66 president's address — section c. 



expressed views as to the age of the diabasic greenstones 

 constituting the tiers of the south-eastern portion of Tasmania 

 are correct, and they really antedate the Permo-Carboni- 

 ferous Period, it is possible that they may be related either 

 to the Snowy River porphyries, or to the volcanic rocks of 

 Middle or to those in the Upper Devonian series of Victoria. 

 The author, however, for reasons which will be discussed in 

 more detail in his paper on the Permo-Carboniferous Volcanic 

 Rocks of New South Wales, considers that the bulk of the 

 Tiers of Tasmania are probably of newer date than the Permo- 

 Carboniferous period, and newer even than the Mesozoic 

 Coal Measures of New Town, near Hobart, of Jerusalem, 

 Fingal, &c. This volcanic action in the Lower Devonian age 

 was probably prolonged at intervals into that of the Middle 

 Devonian, as interstratified with the Buchan group of 

 Middle Devonian age are felsite breccias and felsite tuffs with 

 a sheet of compact felsite and one of basalt. Mr. Howitt 

 remarks* — "The general conditions indicated are, I think, 

 these : — 



" 1. A sinking coast-line, with either marine or littoral 

 volcanoes, from which trachytic materials were 

 ejected as fragments, or emitted as flows of lava 

 (felsite breccias, tufas, compact and porphyritic 

 felsites). 



" 2. Gradual extinction of volcanic activity, as indicated 

 by the finer character of the felsite fragments, 

 their intermixtures with calcareous materials 

 (calcareous felsite -tufas), and their final cessation 

 with succession of purely marine limestones." 



In the Upper Devonian series of Eastern Victoria, con- 

 temporaneous melaphyres occur interbedded with Upper 

 Devonian rocks, and underlying the Avon River sandstones, 

 which latter are characterised by the presence of Lepido- 

 dendron Australe. Derived blocks of melaphyre are found 

 in conglomerates underlying the lepidodendron beds. 



The melaphyres appear to represent the last products of 

 volcanic action in Victoria during the Palaeozoic era. 



The following may be taken as a summary of the events 

 which preceded and immediately succeeded the volcanic out- 

 bursts in Victoria during the Devonian period : — 



Silurian strata were deposited in ht)rizontal layers to a 

 depth of about 30,000 feet. These strata were then plicated 



* Zoc. cit., p. 65. 



