IV.—On the Occurrence of Plants in the Skiddaw Slates
The occurrence of plant-remains in the Silurian and Cambrian rocks is a subject of great interest, but one which has not hitherto been sufficiently investigated. Many supposed plants have been described by Emmons, Hall, Billings, and Dawson, from the older Palæozoic rocks of North America, and little doubt can be entertained of the vegetable nature of some even of the most ancient of these. Many, however, as believed by Professor E. Forbes and Mr. Salter, are certainly referable to the tracks or burrows of marine animals. More recently the Cambrian rocks of Sweden have yielded to the researches of Torell and Linnarsson some remarkable impressions and casts of fossils, which are believed to be of a vegetable nature (Geol. Mag., September, Vol. VI., p. 393, Plates XI., XII., and XIII.). In Britain there is not, as far as I am aware, any instance of the occurrence of plant-remains in deposits of Lower Silurian age, as to the nature of which all authorities are agreed. The Oldhamia of the Cambrian rocks is believed by Mr. Salter to be a plant, but good authorities would place it either amongst the Polyzoa or Hydrozoa. The Cruziana semiplicata of the Lingula Flags has often been assigned to the Fucoids, but it is believed by Mr. Salter to be “the filled-up burrow of a marine worm” (Mem. Gaol. Survey, vol. iii., p. 248). Long ago Professor McCoy described from the Skiddaw slates (lowest Llandeilo) certain fossils which he believed to be fucoids (Quart. Journ. Geol. Soc., vol. iv., p. 223, and Pal. Foss., pl. i. A). After studying a large number of specimens, however, I have been compelled to come to the conclusion, held by Mr. Salter and Professor Harkness, that these fossils (viz. Palæochorda major, P. minor, and Chondrites acutangulus) are truly referable to the action of marine worms. Within the last few years, however, I have obtained from the Skiddaw Slates several fossils, which certainly do not admit of being explained in this manner, though I would not go so far as to assert that they are unquestionably plants. The age of the deposit in which they occur renders them, at any rate—whatever their true nature may be—of sufficient interest to merit a short description.