While the Bell-Rock lighthouse was in progress, Mr. Stevenson was often struck with the frequent and distressing occurrence of shipwrecks at the Carr Rock. The Carr forms the seaward termination of a reef of sunken rocks which appear at low water, extending about a mile and three quarters from the shore of Fifeness, on the northern side of the entrance of the Frith of Forth. The very dangerous position of this rock, as a _turning point_ in the navigation of the northern-bound shipping of the Frith, required that this rock, in connection with the several lighthouses of the Bell Rock, Isle of May, and Inchkeith, should be made as easily distinguishable to the mariner as possible. In the course of nine years no fewer than sixteen vessels had been either lost or stranded on the Carr Rocks. Therefore, in 1809, moorings were laid down for a floating buoy, ‘but owing to the heavy swell of sea and the rocky sand-stone bottom on this part of the coast, it was found hardly possible to prevent the buoy from occasionally drifting, even although it had been attached to part of the great chain made from bar-iron an inch and a half square, with which the Bell-Rock floating-light had been moored for upwards of four years without injury. The moorings of the Carr Rock buoy, from the continual rubbing upon the sand-stone bottom, were worn through with the friction in the course of ten months; and during the four years which it rode here, though regularly examined and replaced in the proper season of the year, it was no less than five times adrift, to the great inconvenience and hazard of shipping.’ Such being the case, it was resolved, however difficult and perilous the undertaking, to erect a beacon of masonry upon the rock. The length of the Carr Rock, from north to south, measures seventy-five feet, but its greatest breadth, as seen at low-water of spring-tides, is only twenty-three feet; hence it was not possible to obtain a base for a building of greater diameter than eighteen feet. The surface of the rock was also so rugged that it was necessary to excavate part of the foundation-pit of the building to the depth of seven feet. The difficulties were still further increased on account of the foundation being partly under the level of the lowest tides, so that a coffer-dam was required. It was further necessary, after each tide’s work, to remove and carry ashore part of this coffer-dam; so that on the return of the workmen at ebb-tide much time was lost in readjusting the coffer-dam, and in pumping the water out of the foundation-pit.