[ 493 ]

XIV. On the Organization of the Fossil Plants of the Coal-Measures. —Part X.Including an Examination of the supposed Radiolarians of the Carboniferous Rocks.

By W. C. Williamson , F.R.S., Professor of Botany in the Owens College, Manchester

.

Received March 5,—Read March 27, 1879.

[Plates 14-21.]

In 1865 my friend Mr. Edward Wunsch, of Glasgow , made the discovery of somethin carboniferous shales imbedded in volcanic ash at Laggan Bay, in Arran . Thesebeds have already been described by their discoverer,* and their fossil contents referredto by Mr. Binney, Mr. Carruthers, and Sir Charles Lyell . From within a verylimited area the bases of more than 13 large erect stems of carboniferous trees havebeen extracted by Mr. Wunsch, the most important of which he has kindly placedin my hands. In the summer of 1877 we conjointly superintended some quarrymen,who tore up large portions of these strata with the result, I believe, of obtaining a fairknowledge of the nature of these beds and their contents.

The trees certainly stood where they originally grew; most of them consisted of athin cylinder of the outer bark, which was deeply fissured longitudinally but exhibitedno true Sigillarian flutings or traces of leaf-scars. The interior was in most casesfilled with volcanic ash, but in a few instances by vegetable debris introduced fromwithout; and in one specimen, imbedded in the vegetable mass, are several decorticatedDiploxyloid vascular axes of very old stems. These have been referred to as younggrowths that sprang up within the bark-cylinder ;t but such is not the case. Eachone is not only decorticated, but is large enough to be the vascular axis of the largetree within which the entire group occurs, and where they are mixed up with frag-ments of the similar vascular axes of Stigmaria and other plants.

The primary question which we endeavoured to determine was the botanical cha-racter of these stems, as indicated by the remains of their bark and by the nature ofthe numerous fragments of twigs, branches, and fruits found in the overlying beds.No one of the trees afforded any evidence of being Sigillarian. The outer surface ofeach stem exhibited a rough and irregular longitudinal fluting, but this was verydifferent from that characterising a Sigillarian bark; the ridges and furrows were

* ‘ Geol. Magazine,’ 1865, p. 474; ‘Trans. Geol. Soc., Glasgow, ’ vol. it, p. 98, 1865.f Lyell’s ‘ Student’s Elements of Geology,’ second edition, p. 547, 1874.

3 S

MDCCCLXXX.