president's address. 569 



In Tasmania the earliest Silurian sediments are graptolite 

 shales similar to those of Victoria anr] New Zealand, and formed 

 in seas of moderate depth. 



There is then distinct evidence, as afforded by ripple-marked 

 sandstones and beds of conglomerate, of shallow-water conditions 

 and probable proximity to shore-lines. Temporary local cessations 

 of sedimentation were marked by the accumulation of coralline 

 and cephalopodan limestones, the corals and cephalopods specially 

 distinguishing this Lower Silurian fauna from the preceding 

 Cambrian fauna. 



In the Macdonnell Ranges the conditions of accumulation of 

 the Lower Silurian strata were probably similar to those of the 

 Tasmanian Lower Silurian rocks, as shown by the nature of the 

 sediments and by that of their contained fossils. 



The New Zealand Lower Silurian rocks were folded on N.E. 

 and S.W. axes, the Tasmanian on N. by W. to N.N.W. axes, the 

 Victorian chiefly on N.N.W. axes, and the Mount Macdonnell 

 rocks on E. and W. axes. 



Amygdaloids are mentioned by Mr. Brown"^ at Wooltana and 

 in the Arrowsmith Ranges and at Mount Jacob. It is uncertain, 

 however, whether these are Cambrian or Silurian. If contempo- 

 raneous they represent the oldest known lavas in Australia. At 

 Mount Jacob boulder conglomerates occur, blocks four to five feet 

 in diameter being imbedded in limestone, quartzite, sandy shale, 

 and clay slate, f The age of these boulder conglomerates is, how- 

 ever, doubtful. 



B. Upper Silurian. — Rocks of this age have been identified 

 in Victoria, New South Wales, Tasmania and New Zealand. 



(1) In Victoria they consist of sandstones, mudstones, rubbly 

 shales, and occasionally slates, schists, and limestones, the last 

 being partly crinoidal and partly coralline. 



* South Australia. Government Geologist's Report re Visit to Far North. 

 By Authority. Adelaide, 1SS4. p. 4. 



t f. Brown, loc. cit. p. 4. 



