419 ORDINARY MEETING. FRIDAY, JULY 4TH, 1884. HENRY HICKS, ESQ., M.D., F.G.S., President, in the Chair. The list of donations to the library since the last meeting was read, and the thanks of the Association were accorded to the donors. The following were elected members of the Association :­ Miss Mary Forster and F. A. Harrison. The following papers were read :- 'On the North-west Highlands and their teachings/ by Pro­ fessor J. F. Blake, M.A., F.G.S. 'On the Stratigraphy and Metamorphism of the Rocks of the Durness-Eriboll district,' by Professor Charles Lapworth, LL.D., F.G.S., a letter to J. H. Teall, Esq., M.A., F.G.S., by whom it was read on Professor Lapworth's behalf. , On the Geology of South Devon, with special reference to the Long Excursion,' by W. A. E. Ussher, F.G.S. THE NORTH-WEST HIGHLANDS AND THEIR TEAOHINGS. By REV. J. F. BLAKE, M.A., F.G.S., Professor of Natural Science, University College, Nottingham. Those who have watched by the advancing tide will have seen that ever and anon a larger wave than usual comes rushing round some unrecovered spot and secures it for the sea j and so the tide comes in. Such waves occur in science, and if, as in geology, there be several fields, one after another thus absorbs the attention of the advancing army. So Palooontology has had its day, and Petrology is in its dawn. As once all hands were eager for the fossil, now all eyes are anxious for the slice. This has led to a deeper interest both in volcanic rocks and in those vast store­ houses of petrological treasure-the Archsean schists and gneisses, and thus he who once found fossils where no one else could find them, now finds Archsean system after system where no one else can follow him. In the study of the Archsean rocks of Britain, the foremost question to be asked has reference to the Highlands of Scotland. Are these wildwastes and loftymountain-tops carved 32 420 J. F. BL AKE ON THE NORTH-WEST HIGHT.ANDS. out of the most ancient of deposits, or have the materials under­ gone so great a change as to turn the verdured hills of Wales into the moorland wilds of the North? In a word, is the great mass of the Highlands Archeean, or is it not? The state of this question, up to a recent date, has been already explained to you by your late President (Mr. Hudleston), and his first impressions of Assynt have also been communicated. In II another place" further con­ tributions have been made. Your President has parcelled out the land. Oallaway and Lapworth have improved the stratigraphy, and last summer the whole forceof the Geological Survey of Scot­ land laid siege to the Highland fortr ess, though they have not yet carried it by assault.e I come before you to-night to tell you what I have seen there and what it has taught me. You will remember that according to Murchison there were many places where a "conformable upward succession" could be traced from the Silurian Limestones into the main Gneisses of the East i and hence that these Gneisses must be of Silurian age. Nicol, on the contrary, maintained that in all these places (except Assynt) there was an ordinary fault or an intrusion of igneous rock separating one series from the other. With regard to these contentions it may be stated plainly that some of Murchison's most crucial sections, e.q., Stroncrubie, are found to be absolutely wrong, when examined with the most ordinary care j and, on the other hand, many of the faults introduced by Nicol lire entirely imaginary, and do not explain the sections in question. On the other hand, it must be admitted that there are several localities, some of them quoted by Murchison, where the eye, not specially instructed, does see a clear conformable upward snc­ cession from the limestone to a gneiss, and it requires the teaching of other sections to inform us that the eye is deceived i and even then the only other interpretation of the appearances is so strange that one doubts if it can be true. I presume the special instruction required may be found in various districts, but we found it in Eriboll. By H we" I mean Mr. Teall and myself, who started last summer (1883), via Lairg, to Durness. There we were fortunate in finding Prof. Lapworth, * Since this pap er was r ead the main results arrived at by the Geological Survey have been announced by the Director General in I Nature,' Vol. xxxi, p. 29. These are quite confirmatory of th e statements of Lapworth, of Callaway, and of the present paper, lIB to the gen er al question , though differing in details, and entirely subversive of the views previously held. J. F. BLAKE ON THE NORTH-WEST HIGHLANDS. 