As we have already intimated, in the present state of our knowledge it is impossible to dogmatize upon rock markings. Caution must be used in any attempt to interpret them. Many are no doubt due to natural causes. The familiar water-marks on the Old Red Sandstone formation may too readily be taken for cuttings made by the hand of man. The late Richard Rolt Brash once observed, in the sections of vertical rock strata in the quarries of South Wales, cup-like holes, with corresponding bosses on the opposing layers, and was of opinion that these were sometimes taken for artificial hollows. The late Dr. Frazer, following on the lines of M. Valenciennes, found the _Echinus lividus_ lodged in a cup-like hollow burrowed for itself in the rocks on the sea-shore of Bundoran. Dr. Frazer expressed his opinion that the cup-markings on the rocks round the shore of Lough Melvin, once probably an arm of the sea, were due to the same cause; and further, that some of the markings on rocks described by Sir James Simpson in _British Archaic Sculpturings_ were pittings of the _Echinus_.[18] Many of the cup-like indentations in the limestone rock are, in the opinion of some scientists, due to acid secretions of the snail, notably the _Helix aspersa_. Making due allowance for these natural causes, yet a mass of rude markings by the hand of man remain, difficult to interpret as to their origin, their meaning, and the people to whom they are to be assigned. In many districts of this country, and some of them widely apart, we find upon the sides of caves and rocks, and within the enclosure of pagan sepulchral tumuli, a certain well-defined class of markings, often arranged in groups, and with few exceptions, presenting what may be styled a family type: we can hardly imagine them to be the result of caprice. In ancient and in modern times, men confined by necessity to a listless existence, in an inhospitable district, or when tending flocks and herds, might very naturally have beguiled their hours by carving with a stone or metallic instrument such figures as their fancy prompted, upon the nearest object which happened to present a surface more or less smooth. Scorings or patterns made under such circumstances would be, in character, as various as the skill or humours of the designers. * * * * *