1879.] Organization of Fossil Plants of the Coal Measures. 445 



March 27, 1879. 



THE PRESIDENT in the Chair. 



The Presents received were laid on the table, and thanks ordered for 

 them. 



The following Papers were read : — 



I. " On the Organization of the Fossil Plants of the Coal 

 Measures. Part X." By W. C. WILLIAMSON, F.R.S., Pro- 

 fessor of Natural History in Owens College, Manchester. 

 Received March 5, 1879. 



(Abstract.) 



The still existing differences of opinion respecting the botanical 

 affinities of the Sigillarise give value to every new fact calculated to 

 throw light upon the question. In 1865, Edward Wunsch, Esq., of 

 Glasgow, macfe a discovery, which proves to have an important bearing 

 upon it. He found, at Laggan Bay, in Arran, a series of rather thin 

 Carboniferous strata, separated by thick beds of volcanic ash, and in 

 one of the Carboniferous shales especially, he discovered the bases of 

 the stems of numerous very large trees, standing perpendicularly to 

 the shales. These trees have been referred to by several authors as 

 Sigillarian. In the summer of 1877, Mr. Wunsch and I employed 

 quarrymen to make extensive excavations amongst these strata, for 

 the purpose of adding to the extensive series of specimens which he 

 had obtained, and the whole of which he kindly placed in my hands. 

 The aggregate result of these explorations was to show that the con- 

 clusion previously arrived at, viz., that the stems had belonged to a 

 grove of Sigillarian trees was unsupported by a solitary fact. These 

 stems were of very large size, showing that they had belonged to fully 

 grown trees. None of them displayed any traces of leaf-scars, having 

 outgrown the stages at which such scars would remain visible. Their 

 outer surfaces were scored with deep irregular longitudinal fissures, 

 resulting from internal growth and consequent expansion, and which 

 appear to have been mistaken for the longitudinal grooves and ridges 

 of a Sigillarian bark. Such, however, they certainly were not, since, in 

 every instance, the surface bark had been entirely thrown off, and the 

 fissures entered deeply into the subjacent bark layer. In most of the 

 stems, this comparatively thin bark layer was the only one that re- 

 mained, the greater portion of the inner bark and the central vascular 

 axis having disappeared, leaving a large cylindrical cavity, which was 



