and the absence of nepheline. An almost identical rock has been described by Boulton from the Old Red Sandstone between Chepstow and Usk, in Monmouthshire.1 Rocks of monchiquitic habit and composition, but without porphyritic constituents, occur contact facies of some kylite and teschenite sills, notably at Craigie and Kilmaurs. B. Rocks with conspicuous Nepheline. as the Rocks belonging to this group occur in far less abundance than these characterized by analcite. They comprise theralites and essexites, with an almost ultra-basic type-kylite. The latter, and the essexites also, contain only a small quantity of nepheline, but are treated here because of their relationship to the conspicuously nepheline-bearing rocks. 1. THERALITE. (a) Bellow type.-This rock has been mentioned in connexion with the teschenite picrite sill of Lugar, in which it forms a stratiform mass, about 10 feet thick, intervening between the upper teschenite and the picrite. In hand-specimens the rock is grey to black in colour, and very fine-grained in texture. Microscopically it is composed of plagioclase, nepheline, titanaugite, olivine, biotite, ilmenite, and apatite in the proportions shown in Table III, column IV (p. 77). Augite is present in two forms-as innumerable minute prismoid grains embedded in the felspathic groundmass, and as larger euhedral pseudo-porphyritic crystals of a deep-purple tint. Olivine occurs in large, fresh, more or less rounded crystals full of magnetiteblackened fissures. Biotite, whilst forming numerous independent flakes, is also commonly associated with very irregular skeletal crystals of ilmenite. All these constituents are embedded in a groundmass of fresh anhedral felspar and turbid nepheline. The felspar is a highly zonal plagioclase, ranging in composition from Ab, An, to Abg An. It is occasionally bordered by a little orthoclase. The nepheline is usually turbid owing to the development of a characteristic streaky micaceous alteration-product, which is arranged parallel to the cleavage. It builds rather large plates to which the felspar is idiomorphic. The felspar and nepheline are crowded with needles of apatite. The rock has a characteristic poikilitic fabric, the granular ferro-magnesian constituents being enclosed in the broad plates of plagioclase and nepheline. The felspars show systems of radiating fissures springing from enclosed olivine where the alteration of the latter has given rise to serpentine and consequent expansion. Another variety (Table III, column V) shows a considerable development of barkevicitic amphibole, with a diminution of olivine and plagioclase and an increase in the amount of nepheline. This rock approaches the Barshaw type described below. The rocks described above belong to the theralite group, but have a distinctly melanocratic facies as compared with typical theralites such as that of Duppau, Bohemia. They differ from the kylite group described below in the small proportion of olivine and the abundance of nepheline. Their textural peculiarities and mineral composition. entitle them to rank as a distinct type, which may be named the Bellow type, after the stream in which they are best exposed. Some thin anastomosing veins penetrating the Bellow rock show the same 1 Proc. Geol. Soc., 1911, p. 104. constituents, with the addition of analcite; but the salic and femic minerals are here more nearly on an equality, as in the typical theralites. Theralites of a more normal type occur at Garlaff and Knock terra, near Old Cumnock. In these there is approximate equality between the amounts of the salic and femic constituents. The deep-purple titanaugite builds large subhedral plates which ophitically enclose small laths of felspar. There is no granulitic generation of augite. Fresh olivine is fairly abundant. The nepheline is decomposed, but may be recognized by its characteristic alteration. (b) Barshaw type.-Mr. E. B. Bailey has described a theralitic rock from a small sill at Barshaw House, near Paisley.' The chief femic constituents are titanaugite and dark brown soda-amphibole, with sparse olivine and iron-ores. Labradorite and large allotriomorphic plates of nepheline form the remainder of the rock. The nepheline is mostly decomposed to various secondary products, chlorite, and analcite; but the latter may also be primary. The rock is decidedly melanocratic as may be gathered both from microscopic study and the chemical analysis. The mineral constituents are the same as those of lugarite, but analcite is more abundant in the latter, which is undoubtedly the leucocratic facies of the Barshaw type. This conclusion is supported by the fact that towards the top of the Barshaw exposure occur contemporaneous bands and veins of lugarite; but the nepheline in this rock is much fresher and more abundant than in the type-occurrence of Lugar. The Barshaw exposure 3 also provides mesocratic types intermediate between theralite and lugarite. With an increase in the salic constituents, especially analcite, goes a significant increase in the idiomorphism of the titanaugite and barkevicite, which culminates in the very perfect forms displayed by these minerals in lugarite. A rock which probably