49 



In the sections of larger trees {Figs. 25-6), however, these 

 rays appear to be ranged more closely together, and become 

 wonderfully twisted and contorted, especially so at the several 

 stages which mark the periodic concentric layers. Whether 

 this peculiarity indicates a different variety, I am not yet 

 prepared to decide. 



FRAGMENTS OF LIMESTONE. 



Intimately associated with these opalized woods, are to be 

 found waterworn fragments of three different varieties of lime- 

 stone. 



The first [!is replete with two or three forms of Bryozea, 

 particularly Fenesfella ampla. It also contains casts of Spirifer, 

 Fecten Avictola, and JPlatyscliisma. This, possibly, is the 

 impure limestone or Hue mudstone rock, abounding in the 

 neighbourhood of Hobart, Chudleigh, and Tork Town. 



The second is a close grained cream coloured limestone, not 

 so commonly distributed as the first, and only contains the 

 remains of a branching coral, possibly a variety of Stenopora. 



The third, more frequently to be met with, is light and 

 porous, and is principally composed of finely comminuted 

 shells. It contains abundant casts of Spirifer and Platyschis- 

 ma ; Fenestella is absent. All these limestones are greatly 

 altered, and are not acted upon by acids. 



FOSSIL IMPEESSED GREENSTONE. 

 Among the gravel I also discovered a fragment of close 

 grained greenstone, containing the well defined cast of a branch 

 of a tree repeatedly divided. The fragment is quite angular, 

 and does not appear to have been waterworn. 



ENQUIRY WHEN, AND UNDER "VVTEAT CONDITIONS, 

 DISTRIBUTED. 



With regard to the distribution of these accumulations, 

 there are two important enquiries, viz : — The means by which 

 they were distributed ; and the period during which such 

 distribution took place. 



It would appear probable that subsequent to marine denuda- 

 tion, which planed down the rocks of the Fer7nia)i and Carboni- 

 ferous age — and at a period prior to the deposition of the Wind- 

 mill Hill beds,Launceston — there existed all over the westward 

 plains, and the Campbell Town Valley, a dense and luxuriant 

 growth of vegetation ; that upon the commencement of the 

 later volcanic eruptions, the natural drainage to the sea 

 was dammed up either by a stream of lava, filling up the old 

 watercourse to the sea, or by dislocation, and so converted the 

 valley of the Tamar and the westward plains into one great 

 lake. The vegetation thus deluged by water, chemically 



