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(1913). A Monograph of British Graptolites. Part IX. Pages 415–486; Plates XLII–XLIX. Monographs of the Palaeontographical Society: Vol. 66, No. 323, pp. 415-486.

I. Introduction. (A) Historical Review. Stretching southward for 70 miles from the shores of the Irish Sea near Conway in North Wales, through Denbighshire and Montgomeryshire into the central parts of Radnorshire near Llanbister, there sweeps a continuous band of massive greywackes, flagstones, and shales, known to geologists as the Denbighshire Grits or Flags. This arenaceous formation is from 1000 to 3000 feet in thickness, and is acknowledged on all hands to be of Wenlock age. Rising out from beneath the Denbighshire Grits, and intervening between them and the older rocks which are at present assigned to the Llandovery and Bala, there occurs a series of relatively shaly strata which are distinguished on the Geological-Survey maps by a special tint of purple, and are indicated upon the legends as ‘Tarannon Shales.’ They are laid down on the maps as forming a narrow belt, seldom exceeding a quarter of a mile in width and entering into all the sinuosities of the outcrop of the lower margin of the Denbighshire Grits. Although these so-called ‘Tarannon’ Beds were not mapped as constituting a distinct formation until 1855, their peculiar mineral characters—‘fine, smooth, slaty strata, grey or light blue, occasionally slightly sandy, and alternating with purple bands’—had not escaped the attention of the earlier geological workers in Wales. As early as 1843 Sedgwick and Sailer had noticed in the Berwyn Hills certain ‘pale-coloured earthy slates’ which ‘seem to pass without a break into the overlying Denbigh Flagstone.’ From the fact that they were aluminous

(1901). A Monograph of British Graptolites. Part I. Dichograptidae. Pages 1–54; Plates I–IV. Monographs of the Palaeontographical Society: Vol. 55, No. 260, pp. 1-54.

(1911). A Monograph of British Graptolites. Part VIII. Pages 359–414; Plates XXXVI–XLI. Monographs of the Palaeontographical Society: Vol. 64, No. 316, pp. 359-414.

The graptolites collected by Dr. John W. Evans from Bolivia, and sent to me for inspection, are marked as coming from five separate localities. The best-preserved forms occur in black pyritic shales exposed at ‘a halting-place on the right bank of the Rio Coranhuata, known as Culi, on the up-stream side of the Puente de Culi (J. 28/4/02).’ The rock is cleaved, and the graptolites are in consequence somewhat distorted, but the well-known species Didymograptus bifidus, Hall, is recognizable. Associated with this abundant form there is one small fragment of a slender extensiform Didymograptus, apparently of the type of D. affinis, Nich., but too fragmentary to admit of specific identification. Black shales occurring at another locality ‘on the left bank of the Rio Coranhuata, on the down-stream side of the Puente de Culi (H. 28/4/02),’ are crowded with graptolites, but unfortunately much distorted and in a poor state of preservation. On one slab from this spot several examples of a species of Phyllograptus are recognizable, and one of Glossograptus. The commonest graptolitic form present, however, is one which it is difficult to assign to any known genus or species. It belongs to the family of the Diplograptidae, and possesses three conspicuous spines at its proximal extremity together with a long virgula distally produced. It is, perhaps, most closely allied to the genus Cryptograptus; but all details as to the form of the thecae are obscure, and the specimens are too distorted to allow of description. Another slab from the same

(1908). A Monograph of British Graptolites. Part VII. Pages cxxi–cxlviii, 273–358; Plates XXXII–XXXV. Monographs of the Palaeontographical Society: Vol. 62, No. 305, pp. cxxi-358.

(1918). A Monograph of British Graptolites. Part XI. Pages cxlix–clxxi, a–m, 527–539; Including Title-Page and Index. Monographs of the Palaeontographical Society: Vol. 70, No. 339, pp. cxlix-539.

I. Introduction. The Lower Ludlow Shales, which form the lowest section of the Ludlow division of the Silurian System, are most typically developed in the neighbourhood of the picturesque old town of Ludlow. It was in this district that they were first defined and described by Murchison. Lithologically, they are here essentially an argillaceous group of strata, the lower and upper limits of which are well marked by two distinct calcareous beds—the Wenlock Limestone below and the Aymestry Limestone above. Palaeontologically, the Lower Ludlow Shales are rich in fossils: brachiopods, cephalopods, crustaeea, and graptolites. When the Lower Ludlow Beds are followed from the Ludlow district north-eastward along their line of strike as far as the valley of the Severn, south-westward as far as Aymestry, and eastward as far as the Malverns and Mayhfil, they are seen to retain their lithologieal characters unaltered, and the Wenlock and Aymestry Limestones are both well developed. But when these beds are traced from the typical area to the west and north-west, the limiting calcareous strata dwindle away and eventually disappear, until, finally, the Lower Ludlow Shales merge lithologically on the one hand into the Wenlock Shales below, and on the other into the Upper Ludlow Flags above. It is clearly impossible, therefore, in these westerly districts to separates on purely lithological grounds, the Lower Ludlow Beds as a distinct group from the formations which overlie and underlie them. The proofs that the Lower Ludlow Beds of Britain contain a Characteristic graptolite-fauna have been gradually

(1902). A Monograph of British Graptolites. Introduction. Pages i–xxviii. Part I.—Dichograptidae. Pages 55–102; Plates V–XIII. Monographs of the Palaeontographical Society: Vol. 56, No. 265, pp. i-102.

(1904). A Monograph of British Graptolites. Part IV. Pages liii–lxxii, 135–180; Plates XX–XXV. Monographs of the Palaeontographical Society: Vol. 58, No. 277, pp. liii-180.

(1906). A Monograph of British Graptolites. Part V. Pages lxxiii–xcvi, 181–216; Plates XXVI, XXVII. Monographs of the Palaeontographical Society: Vol. 60, No. 288, pp. lxxiii-216.

(1903). A Monograph of British Graptolites. Part III. Pages xxix–lii, 103–134; Plates XIV–XIX. [N.B.—The preceding Part, 1902, is wrongly numbered Part I.] Monographs of the Palaeontographical Society: Vol. 57, No. 271, pp. xxix-134.

(1907). A Monograph of British Graptolites. Part VI. Pages xcvii–cxx, 217–272; Plates XXVIII–XXXI. Monographs of the Palaeontographical Society: Vol. 61, No. 297, pp. xcvii-272.