The Significance of the Genus Pleurodictyum in the Palaeozoic Rocks of New Zealand.
[Abstract read by Dr. J. Marwick before the Wellington Philosophical Society, 22nd May, 1929; received by Editor, 5th June, 1929; issued separately, 29th August, 1929.]
Pleurodictyum Problematicum Goldfuss, a characteristic Siegenian and Emsian (Lower Devonian) tabulate coral of the Belgian-Rhine area, was first noticed from the Reefton Beds of the Reefton Subdivision by J. Henderson (N.Z. Geol. Surv. Bull., No. 18, 1917, pp. 78 and 79) who based the record on a positive identification of that species by Professor J. Wanner, of Bonn, Germany, made when the latter visited New Zealand in 1910. This fact, together with other evidence of a relatively slight nature, was considered sufficient to point to a Lower Devonian age for the Reefton Beds. W. N. Benson (Pres. Add., Sect. C, Austral. Assoc. Adv. Sci., 1921, pp. 12–13) pointed out that Pleurodictyum is represented in the Silurian rocks of Victoria and New South Wales, Australia. He likewise quoted a private communication from W. S. Dun, Government Palaeontologist of New South Wales, who stated that in a preliminary examination of a collection of thirty-four species of fossils from Reefton, he had determined a group of forms, comparable with those of the Upper Silurian of Australia. Benson, therefore, placed the Reefton Beds, with the Baton River Beds, in the Silurian. Unfortunately, however, it has been proved that Dun handled Baton River fossils exclusively.
In view of the uncertainty which exists as to the significance of this genus in New Zealand it is suggested that the following summary of its occurrences elsewhere may be of value.
A.—Middle Devonian Occurrences.
(1) Pleurodictyum amazonicum Katzer 1903. Recorded by R. Kozlowski (Ann. de. Paléont., t. 12, 1923, pp. 97–9, pl. 10, figs. 1–2) from the Middle Devonian (Formation de Sicasica) of Bolivia, South America.
(2) Pleurodictyum granuliferum C. Schlüter 1889 Abh. geol. Specialk. Preuss. u. Thüring., Bd. 8, Heft. 4, pp. 103–111, pl. 4, figs. 5–8.
Described from the Middle Devonian of Gerolstein and Prümer Mulde in the Eifel, Germany.
(3) Pleurodictyum lonsdalei Richter 1855 Zeitschr. Deutsch. geol. Gesell., Bd. 7, pp. 559–66, text-figs. 1–6. Described from the Tentaculiten- und Nereitenschicten of Thüringer Wald, Germany. Originally referred to the Silurian but now considered Middle Devonian.
(4) Pleurodictyum stylophorum (Eaton 1832). (See H. A. Nicholson, Tab. Corals, 1879, pp. 143–52, pl. 8, figs. 1, 1b, and text-fig. 22 on p. 145). Recorded from the Middle Devonian (Hamilton) of New York (= Pleurodictyum americanum F. Roemer, Lethaea Palaeozoica, 1876, pl. 23, figs. 2a and 2b).
B.—Lower Devonian Occurrences.
(1) Pleurodictyum amazonicum Katzer 1903 “Geol. d. unteren Amazonsgeb.,” p. 268, pl. 9, figs. 1 a-d. Described from the Lower Devonian (Maecurú) of Brazil.
(2) Pleurodictyum cf. amazonicum Katzer 1903. No species of this genus has been recorded from the “Austral” Lower Devonian of Parana (Brazil), the Falkland Islands, or South Africa (the Bokkeveld Beds). I have to thank my friend, Mr. J. V. L. Rennie, for permission to record his discovery in 1928 of the above form at Gamka Poort, South Africa, in the Bokkeveld Beds.
(3) Pleurodictyum constantinopolitanum F. Roemer 1863. Neues Jahrb. f. Min., 1863, p. 519 (see also Kayser, Beit. z. Pal. Oesterreich Ungarns, Bd. 12, Heft. 1, pp. 34–5, t. 2, fig. 7). Recorded from the Lower Devonian of the Bosporus, Asia Minor.
(4) Pleurodictyum hunsrückianum A. Fuchs, Abh. K. Preuss. Geol. Landesamt, N.F. Heft 79, 1915, p. 4, t. 1, figs. 1–2. Described from the Cauber Horizont (Hunsrückschiefer) and the Bornicher Horizont (Hunsrückschiefer) of the Mittelrhein (Loreleigend). These horizons are probably equivalent to the Upper Siegenian (Hunsrückien supérieur) of Belgium.
(5) Pleurodictyum minimum A. Fuchs 1915, p. 5, t. 18, fig. 1. Described from the Bornicher Horizont of the Hunsrückschiefer of the Mittelrhein.
(6) Pleurodictyum (?) pachyporoides G. F. Whidborne 1901, Geol. Mag., vol. 8, p. 539, pl. 18, figs. 12, 12a. Described from the Lower Devonian of Torquay, England. “It appears to have the structure of Pleurodictyum, but the habit of Pachypora.”
(7) Pleurodictyum petrii F. Maurer 1874, Neues Jahrb. f. Min., 1874, p. 456, t. 7, figs. 1, 2. Described from the Lower Devonian of Giessen in the Eifel, Germany.
