The next Rock that occurs is Bo-rhua, a name derived from the Celtic, and signifying, according to the natives, Red Rock. It lies about 2³⁄₄ miles from Boinshly, and about one mile from the Skerryvore. The passage between it and Boinshly is clear, and has a depth of about fourteen fathoms; but it is too narrow to be safely navigated except by daylight, even under the most favourable circumstances, and then no mariner would run the risk of taking such a passage, but would prefer, even at some sacrifice of time, the fairway of the passage of Tyree. Bo-rhua is completely covered at high, but is dry at low water. The extent of rock uncovered is about forty feet by twenty feet, and the highest point of it is about six feet above low water level of spring tides. A small outlying pinnacle, about ten feet square, is also uncovered at low water. The depth immediately round Bo-rhua is considerable, from three to seven fathoms being found within fifty feet of it; and in this respect it differs from Boinshly, which, as already mentioned, is surrounded by shoal water for some distance. Between Bo-rhua and Skerryvore, however, which is a distance of about a mile, there cannot properly be said to be any clear navigable channel, as will be distinctly seen by referring to the plan. The whole of this tract may, in fact, be termed _foul ground_. * * * * * The Skerryvore or chief rock, and the detached rocks immediately surrounding it, were surveyed with greater minuteness than the others, as it was at once apparent, that on this part of the reef alone could a suitable site for a lighthouse be found. The name is derived from the Gaelic, and signifies the Great Rock. It is very much wasted and cut up; the number of detached rocks, sunk and exposed, in its immediate neighbourhood, whose positions were determined during the survey, amounting to no fewer than 130. The depth of water between those different detached fragments, which extend over a surface of about a mile in length, by half a mile in breadth, is considerable, varying from 2¹⁄₂ to 8¹⁄₂ fathoms at low water of spring tides. * * * * *