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X.-On the Importance of Paleontological Evidence in Geological Studies. By JAMES WILSON. (Abstract.)

(Read 20th February 1879.)

Mr James Wilson read a paper on the importance of Palæontological evidence in the study of geology, whether in the field or in the cabinet, in which he maintained that, while in France and Germany the practice of identifying distant strata by petrological resemblance had almost been entirely abandoned, the antiquated practice was still followed to a great extent by the Official Survey of Britain. To this he attributed the delay in correct stratigraphy of our rocks, and asserted the absolute impossibility of accurately mapping any extensive fossiliferous deposit unless the progression of life-forms furnished by its organic remains were used as a key to the succession of deposition. Rock deposition, he held, had been perpetual, but upon shifting areas, and never uniform in mechanical or chemical character within all the basin of deposition, just as at present the process showed mechanical and chemical differences on coast lines and estuaries, and in deep oceans whether quiescent or swept by currents. We might walk along the strike of fissile saudy slates and find them passing into calcareous flag and limestone, or going in an opposite direction see the slates shade away into conglomerate or sandstone. This was the case with the Collyweston and Stonesfield slates of the English Jurassics, and it would probably be found true of every formation were the beds traceable over the entire extent of the original basin of deposit. The Bath Oolites are clays, limestones, and sands, but in South Yorkshire they are mountainous masses of coal-bearing grit. Reference was here made to the correlation of the north-eastern prolongation of the Jurassics in Lincolnshire with the south-western portion of the formation in Somersetshire, as detailed by Professor Judd in the memoir to sheet 64 of the English Survey, as a clear demonstration that the succession of rocks, comparatively unchanged and undisturbed by igneous or other forces, could not be revealed until their palæontological evidence had been correctly interpreted. These rocks had been more or less examined by every eminent geologist in the world during almost two generations, but it was only in 1875 that Professor Judd revealed their true succession to the geological world, and paleontology was the key that enabled him to find it. Mr Etheridge said, in the memoir to Sheet 64, "There is nothing in common lithologically

between the Oolitic series of Yorkshire and those of the Midland district and south-west of England; yet the species ranging through the series are identical, and hold the same stratigraphical position, and are of equal value in determining the sequence of the beds constituting the Oolitic series through the whole of England." Professor Judd's more recent labours among the Secondary rocks in the west of Scotland were also sketched as affording one of the most brilliant discoveries extant from giving to palæontological evidence the weight to which it is entitled. No more wonderful story had ever been told than Judd's papers in the Quarterly Journal of the Geological Society on these rocks. The story of Dr Emmons and the Taconic rocks of New York was also related by the author of the paper as a striking demonstration of the fallaciousness of inferring succession from supra-position of beds alone, and ignoring the fossil evidence. Analogous instances were referred to in connection with the Paleozoics of Canada, the Jurassics of Petit Cour, and the Silurians of the south of Scotland, showing, according to his view, that both speculation and stratigraphy which proceeded without seeking for and giving great weight to fossil evidence must necessarily be erroneous. The late Sir R. Murchison, in the fourth edition of his "Siluria," published in 1867, offered an interpretation of the succession of the Silurians filling the country from the Cheviots to the Pentlands. It was partially based on his own observations, but chiefly on the data of other observers which the Director of the Survey accepted as correct. The main elements of the interpretation were that an axial dome of Cambrian rose approximately in the line of the river Teviot, throwing off on either side alum and other shales, most probably representatives of the Lingula flags and Llandeilos of South Britain, which were gradually covered to the north by higher Silurian beds until capped in the Pentlands by representatives of the English Wenlocks and Ludlows. Before the British Association, sitting at Liverpool in 1870, a paper written by Mr Lapworth, F.G.S., clearly demonstrated that the shales at Stobbs Castle, on the Slitrig river, marked in Murchison's section as probably Lingula flags, were unmistakably as high as the Wenlocks; that all the Silurian beds southward of a line from the Cheviots cutting the river Jed five miles above Jedburgh; the Slitrig at Stobbs Castle; the Dumfriesshire Esk, near Westerkirk; Annandale, near Lockerbie, and thence running to Kirkcudbrightshire, belonged to the same horizon. In other papers since written by Mr Lapworth, and more especially in one "On the Moffat Series," published in the "Quarterly Journal" of the Geographical Society for May 1878, Mr Lapworth had, the author thought, established that the Moffat anthracitic shales were stratigraphically and palæontologically divisible into three

