Other nations made their Forts circular, an example of which I lately saw a few miles from Bideford, while others consisted of nearly parallel lines, enclosures, and demi-lunes, like those wonderful dykes near Clovelly, which occupy more than thirty acres of land. One of the circular Forts is shown on the right hand of the illustration. As time went on, stone took the place of earth, and the principal object of the builder was to give considerable thickness below, so as to resist the battering-ram, and great height both to walls and towers, so as to be comparatively out of the reach of the arrows and other missiles of the besiegers. For awhile, such castles were impregnable, and the owners thereof were the irresponsible despots of the neighbourhood, recognising no law but their own will, robbing, torturing, and murdering at pleasure, and setting the king at open defiance. When, however, the tremendous powers of artillery became developed, the age of stone castles passed away. Height was found to be equivalent to weakness, as the strongest tower in existence could be knocked to pieces in an hour or two, and do infinite harm within the fortress by its falling fragments. Fortification then returned to its original principles. Earth took the place of stone or brick; and at the present day, instead of erecting lofty walls and stately towers, the military engineer sinks his buildings as far as he can into the ground, and protects them with banks of simple earth, which is found to be the best defence against heavy shot. There is no masonry in existence that will endure the artillery fire of the present day, and even the solid rock can be knocked to pieces by it. But an earth-mound is a different business, and will absorb as many shot and shell as can be poured into it, without being much the worse for it. See, for example, the Proof-mound at Woolwich, which receives the shot of guns as they are being proved. Now, this mound has undergone perpetual battering for many years, and is as strong as ever. The same thing may be said of the celebrated Mamelon before Sebastopol. * * * * * SO much for the Fort made by the hand of man. We now come to that which is formed by the feet of animals. The Elk, or Moose, an inhabitant of Northern Europe, finds itself in great danger during the winter, the wolves being its chief enemies. At certain times of the year there comes a partial thaw during the day, followed by a frost at night. The result is, that a slight cake of ice forms on the surface of the snow, too slight to bear the weight of so heavy an animal, and strong enough to cut the legs of the elk as it ploughs its way along. Now, the wolves are sufficiently light to pass over the frozen surface without breaking it, and accordingly, they can easily run down and secure the elk.