A melancholy sensation pervaded the Rob Roy to-day, in consequence of a sad event, the loss of the captain's knife. We had three knives on board in starting from England; one had been given away in reward for some signal service, and this which was now lost was one with a metal haft and a curious hook at the end, a special description made in Berlin, and very useful to the tourist. It is not to be wondered that in so many leaps and somersaults, and with such constant requirements for the knife to mend pencils, &c., &c., the trusty blade should at last have disappeared, but the event suggests to the next canoeman that his boat-knife should be secured to a lanyard. One singular conformation of the river-bed occurred in my short tour upon this part of the Moselle. Without much warning the banks of rock became quite vertical and narrowed close together. They reminded me of the rock-cutting near Liverpool, on the old railway to Manchester. The stream was very deep here, but its bed was full of enormous stones and crags, very sharp and jagged, which, however, could be easily avoided, because the current was gentle. A man I found fishing told me that a little further on there was an "impossible" place, so when after half a mile the well-known sound of rushing waters came (the ear got marvellous quick for this), we beat to quarters and prepared for action. The ribbon to keep my hat was tied down. Sleeves and trousers were tucked up. The covering was braced tight and the baggage secured below; and then came the eager pleasures of anticipating, wishing, hoping, fearing, that are mixed up in the word excitement. The sound was quite near now, but the river took the strangest of all the forms I had yet seen. If you suppose a trench cut along Oxford-street to get at the gas-pipes, and if all the water of a river which had filled the street before suddenly disappeared in the trench, that would be exactly what the Moselle had now become. The plateau of rock on each side was perfectly dry, though in flood times, no doubt, the river covers that too. The water boiled and foamed through this channel from 3 to 20 feet deep, but only in the trench, which was not five feet wide. An intelligent man came near to see me enter this curious passage, but when we had got a little way in I had to stop the boat, and this too by putting my hands on both sides of the river! Then I got out and carefully let the boat drive along the current, but still held by the painter. Soon it got too narrow and fast even for this process, so I pulled the canoe upon the dry rock, and sat down to breathe and to cool my panting frame. Two other gentlemen had come near me by this time, and on a bridge above were several more with two ladies. I had to drag the boat some hundred yards over most awkward rocks, and these men hovered round and admired, and even talked to me, and actually praised my perseverance, yet not one offer of any help did any one of them give!