Fig. 1. — Diagrammatic represen- 

 tation of a pillar standing on 

 the crown of an arch, showing 

 the Jihrillar structure and the 

 polarization-figure seen between 

 crossed nicols. ( X 390.) 



Fig. 3. — Diagram of the 

 direction of the optic 

 axes, in cases where they 

 are generally transverse 

 to the direction of the 

 fibres. 



Fig. 2. — Diagram showing the 

 prevalent direction of the 

 optic axes. 



Fig. 5. — Diagram represent- 



[_,< ing the direction of the 



optic axes in the section 



shown as a microphotograph 



in PL VII, fig. 5. 



Fig. 4. — A diagram similar to 



fig. 3, but with the fioor, as 



well as the roof of the 



chambers, formed of fibres 



with transverse optic axes. 



Fig 



6. — Diagram showing a 

 common case of complicated 

 arrangement of the optic axes. 