421 who, having made himself acquainted with the district in previous seasons, was our guide to the instructive sections round the Lake of Eriboll. In this district we need take no account of the sections of Murchison or Nicol, though the latter was nearest the mark. In comparison with what may be seen, they both saw nothing. Whether we should have been in an equally bad case, had it not been for Prof. Lapworth, cannot now be known. Under his guid­ ance we did not miss the points, but became gradually convincedof an amount of overturning and churning up of the rocks that I could not have believed possiblein so slightly elevated an area. In the Alps we expect strange things, but here we are scarcely pre­ pared for the stupendous earth-movements which have taken place. The relations between the two series of gneisses being intimately connected with the stratified Assynt series that is caught up be­ tween them, it is necessary in the first place to obtain a clear and undisturbed section of the latter. Such is found at Ant Sron, as shownby Prof. Lapworth in the I Geological Magazine: Here we find about 25 separable portions of the series which in a more minute survey might be found useful, but they must at present be associatedinto groups. At the base are (a) 80ft. of quartzites in about 17 varieties, almost all of which contain round marks re­ ferred to annelids, which are more numerous or conspicuous in certain beds than in others, and, when seen along joints, appear as pipes. Other beds are more crystalline, and others like vein quartz. These varieties are important as they show that difference of structure alone will not prove a bed to be an upper quartzite. Next come (b) earthy, irregularly laminated rocks, weathering brown,and marked on the surface with horizontal branching cords. These are knownas the fucoidbeds, and are about 40ft. in thickness, including a band of green shales at the top. The succeeding rockis avery important one (c), whichhas been calledthe " Salterella Grit," because of the abundance in it of little triangular bodies, once thought to be Orthocerata, but now considered to be tubicolar annelids, and named Salterella, The rock which contains them has a peculiar bluish aspect, by which it can be recognized, even when the annelids are obliterated. Associated with this at the top is a quartzitic rock, with great holes, as of irregular weathering, called by Lapworth,from its resemblance to cinders, the ecoriacecus bed, making together about 25ft. j and, finally, is (d) the long series 422 J. F. BLAKE ON THE NORTH-WEST HIGHLANDS. of limestones,with flaggy bedsat the base, about 200ft. thick. This section is, therefore, imperfect, both above and below. We cannot tell how thick the lower quartzite may be, nor can we predicate anything as to what succeeded the limestone. But we learn that there is a natural upward succession of "anneHdan quartzite," "fucoid beds," " Salterella grit with scoriaceous bed," and" limestones." This being determined, we ascend the neigh­ bouring hill. Starting from limestone at the base, and omitting minor disturbances, we notice that the beds are becoming nearly vertical, and that we pass downwards in the series till we come to the ennelldan quartzite, more of which is here apparently seen. When wereach the first hill-crest the quartzite rolls over to become nearly horizontal, and is lost beneath a narrow bog.* On the other side of this are found the rocks which are usually referred to the Eastern Gneiss. They consist, however, of hardened slates and felspathic quartzites, and though foliated in appearance, have not the genuine crystalline structure of the true schists. Further back on the hill are some very slaty rocks with weathered holes, in which I should not despair of finding fossils. Now what comes in the bog? Certainly not the whole series of fucoid beds and lime­ stones. eo there is no upward succession. Traced indeed along the strike, the upper beds are seen to be unconformable, for to the south they overlie or abut against the limestones. To the north there soon comes in a tiny knob of rock, as it were the little-finger of a mighty giant-the so-called "Arnoboll Rock." What is this? Nicol called it syenite and granulite, and igneous rock. Heddle calls it Logan rock, and considers it intrusive. Murchison and Callaway refer it to the Newer Gneiss. Bonneyby implication would call it Hebridean. Coming direct from the study of the Hebridean on the south of Dnrness, I had no hesitation in referring it to that old gneiss, though in a modified form; but the extraordinary antics it performs, the trouble it causes, and the deception it has practised on all geologists, unite to make the abbreviation O.