108 SECTION AT ONE TREE POINT, 



R.S. TA3. 



in the deposition of Breccia beds bet-ween the well stratified 

 leaf beds. 



The climatic conditions of this period must have been 

 different from those prevailing at the present day, be- 

 cause the list of plants given by Mr. E,. M. Johnston would 

 indicate a somewhat milder climate than that of the pre- 

 sent day. However, as I pointed out above, the deter- 

 minations of the species are not beyond doubt. One fact, 

 however, appears to be certain, the annual rainfall must 

 have been much heavier than it is now during the time 

 the Breccia was dej)osited. 



It is impossible to say anything as to the length of 

 the period that lapsed after the leaf series had been tilted 

 up aiid the outburst of volcanic action- In all probability 

 it was not very long, however. 



It further appears that the destruction and denudation 

 of the newly-formed Basalt cone commenced no sooner 

 than it had been built up. This destruction ^must again 

 have taken place during a time of most energetic denuda- 

 tion. The River Derwent cut its channel right through 

 the leaf series, probably deep into the underlying Permian 

 beds. Simultaneously the whole series was broken by 

 faults ; the latter tectonic movements do not appear to 

 have been very energetic, and they probably ceased very 

 soon, while the denudation of the Basalt cone continued. 

 Until the exact extent of the former cone is known, it is 

 impossible to form an idea as to the quantity of matter re- 

 moved, but it must have been of great magnitude, because 

 what is seen to-day represents only a very small portioR 

 of the original bulk. (PI. viii.). It is, further, probable 

 that the process of active denudation came to a standstill 

 when the level of the sea discontinued to recede, and a 

 movement in the opposite direction set in. By this movement 

 the valley of the Dei-went became filled up to its present 

 level ; in fact, it almost appears as if it had been higher 

 still- The data for this hypothesis are, however, ver}'' 

 insufficient, and I do not wish to say more on this point. 



6. The Age of the Leap Bed Series and the Basalt. 



Mr. R. M. Johnston, when speaking of the leaf bed 

 series in his G-eology of Tasmania, refers it to the Tertiary 

 period generally, but on page 261 he states that in one of the 

 leaf specimens of the Turritella group, near Wynyard, he 

 recognised the well-known form Sapotacites oliyonenris Etting, 

 which occurs in the leaf beds of the Derwent, notably at One 

 Tree Point. Mr. Johnston, therefore, thinks that the infra- 



