102 



DIFFICULTIES AND SOURCES OF ERROR. 



[CH. 



sediment would fill up the depressions and finally, after the 

 complete decay of the stem, the impression on the mould or on 



Fig. 23. A dichotomously branched Lepidodendroid stem (Knorria mirabilis 

 Een. and Zeill.). After Renault and Zeilleri. (| nat. size.) The original 

 specimen is in the Natural History Museum, Paris. 



the cast, formed by the filling up of the space left by the stem, 

 would have the form of regularly disposed projections marking 

 the position of the more delicate tissues. The specimen 

 represented in the figure is an exceedingly interesting and 

 well preserved example of a Coal-Measure stem combining in 

 itself representatives of what were formerly spoken of as distinct 

 genera. 



The surface of the fossil as seen at e affords a typical 

 example of the Knorria type of stem; the spirally disposed 

 peg-like projections are the casts of cavities formed by the 



1 Renault and Zeiller (88) PL lx. fig. 1. 