great zones with numerous well-marked subdivisions. A portion of the lower zone, the Glenkiln, alone belonged to the Llandeilo age, but most of that division of the Moffat series and all the second, the Hartfell, occupy the same geological horizons as the Coniston limestone and Dufton shales, the Hirant and Bala series of North Wales, or what Murchison and the survey designated Caradoc. Since Mr Lapworth had, as the author considered, proved that the Moffat series were the lowest rocks in the Silurian formation in the south of Scotland, it followed that the massive grey grits, flags, and shales overlying them, and constituting the cut and carved plateau filling the country from the Cheviots to the Moorfoots, and stretching from the German Ocean at St Abb's Head to the Galloway coast, were at any rate not lower than Murchison's Caradoc, though that distinguished geologist, as well as his surveying assistants, had assigned the strata to the Llandeilo and Cambrian, with the exception of a limited patch in the neighbourhood of Abington (upper Clydesdale) described as Caradoc. It was upon palæontological evidence alone that the hundreds of square miles south of the Stobbs Castle line were lifted from the Llandeilo to the Wenlock stage; it was chiefly through long continued and laborious study of graptolites, figured from all Silurian deposits in Europe, America, and Britain, and by comparison of these with the kindred fauna of the Moffat anthracite, that Mr Lapworth found a palæontological key to base and succession in south of Scotland Siluria, and was the first to find order in what had hitherto been a confusion. Mr Lapworth's general conclusions had been accepted by M. Barrande, by the Swedish Survey, by many of the ablest students of the Palæozoic rocks in Britain, and though the Official Survey had not yet "made any sign," he (the author) was confident they would be forced to adopt the views, willingly or unwillingly. When that time came Mr Lapworth's labours and methods might be told in detail, and would constitute one of the most powerful proofs of the principle for which he (the author) contended, viz., that all attempts to map folded and crushed strata without fossil evidence which could furnish definite horizons must ever be labour in vain.

The practical conclusions Mr Wilson deduced from his extended remarks were as follow:-(1) That no rocks known to be fossiliferous should be mapped until their characteristic fossils have been made out by systematic exploration; (2) that in this exploration the vertical range of every species should be noted, and the physical and chemical characters of the beds wherein each species is found; (3) that every national survey should have a palæontological department for this registration of fossils, who should carefully tabulate results, and publish them from time to time without waiting on maps, sections, and memoirs of par

ticular areas; (4) that district societies and amateurs should be invited to contribute fossils, with notes descriptive of the beds in which they are found, the department to judge whether the discovery be worthy of registration, and, if registered, the name of the contributor to be entered in the register. This might be expected to add much to palæontological evidence; and annual or periodical publication of such registers would furnish means of easy comparison of the flora and fauna of distant but related areas over all the world, and would much facilitate, and render more accurate, stratigraphical mapping in every fossiliferous formation. Besides, the final aim of geology was to write the biography of extinct life to trace the development of life-forms through successive stages, from the far past and dim dawn till now-and in this view all rock deposition was but incidental to the great problem, after which modern inquiry more and more tended.

XI.-On the Structural Geology of Strathnairn. By THOMAS D. WALLACE, F.S.A. Scot., Head Master of the Inverness. High School. (With a Map.)

(Read 27th February 1879.)

Area of District.

The area included in the district over which the following personal observations have been made is about 130 square miles. It includes the whole of the country drained by the River Nairn and its tributaries, and is bounded on the south-east by the range of hills which separates the Nairn from the Findhorn, or Strathnairn from Strathdearn.

Boundaries.

On the north-west it is bounded by the low range of hummocky hills which separates the Nairn from the Ness and the Moray Firth, and which varies in height from the sea-level at the mouth of the Nairn to the ridge which separates Loch Ceiglais from Loch Ness, and which rises to the height of 1514 feet on TomBailgeann.

The southern boundary may be considered the cross ridge of hills above Dunmaglass and the water-shed going round the east end of Loch Ruthven, and extending westward again through Dalcrombie and Dunchea to Bochruben, the extreme point of the north branch of the Nairn.

Source and Course of the Nairn.

The Nairn rises in the Monadh Liath hills at a height of 2637 feet above the sea-level, and for a few miles of its course may be characterised as a brawling mountain stream, often, however, swollen by sudden rains into a furious torrent, carrying with it into the plain below large quantities of the sand, gravel, clay, and loose rocks through which it flows. There are here extraordinary accumulations of gravel, clay, and boulders, which in certain places are arranged in terraces, very similar to those in Stratherrick, at the entrance of the glen leading to Loch Killin, and also further down the valley. It flows in a north-easterly direction through the parishes of Daviot and Dunlichity (United), Croy, Cawdor, and Nairn, which are situated partly in Invernessshire and partly in Nairnshire, and empties its waters into the Moray Firth at the town of Nairn after a course of 30 miles.

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