf, planed by wave action, along our modern shore has been shaped from the rocky platform previously exca- vated by the Pleistocene seas. This is well seen in Falmouth Bay, at Sunny Cove, where the ancient platform standing but 5 or 6 feet above the present eroded shelf is fringed along the coastal notch by the inner- most edges of the older beach, averaging but a foot or so in thickness, which have not yet succumbed to the ravages of the waves. Looking at that section in which the rock terraces are so closely placed that the shingle of the present beach is driven against its ancient counterpart, with the disintegrated pebbles of which it absolutely mingles, it is difficult to realize the great interval of time which marks the gap between the past and present shore line. Yet that span has been sufficient for the sinking of the land to a depth of at least 60 feet, involving the submergence of the woodland which flourished on its outer fringe. Moreover the valleys thus invaded by the sea have been converted into estuaries which have subsequently been filled with deposits to a depth of 50 feet. In addition, the upheaval which has left 10
