Note on a Basalt Tree Cast. 141 



Mr. Brough Smyth^ refers to this specimen but hesitates to 

 give an opinion on such an occurrence, as the imitative forms 

 approach so closely to the natural. He mentions the behaviour 

 of lava currents in wooded districts as described by Mr. Dana^ 

 in his account of the Kilauea Eruption of 1840. As this has a 

 direct bearing upon the subject it will be of interest to repeat it 

 here : 



" The lava sometimes, as in other eruptions, flowed round 

 stumps of trees ; and as the tree was gradually consumed it left 

 a deep cylindrical hole, either empty or filled with charcoal. 

 Towards the margin of the stream these stump-holes were 

 innumerable ; and in many instances the fallen top lay near by, 

 dead but not burned 



" The rapidity with which lava cools is still more remarkably 

 shown in the fact that it was found sometimes hanging in 

 stalactites from branches of trees ; and although so fluid when 

 thrown off from the stream as to clasp the branch, the heat had 

 barely scorched the bark." 



This being an authentic record of the formation of tree moulds 

 in lava, it is |terfectly reasonable to assume that had anothtn- flow 

 spread over this one at a later period, a number of casts similar 

 to the one under discussion would have resulted. 



With i-egard to the point mentioned by I\Ir. Brough Smyth 

 that imitative forms at times closely approximate to the natural, 

 it must be observed that nearly all such forms are noted in 

 sedimentary rocks when they are mostly due to the segregation 

 of mineral matter taking place after the formation of the rock 

 itself. Concretions in the true sense, 1 believe, are practically 

 unknown in undecomposed volcanic rocks. At times, especially 

 in slow flowing lavas, their surfaces exhibit peculiar ropy and 

 other forms produced by the molten lava in the interior moving 

 more rapidly than that at the surface and causing the chilled 

 crust to twist and wrinkle. This structure, however, is quite 

 foreign to the case in view and merely mentioned as being 

 practically the only forms of lava possessed of anything approach- 

 ing an imitative character. As this is the only alternative 



1 " Gold Fields and Mineral Districts of Victoria," 1869, footnote pag-e 51. 



2 "Characteristics of Volcanoes." James D. Dana, 1890 ed., page 64. 



