UNUSUAL TYPES OF PETRIFACTION. 
35 
Structure of Dandarragan Wood. 
In the upper sandstone bed are numerous fragments 
of white or yellowish fossil wood. In the specimens seen 
they are usually about three inches in diameter and four 
to eight inches long. For the most part they present com- 
plete sections of the stem with the exception of the bark and 
possibly sap wood. They are inclined to be slightly soft 
and powdery on the surface (perhaps this is the sap wood), 
but are quite hard and solid immediately below. On 
cross fractures the annual rings arc readily discerned by the 
unaided eye, whilst vertical sections exhibit a fibrous 
structure, leading to a ready vertical cleavage. In one case 
the external surface had a conical fluting similar to that on 
the present day gimlet wood of Western Australia, Eucalyptus 
salubris. All the specimens so far examined appear to belong 
to the one botancial species, and that a Conifer. 
Thin slices show that for the most part the most minute 
structures have been perfectly preserved. At times, how- 
ever, in areas with a more or less rounded boundary, the 
structure is somewhat obscured. In the accompanying 
Plate XII are seen sections, cross and radial, of a typical 
specimen. 
The average thickness of the annual rings is about 
two millimetres (0.08 inch), but in a single specimen was 
seen to vary from slightly less than one millimetre up to 
4 mm. The greatest width observed was 5 mm. The 
tracheids are arranged in radial lines, and are rounded in 
cross section. I hey are from 0.3 to 0.05 mm. in diameter 
with a cell wall averaging 0.1 mm. in thickness. The 
tracheids have a maximum diameter in the “ spring wood ” 
on the inner side of each season’s growth, gradually flatten- 
ing within each ring as one proceeds outw ards. The length 
of tw'o measured sets of tracheids was found to be 4 mm. 
1 heir method of interlocking is illustrated in the photos of 
the radial section. In parts of this same section the charac- 
teristic pitting of the inner walls of the tracheids is well 
preserved. The pittings form for the most part a single row, 
a single pit, however, is not infrequently replaced by a pair, 
the pits of which arc always opposite, never alternate. 
The medullary rays arc numerous and are composed of 
two to twelve rows of cells in a single series. No structural 
signs of parenchyma or wood vessels were seen. Resin 
canals are absent, but very rarely between certain annual 
rings there is a narrow annular space (Plate XII, Fig.17) which 
would appear to have been once filled with resin. These 
show no traces whatever of cell structure. The present 
filling is apatite, partly colourless, partly brown in colour 