belongs to the Barshaw type occurs in the Inner Nebbock sill at Saltcoats, Ayrshire. Here, however, the felspar and nepheline have entirely disappeared, and fresh titanaugite, barkevicite, serpentinized olivine, and ilmenite are enclosed in a groundmass of brilliantly polarizing zeolites. (To be concluded in the March Number.) V. THE FOSSIL FLORA OF THE INGLETON COAL-FIELD (YORKSHIre). By E. A. NEWELL ARBER, M.A., F.G.S., Trinity College, Cambridge, University Demonstrator in Palæobotany. THE HE Upper Carboniferous rocks of the Ingleton Coal-field in North-West Yorkshire present a difficult study, and at the present time they are very imperfectly known. As mapped by the 1 Summary of Progress of Geological Survey for 1908, 1909, p. 44; also Mem. Geol. Surv., The Geology of the Glasgow District, 1911, p. 134. 2 Summary of Progress of Geological Survey for 1907, 1908, p. 55. This rock is called "bekinkinite or theralite" by Bailey, Mem. Geol. Surv., Geology of the Glasgow District, 1911, p. 134. 3 Summary of Progress of Geological Survey for 1908, 1909, p. 44. 4 J. R. Dakyns, etc., The Geology of the Country around Ingleborough (Mem. Geol. Surv.), 1890. See also Davis & Lees, West Yorkshire (London, 1878), p. 167 Geological Survey,' there is apparently a perfect succession, passing up from the Yoredales, through the Millstone Grits, to the Lower and Middle Coal-measures. The coal-measures are in part overlain by a series of red rocks, which have been assigned to the Permian, as in the case of other of the Midland Coal-fields. In the index of the Survey map of the north-eastern portion of the coal-field, the Deep Coal is taken as the top of the Lower, and the bottom of the Middle Coal-measures. So far as I am aware no fossil plants have hitherto been recorded from the coal-field.2 The specimens discussed here are in the Sedgwick Museum, Cambridge, and were collected during the visits. of Professor Hughes' field classes to the district in 1886 and on other occasions. Another collection, formed by the donor from the same locality, has recently been presented to the Museum by Miss Elles. The plants occur both in the shales and also in the clay ironstone nedules, as is so commonly the case in the Midlands. They were chiefly obtained from the waste heap of Newfield Pits, Ingleton. The section of this colliery is published in the Survey Memoir. The Coal measures penetrated in these pits are only 114 feet in thickness, and include the Crow, Main or Four Foot, and the Six Foot Coals. The specimens in shale presented by Miss Elles were obtained in situ from the shales forming the roof of the Six Foot Coal. The ironstone nodules no doubt occur in more than one bed. They are frequent in the so-called soapstone', or argillaceous shales, above the lowest seam. There is thus little doubt that all the specimens described here were closely associated. The flora of these beds, though small, is of much interest. There is a considerable variety of fern-like fronds, including one belonging to Sphenopteris, which may be compared with S. Laurenti, Andre, but which is not sufficiently well preserved to be determinable specifically. There are several Neuropterids, Neuropteris acuminata (Schloth.) being frequent. N. heterophylla, Brongn., N. obliqua (Brongn.), and N. gigantea, Sternb., also occur. Cyclopterid pinnules of the type of Cyclopteris trichomanoides, Sternb., are present. Alethopteris is probably represented by three species-A. lonchitica (Schloth.), A. decurrens (Artis), and A. davreuxi (?) (Brongn.). Mariopteris muricata (Schloth.) is frequent, and it is especially interesting to find that several examples of Dictyopteris sub-Brongniarti, Grand'Eury, have been collected, and that this plant appears to be of fairly frequent occurrence. The Lycopods are represented by stems of Lepidodendron obovatum, Sternb., and L. lycopodioides, Sternb., as well as a large number of leafy twigs, some of which no doubt belong to the latter species. A single specimen of Lepidophloios laricinus, Sternb., is present. 1 As is well known, this coal-field is intersected by four sheets of the Geol. Surv. Maps. Sheets N.S. 49 (= 98 S.E. of O.S.) and N.S. 50 (= 97 S.W. of O.S.), however, contain the greater part of the area of Upper Carboniferous rocks. " Davis & Lees (ibid., p. 169), however, noticed the occurrence of fossil plants in the ironstone nodules of the Coal-measures. * Carb. Plant. Coll., Nos. 1114, 1360-1, 1364, 1367-8, 1370-1, and 2178-2209. 4 Dakyns, ibid., p. 81. DECADE V.-VOL. IX.-NO. II. 6 There are also several examples of Lepidostrobus, and, in some of the shales, masses of rootlets, of unknown affinity, are conspicuous. The following is a list of the species which were recorded : FILICALES OR PTERIDOSPERMS. N. gigantea, Sternb. Alethopteris lonchitica (Schloth.). A. decurrens (Artis). A. davreuxi (?) (Brongn.). Mariopteris muricata (Schloth.). LYCOPODIALES. Lepidodendron obovatum, Sternb. Lepidophloios laricinus, Sternb. This flora is quite a typical Middle Coal-measure assemblage, and there is thus no doubt that the coals worked at the Newfield pits belong to that horizon. Several of the species are unknown from the Lower Coal-measures, especially Alethopteris Davreuxi (Brongn.) and Lepidophloios laricinus, Sternb. Dictyopteris sub-Brongniarti, Grand'Eury, have been recorded only from the Middle Coal-measures. As a whole the Ingleton Coal-measures seem to be closely related to the Yorkshire Coal-field, and all the species recorded here, except Dictyopteris sub-Brongniarti, Grand' Eury, are already known from that coal-field. A VI.