What the bowl-shaped hollows, which vary in size from 1 to 2 inches in diameter and are generally about 1 inch deep, and which are shown on the illustrations by small black dots, represent will probably always remain an enigma. The reader will also notice peculiar figures, such as circular rings, divided by crosses or double crosses, footprints, &c. Only two rock-tracings thus far have been discovered, where waggons are seen with wheels and horses attached to them. [Illustration: Fig. 913.—Stone with round hollows. ] In Denmark, tracings have thus far only been discovered on the slabs of passages in graves, such as those of Herrestrup in Zealand, and Ullerup in Northern Jutland, and their absence is to be accounted for by the want of rocky formation. ----- Footnote 117: This subject would naturally be included in the earlier part of the work, but the tracings contain so many figures of ancient ships that I have thought it appropriate to introduce the chapters at this stage. Footnote 118: Two valuable works on rock-tracings are those of A. E. Holmberg and L. Baltzer. Footnote 119: “Etudes sur l’antiquité historique d’après les sources Egyptiennes et sur les monuments réputés préhistoriques,” par F. Chabas. Footnote 120: The finest example of those without figures is to be seen in the Museum of St. Germain near Paris. Footnote 121: See ‘Land of the Midnight Sun,’ vol. i., p. 355. Footnote 122: Several representations, on account of their coarseness, are not as correct in the illustrations as they should be. CHAPTER IX. WAR-SHIPS. The Northmen pre-eminently a seafaring people—Figurative names given to ships—Classification and names of ships of war—Ironclads—Swift cruisers—Transport vessels—Foreign ships—Different parts of a war-ship—Oars—Ship’s boats—Tents—Ship’s moorings—Sheds—Launching—Ornamentations—Beautiful sails—Colour of war-ships—Standards—Ornamentation of ship’s sides with shields—The port of Jomsburgh—Size of ships—The Tuneship—Shipbuilding—Crews—Description of a storm. One of the most important features in the life of the Viking Age was the ships in which the hardy Norsemen were able to rove over the seas of Europe, and conquer and plunder the lands around them. In the Eddas and Sagas these ships are often minutely described, so that we are able to form a fair idea of the shipbuilding art of those days. The ships were called by figurative and most poetical names, and from many of these we see that speed was valued very highly:—