One of the great curiosities of Clonmacnois is the powder-blown-up castle built by Hugo de Lacy in the latter part of the twelfth century, the remains of which stand on a hill about two hundred yards from the cemetery. It is generally known as the Prior's house, but it was evidently built as a place of defence. It was one of the strongest castles ever erected in Ireland. Although comparatively small, building and enclosure not covering more than half an acre, it was a place of immense strength, and before the invention of gunpowder could have defied a host. It is encompassed by a fosse in some places forty feet in depth, that descends sheer from the walls. The walls are of immense thickness and strength, from six to eight feet thick in many places, and so firmly are the stones embedded in grouting that to detach one of them from the powder-riven walls, or from the vast masses of blown-up masonry that lie scattered around, a hammer and chisel would be required. Huge heaps of the ruined walls, some of them tons in weight, have been tumbled into the deep fosse that surrounds the castle, but they are still almost as solid as rocks. If ever the art of building solid walls was brought to perfection, it was by those who reared this now ruined pile. To know the strength of gunpowder and the solidity of ancient masonry, one should see this ruined castle of Clonmacnois. With all the beauties and diversity of scenery of the Shannon, on the banks of which stands all that remains of Clonmacnois, and with all the places of historic interest laved by its waters, it is a disgrace to Ireland at large that there is not a single passenger steam-boat on it above Limerick. It is nearly a hundred and fifty miles from Carrick-on-Shannon to Killaloe, and in all that vast distance of spreading lake and winding river there is not a passenger steam-boat to be seen! There may be said to be no obstacle to navigation in all that distance for boats drawing from five to six feet of water, and there are only four or five locks to pass through. No other river of equal length affords more variety of scenery than the Shannon. Sometimes the voyager passes by wooded banks, anon through apparently illimitable meadows, and then through great lakes like veritable inland seas,--island-studded or mountain-girded,--change of scene occurring in almost every mile. Let it be hoped that a line of passenger steamers will soon again be seen on the waters of this great and beautiful river,--this "ancient stream," as its Gaelic name is said to mean,--that has on its banks so many relics of the past-the grass-grown rath, the hoary round tower, the crumbling castle, and above all, the ruined fanes of Clonmacnois. KNOCK AILLINN