(8) Pleurodictyum problematicum G. A. Goldfuss, Petref. Germ., 1 (2), 1829, pp. 113–4, pl. 43, figs. 18 a-g. This species, the type by monotypy of the genus, occurs in the Lower Hunsrückian (i.e. Middle Siegenian) of the Belgian Ardennes (Asselberghs, Mém. Inst. Géol. Univ. Louvain, t. 1, mém. 1, 1913, p. 88), and in the Upper Hunsrückian of the same area. (Asselberghs, Bul. Soc. géol. Belge, t. 36 (1926), 1927, p. 208). It is recorded by Maillieux (C.R. 5. Sess. Extraord. Soc. Géol. Min. de Bretagne 1925, 1926, pp. 135, 137 and 140) from the Taunusian, Lower and Upper Hunsrückian, and base of the Emsian in the Southern Dinant area. In Germany Quiring (Jahrb. Preuss. Geol. Landesamt für 1922,
Bd. 43, 1923, pp. 90–112) has noted it from all three stages, Tonsehiefer, Rauhflaser and Herdorfer, of the Siegener Schichten. In horizons Drevermann (Palaeontographica, Bd. 49, 1902, p. 119) found it abundantly in the Untereoblenzschichten of Oberstadtfeld in the Eifel, while Dienst (Jahrb. K. Preuss. Geol. Landesamt f. 1913, Bd. 34, teil 1, Heft 3, 1913, p. 602) recorded it from the Untercoblenzschichten (Michelbacher Schichten) in the Kellerwald.
Other references could be cited but the above are sufficient to show that Pleurodictyum problematicum is typical of, and widespread in, Siegenian and Emsian horizons in Western Europe.
(9) Pleurodictyum cf. problematicum Goldfuss 1829. Recorded by Williams and Breger (U.S. Geol. Surv. Prof. Paper 89, 1916, p. 14, pl. 24, fig. 2) from the Chapman Sandstone (Lower Devonian) of Maine, New York.
(10) Dendrozoum rhenanum A. Fuchs 1915, p. 5, t. 1, fig. 4. Described from the Bornicher Horizont of the Hunsrückschiefer, and from the Eeger Horizont Untercoblenzschicten of the Mittelrhein. Fuchs remarks “Die Gattung Dendrozoum schliesst sich unmittelbar an Pleurodictyanum.” One wonders why a new genus was proposed for such poor material!
(11) Pleurodictyum sancti-johannis Schlüter 1887 (see Schlüter, Abh. geol. Specialk. Preuss. u. Thüring, Bd. 8, Heft 4, 1889, pp. 112–4). Recorded from the “mittleren Unter-Devon” of St. Johann in the Eifel, Germany.
(12) Pleurodictyum selcanum Giebel 1858 (see Kayser, 1878, Abh. geol. Specialk. Preuss. u. Thüring, Bd. 2, Heft 4, pp. 227–8, t. 33, figs. 8 and 12). Recorded from the Lower Devonian of the Harz, Germany.
(13) Pleurodictyum zorgense E. Kayser 1878 as above, pp. 229–30, t. 33, figs. 9, 10. Described from the Lower Devonian of the Harz, Germany.
(14) Pleurodictyum sp. ind. R. Kozlowski, Ann. de Paléont., t. 12, 1923, p. 99, pl. 10, figs. 3, 4. Recorded from the Schistes de la Cordillere Real (Lower Devonian) of Bolivia, South America.
(1) Pleurodictyum megastomum F. Chapman 1903 (ex McCoy MS.) Proc. Roy. Soc. Vict., 15 (N.S.) pt. 2, pp. 105–7, pl. 16, figs. 2–5.
This species has been recorded from Bowning, New South Wales in Upper Silurian rocks. (Foerste, Bull. Sci. Lab. Denison Univ., 3 (2) 1888, pp. 132–5, pl. 13, fig. 22 as P. problematicum (?) Goldfuss). In Victoria it occurs in numerous Yeringian (Upper Silurian) localities but is not known from Melbournian strata. It has been noted also from Zeehan in Tasmania. (R. Etheridge jun. Rep. Secy, for Mines Tas. for 1895–6  p. 42, pl. fig. 1.) It is not closely related to Pleurodictyum problematicum Goldfuss.
Summary (New Zealand occurrences excluded.)
(1) Pleurodictyum, as a Silurian genus, is restricted to the Upper Silurian of Australia. Only a single species is known.
(2) In the Lower Devonian Pleurodictyum is widespread and characteristic in the Siegenian and Emsian of Western Europe. It also occurs in homotaxial strata in Asia Minor, Bolivia, Brazil, South Africa and North-Eastern America. Species of the problematicum type are characteristic of this period. Ten species are known and most of these are described from Western Europe.
(3) In Middle Devonian strata the genus occurs in Germany, in Bolivia and in North America. Four species are known. The state of preservation of Middle Devonian species in limestone makes comparison with the casts of Lower Devonian forms difficult. However, the problematicum type is represented by P. lonsdalei Richter, and probably by P. amazonicum Katzer.
New Zealand Occurrences.
In the Reefton Beds the rather poor material available is clearly of the problematicum type. In view of the distribution noted above it is safe to conclude from this that the Reefton Beds are of Devonian age. That they are Lower Devonian, and not Middle Devonian, is placed beyond doubt by the association with Pleurodictyum of the problematicum type of such characteristic Siegenian and Emsian species as Spirifer of the hercyniae Giebel type, Spiri-fer of the hystericus Schlotheim type and Leptostrophia of the explanata (Sowerby) type.
In the Baton River Beds, on the other hand, the common Pleurodictyum is definitely of the megastomum type, and hence indicates a Yeringian age. The Yeringian stage of Victoria is not a clearly defined unit, and any exact correlation thereof with the Silurian sequence of Great Britain must be considered entirely provisional. In this connection the importance of facies has not been fully appreciated by Australian geologists.