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NOTES ON THE GEOLOGY AND FOSSILS OF THE LUDLOW DISTRICT. By A. SMITH WOODWARD, LL.D., F.R.S., President. (A few ad,'ance coft'es issued /0 11ttlnbtr, in July, ' 901.) NDE R the presidency of a palreontologist it seems appro­ U priate that the Geologists ' Association should devote its Long Excursion this year to the study of fossils in the field. It becomes more and more evident, as researches progress, that the past history of life on the earth can only be satisfactorily deciphered when the exact stratigraphical position of each fossil has been determined by careful collecting. The variations of an organism in time and space, and its successive migrations, can only be ascertained by more detailed field-work and more precise labelling than has hitherto been customary among palreontolo­ gists. It is therefore necessary to follow the lead of Lapworth, Buckman, Rowe, Wheelton Hind, Miss Elles, Miss Wood, and others who are inaugurating a new era in the study of British fossils by a most exact and exhaustive method of collecting. The Association, indeed, cannot do better at the present time than attempt to arouse renewed interest in a classic district, which has been much neglected by geologists during recent years, and has scarcely been examined in any respect from the modern standpoint. The classic ground we have chosen to visit is the old country of the Silures, where Murchison originally worked out the details of his Silurian System. Much of it has never been visited by the Association before, and thirty-two years have now elapsed since Ludlow was the centre of one of our excursions. Atthe present time, in fact, the district is probably much more familiar to archreologists than to geologists, The generation of local geologists whom Murchison inspired half a century ago, has now passed away, and this band of pioneers has fewer successors than might be expected in a country so replete with interest. Ludlow itself is situated chiefly on the Lower Old Red Sand­ stone, but also partly on the Upper Silurian Rocks, which crop out in regular succession beneath it. The strata are more or less disturbed by faults connected with a great line of dislocation which extends in a N.E. and S.W. direction from Lilleshall in the north to Kington in the south (see Lapworth and Watts, 1894). The Old Red forms a gently undulating pastoral country, while the alternating layers of shaly mudstone and hard limestone in the Upper Silurian produce steeply scarped ridges, which are covered for the most part with plantations, and are separated from each other by rich arable land in the hollows. Pace, GEOL. Assoc., VOL. XVIII,PART 9. 1904.] 31 430 A. SMITH WOODWARD: NOTES ON THE The general succession of the rocks, long ago established by Murchison and his fellow-geologists on the spot, and little modified by subsequent observers, is as follows: I Upper Sandstones, with Bothrio/tpis, H%pt;chills, OLD RED' Sauripterus, &c. SANDSTONE. ) Lower Sandstones, Marls, and Cornstones, with . Ctpha/asfJis, Pterasois, &c. ( (Tilestones. I Downton Sandstone. Ludlow Group. ~ Upper Ludlow. I Aymestry Limestone. l Lower Ludlow. SILURIAN. : JWenlock Limestone. vVenlock Group. Wenlock Shales. !Woolhope Limestone. Tarannon or Wool hope Shales. Llandovery Group. Upper Llandovery and May Hill J Sandstone. 1l ILower Llandovery. These strata are a conformable series, and the Upper Old Red Sandstone passes gradually into the Carboniferous Lime­ stone above; but there is a marked unconformity at the base between the Llandovery group and the underlying Ordovician rocks, as is well seen between the Longmynd and Wenlock Edge (Fig. 9). DOLERITE AND CARBONIFEROUS SERIES. Before considering these Old Red Sandstone and Silurian formations more in detail, however, it is interesting to refer to the flat-topped Clee Hills, which rise to a height of 1,530 and 1,75° feet above sea level five or six miles to the eastward of Ludlow. It happens that in this locality at some post-Carbon­ iferous date (probably Permian) there was a volcanic outburst, by which a thick sheet of dolerite was spread over the Coal Measures. The comparatively soft strata of shales and sandstones, with their included seams of coal, were thus preserved from denudation by a capping of intensely hard rock; and whereas the Western Coalfield has been denuded off the Ludlow Dis­ trict, and indeed off the whole of the country between Shropshire and the South Wales Coalfield, a small outlier remains intact beneath the Clee Hill volcanic flow, and rises above the level of the adjoining land. The dolerite itself was studied by the late Mr. Allport, and described in his well-known paper in which he proved for the first time the essential identity of the lava of all geological ages. It is a coarse rock remarkable for the fresh­ ness of its constituents, even exhibiting much olivine with very little trace of serpentinisation. It is extensively worked for road-metal, and its columnar structure is often well seen in the quarry face. It is locally known as dhu stone, the name being GEOLOGY AND FOSSILS OF THE LUDLOW DISTRICT. 