In exploring our Scotch formations, I have had frequent occasion, in Ross, Sutherland, Caithness, and now once more in Skye, to pass over ground described by Sir R. Murchison; and in every instance have I found myself immensely his debtor. His descriptions possess the merit of being true: they are simple outlines often, that leave much to be filled up by after discovery; but, like those outlines of the skilful geographer that fix the place of some island or strait, though they may not entirely define it, they always indicate the exact position in the scale of the formations to which they refer. They leave a good deal to be done in the way of mapping out the interior of a deposit, if I may so speak; but they leave nothing to be done in the way of ascertaining its place. The work accomplished is _bona fide_ work,--actual, solid, not to be done over again,--work such as could be achieved in only the school of Dr. William Smith, the father of English Geology. I have found much to admire, too, in the sections of Sir R. Murchison. His section of this part of the coast, for example, strikes from the extreme northern part of Skye to the island of Holm, thence to Scrapidale in Rasay, thence along part of the coast of Scalpa, thence direct through the middle of Pabba, and thence to the shore of the Bay of Laig. The line thus taken includes, in regular sequence in the descending order, the whole Oolitic deposits of the Hebrides, from the Cornbrash, with its overlying fresh-water outliers of mayhap the Weald, down to where the Lower Lias rests on the primary red sandstones of Sleat. It would have cost M'Culloch less exploration to have written a volume than it must have cost Sir R. Murchison to draw this single line; but the line once drawn, is work done to the hands of all after explorers. I have followed repeatedly in the track of another geologist, of, however, a very different school, who explored, at a comparatively recent period, the deposits of not a few of our Scotch counties. But his labors, in at least the fossiliferous formations, seem to have accomplished nothing for Geology,--I am afraid, even less than nothing. So far as they had influence at all, it must have been to throw back the science. A geologist who could have asserted only three years ago ("Geognostical Account of Banffshire," 1842), that the Old Red Sandstone of Scotland forms merely "a part of the great coal deposit," could have known marvellously little of the fossils of the one system, and nothing whatever of those of the other. Had he examined ere he decided, instead of deciding without any intention of examining, he would have found that, while both systems abound in organic remains, they do not possess, in Scotland at least, a single species in common, and that even their types of being, viewed in the group, are essentially distinct.