-NEW DEVONIAN FOSSILS FROM CORNWALL. By IVOR THOMAS, D.Sc., Ph.D., F.G.S. (Communicated by permission of the Director of the Geological Survey.) SHORT time ago a Devonian fossil of considerable interest was found in the grits of the Ladock neighbourhood. It had been found by a workman in a road-heap on the Grampound Road and was placed for preservation in the Truro Museum. A cast was kindly made by Mr. C. Davies Sherborn and presented to the Museum of Practical Geology [22466]. This fossil was named Orthis sp., and is referred to as such in the Memoir of the Geological Survey on the geology of the country near Newquay (p. 35). More recently Messrs. C. Davies Sherborn and Upfield Green were fortunate enough to secure another example of this Brachiopod from the Ladock quarry. Mr. Upfield Green succeeded through patient developing of the second specimen in exposing the muscle impressions of one valve, and this has justified the previous allocation of the specimens to Orthis. The second example has been presented by Mr. C. D. Sherborn to the British Museum (Nat. Hist.). Though the preservation of the specimens leaves much to be desired, it is considered advisable to publish this note in order to induce further careful search in a locality hitherto considered to be practically unfossiliferous. First example. This shows the two valves in conjunction, with prominent umbones and well-developed area in the brachial valve. The latter has a broad sinus, due probably in part to deformation, as the opposite valve has no appreciable fold. The surface is ornamented with strong coste, which are widely spaced, the breadth of each interspace being about twice the thickness of a costa. Smaller ones are occasionally interpolated. The middle of the anterior margin of the brachial valve has six costa within a space of 10 mm., while the maximum length of the shell is 26 mm. and the maximum width 41 mm. Second example.-This specimen does not show the costation so well as the preceding, though the anterior portion is somewhat better preserved. At the anterior part of the middle portion of the valve there are about eleven costa within a space of 10 mm. The greatest length of the preserved part of the shell, consisting only of the brachial valve, is 23 mm., while the greatest preserved width is 52 mm. The fairly high triangular area lies in the plane of the shell, while the cast of two strong delthyrial supporting plates, imperfectly preserved, and an open delthyrium with a strong cardinal process are present. The process is produced forward as a strong median septum for a distance of about 16 mm. The adductor muscle-impressions cover a pear-shaped area and are divided into two portions by the median septum. Each of these portions is further subdivided by two longitudinal grooves, another groove forming the lateral and anterior boundary of each half of the muscular area. The whole muscle-impression has a maximum length of 17 mm. and a maximum width of 10 mm. Both specimens are compressed along the longitudinal axis, so that the width-measurement is greater than in the original state. 2 Affinities.-No described form appears to agree with this species. The deformation of the examples makes comparison difficult, but they suggest nearest relationship to the robust form described by Professor Kayser1 and Dr. Drevermann from the Siegener Grauwacke as Orthis personata, Zeiler. The British form, however, is more coarsely costate and has a more rotund and less elongated muscular area in the brachial valve. Locality and Horizon.-Mr. C. Davies Sherborn informs me that the first-mentioned specimen was obtained by a road-mender on a roadheap on the road to Grampound and about two miles south of Ladock. Other shells' were said to have been present with it on the same heap. The second fossil is in undoubted Grampound Grit matrix, and was found by a quarryman named Bennett in response to a reward offered by Mr. Upfield Green. Mr. Green was informed of the discovery by the Ladock schoolmaster, Mr. Clemmow. The quarry is on the west side of the river over the bridge from the inn. Though there exists a certain divergence of opinion regarding the correlation of the Grampound Grit with beds of other localities, there is now practical unanimity in allocating it to a Lower Devonian horizon. Mr. Ussher defines the term as a 3 66 name given to the 1 E. Kayser, "Beiträge zur Kenntniss der Fauna der Siegenschen Grauwacke": Jahrb. d. K. p. geol. Landesanst., Bd. xi (1890), p. 98, pl. xi, figs. 3-5; pl. xii, figs. 1-4; Berlin, 1892. 2 F. Drevermann, "Die Fauna der Siegener Schichten, etc. ": Palæontographica, Bd. 1, p. 264, pl. xxxi, figs. 1-8, Stuttgart, 1904. 3 Mem. Geol. Surv., The Geology of the Country around Bodmin and St. Austell, Sheet 1" 347, p. 25, London, 1909. |