142 Proceedings of the Royal Society of Victoria. 



suggestion brought forward, we may I think, safely reject it and 

 accept the cast theory as being perfectly satisfactory and 

 consistent with observed occurrences. It is certainly an isolated 

 example, as far as can be ascertained, but when we consider the 

 small extent of quarrying to which lava flows have been subjected 

 and the unusual conditions necessary for the production of basalt 

 tree casts that fact should not influence our acceptance of this 

 explanation. 



In the absence of authentic data we must be guided by the 

 features which the specimen itself offei's, in attempting to trace 

 out the history of its formation. 



In the flrst place a necessary condition for the preservation of 

 the tree form would lie in its being rapidly surrounded by the 

 molten lava so that the carbonized remains would be inaccessible 

 to the air, and maintain the mould in its proper shape until the 

 lava had cooled sufficiently to prevent it from closing in. This 

 implies a rather fluid state of the lava, because, had it been a 

 viscid mass slowly advancing, it is probable that the tree would 

 have been completely destroyed before it was enveloped and 

 protected from this otherwise inevitable fate. Close examination 

 of the specimen does not reveal any point which can be satis- 

 factorily considered as representative of the lava inlet to the 

 mould. It is therefore not quite evident what position the tree 

 occupied when it was ingulfed in the rapidly flowing lava stream. 

 If the superficial crust previously mentioned can be taken as an 

 integral part of the cast, although of different composition, it 

 must be composed of detrital matter which has been carried 

 mechanically into the mould during the interval which elapsed 

 between the successive lava flows, and after the charred remnants 

 of the tree had been removed. It is certainly not a decomposition 

 product of basalt, the quartz grains being of course quite foreign 

 to that rock, and, moreover, the crust is sharply defined and 

 easily detached from the stem without showing the usual 

 gradation of decomposition, so that it must have been derived 

 from some outside source. Should this view be correct, then the 

 tree must have been in a more or less horizontal position, for had 

 it retained its upright position any detrital matter would 

 naturally have gravitated to the bottom of the mould and formed 

 the lower part of the root cast. In order to provide an entrance 



