158 PROF. W. C. WILLIAMSON ON THE STRUCTURE 



bark (e) disappeared and was similarly replaced. In this 

 case the small portion of ligneous zone thus preserved at 

 the base of the plant might have become slightly detached 

 from its original position, and floated upwards into an 

 internode occupying a higher position in the outer stem 

 than those of which it was originally the centre. The 

 specimen indicates that only about two inches of the lower- 

 most portion of the woody zone had been thus preserved, 

 the external lineaments of the pith and medullary radii 

 having been preserved along with it. I presume that after 

 the base of the plant became imbedded in the stratified 

 sandstone, according to the fashion common amongst the 

 coal-measure plants, the greater portion of the woody con- 

 tents decayed and floated out, this fragment at its extreme 

 base alone escaping the general decomposition, and being 

 permanently fossilized"^. 



Which of the above explanations may prove the true one 

 can only be determined by future discoveries ; but that 

 the Calamite-like medulla, with its verticils of medullary 

 radii, belongs to the black ligneous zone surrounding it, 

 I shall now proceed to demonstrate from the structure of 

 the specimen represented in fig. 2. This drawing exhibits 

 the appearance of the specimen previous to my cutting it 

 up into sections. It will at once be recognized as con- 

 sisting of portions of three internodes from the lower part 

 of a stem ; owing to the preservation of the innermost por- 

 tion of the ligneous cylinder, the medullary cast, repre- 

 senting the common type of Calamite, is not seen in its 

 usual form, the transverse constrictions of the latter being 

 here replaced by a projecting mass of organized carbonaceous 

 substance (6), whilst the longitudinal grooves usually farrow- 

 ing the several internodes are represented by sharply defined 



* My friend Mr. Binney, whose extensive experience of Calamites gives 

 weight to his opinion, authorizes me to state that he entirely concurs in the 

 above conclusions. 