431 supposed to have been derived from a Celtic word meaning black. As shown by Murchison's section (Fig. 24) the Coal Measures of the Clee are arranged in a slight syncline, and if the gradual slope of the hills be descended to the north-east the Lower Carboniferous strata can be observed dipping at a very high angle. The fine section of the Carboniferous Limestone Series in the Oreton quarries is especially interesting, and shows a gradual passage downwards from the typical marine limestones to the yellow and probably lacustrine sandstones of the Upper Old Red. The Oreton section does not appear to have been studied for more than forty years, when Morris and Roberts presented the accompanying sketch of it (Fig. 25) to the Geological Society. It will be observed that there are no massive beds, but only a C.M. Coal Measures. M.G. Millstone Grit. C.L. Carboniferous Limestone. O.R.S. Upper Old Red Sandstone. B. Dolerite. succession of comparatively thin layers of oolitic or shelly limestone, clay, and even sandy rock. Brachiopods are abundant in the limestone; and one layer consists of the scattered remains of crinoids mingled with Polyzoa. The most interesting fossils, however, are the teeth and fin-spines of pelagic sharks, which are not uncommon in certain beds. Most of the species are peculiar to Oreton, though they belong to widely distributed genera, and the list given by Morris and Roberts in 1862 needs much revision. The fine teeth of Orodus ramosus and Sanda­ lodus morrisi, and the fin-spines named Ctenacant/zus major and C. sulcatus, are identical with fossil teeth and spines occurring in the Black Rock at Clifton, Bristol; but so far as I have observed, there is no similarity between the Oreton fish-fauna and that met with in the bone-bed of the Lower Limestone Shales at Clifton. This is a fact of peculiar interest to those who are studying the life-zones of the Lower Carboniferous Series. UPPER OLD RED SANDSTONE. The Old Red Sandstone of the" Welsh Lake" (as it has been termed by Sir Archibald Geikie) needs much more detailed in­ vestigation than has hitherto been bestowed upon it; but whether 432 A. SMlTH WOODWARD: NOTES ON THE it consists of one conformable series of deposits, as commonly supposed, or whether it exhibits unconformities at any horizons, the fossil fishes contained in it represent two very distinct faunas. Where the strata are clearly the upper- foi most of the Old Red CIi Series, like the yellow vi sandstones of Far­ low which immedi­ ately underlie the Carboniferous Lime­ stone near Oreton (Fig. 25), the fish- fa una corresponds with that which is definitely known to characterise the Upper Old Red Sandstone of Scot­ land. This fauna was first noticed half a century ago in a small quarry in the yellow sandstone at Farlow, which was temporarily worked for the reb u i I d ­ ing of the church. Numerous fragment­ ary fish-remains, in fact, were collected here by Mr, T. Baxter, Mr. G. E. Roberts, and others; and among them were several fine examples of a pecu­ liar s pee i e s 0 f Bothriolepis, which Sir Philip Egerton described under the name of Pteni:hthys macrocephalus. A s first recognised by Dr. Traquair, this fish is shown to be :i a typical Upper Old ;i Red Bothn'olepis by ;i GEOLOGY AND FOSSILS OF THE LUDLOW DISTRICT. 433 there is stratigraphical evidence of the high place in the Old Red series occupied by the sandstone which contains these fossils. It may, in fact, be stated that Holoptychius and Saurioterus (or Crossopterygian genera of equivalent rank) with Bothn'olepis and Asterolepis characterise the Upper Old Red Sandstone or Upper Devonian wherever it occurs-in Britain, Belgium, Ger­ many, Russia, Spitzbergen, Greenland, Canada, and the Catskills of New York. All assertions to the contrary are based on the 434 A. SMITH WOODWARD: NOTES ON THE wrong interpretation of the fragments, by which alone the fishes are so frequently represented. Below the Upper Old Red Sandstone in the north of Scotland (" Lake Orcadie ") there is a series of rocks- the Middle Devonian of Murchison-yielding another fish-fauna, which is characterised by Dipterus, Osteolepis, Coccosteus and Pten'chth)'s, and has not yet been found in the Welsh area. It is very desir­ able that a special search should be made for this group of genera in the sandstones immediately beneath the Upper Old Red in the district now being described.

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