874 ERNEST WAREEX. 



tion becomes more evident, and, in addition to this, alternat- 

 ing dark and light squarish areas are cons])icuous. This 

 section is a longitudinal tangential one, and the dark and light 

 areas appear to be the cross-sections of the dark and light 

 bands which tend to run radially in the transverse sections. 



In a longitudinal more or less radial section (fig. 24) the 

 appearance in ordinary transmitted light remains much the 

 same. The trace of what was apparently a vessel showing a 

 cross-striation is seen at r. At vu./'j. the medullary ray 

 has been less altered than usual. With crossed prisms (tig. 25), 

 long dark and light bands running horizontally are con- 

 spicuous. In certain places coarse cross-hatched structures 

 are observable, and it is thought that these indicate the position 

 of former medullary rays. 



It appears that sometimes the medullary rays became less 

 changed than usual, and the cellular structure remained 

 distinct, while the surrounding tissue of wood fibres had 

 been converted into the jet-like substance. These less 

 altered areas weather out more readily than the surrounding 

 substance, and constitute places of weakness whereby the 

 whole mass may become riddled by spaces which are lenticular 

 in tangential section. Such a condition is seen in PI. XXV, 

 fig. 26, A, where a medullary ray is shown Avhich has not yet 

 been weathered out. With crossed prisms (fig. 26, B) the 

 cellular structure is seen extending into the jet-like substance. 

 A weathered out medullary ray with the jet-like substance 

 flaking oi¥ around the space is represented at tcs^). 



Less altered tissue {l.a.m.r., m.ri.) in the midst of the jet- 

 substance is shown in PI. XXV, fig. 27. 



In some of the sections a good deal of perfectly opaque 

 black substance, especially in the medullary rays, occurs. At 

 first this was thought to be simply iron oxide ; but it is quite 

 possible that a considerable portion is carbon, since there 

 appears to be more of this opaque substance present than the 

 percentages of iron oxide (1*21 per cent, in fossil Avood, and 0*60 

 per cent, in the jet) shoAvn in the analyses would account for. 



The description above given deals with the structural 



