A HISTORY OF CORNWALL direct action of wind, and form extensive sand dunes and towans. These aeolian deposits are most strongly developed on the northern coast, where large areas are permanently cut off from the operations of the plough. The most considerable of these fronts St. Ives Bay, forming the Lelant, Phillack, Upton, Gwithian and Godrevy towans. Another extensive tract constitutes the Perran Sands, and isolated patches continue as far as Newquay. Further to the north the solid rocks forming the promontory of Trevose Head are severed by the towans extending from Constantine Bay to Perleze Bay, and opposite Padstow a tract of sandhills extends from St. Michael to the Dunbar. Smaller patches occur at Gunwalloe and along the southern coast. These accumulations of sand are mainly composed of finely com- minuted sea shells, such as form our shelly beaches, and have been largely utilized in Cornwall for enriching the soil by the lime con- tained in their composition. The sandhills now occupying such ex- tensive tracts rest on the solid rocks and have been formed by the beach detritus driven landwards by the wind. The sands, ever on the move, have piled up deposits which have overwhelmed ancient buildings, the most noted instances of which are the old churches of Perranzabuloe, St. Enodoc and St. Constantine. The spread of these sand drifts is con- siderably checked by the vegetation which they support, but the dunes are continually receiving fresh accession of material by the windborne sand from the coast, which is blown considerably beyond their limits. Mr. Clement Reid, F.R.S., has described other effects seen at Carbis Bay during gusty E.N.E. winds in the year 1 900, from a height of 270 feet above the sea, where swirls and puffs of dust were observed to rise from the flat at the entrance of the Red river to a height of at least 240 feet, blotting out Godrevy towans and Godrevy lighthouse, and then spreading in a well defined belt across St. Ives Bay for over 3 miles in the direction of St. Ives Head, which it must have passed. He suggested that the dust, largely composed of the river-mud, might account for some local falls of ' red rain.' 1 The modifications which the outlines of our county are at present undergoing have now been briefly touched upon. Under the influence of tide and current the shore materials are continually being assorted, while in some instances they have formed barriers behind which the seaward passage of the river-borne detritus has been checked. At Loe Pool for instance, below Helston, a beach has been piled up by the Atlantic breakers and has dammed back a considerable freshwater lake. The similar lake of Swanpool near Falmouth likewise owes its existence to the beach thrown up across the mouth of the valley. Our exact observation of the sub- marine floor is necessarily confined to that portion of its innermost margin which is laid bare between tidemarks. The incessant changes of the bottom beyond that zone are exemplified by the salvage operations at present being carried on in Mounts Bay on the wreck of the Anson, a ship of war lost a century ago. The shifting of the shingle on the 1 Nature, Ixv. 414. 6
