140 Proceedings of the Royal Society oj Victoria. 



the other smaller and carried on a prominence at the side. Both 

 these structures are evidently scars left by old limbs which were 

 lost long before the advent of the lava streams. From the larger 

 depression a groove, becoming gradually shallower, extends down- 

 wards, and on the opposite side a similar but smaller groove 

 appears. The vertical height of the tree from roots to tip of 

 branch is 10 feet. The surface bears a number of corrugations 

 and has the identical appearance of bark. The basalt of which 

 the tree is composed seems to be of the ordinary vesicular variety 

 and calls for no special notice. Its nature is evident from a 

 macroscopic examination, and a microscopic investigation was 

 deemed unnecessary and valueless. On one side of the stem a 

 portion is seen to be composed of a different material. It forms 

 a crust about | of an inch in the thickest part and consists of 

 quartz sand, clay and calcium carbonate. Where intact the 

 surface of this crust is indistinguishable from the remainder and 

 the basalt underneath is comparatively smooth and exhibits none 

 of the characteristics observed elsewhere. The surrounding 

 basalt comprising the mould in which the tree was formed, 

 judging from the two available pieces, is to all appearances of the 

 same nature as the cast. It has a light coloured coating and 

 shows very distinctly an impress as of bark. The latter fact 

 supports strongly the contention that the specimen is a cast and 

 not a result of concretionary action. 



In dealing with this subject care must be taken not to confuse 

 it with what are generally known as fossil or petrified ti'ees. 

 These are comparatively common and are the result of a gradual 

 replacement of the organic material of the trees by some mineral 

 substance, usually silica, derived from the circulation of waters 

 holding it in solution. Tree petrifactions are so complete in 

 some instances that the woody structure is preserved in perfect 

 detail ; they are in fact pseudomorphs by substitution, bearing 

 the form and structure of wood but possessing a mineral instead 

 of an organic composition. In the present instance, however, 

 the original body has first been entirely removed, leaving a cavity 

 or mould which has been subsequently filled by a molten mass of 

 lava. The cast retains the external appearance of a tree but is 

 quite devoid of all other similarity, the interior only showing a 

 basaltic structure. 



