A YORKSHIRE NATURALIST 175 



trees was buried, and thus exposing additional stems. 

 These were generally about two feet in diameter, and 

 mostly in a curious condition. They were merely 

 cylinders of the outer barks, all the more internal 

 structures had disappeared. In addition to the more 

 delicate internal zones of the bark, each trunk should 

 have had a strong central axis of pith and woody 

 tissue, nearly three inches in diameter, but of this 

 no trace remained. Fragments of these axes were 

 discernible here and there in the surrounding vol- 

 canic ash, but none in the trees themselves. How- 

 ever, one large stem contained no fewer than six of 

 these missing structures, most of them being of the 

 largest size ; whilst associated with them, within the 

 cortical cylinder, was a large quantity of foreign 

 vegetable material, including fragments of the roots 

 of these trees, now known as Stigmaria. It was 

 impossible that more than one of these vascular axes 

 could have belonged to the tree in which we disco- 

 vered them. What had happened is not difficult to sur- 

 mise. There had primarily been a grove of trees grow- 

 ing on the spot where we found their remains. When 

 living, they were in the centre of a region as volcanic 

 as Auvergne. Nevertheless, the trees continued to 

 flourish until they attained to their maximum 

 normal dimensions, but at length they perished, 

 probably in consequence of the mephitic vapours 

 which filled the atmosphere, and were derived not 

 only from the volcanic vents with which Arran itself 

 must have abounded, but also from the volcanoes of 



