SPECIMENS OK FOSSIL WOODS IN NATAL ilUSKLM, 361 



times, and consequently the course of tlie medullary rays is 

 remarkable. Fig. C shows a more unusual case where great 

 pressure from the sides and also from al)ove occurred. 



These sheering movements may occur before, during or 

 subsequently to complete siliciticfition. If they occur before 



Text-fig. 3. 



e.a 



s s 





zf-^-^^-^-C- r '; '} ildx 







i±t 



'^iMmmsSm^^ ^ Ji^^ 





^m: 



Annual ring 



Ptor 



Dadoxyloii sp. — X 35. Transverse section showing sheering 

 areas (s. a.) running through early spring-wood near to, but 

 not necessarily quite in cont;iet with, the edge (e.a.) of the 

 autumn-wood of tlie previous year. 



fossilization the outlines of the flattened cells would tend to be 

 more or less observable, if during fossilization the outlines 

 would be less clear, and if subsequently the silicified walls 

 would be shattered, especially if the cavities of the elements 

 had not been completely filled, and the ^organic structure 

 would tend to be completely lost. 



The silica which impregnates and ultimately replaces the 

 walls of the tracheides and cells may contain dai'k granules 

 which have the appearance of being oxide of iron (PI. XXV, 

 tig. 1, h.s.t.w.). Sometimes this blackened silica occurs over 



